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Aurora

Aurora, commonly known as the northern lights (aurora borealis) in the Northern Hemisphere or the southern lights (aurora australis) in the Southern Hemisphere, is a natural phenomenon characterized by colorful displays of light in the night sky, typically visible in high-latitude regions near the Earth's magnetic poles.^[1]^[2] These luminous arcs, curtains, or bands of light—often in shades of green, red, blue, and purple—result from the collision of charged particles from the Sun with atoms and molecules in Earth's upper atmosphere.^[3]^[4] The scientific understanding of auroras stems from the interaction between solar activity and Earth's magnetosphere. Solar wind, a stream of charged particles ejected from the Sun's corona, carries energy that disturbs Earth's magnetic field, allowing particles to penetrate and accelerate along magnetic field lines toward the poles.^[5]^[6] Upon colliding with atmospheric gases like oxygen and nitrogen at altitudes of 80 to 500 kilometers, these particles excite the atoms, causing them to release photons and produce visible light; green hues predominate from oxygen at lower altitudes, while red comes from higher-altitude oxygen and nitrogen emissions yield blue or purple.^[4]^[7] Auroral activity intensifies during periods of heightened solar activity, such as solar maximum in the 11-year sunspot cycle, and can extend visibility to lower latitudes during strong geomagnetic storms.^[2]^[8] Historically, auroras have been observed and interpreted across cultures for millennia, often as omens or divine signs, with ancient records from Chinese, Greek, and Indigenous Arctic peoples describing the lights as spirits or celestial battles.^[9] The term "aurora borealis" was coined by Galileo Galilei in 1619, drawing from the Roman goddess of dawn (Aurora) and the north wind (Boreas), while "aurora australis" refers to the southern counterpart.^[10] Scientific explanations evolved in the 19th and 20th centuries, with key advances including Kristian Birkeland's 1908 electromagnetic theory linking auroras to solar particles and Earth's magnetic field, later confirmed by satellite observations in the space age.^[9] Today, auroras not only captivate observers but also serve as indicators of space weather, influencing satellite operations, power grids, and radio communications.^[3]

Etymology and Nomenclature

Etymology

The term "aurora" originates from the Latin word for "dawn," referring to the Roman goddess Aurora, who personified the morning light, a metaphor apt for the luminous display's resemblance to early sunlight.^[11] This classical root underscores the phenomenon's perceived similarity to a rosy dawn in polar skies. The full designation "aurora borealis," meaning "northern dawn," was first coined by Italian astronomer Galileo Galilei in 1619 in correspondence describing the lights, combining "aurora" with "Boreas," the Greek god of the north wind. By analogy, the southern counterpart "aurora australis," or "southern dawn," emerged in the early 18th century, with "australis" derived from the Latin for "southern," reflecting observations in the opposite hemisphere. In English-speaking regions, the colloquial name "northern lights" appeared by the early 18th century, emphasizing the phenomenon's location and glow, and entered common usage around 1721. Various indigenous cultures have employed descriptive terms rooted in their languages, such as "dance of the spirits" among some Cree and Inuit communities in North America, evoking the lights' undulating motion.^[10] Similarly, in Finland, "revontulet" translates to "fox fires," drawing from folklore of arctic foxes sparking flames with their tails.^[10] Following the 19th century, as electromagnetic theory and spectroscopy advanced, scientific nomenclature evolved from these mythological and descriptive origins toward terms grounded in physical processes, such as "proton aurora" for particle-driven emissions, though traditional names like "aurora borealis" remain standard in both popular and academic contexts.^[12] This shift paralleled broader developments in geophysics, prioritizing mechanisms over visual analogies.^[13]

Terminology for Forms and Types

Auroral forms are classified using standardized terminology to describe their structural characteristics, primarily based on observations of their shape, orientation, and complexity. The International Auroral Atlas, published in 1963 by the International Association of Geomagnetism and Aeronomy, provides a foundational classification system that categorizes forms according to the configuration of their lower borders and overall morphology, such as Type A for simple arcs and Type B for more irregular bands.^[14] This system has influenced subsequent standards, including those in the World Meteorological Organization's International Cloud Atlas, which defines key forms as follows: a glow is a diffuse, horizon-bound luminescence without defined structure; an arc is a uniformly curved, horizontal band with a clear lower edge and no vertical elements; a band is an elongated, twisting form lacking a regular arc shape and featuring an irregular lower border; a curtain refers to a rayed band exhibiting folds or kinks that evoke drapery; a corona consists of rays converging overhead to a central point, resembling a crown; and rays are vertical luminous shafts that may appear isolated or bundled.^[15] Additional terms include homogeneous patches, which are shapeless, diffuse areas of light, and veils, which denote widespread, unstructured coverage across the sky.^[15] These definitions emphasize morphological distinctions rather than intensity or color, allowing observers to record auroral displays consistently for scientific analysis.^[2] Auroras are further distinguished by geomagnetic activity levels, with quiet-time displays typically featuring stable, homogeneous arcs that remain relatively motionless, while active-time auroras exhibit dynamic structures such as rayed arcs, folded bands, or pulsating rays during heightened solar activity.^[2] For instance, under low geomagnetic indices (Kp 3-4), arcs predominate as simple, east-west oriented features, whereas during substorms (Kp 5+), they evolve into rayed bands or curtains with vertical rays.^[2] This temporal classification aids in correlating forms with magnetospheric processes, though it relies on the core morphological terms outlined above.^[16]

Observation and Characteristics

Geographic Occurrence and Visibility

Auroras, known as the aurora borealis in the Northern Hemisphere and aurora australis in the Southern Hemisphere, primarily occur within the auroral ovals, which are ring-shaped regions encircling the Earth's magnetic poles. In the Northern Hemisphere, the auroral oval is centered around the geomagnetic North Pole and typically spans latitudes between 60° and 75° north, encompassing areas such as the Arctic Circle, including northern Canada, Alaska, Scandinavia, and Russia.^[2]^[17] In the Southern Hemisphere, the auroral oval surrounds the geomagnetic South Pole, primarily over Antarctic regions and the Southern Ocean, with occasional extensions to the edges of southern continents like New Zealand.^[18]^[19] Visibility of auroras is influenced by several key factors, including seasonal alignments and solar activity cycles. Auroral displays are most frequent and intense during the equinoxes in March and September, attributed to the Russell-McPherron effect, which enhances magnetic reconnection between Earth's magnetosphere and the solar wind due to the alignment of the Sun-Earth magnetic fields.^[20]^[21] Additionally, auroral activity correlates with the 11-year solar cycle; during Solar Cycle 25, which reached its maximum phase between 2024 and 2025, increased solar activity has led to more widespread and vivid displays.^[22]^[23] Strong geomagnetic storms during this period, such as those in May 2024 and October 2024, have expanded the auroral ovals equatorward, making auroras visible at mid-latitudes in regions like the northern United States, central Europe, and even as far south as Arizona and Italy.^[24]^[25] Auroras are observed through a combination of ground-based and space-based methods, which provide both real-time viewing and scientific mapping. Ground-based observations involve direct visual sightings or photography from dark-sky locations within or near the auroral ovals, ideally during clear, moonless nights away from light pollution.^[26] Satellite missions, such as NASA's THEMIS constellation and the European Space Agency's Swarm satellites, capture global auroral imagery and measure magnetic field variations to track oval dynamics.^[27]^[28] The position and intensity of the auroral ovals are mapped using the planetary Kp index, a 3-hourly measure of global geomagnetic activity on a scale from 0 to 9, where higher values (Kp ≥ 5) indicate equatorward expansion and enhanced visibility at lower latitudes.^[29]^[30]

Altitude and Structure

Auroral displays manifest at varying altitudes within Earth's upper atmosphere, determined by the energy and type of precipitating particles. Discrete auroras, featuring well-defined structures like arcs and rays, predominantly occur between 100 and 200 km altitude in the mesosphere and lower thermosphere, where electron precipitation excites atomic oxygen to produce green emissions.^[3] Diffuse auroras, appearing as broad, unstructured glows, extend to higher altitudes of 200 to 500 km in the upper thermosphere, resulting from scattered electron populations that interact over larger vertical scales.^[31] Proton auroras, driven by energetic hydrogen ions, exhibit peak precipitation and emission heights around 110 km, lower than typical electron-induced displays due to differing energy loss mechanisms.^[32] The vertical structure of auroras aligns with the ionospheric E- and F-regions, reflecting layered atmospheric responses to particle influx. The E-region (90–150 km) serves as the main locus for electron precipitation, where collisions generate ionization and prompt emissions through excitation of neutral species.^[33] In the F-region (150–500 km), ion interactions dominate, supporting extended auroral features from particles that penetrate beyond the E-layer.^[34] Penetration depth varies with incident particle energy: lower-energy electrons (~1–10 keV) deposit energy higher up, while higher-energy ones (>10 keV) descend deeper, modulating the altitude profile of emissions within these regions.^[34] These altitude ranges and structural features are quantified through specialized observational techniques. Incoherent scatter radar measures ionospheric electron densities and velocities, enabling height-resolved profiles of auroral precipitation zones.^[35] Lidar instruments detect backscattered light from excited atmospheric molecules, mapping emission layers from ~80 to 300 km.^[36] Satellite-based particle detectors and altimeters, operating in low-Earth orbit, provide global context by linking in-situ flux measurements to optical altitudes.^[37]

Forms and Shapes

Auroral displays exhibit a variety of visual morphologies determined by the configuration of precipitating charged particles and Earth's magnetic field lines. The most common forms include arcs, bands, rays, curtains or draperies, and coronas, each characterized by distinct structural features and dynamics.^[18]^[2] Arcs represent the simplest and most stable form, appearing as long, narrow, linear structures oriented primarily east-west along the auroral oval. These quiet-time features often manifest as single or multiple parallel lines, extending for hundreds to thousands of kilometers in length while maintaining widths on the order of 1 to 10 kilometers or less.^[38]^[39]^[2] Bands are more dynamic and sinuous variations, forming twisted or folded structures that can pulsate or ripple across the sky. They typically evolve from arcs during periods of moderate geomagnetic activity, stretching across wide expanses and exhibiting undulating patterns due to plasma instabilities in the magnetosphere.^[18]^[40] Rays appear as vertical streaks or shafts of light, aligned with magnetic field lines and resulting from field-aligned currents that accelerate electrons into the atmosphere. These fine-scale features often bundle within arcs or bands, with typical widths ranging from 1 to 10 kilometers and lengths extending vertically for hundreds of kilometers.^[41]^[42]^[2] Curtains or draperies describe folded, sheet-like formations that resemble hanging fabric, created when multiple rays or bands fold and ruffle under intensifying particle precipitation. This form is prevalent in active displays, where the structures can span tens to hundreds of kilometers horizontally while displaying wavy, undulating edges.^[18]^[40] Coronas form when rays converge radially toward the zenith, producing a starburst-like pattern overhead that signals high-intensity activity directly above the observer. This perspective-dependent morphology arises from the projection of overhead arcs or bands, with rays appearing to emanate from a central point.^[18]^[40] During magnetospheric substorms, auroral forms undergo characteristic transitions, evolving from stable quiet arcs into more complex structures such as spiraling bands, omega bands, or diffuse patches. Omega bands, resembling the Greek letter Ω, emerge in the post-midnight recovery phase, propagating westward as large-scale swirls hundreds of kilometers across.^[2]^[43] Auroral features operate on scales from fine structures (sub-kilometer widths) to meso-scale extents (hundreds of kilometers in length), with motions including flickering along arcs at rates of seconds and propagation speeds typically ranging from 1 to 5 kilometers per second for surges and waves. These dynamics reflect the underlying plasma flows and wave-particle interactions in the ionosphere.^[44]^[45]^[2]

Colors, Wavelengths, and Spectra

The dominant color observed in auroras is green, resulting from the forbidden transition of excited atomic oxygen emitting at a wavelength of 557.7 nm.^[2] Red hues appear from atomic oxygen emissions at 630.0 nm, primarily in the upper atmosphere where collision rates are lower, allowing the longer-lived excited state to radiate.^[46] Blue and purple colors stem from molecular nitrogen emissions, particularly the first negative band of N₂⁺ spanning 391–470 nm.^[47] Rare pink or magenta shades arise from the combination of N₂⁺ violet emissions with atomic oxygen lines.^[48] Key spectral lines include the green OI line at 557.7 nm and the red OI line at 630.0 nm from atomic oxygen, alongside the violet N₂⁺ first negative band peaking near 427.8 nm from ionized nitrogen.^[49] Intensity variations depend on altitude: the green emission dominates at lower altitudes (around 100–150 km) due to higher oxygen density and frequent collisions, while red emissions intensify at higher altitudes (above 200 km) where the excited state's lifetime exceeds collision times.^[50] Auroral spectra are characterized by discrete emission lines from these forbidden transitions, observed via ground-based spectrographs that resolve the pure line spectrum without significant continuum emission.^[51]

Temporal Changes and Dynamics

Auroral displays exhibit a range of short-term variations that manifest as dynamic intensity modulations over seconds to minutes. Pulsations, commonly observed in diffuse auroras, involve quasi-periodic on-off cycles with typical periods of 2–20 seconds, creating patchy, rhythmically brightening regions equatorward of the main auroral oval.^[52] Flickering represents a higher-frequency phenomenon, characterized by rapid intensity oscillations at 5–15 Hz (periods less than 1 second), often appearing as fine-scale patches within brighter auroral structures and linked to multi-ion precipitation.^[53] Traveling surges, meanwhile, are eastward-propagating wave-like forms that expand across the auroral oval at speeds of approximately 5–10 km/s, contributing to the overall dynamism during active periods.^[54] On larger timescales, auroral substorms drive cyclic evolutions tied to magnetospheric processes. A substorm begins with the onset phase, marked by sudden brightening of a pre-existing arc in the premidnight sector, followed by the expansion phase where intricate rayed and curled structures rapidly develop and propagate poleward or azimuthally over 10–30 minutes.^[55] The recovery phase then sees gradual fading and dissipation of these features, typically lasting 30–60 minutes in total for the expansion and recovery combined, as energy release from magnetotail reconnection disrupts stored magnetic flux and accelerates plasma earthward. These cycles repeat multiple times per night during geomagnetic activity, reshaping the auroral configuration. Longer-term patterns reveal systematic modulations influenced by Earth's orbit and solar activity. Auroral occurrence peaks during equinoctial seasons (March and September), with enhanced visibility and intensity due to optimal alignment of the geomagnetic field with the solar wind, known as the Russell-McPherron effect. Diurnally, activity shows a strong preference for the nightside, particularly the premidnight sector, where darkness allows full visibility and ionospheric conductivity supports intensified precipitation.^[56] Over the 11-year solar cycle, auroral displays intensify during solar maximum, as heightened solar wind and coronal mass ejections drive more frequent and powerful geomagnetic storms; for instance, Solar Cycle 25's maximum phase in 2024–2025 has led to widespread auroral expansions to mid-latitudes.

Associated Phenomena

Auroral sounds, often described as low-frequency crackling, hissing, or rustling noises, have been reported by observers during intense displays, particularly in regions with cold, clear conditions and temperature inversions.^[58] These auditory phenomena occur in the frequency range of 0.1-20 Hz, spanning infrasound to low audible tones, and are typically heard for short durations of a few minutes.^[59] The mechanisms remain debated, with proposed explanations including electroacoustic coupling, where electromagnetic waves from auroral activity interact with atmospheric ions to generate acoustic waves, and corona discharges in the lower atmosphere triggered by enhanced Schumann resonances during geomagnetic storms.^[60] Observations suggest these sounds originate at altitudes of 70-80 meters, activated by electric fields in temperature inversion layers, and are more common than previously thought, as evidenced by field recordings in Finland.^[59]^[61] Beyond audible effects, auroras produce various non-visible radiations across the electromagnetic spectrum. Ultraviolet emissions include the hydrogen Lyman-alpha line at 121.6 nm, arising from the precipitation of energetic protons that excite atmospheric hydrogen atoms, a signature particularly prominent in proton auroras.^[62] X-ray emissions in the 1-20 keV range result from bremsstrahlung processes, where precipitating electrons decelerate in the upper atmosphere, producing soft X-rays observable during substorm events.^[63] Radio emissions encompass very low frequency (VLF) hiss, broadband noise from about 4-10 kHz generated near auroral zones by electron interactions with plasma waves, and auroral kilometric radiation (AKR), intense bursts in the 100-500 kHz range emitted from acceleration regions in the magnetosphere.^[64]^[65] During the solar maximum phase of 2023-2025, enhanced geomagnetic activity has led to more frequent and intense auroral events, including amplified radio bursts such as stronger AKR emissions correlated with solar wind interactions.^[22] These observations, facilitated by ground-based and satellite instruments, underscore the increased dynamism of auroral radio phenomena amid heightened solar activity.^[66]

Unusual Auroral Phenomena

STEVE

STEVE, or Strong Thermal Emission Velocity Enhancement, is an atmospheric optical phenomenon that manifests as a narrow, east-west aligned ribbon of purple-red light, typically appearing equatorward of the main auroral oval.^[67] This structure spans thousands of kilometers in length but remains only tens of kilometers wide, with emissions occurring at altitudes ranging from approximately 130 to 270 km.^[68] Events usually last 20 to 60 minutes during premidnight hours, often accompanied by faint green, picket-fence-like emissions at lower altitudes below the main arc.^[67] The phenomenon was first systematically identified in 2016 through citizen science contributions, including photographs uploaded to the Aurorasaurus platform by members of the Alberta Aurora Chasers group, who had observed it for years prior.^[67] Initially named "Steve" in a casual reference to a 2006 film, it was later formalized with the backronym STEVE to reflect its association with enhanced ion velocities; unlike traditional auroras driven by particle precipitation, STEVE is linked to subauroral ion drift (SAID) events.^[67] Recent observations from 2023 to 2024, including satellite data from missions like Swarm, have connected STEVE occurrences to ionospheric temperature enhancements reaching up to 3000 K within the plasma flows.^[69] These studies also highlight ion velocity shears, with rapid flows exceeding 2.5 km/s and steep gradients at field-aligned current boundaries, underscoring STEVE's role in subauroral dynamics during geomagnetic disturbances.^[70]

Picket Fence Aurora

The picket fence aurora is a distinctive subauroral optical phenomenon characterized by a series of parallel, vertical green rays resembling evenly spaced fence posts. These rays, primarily emitting at 557.7 nm wavelength due to excited atomic oxygen, are spaced 15–25 km apart on average and occur at altitudes ranging from 95 to 150 km. The structures are generated by the precipitation of kiloelectron volt electrons into the atmosphere, enhancing local plasma density and producing discrete auroral-like emissions aligned with magnetic field lines.^[71]^[72]^[71] This phenomenon typically manifests in mid-latitudes, equatorward of the main auroral oval, during periods of enhanced geomagnetic activity associated with storms. It is linked to structured electron precipitation patterns, including inverted-V distributions, which indicate accelerated particles from the magnetosphere. Events often last 10–20 minutes, though the overall display may persist longer, with the rays exhibiting quasi-periodic intensity variations and rapid apparent motion at speeds of 400–600 m/s, either westward or eastward.^[73]^[71]^[74] Observations of the picket fence aurora have been documented through citizen science photography and corroborated by satellite measurements, notably during events from 2017 to 2024. For instance, triangulation of amateur images from a 2017 event in Alberta, Canada, confirmed its altitude profile, while Swarm satellite data revealed corresponding ionospheric enhancements. It differs from rays in standard auroras by its uniform spacing, subauroral location, and consistent collimated structure without the broader diffuse glow typical of poleward forms. The picket fence is frequently observed in conjunction with STEVE, appearing below the purple arc as a green underlayer, though it can occur independently.^[75]^[71]^[74]

Dune Aurora

Dune aurora is a distinctive auroral phenomenon characterized by horizontal, undulating patterns of parallel emission stripes that resemble wind-swept sand dunes. These structures appear as wave-like fields within the green diffuse aurora, with horizontal wavelengths typically around 45 km (ranging from 20 to 100 km across events) and occurring at altitudes of approximately 100–110 km. The emissions are monochromatic green, resulting from excited atomic oxygen, and the formations generally persist for 5–15 minutes before dissipating.^[76]^[77] This auroral form was first systematically imaged and documented by Finnish citizen scientists using all-sky cameras during an event on 7 October 2018, though similar patterns had been noted as early as 2015. Observations occur equatorward of the main auroral oval, primarily during quiet to moderate geomagnetic conditions in the evening sector, often spanning large horizontal distances of up to 1,500 km.^[76]^[77] The dune aurora is believed to arise from atmospheric gravity waves, possibly manifesting as mesospheric bores propagating within a thin inversion layer near 100 km altitude, driven by electron precipitation and associated heating. It is linked to medium-scale traveling ionospheric disturbances (MSTIDs), with studies indicating that strong neutral winds (around 200 m/s) couple with these disturbances to facilitate the wave propagation and visible structuring. Recent modeling from 2023 further supports this neutral wind coupling as a key driver in generating the observed dune morphology during substorm-related activity.^[76]^[77]^[78] Unlike more common auroral waves, dune aurora remains relatively rare, requiring specific mesospheric stability for its development.^[76]

Horse-Collar Aurora

The horse-collar aurora (HCA) is a distinctive auroral configuration observed in the dayside high-latitude ionosphere, characterized by the poleward expansion of the dawn and dusk sectors of the auroral oval, forming a U-shaped or collar-like structure around the noon sector. This feature creates a teardrop-shaped polar cap, with two prominent arcs separated by a faint "web" of weak emissions from soft particle precipitation. The arcs typically span latitudes of 70°–80° magnetic latitude in the cusp region, with the dawn-side arc often brighter than the dusk-side counterpart by about 62% in ultraviolet emissions. The overall structure has a characteristic scale of approximately 1000 km in diameter, appearing as a red glow primarily due to proton precipitation exciting atomic oxygen emissions at higher altitudes in the atmosphere.^[79]^[80]^[81] HCA events occur predominantly under conditions of prolonged northward interplanetary magnetic field (IMF), with clock angles typically between -33° and 25°, facilitating dual-lobe reconnection at the magnetopause. This reconnection process reconfigures the magnetosphere, leading to the observed poleward motion of the auroral boundaries. First identified in the 1980s using Dynamics Explorer-1 (DE-1) imager data during quiet geomagnetic conditions, HCAs were later imaged extensively by the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite in the early 2000s and more recently by the Defense Meteorological Satellite Program (DMSP) Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) from 2010 to 2016, which cataloged over 600 events. These observations confirm HCAs as a common phenomenon, occurring roughly 8 times per month regardless of season, with no significant diurnal or annual biases.^[79]^[80]^[82] The significance of the horse-collar aurora lies in its indication of an open magnetosphere configuration during northward IMF, where lobe reconnection maintains elevated open magnetic flux and alters convection patterns in the ionosphere. Events are remarkably stable, persisting for an average of 2.3 hours, providing a visual proxy for magnetospheric dynamics and solar wind coupling under quiet conditions. This stability allows for detailed study of reconnection processes, though the feature's faint web often requires ultraviolet or proton-sensitive instruments for clear detection from space.^[79]^[82]

Conjugate Auroras

Conjugate auroras are simultaneous luminous displays that occur in both the Northern and Southern Hemispheres at geomagnetically conjugate locations, which are the endpoints of the same closed magnetic field line on Earth's surface. These phenomena manifest as mirrored features along identical magnetic longitudes but at opposite invariant latitudes, typically one in the Arctic region and its counterpart in the Antarctic, as energized charged particles spiral along the field line and precipitate into the upper atmosphere in both hemispheres. This symmetry arises from the near-dipolar structure of Earth's magnetosphere, where processes accelerating particles in the equatorial magnetosphere affect both footpoints equivalently.^[83]^[84] Observing conjugate auroras directly is rare owing to the inaccessibility of paired sites, such as remote Antarctic stations conjugate to Arctic observatories. Historical ground-based efforts, like the early 20th-century Gjøa Haven and Cape Armitage expeditions, offered initial comparative insights into polar cap auroral forms over seven months of overlapping visibility, revealing shared characteristics such as streamers and bands. Satellite observations have since revolutionized such studies; the Viking spacecraft in the 1980s provided high-resolution ultraviolet imagery of the northern auroral oval, which was coordinated with all-sky and keogram cameras at the South Pole to demonstrate optical conjugacy in discrete arcs and diffuse emissions. More contemporary data from the European Space Agency's Swarm satellites, which track magnetic footprints to both concurrent and conjugate points, confirmed conjugate auroral responses during the severe geomagnetic storm of 10–11 May 2024, with in-situ measurements showing symmetric ionospheric enhancements linked to particle precipitation across hemispheres.^[85]^[86]^[87]^[88] These paired events serve as key evidence for the fidelity of field-line mapping in the magnetosphere, illustrating how magnetospheric disturbances propagate uniformly to both hemispheres. Nonetheless, observed asymmetries in auroral brightness or morphology—such as brighter displays in one hemisphere—often stem from differential atmospheric scattering of particles or variations in ionospheric conductivity, which can alter precipitation efficiency without disrupting the underlying magnetic connectivity. Such discrepancies emphasize the role of hemispheric-specific environmental factors in modulating global auroral dynamics.^[89]^[84]

Magenta and Blue Auroras

Magenta auroras manifest as extended pinkish-purple bands, particularly prominent during intense geomagnetic storms, resulting from the superposition of red emissions from atomic oxygen at 630.0 nm and blue-violet emissions from the N₂⁺ first negative system at 391.4 nm and 427.8 nm. These high-altitude displays, reaching approximately 1000 km, arise from a combination of broadband electron precipitation producing the red component and low-energy (<1 keV) electron precipitation along with heavy particle (ions and neutrals >10 keV) aurora contributing to the blue-violet hues. A 2024 citizen science study utilizing over 775 photographic observations from Japan during the May 10–11 geomagnetic superstorm (Dst index of -412 nT) revealed that the enhanced N₂⁺ density (~30 cm⁻³ above 350 km) at these altitudes creates the distinctive magenta coloration, distinguishing it from typical lower-altitude red auroras. This phenomenon is linked to increased proton and heavy ion fluxes, which preheat the atmosphere and extend emissions to subvisual levels observable across mid-latitudes (27°–46° N).^[90] Blue auroras appear as rare, bright blue features originating from the first negative band system of N₂⁺, peaking around 427.8 nm, excited by precipitating electrons interacting with atmospheric nitrogen molecules. These emissions require high-energy electrons exceeding 10 keV to ionize and excite N₂ into the necessary states, producing the characteristic blue glow at altitudes of about 130–200 km. The first hyperspectral imaging capture of such a blue aurora's precise altitude distribution occurred using the HyperSpectral Camera for Auroral Imaging (HySCAI) during twilight observations in Kiruna, Sweden, on October 21, 2023, with results published in November 2025; this revealed peak intensities at ~200 km due to resonant scattering of sunlight-excited N₂⁺ emissions intersecting the instrument's field of view. Unlike common green or red auroras dominated by oxygen emissions, blue variants highlight nitrogen ion dominance under specific precipitation conditions.^[91]^[92] Both magenta and blue auroras have become more frequent and visible during the 2023–2025 solar maximum, driven by heightened solar activity including coronal mass ejections that intensify geomagnetic storms. Observations of these rare colors extended to lower latitudes, such as widespread sightings across Europe during the May 2024 superstorm, where magenta bands were reported as far south as central France and Italy due to the storm's extreme intensity. This period's elevated solar wind speeds and interplanetary magnetic field strengths facilitated particle precipitation reaching subauroral regions, enhancing the detectability of these spectral variants through citizen photography and ground-based spectrometers.^[93]^[90]

Physical Mechanisms

Solar Wind and Interplanetary Medium

The solar wind originates from the Sun's corona and consists of a magnetized plasma primarily composed of electrons, protons (approximately 95%), and alpha particles (about 4%), with trace amounts of heavier ions. This plasma streams continuously toward Earth at typical speeds ranging from 300 to 800 km/s, with densities of 5 to 10 particles per cm³ at 1 AU.^[94]^[95] Coronal mass ejections (CMEs) introduce transient high-speed enhancements to the solar wind, often exceeding 1000 km/s and increasing plasma density by factors of 10 or more, thereby amplifying the energy flux delivered to the heliosphere.^[96] Embedded within the solar wind is the interplanetary magnetic field (IMF), a frozen-in magnetic structure spiraling outward from the Sun with a typical magnitude of 3 to 7 nT at Earth's orbit. The orientation of the IMF, especially its north-south component (Bz), critically influences the transfer of solar wind energy to Earth's magnetic environment; a southward Bz orientation aligns antiparallel to Earth's northward field, promoting efficient magnetic reconnection. The reconnection rate, which governs the opening of magnetic flux lines, is approximated by the formula

\varepsilon = \frac{V_{\mathrm{sw}} B_{\mathrm{IMF}}^2 \sin^4(\theta/2) L^2}{\mu_0},

where V_{\mathrm{sw}} is the solar wind velocity, B_{\mathrm{IMF}} is the IMF magnitude, \theta is the clock angle between the IMF and Earth's field, L is the effective length scale (approximately 10 R_E), and \mu_0 is the permeability of free space.^[97] This process sets the stage for enhanced auroral activity during periods of strong southward IMF.^[98] Solar wind and IMF parameters are monitored in real-time by spacecraft such as the Advanced Composition Explorer (ACE) and Deep Space Climate Observatory (DSCOVR), positioned at the Sun-Earth L1 point approximately 1.5 million km upstream of Earth. These missions measure plasma speed, density, temperature, and IMF components every few minutes, enabling predictions of geomagnetic disturbances like those quantified by the Kp index, which correlates directly with auroral intensity. For instance, sustained solar wind speeds above 500 km/s combined with southward Bz below -5 nT often precede Kp values exceeding 5, signaling widespread auroras.^[99] These observations provide critical lead times of 30 to 60 minutes for space weather forecasting.

Earth's Magnetosphere

Earth's magnetosphere forms a protective cavity around the planet, shaped by the interaction between its intrinsic dipole magnetic field and the incoming solar wind. The dipole field, tilted approximately 11 degrees from Earth's rotational axis, extends roughly 10 Earth radii (R_E, where 1 R_E ≈ 6,371 km) sunward on the dayside, creating a compressed, bullet-like structure. Antisunward, the field lines are stretched by the solar wind into an elongated magnetotail exceeding 100 R_E in length, with the distant tail observed to extend several hundred R_E beyond the Moon's orbit at ~60 R_E. The magnetopause, the inner boundary of this cavity at about 10 R_E subsolar, separates the magnetospheric plasma from the solar wind, while the bow shock forms farther out at approximately 13 R_E, where the supersonic solar wind (typically 300–800 km/s) is decelerated and heated, producing the turbulent magnetosheath. The magnetotail is divided into two oppositely directed lobes of low-density plasma, separated by the central plasma sheet, a region of hotter, denser plasma spanning ~10–20 R_E in cross-section near Earth and thinning distally.^[100]^[101]^[102] The solar wind drives dynamic processes within the magnetosphere through magnetic reconnection, particularly at the dayside magnetopause. When the interplanetary magnetic field (IMF) points southward (opposite to Earth's field), reconnection opens field lines, allowing solar wind plasma to enter and couple energy into the system, with flux transport rates scaling with the IMF strength and solar wind speed. For northward IMF, reconnection shifts to the magnetotail lobes, enabling high-latitude entry of solar wind ions and maintaining a closed configuration on the dayside while still facilitating energy input. This opened flux is convected tailward over the polar caps, accumulating magnetic energy in the plasma sheet, where it stretches the cross-tail current and thins the sheet to ion-scale thicknesses (~1,000 km) during the substorm growth phase. Substorms then release this stored energy explosively via near-tail reconnection (typically at ~20–30 R_E), converting magnetic energy into particle kinetic energy and electromagnetic waves, with power outputs reaching 10^{11}–10^{12} W during intense events.^[103]^[104] Auroral phenomena are intimately linked to magnetospheric currents and plasma entry regions. Field-aligned currents, also known as Birkeland currents, flow along magnetic field lines from the magnetosphere to the ionosphere, forming large-scale systems that map directly to the auroral oval—a ring of precipitation centered at ~65–75° magnetic latitude. Region 1 currents (poleward) connect the tail lobes to the oval's poleward boundary, driven by plasma pressure gradients, while Region 2 currents (equatorward) link the inner magnetosphere's ring current to the equatorward edge. Plasma entry occurs primarily through the cusp—a funnel-shaped region near local noon at ~75–80° latitude, allowing direct access of magnetosheath plasma—and the low-latitude boundary layer along the magnetopause flanks, where reconnection injects energetic particles that precipitate along field lines to produce dayside auroras. The density of these field-aligned currents can be estimated from Ampère's law projected along the field, given by

J_{\parallel} = \frac{ (\nabla \times \mathbf{B})_{\parallel} }{\mu_0},

where (\nabla \times \mathbf{B})_{\parallel} is the parallel component of the curl and \mu_0 is the vacuum permeability; typical intensities reach 0.1–1 μA/m² in the oval, scaling with substorm activity.^[105]

Auroral Particle Acceleration

Auroral particle acceleration occurs primarily in the auroral acceleration region, situated at altitudes of approximately 1–2 Earth radii (about 6000–12,000 km) above the Earth's ionosphere, where quasi-static parallel electric fields drive the energization of charged particles along magnetic field lines.^[106] These fields manifest as potential drops typically ranging from 10–20 kV, with higher values observed during intense auroral activity, enabling the acceleration of particles to keV energies necessary for auroral precipitation. Key structures within this region include double layers—regions of charge separation that sustain strong, localized parallel electric fields—and wave-particle interactions, such as those involving whistler waves, which can further modulate particle energies through resonant scattering. In-situ observations from the MMS mission have confirmed electron-scale reconnection sites contributing to these parallel electric fields.^[107] The accelerated particles consist mainly of electrons and protons originating from the plasma sheet in Earth's magnetotail. Electrons, typically energized to 1–20 keV, are the primary drivers of discrete auroral arcs due to their efficient precipitation and interaction with atmospheric constituents.^[108] Protons, accelerated to 1–100 keV, contribute more to diffuse red auroras through charge exchange processes. Particle fluxes in these events can reach up to $10^8 cm^{-2} s^{-1} sr^{-1} (differential), representing intense precipitation capable of depositing significant energy into the upper atmosphere.^[109] Beyond direct parallel electric field acceleration, additional mechanisms enhance particle energies in the auroral region. Fermi acceleration occurs as particles bounce between the hemispheres, gaining energy through repeated encounters with converging plasma flows or waves, while betatron acceleration arises from adiabatic invariance in the increasing magnetic field strength toward lower altitudes. For relativistic particles, the energy gain in Fermi processes approximates \Delta E / E \approx v_\parallel / c, where v_\parallel is the parallel velocity and c is the speed of light; however, auroral particles are non-relativistic, so such gains are instead dominated by lower-order effects like pitch-angle scattering mediated by lower hybrid waves, which isotropize distributions and facilitate further energization.^[110]^[111]

Interaction with Atmosphere and Ionosphere

Precipitating auroral electrons, typically with energies of a few keV, collide with neutral atoms and molecules in Earth's upper atmosphere, primarily atomic oxygen (O) and molecular nitrogen (N₂), leading to excitation of their electronic states.^[112] Upon collisional de-excitation, these excited species emit photons at characteristic wavelengths, such as the green 557.7 nm line from the O(¹S → ¹D) transition, producing the visible auroral glow.^[113] The efficiency of this process is governed by electron impact excitation cross sections, which for the production of the 557.7 nm emission via oxygen are on the order of 10^{-16} cm² at peak energies around 100 eV.^[114] Similar cross sections apply to N₂ excitation, contributing to blue emissions like the N₂⁺ first negative band at 427.8 nm.^[115] Concurrently, electron impacts cause ionization of atmospheric constituents, increasing free electron and ion densities, which in turn enhances electrical conductivity in the ionosphere.^[116] In the E-region (approximately 90–150 km altitude), this enhanced ionization significantly boosts the Hall and Pedersen conductivities, enabling stronger electrodynamic currents that couple the magnetosphere to the ionosphere.^[117] Hall conductivity peaks around 94–96 km due to its dependence on electron motion perpendicular to both the magnetic field and electric field, while Pedersen conductivity, involving motion across field lines, maximizes near 116 km.^[117] These conductivities facilitate field-aligned currents and horizontal ionospheric currents, driving auroral electrojets. The interaction also generates Joule heating through ohmic dissipation, with rates reaching up to 100 mW/m² during intense precipitation, contributing to atmospheric heating and upwelling. The volume emission rate for excited states, which determines observable intensities, can be approximated by the excitation production rate:

\frac{dN}{dt} = n_e \sigma v N_g

where N is the density of excited atoms, n_e is the electron density, \sigma is the excitation cross section, v is the electron velocity, and N_g is the ground-state neutral density.^[113] Auroral interactions also induce feedback mechanisms, including ionospheric outflows of O⁺ ions into the magnetosphere, particularly during substorms when enhanced electric fields and heating drive ion upwelling.^[118] These outflows supply heavy ions to the magnetosphere, influencing ring current dynamics and storm-time evolution. Recent 2024 studies using FAST satellite data reveal that O⁺ outflow fluxes vary significantly between storm phases, with peaks shifted to the dawn sector during sawtooth events and up to tenfold higher initial-phase outflows in non-sawtooth storms compared to sawtooth ones.^[119] This upwelling is tied to substorm intensification, where precipitating electrons and Joule heating accelerate polar wind-like flows, enriching the inner magnetosphere with ionospheric plasma.^[119]

Historical and Cultural Significance

Notable Historical Events

One of the most significant historical auroral events was the Carrington Event of September 1-2, 1859, triggered by a massive solar flare observed by Richard Carrington, which produced a geomagnetic storm that made auroras visible worldwide, including as far south as Hawaii, Colombia, and Mexico.^[120] This extreme disturbance induced strong currents in telegraph lines, causing widespread disruptions, fires at telegraph stations, and operators receiving electric shocks, marking the first documented link between solar activity and terrestrial technology impacts.^[121]^[122] In January 1938, a series of intense geomagnetic storms, peaking around January 25, generated auroras visible across North America from the far north of Canada to Southern California and even Bermuda, ranking among the most severe storms recorded up to that time.^[123] These events raised early concerns about potential blackouts and infrastructure vulnerabilities in the United States, as the storms induced geomagnetic currents that could affect power systems, though no major outages occurred.^[124] The storms' intensity, with rapid field variations, highlighted the global reach of solar-terrestrial interactions.^[123] The March 13, 1989, geomagnetic storm, classified as G5 (extreme), resulted from a coronal mass ejection that struck Earth's magnetosphere, causing a major power blackout in Quebec, Canada, affecting six million people for up to 12 hours and leading to an estimated $2 billion in economic losses.^[125]^[126] Auroras were visible as far south as Cuba during this event, underscoring the storm's scale and its direct impact on modern electrical grids.^[127] During the Halloween solar storms of October 19 to November 4, 2003, a series of 17 major solar flares and coronal mass ejections produced intense geomagnetic activity, pushing auroras equatorward to latitudes as low as Florida, Texas, and even the Mediterranean.^[128]^[129] These storms disrupted satellite operations, GPS signals, and high-frequency radio communications, with economic impacts estimated in the hundreds of millions of dollars.^[121] More recently, the G5 geomagnetic storm of May 10-11, 2024—the strongest since 2003—stemmed from multiple solar flares and coronal mass ejections, making auroras visible in unusually low latitudes such as Arizona and Florida for the first time in decades.^[130]^[131] This event prompted warnings for potential power grid fluctuations and satellite drag, though no major outages were reported.^[132] In October 2025, heightened solar activity during solar maximum led to geomagnetic storms around October 28-29, with auroras visible across multiple U.S. states, including northern and mid-latitude regions like the Midwest and Northeast.^[133]^[134] These displays, driven by coronal mass ejections, extended visibility farther south than typical, captivating observers amid ongoing solar cycle peaks.^[24] A severe geomagnetic storm on November 10-12, 2025, triggered by an X-class solar flare and coronal mass ejections, produced vivid auroras visible across the United States from Washington to Florida, including states like Texas, Tennessee, and New York.^[135]^[136] This G4-level event caused minor disruptions to satellite operations and high-frequency radio but no widespread power outages.^[137] Southern Hemisphere events also gained prominence in 2025 due to solar maximum conditions. On June 1, 2025, a G4/G5 geomagnetic storm produced a vivid aurora australis visible in Sydney, Australia, with pink and green hues illuminating the night sky for stargazers in urban areas.^[138]^[139] Earlier, in January 2025, aurora australis displays lit up southern Australia from Tasmania to the mainland, coinciding with the onset of solar maximum and offering rare sightings during the summer season.^[140]^[141] These events emphasized the heightened auroral activity expected through 2025 as sunspot numbers peak.^[142]

Folklore and Cultural Interpretations

In various Indigenous cultures of the Arctic regions, the aurora borealis held profound spiritual significance, often interpreted as manifestations of ancestral spirits or otherworldly beings. Among the Inuit peoples, particularly in northern Greenland and Alaska, the lights were commonly viewed as the spirits of the deceased engaging in games, such as playing with a walrus skull as a ball, or as torches held by souls guiding the recently departed to the afterlife.^[143]^[144] Similarly, the Sámi people of northern Scandinavia associated the aurora with the mythical "fire fox" (revontuli in Finnish-related lore), a swift creature whose tail brushed against the snowy landscape, scattering sparks that ignited the sky as a sign of good fortune or impending change.^[143]^[145] A popular legend attributes the shimmering displays to reflections from the armor and shields of Valkyries, the warrior maidens who escorted fallen heroes to Valhalla in Norse folklore, evoking a sense of divine selection and battle glory.^[143]^[145] During the medieval period in Europe, auroral sightings, especially those with a reddish hue visible farther south, were frequently regarded as ominous portents of conflict, divine wrath, or catastrophe. Chronicles from the early Middle Ages, such as those by Gregory of Tours, described red auroras as harbingers of bloodshed, famine, or plague, interpreting them as celestial warnings to humanity.^[146] In continental Europe, a notable 1574 auroral event was chronicled as a fiery red phenomenon, akin to blood rain, fueling fears of impending war or apocalyptic events among observers in England and beyond.^[147] These interpretations reflected a broader cultural tendency to link unusual sky events with moral or political upheaval, absent any scientific understanding of their solar origins.^[145] In modern times, the aurora has inspired artistic and literary works that blend wonder with existential themes, while also driving significant economic and touristic interest. The 19th-century Hudson River School painter Frederic Edwin Church captured the aurora in his 1865 oil painting Aurora Borealis, portraying it as a dramatic Arctic spectacle that symbolized both natural majesty and post-Civil War hope, based on sketches from explorer Isaac Hayes.^[148] In literature, H.P. Lovecraft evoked the aurora's eerie glow in his 1918 short story "Polaris," where it illuminates a night of cosmic dread over a swamp, tying into themes of ancient, otherworldly forces in his cosmic horror genre.^[149] The heightened solar activity during the 2024-2025 solar maximum, marking one of the strongest auroral displays in 500 years, has spurred a tourism boom, with northern lights viewing generating over $843 million globally in 2023 and projected growth into 2025, attracting record visitors to Arctic destinations like Norway, Iceland, and Alaska through specialized noctourism experiences.^[150]^[151]^[152]

Extraterrestrial Auroras

Auroras on Planets

Auroras occur on several planets beyond Earth, driven by interactions between solar wind particles and planetary magnetic fields or atmospheres, though the mechanisms vary due to differences in magnetospheres and compositions. On gas giants like Jupiter and Saturn, robust magnetospheres channel charged particles into auroral displays, often enhanced by internal plasma sources from moons. In contrast, unmagnetized planets like Mars and Venus exhibit more diffuse or induced auroras from direct solar wind penetration.^[153] Jupiter's auroras are among the brightest in the solar system, primarily observed in ultraviolet wavelengths due to emissions from molecular hydrogen (H₂). A key feature is the influence of the Io plasma torus, where volcanic material from the moon Io ionizes and forms a ring of charged particles that injects plasma into Jupiter's magnetosphere, fueling equatorward auroral emissions.^[154] The main auroral oval results from solar wind interactions compressing the magnetosphere, while polar regions show discrete spots linked to magnetic field anomalies. Observations from the Hubble Space Telescope and Juno spacecraft have mapped these features, revealing dynamic structures with brightness variations tied to solar activity and internal dynamics.^[155]^[153] Saturn's auroras, also prominent in ultraviolet and infrared, are shaped by its ring system and moon Enceladus, which supplies water-group ions (such as H₂O⁺ and OH⁺) through cryovolcanic plumes that become ionized plasma in the magnetosphere. These ions contribute to auroral precipitation, particularly in the main oval, distinguishing Saturn's displays from those powered solely by solar wind. Cassini spacecraft observations from 2004 to 2017 documented seasonal variations, with auroral intensity peaking during solstices due to the planet's 26.7-year orbital tilt, shifting plasma distributions and solar wind access.^[156]^[157]^[158] Mars, lacking a global magnetosphere, experiences diffuse, widespread auroras from solar wind protons directly exciting atmospheric oxygen across the planet. These proton auroras, first detected by Mars Express in ultraviolet, are global rather than localized ovals. In March 2024, NASA's Perseverance rover captured the first visible-light aurora from Mars' surface—a green glow from the 557.7 nm atomic oxygen emission line—during an intense coronal mass ejection event. With Solar Cycle 25 reaching maximum in 2025, predictions indicate enhanced auroral activity on Mars due to increased solar flares and coronal mass ejections, potentially making visible auroras more frequent and intense.^[159]^[160]^[161] Venus, without an intrinsic magnetic field, hosts auroras induced by solar wind draping around its ionosphere, creating a magnetotail where particles precipitate into the upper atmosphere. These displays are faint and observed mainly in ultraviolet from nitric oxide and carbon monoxide emissions, with detections by Pioneer Venus Orbiter confirming activity during solar storms. Similarly, Uranus and Neptune exhibit hydrogen-based auroras, with Voyager 2 detecting ultraviolet H₂ emissions and radio signatures in 1986, linked to their tilted, offset magnetospheres that allow irregular particle acceleration. Recent James Webb Space Telescope observations of Neptune in 2025 revealed prominent H₃⁺ infrared emissions, indicating auroral heating in the stratosphere.^[162]^[163]^[164]

Auroras on Moons and Other Bodies

Auroras on Jupiter's moon Io are among the most intense in the solar system, driven by the moon's extreme volcanic activity that ejects sulfur and oxygen into Jupiter's magnetosphere. Volcanic plumes on Io release gases, primarily sulfur dioxide, which become ionized and form a plasma torus encircling Jupiter, generating powerful currents that accelerate particles to produce bright ultraviolet and X-ray emissions in Io's auroral footprint on Jupiter's atmosphere.^[165] These auroras exhibit rapid variability tied to Io's eruption rates, with the plasma loading Jupiter's magnetic field and causing pulsed brightenings observable from spacecraft like Juno.^[166] Ganymede, Jupiter's largest moon, features auroras influenced by its unique intrinsic magnetic field, which creates a protective bubble within Jupiter's stronger magnetosphere and leads to distinctive oxygen-based emissions. This mini-magnetosphere interacts with Jupiter's rotating field, producing auroral footprints on Jupiter's poles that appear as bright, spot-like ultraviolet features displaced from the main auroral oval.^[167] Observations from the Galileo mission confirmed Ganymede's own polar auroras, generated by electrons trapped in its magnetic bubble, with emissions peaking in the far-ultraviolet range due to oxygen excitation.^[168] Recent Juno data further reveal how Ganymede's field modulates electron beams, enhancing the footprint's intensity during specific orbital alignments.^[169] On Saturn's moon Enceladus, auroral activity stems from its water vapor plumes, which supply neutral hydrogen and oxygen to Saturn's magnetosphere, resulting in hydrogen and water-related emissions. The moon's south polar geysers eject H₂O molecules that are ionized and picked up by Saturn's magnetic field, creating a plasma wake that generates ultraviolet auroral spots in Saturn's ionosphere.^[170] Cassini observations detected these footprint emissions as enhanced H Ly-α and O I lines, with intensities varying with plume activity and solar wind conditions.^[171] Beyond planetary moons, aurora-like phenomena occur on the Sun itself, where long-lasting radio bursts resembling planetary auroral emissions have been observed emanating from sunspots. In 2024, a NASA-supported study using ground-based radio telescopes identified GHz-frequency radio bursts lasting over a week, produced by electron cyclotron maser instability in the Sun's corona above active regions, analogous to auroral radio emissions on magnetized planets.^[172] For exoplanets, particularly hot Jupiters, ultraviolet auroras are inferred from spectroscopic searches using the James Webb Space Telescope (JWST), focusing on tracers like H₃⁺ emission that indicate magnetic field interactions with stellar winds. A 2025 study on hot Jupiter WASP-80b set stringent upper limits on H₃⁺ auroral signals in the infrared, suggesting potential weak auroras driven by intense stellar irradiation but below detectable thresholds with current instruments.^[173] Similar analyses for other hot Jupiters imply UV auroras could dominate due to their close orbits, providing indirect evidence of planetary magnetism.^[174]

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Exploring the relationship between STEVE and SAID during three ...
Jul 22, 2024 · The highest velocities were observed between 59° and 60°mlat, and, in this case, were at a lower magnetic latitude than the STEVE. It should be ...
[70]
The Vertical Distribution of the Optical Emissions of a Steve and ...
Sep 3, 2019 · The optical emissions of Steve range from 130 to 270 km in altitude The optical emissions of the green Picket Fence range from 95 to 150 km ...
[71]
It's Not Easy Being Green: Kinetic Modeling of the Emission ...
Nov 3, 2023 · Like green aurora, the picket fence primarily consists of 557.7 nm ... 25 km of the altitudinal profile for the selected observations ...
[72]
Citizen scientists lead to the discovery of optical structure in ... - NIH
Mar 14, 2018 · In addition, the green picket fence aurora we report has not been documented in the literature at these latitudes. During an SAID event ...
[73]
The Apparent Motion of STEVE and the Picket Fence Phenomena
Oct 16, 2020 · The emission altitude of the Picket Fence is found to be ~110 km, similar to typical auroras (Archer, Gallardo-Lacourt, et al., 2019; Hunnekuhl ...
[74]
Aurora-Chasing Citizen Scientists Help Discover A New Feature of ...
Nov 13, 2020 · “STEVE is different than the usual aurora, but it is made of light and it is driven by the auroral system. In finding these tiny little streaks, ...Missing: characteristics | Show results with:characteristics
[75]
Citizen Scientists Discover a New Auroral Form: Dunes Provide ...
Jan 28, 2020 · We present a new auroral form named “the dunes”. On 7 October 2018, citizen observers took multiple digital photographs of the same dunes simultaneously.
[76]
Large‐Scale Dune Aurora Event Investigation Combining Citizen ...
May 4, 2021 · During a dune aurora event spanning over 1500 km, satellite observations indicate that auroral precipitation takes place in the dune area ...
[77]
Sawtooth and dune auroras simultaneously driven by waves around ...
The dune aurora, at a scale of ~30 kilometers, was reported recently using ground camera. The small-scale dune aurora occurs on the duskside and exhibits a ...
[78]
Occurrence Statistics of Horse Collar Aurora - Bower - 2022
May 15, 2022 · Horse collar aurora, teardrop shaped polar cap, occur frequently approximately 8 times per month and are linked to dual lobe reconnection ...
[79]
The horse‐collar aurora: A frequent pattern of the aurora in quiet times
This initial report of the DE 1 observations illustrates the horse-collar aurora with a 2-hour image sequence that displays its basic features and shows an ...
[80]
Horizontal profile of a moving red line cusp aurora - AGU Journals
Feb 13, 2017 · The moving red line cusp aurora typically has a latitudinal extent ... The proton density was between ~7 cm−3 and ~12 cm−3 for that ...
[81]
Dual‐Lobe Reconnection and Horse‐Collar Auroras - AGU Journals
Oct 14, 2020 · We propose a mechanism for the formation of the horse-collar auroral configuration during periods of strongly northward interplanetary magnetic field (IMF).Missing: diameter | Show results with:diameter
[82]
Simultaneous images of the northern and southern auroras from the ...
Apr 3, 2003 · Aircraft observations at conjugate points with magnetic latitudes in the range of 63°–65° showed that auroral forms were conjugate but during ...
[83]
Auroral conjugacy studies based on global imaging - ScienceDirect
For these reasons, conjugate simultaneous global imaging from space is really what can resolve the degree of conjugacy and non-conjugacy of auroral phenomena.
[84]
Conjugate aurora observations by the Gjøa and Discovery expeditions
Jul 8, 2024 · Auroras were observed during 7 months per year. This gave a unique possibility to compare conjugate characteristics of polar cap auroras.
[85]
Optical auroral conjugacy: Viking UV Imager—South Pole Station ...
May 1, 1990 · High time resolution satellite UV images of the northern auroral oval are compared with South Pole station keogram camera and all-sky camera ...
[86]
Significant Midlatitude Plasma Density Peaks and Dual‐Hemisphere ...
Nov 11, 2024 · This study investigates midlatitude ionospheric responses during the super geomagnetic storm on 10–11 May 2024, using multi-instrument data from ...
[87]
Data - Swarm-Aurora
Satellite position is shown as a geographic footprint of the North and South magnetic field trace. We display both the concurrent and conjugate footprint ...Missing: definition observations Viking<|control11|><|separator|>
[88]
Conjugate auroras and the interplanetary magnetic field - 1997
Feb 1, 1997 · It is suggested that while the diffuse aurora is conjugate, the discrete aurora is nonconjugate but still on closed field lines.
[89]
Extended magenta aurora as revealed by citizen science - Nature
Oct 28, 2024 · In this study, we demonstrate that the magenta hue is created by a mixture of red (O) and a blue (N 2 + ) aurora at extremely high altitudes.
[90]
Estimate of N2+ $ Altitude Profile Using Blue Auroral Resonant ...
The spectrum of high-altitude blue auroral emissions was observed with HyperSpectral camera for auroral imaging (HySCAI) during morning ...
[91]
Bright blue aurora formation: Hyperspectral camera captures first precise altitude distribution
### Summary of Blue Aurora and Hyperspectral Capture (November 2025)
[92]
2025 will be a bumper year for northern lights sightings. Here are ...
Dec 27, 2024 · The northern lights have been dancing with increased frequency over Europe's skies in late 2024 as well as appearing much further south than ...
[93]
[PDF] (nasa-tm-19736_) solar wind composition
The solar wind is approximately 95% protons (H+), 4% alpha particles (He ++) and 1% minor ions, of which carbon, nitrogen, oxygen, neon, magnesium, silicon and ...
[94]
Solar Wind Variations - NASA/Marshall Solar Physics
The solar wind speed is high (800 km/s) over coronal holes and low (300 km/s) over streamers. These high and low speed streams interact with each other and ...
[95]
A Coronal Mass Ejection strikes the Earth! - NASA SVS
Jan 24, 2012 · The enormous density enhancement in the solar wind is the coronal mass ejection. As the CME reaches the Earth, we see how effective the ...
[96]
Contribution of magnetotail reconnection to the cross‐polar cap ...
Aug 16, 2011 · The dayside source was parameterized by solar wind–based “dayside merging potential” Φd = LeffVBt sin4(θ/2), whereas to characterize the ...
[97]
Determination of interplanetary magnetic field strength, solar wind ...
Average B during 1872-2003 was 6.4 nT with no long-term trend (other than a general correlation with the sunspot number) and average V for the interval 1890- ...
[98]
SPDF - OMNIWeb Service
Spacecraft-specific data sets (near 1 AU, including near-Earth) ; 15-sec. magnetic field data, solar wind only · Plots, listings, subsetted files ; 1-min, magnetic ...Missing: index | Show results with:index
[99]
Earth's magnetosphere | NOAA / NWS Space Weather Prediction Center
### Summary of Earth's Magnetosphere
[100]
https://www.swpc.noaa.gov/phenomena/earths-magnetosphere
[101]
[PDF] 1 1 Size and Shape of the Distant Magnetotail 2 3 4 D. G. Sibeck ...
magnetospheric magnetic field lines within the slow mode expansion fan near Earth to gradually. 286 gain the antisunward orientations expected for the south ...
[102]
Pivotal role of magnetic reconnection in the Earth's magnetosphere
The energy released by this reconnection accelerates the plasma in the magnetotail and produces the global disturbance called magnetospheric substorm. The above ...
[103]
Solar Wind Energy Input: The Primary Control Factor of Magnetotail ...
Aug 7, 2022 · The strong solar wind energy input produces favorable conditions for an onset of magnetic reconnection in the postmidnight sector of the ...
[104]
Boundary layer plasmas as a source for high-latitude, early ...
A mechanism for driving the gross Birkeland current configuration in the auroral oval. J. geophys. Res., 81 (1976), p. 235. Google Scholar. Russell and Elphic ...
[105]
Altitude Distribution of the Auroral Acceleration Potential Determined ...
Feb 1, 2011 · Here, Cluster data are used to determine the acceleration potential above the aurora and to address its stability in space and time.
[106]
Auroral particle acceleration by strong double layers: The upward ...
Dec 24, 2004 · The purpose of this article is to examine the role of double layers in auroral electron acceleration using direct measurements of parallel ...
[107]
Comparison of Auroral Processes: Earth and Jupiter - ResearchGate
Aug 5, 2025 · ... energy electrons: 1-20 keV. protons: 1-100 keV. electrons: 20-50 keV. protons: ? O. +. , S. +. : 20 keV to 20 MeV. Hemispheric power 1-300 GW 10 ...<|control11|><|separator|>
[108]
Measurements of precipitated 1-20 kev protons and electrons during ...
... energy (1-20 kev) protons and electrons during a breakup aurora are described. The observed proton fluxes were as high as 10 8 cm -2 sec -1 kev -1 ster -1 ...Missing: 1-100 sr^
[109]
Fermi and betatron acceleration of suprathermal electrons behind ...
Aug 20, 2011 · Our results show that Fermi acceleration dominates inside a decaying flux pileup region (FPR), while betatron acceleration dominates inside a growing FPR.
[110]
Electron acceleration driven by the lower-hybrid-drift instability
Our study is aimed at quantifying the efficiency of the lower-hybrid-drift instability to accelerate or heat electrons parallel to the ambient magnetic field.Missing: betatron | Show results with:betatron
[111]
Electron Collisions with N2, O2, and O: What we do and do not Know
A part of the aurora is excited by high-energy electrons entering the polar atmosphere (Vallance Jones and Gattinger, 1990). The transport of these electrons ...
[112]
[PDF] The altitude of green OI 557.7 nm and blue N 427.8 nm aurora
Peak emission heights of 557.7nm aurora (green) and. 427.8 nm aurora (blue) as a function of characteristic electron pre- cipitation energy for Gaussian ...
[113]
https://angeo.copernicus.org/articles/41/1/2023/angeo-41-1-2023.pdf
[114]
Synthetic spectra of the aurora: N2, N2+, N, N+, O2+ and O emissions
May 20, 2025 · In this paper, we simulate auroral emission spectra for a given distribution of precipitating electrons using Transsolo, a kinetic code solving the transport ...
[115]
Ionospheric Electron Density and Conductance Changes in the ...
Jul 12, 2021 · Enhanced precipitation of magnetospheric energetic electrons during substorms increases ionospheric electron density and conductance.
[116]
Three-dimensional ionospheric conductivity associated ... - ANGEO
Nov 20, 2023 · The study reconstructed 3D ionospheric conductivity for pulsating auroras, finding Hall conductivity at 94km and Pedersen at 116km, with a ...
[117]
Nightside Auroral H+ and O+ Outflows Versus Energy Inputs During ...
Nov 12, 2022 · This paper finds that the H + outflow increases with increased precipitating electrons in the nightside aurora. The O + outflow increases with both electron ...
[118]
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022JA030923
[119]
What Was the Carrington Event? | NESDIS - NOAA
Today, such a storm could severely damage satellites, disable communications by telephone, radio, and TV, and cause electrical blackouts over whole continents.
[120]
Five historically huge solar events - NOAA
Apr 14, 2025 · The effects were astounding, causing the northern lights (aurora borealis) to be seen farther south than had ever been recorded before.
[121]
[PDF] Eyewitness Reports of the Great Auroral Storm of 1859
Aug 5, 2005 · ABSTRACT. The great geomagnetic storm of 1859 is really composed of two closely spaced massive worldwide auroral events. The first event ...
[122]
The Intensity and Evolution of the Extreme Solar and Geomagnetic ...
Mar 17, 2021 · Jones (1955) identified the geomagnetic storm on 1938 January 25 as among the top 11 storms of the 112 great storms listed between 1874–1954.
[123]
[PDF] th a M ther ea e W pac S - Space Math @ NASA
strong geomagnetic storms and X or M-class solar flares increases significantly, and remains ... the January 26, 1938 storm which caused disruptions for a ' few ...
[124]
Space Weather and Safety
On March 13, 1989, a powerful geomagnetic storm triggered a major power blackout in Canada that left 6 million people without electricity for 9 hours.
[125]
[PDF] Storms on the Sun - Space Weather Prediction Center - NOAA
A dramatic example of the effects of space weather occurred in. March 1989 when a solar storm knocked out power in Quebec for up to 36 hours. The. Hydro-Quebec ...
[126]
Top 5 Times Solar Activity Affected Earth | NESDIS - NOAA
Sep 15, 2020 · Sept 1, 1859. Astronomers Richard Carrington and Richard Hodgson independently observed patches of intensely bright light on the solar surface ...
[127]
Remembering the Great Halloween Solar Storms | News
Oct 31, 2023 · Aurora sightings occurred from California to Texas to Florida. People in Australia, central Europe, and even as far south as the Mediterranean ...
[128]
Looking Back at 2003s Spooky Halloween Solar Storms - NASA SVS
Oct 30, 2008 · From October 25, 2003, to November 7, 2003, the sun sent a series of solar storms that lit up the sky with ghoulish auroras.
[129]
How NASA Tracked the Most Intense Solar Storm in Decades
May 16, 2024 · On May 14, 2024, the Sun emitted a strong solar flare. This solar flare is the largest of Solar Cycle 25 and is classified as an X8.Missing: Arizona Florida
[130]
Jaw-dropping northern lights from massive solar flares amaze ...
May 11, 2024 · A rare G5 geomagnetic storm not seen since Halloween 2003 is supercharging the northern lights around the world.
[131]
Northern lights forecast: Where will they be visible Saturday?
May 11, 2024 · The northern lights were seen as far south as Florida, Oklahoma, Texas and Arizona overnight. Saturday night could bring another spectacular ...
[132]
Northern lights could be visible in these US states. See where.
Oct 28, 2025 · The northern lights could be visible in certain states on Tuesday night, Oct. 28, and Wednesday night, Oct. 29, according to SPWC. Hurricane ...
[133]
Northern Lights likely visible in these 15 states. Here's how to see ...
Oct 28, 2025 · The activity is expected to fluctuate between Oct. 28 through the evening of Oct. 29.
[134]
Aurora australis thrills light show chasers - ABC News
Jun 2, 2025 · Australian stargazers enjoyed a brilliant show Sunday night, with auroras illuminating the dark winter sky with pink and green hues.
[135]
The Aurora Australis could be visible from Sydney tonight - Time Out
An aurora alert has just been issued by the Australian Space Weather Forecasting Centre – here's the lowdown on seeing the Aurora Australis from NSW.
[136]
Vibrant aurora australis lights up vast areas from Tasmania to ...
Jan 1, 2025 · The solar maximum is expected to last for about a year, however there have been recorded double peaks in the past. Posted Wed 1 Jan 2025 at 3: ...
[137]
Spectacular aurora australis thrills sky gazers across south-east ...
Jan 1, 2025 · South-eastern Australia was treated to a dazzling natural light show to begin 2025. A vibrant aurora australis was visible to the naked eye ...
[138]
Solar Maximum Makes 2025 a Great Year for Northern Lights
Jan 13, 2025 · With the Sun at solar maximum, 2025 promises more chances to witness incredible displays of the northern and southern lights.
[139]
Mythology of the Northern Lights | The Aurora Zone
Aurora Borealis is derived from the Greek words “Aurora” meaning “sunrise” and “Boreas” meaning “wind”. For the ancient Greeks to have seen the lights, there ...
[140]
Aurora in Eskimo Legend | Geophysical Institute
Nov 21, 1977 · In Eskimo legend, the aurora is the highest heaven, caused by spirits playing ball, and some believe it brings fine weather. Some also fear it.
[141]
History of the Northern Lights: myths and legends - Hurtigruten
The Inuits of northern Greenland believed the lights were the spirits of the dead playing celestial games with a walrus skull, though other local Inuit ...
[142]
Red lights in the sky, hunger in sight: aurora borealis and famine ...
Jan 4, 2019 · Red lights in the sky, hunger in sight: aurora borealis and famine between experience and rhetoric in the early Middle Ages.Missing: 1574 rain
[143]
Out of Old Books-Absence of Aurorae in the Seventeenth Century
Now in England, during the whole of the seventeenth century, not an auroral glimmer was chronicled. Stowe recounts that on the 14th and 15th of November, 1574, ...
[144]
Aurora Borealis | Smithsonian American Art Museum
Today, let's take a look at one of the paintings in the museum's 19th century landscape collection. Completed in 1865, Frederic Church's “Aurora Borealis” ...
[145]
"Polaris" by H. P. Lovecraft
Aug 20, 2009 · Well do I remember the night of the great Aurora, when over the swamp played the shocking coruscations of the daemon-light. After the beams ...
[146]
Northern Lights Displays Hit A 500-Year Peak In 2024—Here's ...
Dec 30, 2024 · An uptick in activity on the sun's surface this year produced the strongest displays of aurora borealis in the last 500 years, according to ...Missing: boom | Show results with:boom<|control11|><|separator|>
[147]
How the Northern Lights and Digital Photography Have Boosted ...
Jan 10, 2025 · According to the market research company Grand View Research, northern lights tourism generated $843 million in 2023 and is projected to grow ...<|control11|><|separator|>
[148]
Northern Lights Tourism Market To Reach $1,647.9Mn By 2030
The upcoming Solar Maximum is anticipated to enhance the visibility and intensity of the auroras, making 2024 and 2025 prime years for aurora enthusiasts.
[149]
Jupiter's magnetosphere and aurorae observed by the Juno ...
May 26, 2017 · The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles.Missing: torus H2
[150]
Jupiter's Aurora Observed With HST During Juno Orbits 3 to 7
Mar 12, 2018 · These equatorward emissions are likely associated with injection of hot plasma resulting from an enhanced plasma transport from the Io torus.
[151]
Hubble Captures Vivid Auroras in Jupiter's Atmosphere
Jun 30, 2016 · This observation program is supported by measurements made by NASA's Juno spacecraft, currently on its way to Jupiter. Jupiter, the largest ...
[152]
Cassini: Saturn's Magnetosphere - NASA Science
Nov 5, 2024 · Material blasted into space by Enceladus feeds Saturn's giant E ring and is a major source of material (plasma) fueling Saturn's magnetosphere.
[153]
Cassini observations of ionospheric plasma in Saturn's magnetotail ...
Dec 30, 2015 · Studies of Saturn's magnetosphere with the Cassini mission have established the importance of Enceladus as the dominant mass source for ...
[154]
Seasonal variations in Saturn's plasma sheet warping - AGU Journals
Nov 23, 2016 · ENA measurements of Saturn's magnetosphere have been conducted throughout the Cassini mission beginning in 2004 and continuing through the ...
[155]
Detection of visible-wavelength aurora on Mars | Science Advances
May 14, 2025 · The SuperCam aurora observations consist of sets of 75 spectra each with 0.75-s integration time, for which means and medians but not ...
[156]
NASA Observes First Visible-light Auroras at Mars
May 14, 2025 · NASA's Perseverance Mars rover made history by detecting them for the first time from the surface of another planet, and MAVEN confirmed the detection.Missing: diffuse | Show results with:diffuse
[157]
The sun just spat out the strongest solar flares of 2025 - Live Science
May 15, 2025 · NASA models show that the CME is due to hit the Red Planet on Sunday (May 18), and could trigger auroras across Mars' atmosphere. RELATED ...
[158]
Surprise! Venus May Have Auroras Without a Magnetic Field | Space
Apr 5, 2012 · Scientists have discovered the mechanism for creating auroras around the planet Venus, which lacks the magnetic field thought necessary for ...
[159]
Auroral emissions from Uranus and Neptune - PMC
Nov 9, 2020 · Apart from in situ field and plasma measurements, Voyager 2 remotely detected auroral emissions at radio and ultraviolet (UV) wavelengths.
[160]
NASA's Webb Captures Neptune's Auroras For First Time
Mar 26, 2025 · For the first time, they found an extremely prominent emission line signifying the presence of the trihydrogen cation (H3+), which can be ...Missing: hydrogen | Show results with:hydrogen
[161]
Response of Jupiter's Aurora to Plasma Mass Loading Rate ...
Feb 27, 2018 · The dominant plasma source is the moon Io. Io's volcanoes supply neutral gases, which mainly consist of mainly sulfur dioxide (SO2) and ...
[162]
How a Magnetic 'Tug-of-War' With Io's Volcanic Eruptions Creates ...
Feb 5, 2022 · The results confirm the relationship between Io's volcanic eruptions, electrical currents in Jupiter's magnetic field, and the aurora – but the ...
[163]
Satellite Footprints Seen in Jupiter Aurora
Jul 21, 2001 · Auroral footprints can be seen in this image from Io (along the lefthand limb), Ganymede (near the center), and Europa (just below and to the ...Missing: oxygen bubble
[164]
Decades-Old Data Shows Auroras on Jupiter's Moon Ganymede in ...
May 2, 2018 · This magnetic-field region surrounds Ganymede like a bubble and shelters it from cosmic radiation. And, just like on Earth, the ...Missing: oxygen | Show results with:oxygen
[165]
The influence of Ganymede's magnetosphere seen right down to its ...
Jul 3, 2024 · The influence of Ganymede's magnetosphere seen right down to its auroral footprint on Jupiter. Jupiter has the brightest aurora in the solar ...
[166]
Cassini UVIS Observations of the Enceladus Auroral Footprint on ...
Jan 24, 2024 · Here we focus on the search for UVIS auroral emissions on Saturn on magnetic field lines associated with its moon Enceladus, which has ...Missing: H2O | Show results with:H2O
[167]
Cassini Sees Saturn Electric Link With Enceladus
Apr 20, 2011 · After analyzing data that Cassini collected in 2008, scientists saw a glowing patch of ultraviolet light emissions near Saturn's north pole that ...Missing: H2O | Show results with:H2O
[168]
NASA-Supported Team Discovers Aurora-Like Radio Bursts Above ...
Mar 13, 2024 · A NASA-funded team of scientists has discovered long-lasting radio signals emanating from the Sun that are similar to those associated with auroras.
[169]
Stringent Limits on H Emission from the Hot Jupiters WASP-80b and ...
May 22, 2025 · Auroras from exoplanets can provide a detection and potential measurement of the planetary magnetic field, probe the stellar wind ...
[170]
Search for Auroral H₃⁺ in Brown Dwarf and Hot Jupiter Atmospheres
Jun 20, 2022 · Detection of H3+ emission in brown dwarfs may be possible with the James Webb Space Telescope (JWST), or future thirty-meter class telescopes.Missing: auroras | Show results with:auroras