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Pressure system

A pressure system in meteorology is a large-scale atmospheric feature defined by a region of relatively high or low air pressure at the Earth's surface compared to surrounding areas, which organizes air movement and significantly influences local and regional weather patterns. High-pressure systems, also known as anticyclones, occur where air descends from higher altitudes, compressing and warming as it approaches the surface, typically resulting in clear skies, light winds, and stable conditions.^[1]^[2] In contrast, low-pressure systems, or cyclones, form where air rises due to convergence at the surface, cooling and condensing to produce clouds, precipitation, and often turbulent weather such as storms.^[1]^[3] These systems are depicted on weather maps with isobars—lines of equal pressure—encircling their centers, where the spacing of isobars indicates the pressure gradient and thus wind strength.^[4]^[5] Pressure systems arise primarily from uneven heating of the Earth's surface by the sun, which causes temperature variations that alter air density and initiate pressure differences; for instance, warmer air expands and rises, creating lows, while cooler air sinks, forming highs.^[6]^[7] The rotation of the Earth introduces the Coriolis effect, deflecting winds to create clockwise circulation around highs in the Northern Hemisphere and counterclockwise around lows, with opposite directions in the Southern Hemisphere.^[8]^[9] Globally, semi-permanent pressure systems like the subtropical highs and subpolar lows, such as the Icelandic Low and Aleutian Low, drive major circulation patterns, such as trade winds and jet streams, while transient systems migrate with seasonal changes and can intensify into extratropical cyclones or tropical storms.^[10]^[11] Understanding these systems is crucial for weather forecasting, as their movement and interaction with fronts predict phenomena from fair weather to severe events like hurricanes.^[4]^[3]

Fundamentals of Atmospheric Pressure

Definition and Basics

A pressure system in meteorology is defined as a distinct region in the atmosphere characterized by a relative maximum or minimum in sea level pressure compared to surrounding areas, rather than based on absolute pressure thresholds. These systems, often visualized as highs or lows on weather maps, form the basis for synoptic-scale weather analysis, where relative pressure differences dictate large-scale atmospheric circulation patterns.^[2] Sea level pressure is a standardized measure obtained by reducing station-level observations to an equivalent value at mean sea level, accounting for elevation using the hypsometric equation and assuming a standard atmospheric lapse rate. This normalization enables consistent global comparisons unaffected by topography. Globally, sea level pressure typically ranges from approximately 87 kPa (870 hPa) in extreme low-pressure events, such as intense tropical cyclones, to 108.3 kPa (1083 hPa) in record high-pressure conditions over cold continental interiors.^[12]^[13]^[14] The spatial variations in pressure within and between these systems create pressure gradients, quantified as the change in pressure per unit distance. These gradients produce the pressure gradient force, which accelerates air parcels from regions of higher pressure toward lower pressure, initiating wind flows that shape weather on regional and continental scales.^[9]^[15] The foundational understanding of pressure systems and their influence on winds traces back to George Hadley's 1735 paper, which provided the first systematic physical explanation linking latitudinal pressure differences to the persistent trade winds through large-scale atmospheric circulation.^[16] For instance, high-pressure systems represent relative peaks that diverge air outward, while low-pressure systems denote troughs that converge air inward, illustrating the core relative nature of these features.^[1]

Measurement and Units

Atmospheric pressure is primarily measured using barometers, with the mercury barometer serving as the foundational instrument. Invented by Italian physicist Evangelista Torricelli in 1643, this device consists of a glass tube filled with mercury, inverted into a reservoir, where the height of the mercury column is supported by atmospheric pressure, creating a vacuum above it.^[17] The mercury barometer provides highly accurate readings but is less portable due to the liquid's toxicity and fragility. Complementing it is the aneroid barometer, developed by French inventor Lucien Vidie in 1843, which uses a flexible metal capsule evacuated of air; changes in external pressure cause the capsule to expand or contract, linked mechanically to a dial for measurement without fluids.^[18] In meteorology, the standard unit for atmospheric pressure is the hectopascal (hPa), defined as 100 pascals (Pa), where the pascal is the SI unit of pressure equivalent to one newton per square meter.^[19] The millibar (mb) is numerically identical to the hPa (1 hPa = 1 mb) and remains in widespread use as a legacy unit from earlier conventions. In aviation and some national weather services, particularly in the United States, pressure is expressed in inches of mercury (inHg), with the standard sea-level pressure of 1013.25 hPa corresponding to 29.921 inHg (or approximately 30 inHg). Conversions between units are straightforward; for example, 1 inHg ≈ 33.86 hPa.^[20] Station pressure, measured at the elevation of the observing site, is routinely adjusted to a hypothetical sea-level value to enable consistent comparisons across locations and facilitate weather map analysis. This sea-level reduction process employs the hypsometric equation in its integrated form: p_{sl} = p_z \exp\left( \frac{g \Delta z}{R_d \bar{T}_v} \right), where p_{sl} is sea-level pressure, p_z is station pressure, g is gravitational acceleration, \Delta z is station elevation, R_d is the gas constant for dry air, and \bar{T}_v is the mean virtual temperature of the air column.^[21] This adjustment accounts for the decrease in pressure with altitude under hydrostatic equilibrium. The lowest recorded sea-level pressure is 870 hPa, observed in the eye of Typhoon Tip over the western Pacific Ocean on October 12, 1979.^[22] Conversely, the highest verified sea-level pressure is 1083.8 hPa, measured at Agata, Russia, on December 31, 1968, during an extreme cold anticyclone.^[13] These extremes highlight the range of atmospheric pressure variations, with reduced pressures associated with intense tropical cyclones and elevated pressures with polar high systems. Pressure measurements, whether in raw or reduced form, are essential for constructing isobaric weather maps that reveal pressure gradients driving wind patterns.

Formation and Dynamics

Development of Low-Pressure Systems

Low-pressure systems, also known as cyclones, develop through processes that reduce atmospheric pressure at the surface, primarily driven by upper-level divergence and surface convergence. Upper-level divergence, often associated with jet stream dynamics such as jet streaks or troughs, removes air mass from atmospheric columns, lowering surface pressure below it.^[23]^[24] This divergence is complemented by surface convergence, where air flows inward toward the low-pressure center, further evacuating mass and intensifying the system.^[25] In contrast, high-pressure systems involve upper-level convergence and surface divergence, promoting subsidence rather than ascent.^[25] A specific type of low-pressure system, the thermal low, forms in arid regions due to diurnal heating of the land surface, which warms the overlying air and creates a shallow pressure minimum through thermal expansion.^[26] These systems are most prominent in summer over subtropical deserts, where intense solar insolation enhances the effect without significant moisture influence.^[27] Cyclogenesis, the process of low-pressure system formation and intensification, occurs in various stages and types, guided by quasigeostrophic theory, which approximates mid-latitude dynamics through the vorticity equation. This equation highlights how advection of planetary vorticity and stretching due to ascent amplify relative vorticity, fostering cyclone growth.^[28] Frontal cyclogenesis involves baroclinic instability along boundaries between warm and cold air masses, leading to wave development on the front. Warm-type cyclogenesis develops when a preexisting low moves poleward along a warm front, intensifying via warm air advection, while cold-type cyclogenesis forms in cold air outbreaks over warmer surfaces, such as oceans. Explosive cyclogenesis, or "bomb" development, features rapid pressure drops exceeding 24 hPa in 24 hours, often over marine areas during winter.^[29]^[30] Key influences on low-pressure development include the Coriolis effect, which deflects inflowing air to the right in the Northern Hemisphere, resulting in counterclockwise rotation around the low center.^[31] In moist environments, latent heat release from condensation during ascent provides additional energy, deepening the system by enhancing upward motion and vorticity.^[32] Globally, polar lows exemplify winter cyclogenesis in high latitudes, forming over relatively warm polar seas within cold air masses due to baroclinic zones and convective instability.^[33] Heat lows over deserts like the Sahara illustrate thermal-driven development, peaking in summer from extreme surface heating.^[26]

Development of High-Pressure Systems

High-pressure systems, also known as anticyclones, develop through a combination of upper-level convergence and surface processes that promote subsidence and atmospheric stability. In the upper troposphere, air converges toward the center of the developing high, adding mass to the atmospheric column below and increasing surface pressure. This convergence exceeds low-level divergence, resulting in net sinking motion or subsidence throughout the column. As air descends, it undergoes adiabatic compression, leading to warming that enhances stability by inhibiting vertical motion and cloud formation.^[34]^[24] At the surface, radiative cooling plays a crucial role, particularly in continental interiors where clear skies allow heat loss to space, cooling the lower atmosphere and densifying the air. This cooling contributes to high-pressure buildup by increasing the weight of the air column. In contrast to low-pressure systems, where convergence drives ascent and instability, the subsidence in highs promotes a stable, descending flow that maintains the pressure gradient.^[24] Anticyclogenesis, the formation or intensification of high-pressure systems, often occurs through cold air outbreaks following the passage of frontal systems, where chilled surface air pools and radiatively cools further. Alternatively, blocking highs arise from amplified Rossby waves in the jet stream, creating persistent ridges of high pressure that divert the typical west-to-east flow. These processes establish semi-permanent or transient anticyclones, with the former linked to large-scale circulation patterns and the latter to synoptic-scale events.^[24] Dynamically, high-pressure systems achieve geostrophic balance, where the pressure gradient force outward is counteracted by the Coriolis force, resulting in nearly straight-line flow parallel to isobars. In the Northern Hemisphere, the Coriolis effect deflects winds to the right, producing clockwise rotation around the high's center, while in the Southern Hemisphere, rotation is counterclockwise. This balance is slightly modified by centrifugal forces in curved flows, but geostrophy dominates at larger scales, sustaining the system's integrity.^[2] Prominent examples include subtropical highs, such as the Azores High, formed by subsidence in the poleward branch of the Hadley cell. Near 30° latitude, upper-level air from equatorial ascent converges and descends, compressing and warming to create a belt of elevated pressure that shifts seasonally. The Siberian High exemplifies a winter continental anticyclone, developing in October over snow-covered Asia through intense radiative cooling and cold air accumulation, peaking in intensity during boreal winter with surface pressures often exceeding 1050 hPa. Recent studies indicate a long-term weakening trend in the Siberian High due to climate change, with a downward pressure trend of approximately 2-3 hPa per decade since the late 20th century, influencing regional winter weather patterns.^[35]^[36]^[37]

Types and Characteristics

Low-Pressure Systems

Low-pressure systems in meteorology are broadly classified into extratropical cyclones, tropical cyclones, and mesoscale lows, each distinguished by their geographic origin, structural complexity, and associated weather features. Extratropical cyclones, also known as mid-latitude cyclones, develop in the westerlies poleward of 30° latitude and are characterized by frontal boundaries separating contrasting air masses.^[38] Tropical cyclones form over warm tropical or subtropical oceans and lack fronts, instead featuring a symmetric structure driven by latent heat release.^[39] Mesoscale lows, such as those associated with squall lines, are smaller convective phenomena often embedded within larger systems or triggered by local instabilities.^[40] The structural elements of these systems vary by type but commonly include a central pressure minimum surrounded by isobars indicating cyclonic circulation. In extratropical cyclones, warm fronts slope upward over cooler air, cold fronts advance as denser air undercuts warmer air, and occluded fronts form when the cold front overtakes the warm front, lifting the warm sector aloft; these fronts often manifest in satellite imagery as spiral cloud bands with a characteristic comma shape.^[38] Tropical cyclones exhibit a central eye of descending air encircled by intense updrafts in the eyewall, with spiral rainbands extending outward, while mesoscale lows like squall lines display linear cloud arches and rear-inflow jets enhancing precipitation efficiency.^[40] These features arise, in part, from upper-level divergence that initiates ascent and pressure falls at the surface.^[38] Low-pressure systems operate on distinct spatial scales: synoptic-scale systems, such as extratropical and tropical cyclones, span 1,000 km or more horizontally, influencing weather over continental regions.^[41] In contrast, mesoscale lows range from 10 to 1,000 km, allowing for rapid evolution driven by local convection.^[42] Lifespans differ accordingly, with extratropical cyclones typically persisting for several days as they traverse mid-latitudes, tropical cyclones lasting from days to weeks depending on sea surface temperatures and wind shear, and mesoscale lows enduring hours to a day before dissipating.^[39] Globally, low-pressure systems are distributed along dynamic boundaries like polar fronts, where extratropical cyclones cluster during winter, and monsoon troughs, elongated low-pressure zones near the intertropical convergence zone that spawn tropical disturbances.^[38]^[43] In the North Atlantic, approximately 120 extratropical cyclones form annually, with peaks in winter contributing to storm tracks across Europe and North America.^[44]

High-Pressure Systems

High-pressure systems, also known as anticyclones, are regions of elevated atmospheric pressure relative to surrounding areas, characterized by descending air motion that promotes stability and often persistent clear weather conditions. These systems exhibit a distinct anatomy, with air converging aloft and diverging at the surface in a clockwise rotation in the Northern Hemisphere (and counterclockwise in the Southern Hemisphere), leading to their role as semi-permanent or transient features in global circulation. Their stability arises from the suppression of vertical motion, which inhibits cloud formation and convective activity, allowing them to endure for extended periods compared to more dynamic low-pressure systems. High-pressure systems are classified into several types based on their thermal characteristics and origins. Warm highs, often thermal in nature, predominate during summer months over continental interiors where surface heating contributes to upper-level divergence, though subsidence maintains the high pressure at the surface. Cold highs, conversely, form in winter over continental or polar regions due to the influx of dense, cooled air masses that increase surface pressure. Additionally, ridge extensions from planetary waves, such as Rossby waves, create elongated zones of high pressure that extend from larger-scale circulations, influencing mid-latitude weather patterns. Key features of high-pressure systems include broad and shallow pressure gradients, which result in light winds and minimal horizontal variability in atmospheric conditions. These systems often feature temperature inversion layers near the surface, where warmer air aloft caps cooler air below, effectively trapping pollutants and reducing vertical mixing. Unlike low-pressure systems, high-pressure areas typically lack associated fronts, as they represent uniform air masses without sharp boundaries between contrasting air types. High-pressure systems operate across various spatial scales and durations, contributing to both short-term and long-term atmospheric patterns. On the planetary scale, semi-permanent subtropical high-pressure belts, such as the Azores High in the North Atlantic and its counterparts, persist seasonally and drive global wind regimes, serving as counterparts to subpolar lows like the Icelandic Low. Synoptic-scale highs, measuring hundreds to thousands of kilometers, typically last from days to weeks, migrating with mid-latitude Rossby waves and influencing regional weather persistence. In terms of global distribution, polar highs form over cold Arctic and Antarctic regions, exhibiting intense surface pressures due to radiative cooling and air density. Trade wind highs, centered in the subtropical latitudes around 30°N and 30°S, generate the persistent easterly trade winds that converge toward the equator. Observations indicate a strengthening of subtropical highs in recent decades, particularly in the Pacific sector, linked to shifts in atmospheric circulation patterns.^[45] Subsidence within these systems acts as a key maintaining factor by continuously compressing air and enhancing pressure.

Weather and Climate Effects

Impacts of Low-Pressure Systems

Low-pressure systems drive significant weather patterns through the upward motion of air, which cools and condenses to form extensive cloud cover, leading to precipitation such as rain and thunderstorms.^[11] This persistent cloudiness traps heat during the day and prevents radiative cooling at night, resulting in minimal diurnal temperature variations compared to clear-sky conditions.^[46] These systems can intensify into severe weather events, generating high winds that correspond to higher levels on the Beaufort scale, often exceeding gale force (34-47 knots) and reaching storm force (48-63 knots) or hurricane force (64+ knots) in extreme cases.^[47] Associated storm surges, caused by the low central pressure and strong onshore winds, elevate sea levels by several meters, exacerbating coastal flooding.^[48] Inland, heavy rainfall from these systems frequently triggers flash flooding and river overflows, with tropical cyclones categorized under the Saffir-Simpson Hurricane Wind Scale experiencing wind speeds from 74 mph (Category 1) to over 157 mph (Category 5), amplifying destructive potential.^[49] In mid-latitudes, low-pressure systems enhance precipitation by drawing moist air into frontal boundaries, contributing to much of the active weather and associated precipitation in regions like North America and Europe.^[50] They also play a critical role in seasonal monsoons, where monsoon low-pressure systems account for 40% to over 80% of summer precipitation across regions such as South Asia and North America, sustaining agriculture but occasionally leading to excessive rains.^[51] The human impacts of low-pressure systems are profound, often necessitating large-scale evacuations and incurring substantial economic losses; for instance, Hurricane Katrina in 2005, a Category 3 system at landfall, caused over $200 billion in damages and displaced more than one million people.^[52] These events disrupt infrastructure, agriculture, and daily life, with recovery efforts highlighting vulnerabilities in coastal and low-lying areas.^[53]

Impacts of High-Pressure Systems

High-pressure systems, characterized by sinking air or subsidence, typically lead to stable atmospheric conditions that suppress cloud formation and precipitation. This subsidence warms and dries the air as it descends, resulting in clear skies and reduced humidity across the affected region. For instance, under the influence of a semi-permanent high like the Azores High, the subtropical Atlantic experiences prolonged periods of sunny weather with minimal rainfall, enhancing visibility but limiting convective activity.^[35] The dominance of high-pressure systems often amplifies diurnal temperature variations due to the absence of clouds, which allows for efficient daytime heating and rapid nighttime cooling at the surface. During the day, solar radiation warms the ground unchecked, leading to higher maximum temperatures, while at night, the lack of cloud cover facilitates radiative cooling and increases the risk of frost, particularly in continental interiors during winter. In the United States, for example, persistent highs over the Great Plains have been associated with temperature swings exceeding 20°C in a single day, exacerbating agricultural stress on crops sensitive to cold snaps. Secondary effects of high-pressure systems include the trapping of pollutants and moisture near the surface, often under temperature inversions formed by the subsidence layer. These inversions act as a lid, preventing vertical mixing and allowing fog, haze, and smog to accumulate, which can degrade air quality in urban areas. In cities like Los Angeles, the Great Basin High contributes to wintertime smog episodes by confining emissions from traffic and industry.^[54] Persistent highs also prolong droughts by inhibiting rainfall, as seen in the 2012–2016 California drought, where a semi-permanent ridge of high pressure diverted storms northward, leading to record-low precipitation and water shortages.^[55] On a climatic scale, high-pressure blocking patterns can intensify extreme weather events, such as heatwaves, by locking weather systems in place and preventing the influx of cooler air masses. The 2003 European heatwave, which caused over 70,000 excess deaths, was exacerbated by a blocking high over Russia that stalled the jet stream, allowing hot continental air to dominate western Europe for weeks.^[56] Socioeconomically, while high-pressure systems benefit agriculture through extended sunlight for photosynthesis and crop drying, they pose risks from soil moisture depletion and frost damage, potentially reducing yields in rain-fed regions. In urban settings, the associated air quality deterioration from trapped pollutants leads to health issues, including respiratory problems, and economic costs from reduced productivity and healthcare demands.^[57]

Observation and Analysis

Surface Weather Maps

Surface weather maps provide a graphical depiction of atmospheric pressure patterns at sea level, enabling meteorologists to visualize and analyze pressure systems. These maps plot isobars, which are contour lines connecting points of equal atmospheric pressure, typically in millibars or hectopascals. Closed loops of isobars encircle low-pressure centers, marked by an "L," and high-pressure centers, marked by an "H." The spacing between isobars indicates the pressure gradient; closely spaced isobars signify a steep gradient, correlating with stronger winds due to the increased force driving air movement from high to low pressure areas.^[58]^[59] The analysis of surface weather maps involves identifying key features beyond pressure centers to understand airflow and weather evolution. Fronts are delineated by specific symbols—such as triangles for cold fronts and semicircles for warm fronts—along boundaries where air masses meet, often coinciding with pressure troughs. Troughs represent elongated regions of low pressure, depicted as dashed lines bending toward the low center, while ridges are elongated high-pressure areas shown with smoother, outward-bulging isobars. Streamlines, curved lines tangent to the wind direction, may overlay the map to illustrate surface wind flow, which generally parallels isobars in the Northern Hemisphere due to the Coriolis effect, veering slightly to the right. Pressure data for these maps is derived from barometer readings at weather stations.^[60]^[58] The historical development of surface weather maps traces back to 1816, when German physicist Heinrich Wilhelm Brandes constructed the first synoptic charts using pressure and wind observations from 1783 across central and western Europe. These early maps laid the groundwork for visualizing weather patterns over space and time. Modern standards for surface weather map conventions, including symbols for pressure centers, fronts, and isobars, are established by the World Meteorological Organization (WMO) to ensure international consistency in meteorological charting and analysis. Interpretation of pressure gradients on these maps aids forecasting; for instance, tightly packed isobars around a low-pressure system predict gale-force winds, guiding predictions of storm intensity and movement.^[61]^[59]

Modern Forecasting Techniques

Modern forecasting techniques for atmospheric pressure systems integrate advanced remote sensing, in situ observations, and computational modeling to enhance detection, tracking, and prediction accuracy. Satellite imagery from systems like the Geostationary Operational Environmental Satellites (GOES) captures dynamic cloud patterns indicative of low-pressure cyclogenesis and high-pressure subsidence, enabling real-time monitoring of system intensity and evolution over vast ocean basins.^[62] Radiosondes, deployed via weather balloons twice daily from global stations, provide high-resolution vertical profiles of atmospheric pressure, temperature, and winds up to 30-40 km altitude, serving as essential inputs for model initialization and validation of pressure gradients.^[63] Complementing these, drifting and moored buoys in networks like the Global Drifter Program measure sea-level pressure in data-sparse marine environments, such as the northeast Pacific, where assimilation of their observations contributes to forecast error reductions of approximately 3% on average, with greater benefits (up to several percent) in regions featuring strong pressure gradients and cyclones, such as atmospheric rivers.^[64]^[65] Numerical weather prediction models, exemplified by the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System, assimilate pressure data from these sources into high-resolution simulations that resolve isobaric levels and predict system trajectories over 10-15 day horizons.^[66] These models incorporate ensemble methods, running multiple simulations with varied initial conditions and physics parameterizations to quantify uncertainty in pressure system development, such as the branching of mid-latitude lows, thereby producing probabilistic forecasts that improve decision-making for severe weather events.^[67] Recent advancements since 2020 leverage artificial intelligence for enhanced pattern recognition in vast datasets from satellites and models. Machine learning algorithms, such as convolutional neural networks, identify subtle pressure system signatures—like vorticity maxima in lows or divergence in highs—faster than traditional methods, with models like GenCast achieving superior skill in probabilistic medium-range predictions compared to operational ensembles.^[68] These AI tools process multi-spectral imagery to forecast system intensification, reducing computational demands while maintaining or exceeding accuracy in nowcasting applications.^[69] Forecasting frameworks increasingly account for climate change influences on pressure systems, drawing from IPCC Sixth Assessment Report (AR6) analyses up to 2023. Subtropical high-pressure systems are projected to intensify and expand poleward under greenhouse gas forcing, exacerbating aridity in regions like the Mediterranean and southwestern North America through strengthened Hadley Cell circulation (high confidence).^[70] Concurrently, mid-latitude low-pressure systems, including storm tracks, exhibit a poleward shift, particularly in the Southern Hemisphere (high confidence) and North Pacific (medium confidence), driven by thermal gradients and ozone depletion, which alters precipitation patterns and extreme event frequencies.^[70] To address observational and modeling gaps in polar regions, techniques now incorporate trends like the weakening of the Icelandic Low, linked to Arctic amplification from sea ice loss, which reduces pressure anomalies and modifies Northern Hemisphere westerly flows.^[71] This integration of climate projections into operational models helps anticipate long-term shifts, such as diminished cyclone frequency in the North Atlantic, improving seasonal outlooks for affected sectors like aviation and agriculture.^[70]

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[PDF] USA Glossary of Features - NHC
Monsoon Trough: an elongated area of low pressure along the. Intertropical Convergence Zone (ITCZ) that leads to an enhancement of monsoon precipitation over ...Missing: polar | Show results with:polar
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[PDF] Time-Varying Biases in U.S. Total Cloud Cover Data
Diurnal temperature range (DTR) tends to be inversely related to cloud cover (Dai et al. 1997); correlations using ISD and DSI-3280 NWS stations for 1949–94 ...
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Beaufort Wind Scale - National Weather Service
The scale starts with 0 and goes to a force of 12. The Beaufort scale is still used today to estimate wind strengths.Missing: pressure | Show results with:pressure
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Storm Surge Overview - NOAA
Storm surge is an abnormal water level rise generated by a storm over and above the predicted astronomical tide. Storm tide is the water level rise due to the ...National Storm Surge Risk Maps · Storm Surge Unit · Storm Surge Products
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Saffir-Simpson Hurricane Wind Scale - NHC - NOAA
The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based only on a hurricane's maximum sustained wind speed. This scale does not take into account ...Wind ScaleSaffir-Simpson Hurricane Wind ...
[47]
[PDF] Cyclones and Anticyclones in the Mid-Latitudes
What is a Cyclone? • A cyclone is simply an area of low pressure around which the winds flow counterclockwise in the Northern. Hemisphere ...
[48]
[PDF] A global climatology of monsoon low-pressure systems - Faculty
Low-pressure systems in nearly all monsoon regions are estimated to account for a large fraction, from about 40% to more than 80%, of summer precipitation on ...
[49]
[PDF] Costliest U.S. Tropical Cyclones
For all United States hurricanes, Hurricane Katrina (2005, $201.3B*) is the costliest storm on record. Hurricane Harvey (2017, $160.0B*) ranks second, Hurricane ...
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[PDF] 1 Tropical Cyclone Report Hurricane Katrina 23-30 August 2005 ...
Aug 29, 2025 · Adjusting for inflation (2022 dollars) Katrina remains the costliest U.S. hurricane, with an estimated $186.3 billion in damage compared to ...
[51]
How to read Surface Weather Maps - NOAA
Sep 23, 2025 · Cold fronts nearly always extend south and west of the center of a low pressure area and never from high-pressure systems. Warm Front. Warm ...
[52]
Surface Weather Analysis Chart
Jun 10, 1996 · The packing of the isobars reveals how rapidly the pressure varies with distance in the horizontal direction. A tighter packing indicates a much ...
[53]
[PDF] Chapter 12 - Weather Theory
On the return flight, the most favorable winds would be along the southern side of the same high-pressure system or the northern side of a low-pressure system.
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[PDF] An Outline of the History of Meteorology
Aug 20, 2005 · 1 – First weather map, issued by U.S. Army Signal Service with isobars. Synopsis and probabilities enlarged below. Page 42. 1882 – John .P ...
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6 tools our meteorologists use to forecast the weather - NOAA
Aug 14, 2017 · This system uses NOAA supercomputers to process data from doppler radar, radiosondes, weather satellites, ASOS, and other sources using models ...
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Radiosonde Observation - National Weather Service
As the radiosonde rises at about 300 meters/minute (about 1,000 feet/minute), sensors on the radiosonde transmit pressure, temperature, relative humidity and ...
[57]
Drifting buoys deployed in the northeast Pacific - ECMWF
For ECMWF, a key feature of these buoys is their pressure sensors, which provide valuable sea-level pressure observations in this data-sparse region. These ...
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Integrated Forecasting System | ECMWF
It includes a sophisticated data assimilation system and global numerical model of the Earth system, as well as supporting infrastructure to make forecast ...Missing: pressure | Show results with:pressure
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Section 5 Forecast Ensemble (ENS) - Rationale and Construction
Nov 12, 2024 · The ECMWF forecast ensemble is based upon the idea that incorrect forecasts result from a combination of initial analysis errors and model deficiencies.
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Probabilistic weather forecasting with machine learning - Nature
Dec 4, 2024 · Here we introduce GenCast, a probabilistic weather model with greater skill and speed than the top operational medium-range weather forecast in the world, ENS.Missing: enhancements recognition
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Improving Data‐Driven Global Weather Prediction Using Deep ...
Aug 12, 2020 · We present a significantly improved data-driven global weather forecasting framework using a deep convolutional neural network (CNN) to forecast several basic ...<|separator|>
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[PDF] Chapter 8: Water Cycle Changes - IPCC
This chapter discusses observed water cycle changes, regional variability, and projected changes, including seasonality, based on multiple datasets.
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Impact of Reduced Arctic Sea Ice on Northern Hemisphere Climate ...
A strong amplification of temperatures over the Arctic is induced by sea ice loss, with values reaching up to 25°C near the surface in autumn.