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Geostrophic current

A geostrophic current is a large-scale horizontal flow in the ocean or atmosphere where the Coriolis force exactly balances the horizontal pressure gradient force, resulting in motion parallel to isobars (lines of constant pressure) with negligible influence from friction or other forces.^[1]^[2] This balance arises under steady-state conditions over spatial scales larger than 100 km and temporal scales exceeding a few days, making it a dominant mechanism for mid-latitude ocean circulation away from boundaries.^[2]^[1] Geostrophic currents typically develop from wind-driven Ekman transport, which piles up water to create a sea surface slope; over 1–2 weeks, the resulting pressure gradient adjusts to counteract the Coriolis deflection, establishing equilibrium flow.^[3]^[4] In the Northern Hemisphere, this flow is to the right of the pressure gradient, forming clockwise gyres, while in the Southern Hemisphere, it is counterclockwise.^[4] These currents persist for months to years, storing momentum even after wind forcing changes, and are characterized by stronger, narrower western boundary currents (e.g., the Gulf Stream) compared to broader, slower eastern flows.^[3]^[2] In oceanography, geostrophic currents are inferred from sea surface height measurements via satellite altimetry, such as those from the Jason series, which detect slopes of 1–10 microradians corresponding to velocities of 0.1–1.0 m/s at mid-latitudes.^[1] The approximation breaks down near the equator (where the Coriolis parameter f=0), in coastal regions with friction, or on short timescales, but it underpins models of basin-wide circulation like subtropical gyres and mesoscale eddies.^[2]^[1]

Introduction

Definition and Basic Concept

A geostrophic current is a type of fluid flow observed in rotating systems such as Earth's oceans and atmosphere, where the Coriolis force precisely balances the pressure gradient force, leading to a steady, frictionless flow parallel to lines of constant pressure, known as isobars in the atmosphere or contours of constant pressure (such as sea surface height) in the ocean.^[5]^[6] This balance applies to large-scale motions, typically spanning horizontal distances greater than about 50 kilometers and timescales longer than a few days, away from boundaries where friction dominates.^[5] In this configuration, the flow proceeds at a right angle to the pressure gradient—the direction from high to low pressure—with the specific orientation determined by the hemisphere. In the Northern Hemisphere, the current veers to the right of the pressure gradient, resulting in clockwise circulation around high-pressure centers; in the Southern Hemisphere, it veers to the left, producing counterclockwise circulation.^[5]^[7] This perpendicular motion ensures no net acceleration across the lines of constant pressure, maintaining the flow's stability.^[6] The Coriolis effect serves as the apparent deflecting force in the rotating Earth frame that allows this equilibrium to form, analogous to a cyclist leaning into a turn where the outward centrifugal tendency balances the inward component of the normal force from the road.^[8]

Historical Context

The concept of geostrophic currents emerged in the 19th century, rooted in the recognition of rotational effects on fluid motion. In 1835, French mathematician Gaspard-Gustave de Coriolis described a fictitious force arising in rotating reference frames, which later became essential for understanding deflections in atmospheric and oceanic flows.^[9] Building on this, American meteorologist William Ferrel applied the Coriolis effect in his 1856 essay "An Essay on the Winds and Currents of the Ocean," proposing that large-scale wind systems arise from a balance between pressure gradients and this rotational force, laying the groundwork for geostrophic balance in geophysical fluids.^[10]^[11] Key advancements occurred in the late 19th and early 20th centuries as theorists integrated these ideas into dynamic models. Norwegian physicist Vilhelm Bjerknes formalized the application of geostrophic principles to atmospheric circulation in his 1897 work on hydrodynamics and thermodynamics, enabling systematic predictions of pressure-driven flows in the atmosphere.^[12] Extending this to oceanic contexts, Swedish oceanographer Vagn Walfrid Ekman developed his theory of wind-driven currents in 1902–1905, distinguishing the frictional Ekman layer near the surface—where winds directly influence motion—from the underlying geostrophic interior flow that dominates large-scale oceanic circulation.^[13]^[14] Subsequent milestones integrated geostrophy into computational frameworks and observational validation. In the 1940s, Jule Charney and collaborators at the Institute for Advanced Study incorporated quasi-geostrophic approximations into early numerical weather prediction models, revolutionizing forecasting by simulating balanced flows on computers like the ENIAC.^[15] Post-1970s advancements in satellite altimetry, beginning with missions like Seasat in 1978, provided direct measurements of sea surface height anomalies, confirming the prevalence of geostrophic currents in large-scale oceanic gyres and eddies through derived velocity fields.^[16]^[17]

Underlying Physics

Coriolis Force

The Coriolis force is a fictitious force that arises in non-inertial reference frames rotating with constant angular velocity relative to an inertial frame, such as Earth's surface. It acts on objects in motion within the rotating frame, appearing as an apparent deflection perpendicular to both the velocity vector \mathbf{v} and the angular velocity vector \boldsymbol{\Omega} of the rotation. The magnitude of this force is given by $2 m \Omega v \sin \theta, where m is the mass of the object, \Omega is the angular speed of rotation, v is the speed of the object, and \theta is the angle between \mathbf{v} and \boldsymbol{\Omega}; in vector form, it is \mathbf{F}_c = -2 m \boldsymbol{\Omega} \times \mathbf{v}. This force does not perform work or change the speed of the object, only its direction, making it distinct from real forces like gravity or friction.^[18]^[19] On Earth, the Coriolis force deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, relative to their direction of motion. This deflection is zero at the equator, where the rotational velocity is horizontal and parallel to the motion for meridional flows, and reaches its maximum at the poles, where the rotation axis is vertical. The effect's strength is quantified by the Coriolis parameter f = 2 \Omega \sin \phi, where \phi is the latitude and \Omega \approx 7.292 \times 10^{-5} rad s^{-1} is Earth's angular velocity; thus, f varies from 0 at the equator to approximately $1.46 \times 10^{-4} s^{-1} at the poles. In the Southern Hemisphere, f is negative due to the sign of \sin \phi.^[20]^[21]^[18] The physical origin of the Coriolis force lies in the conservation of angular momentum for objects moving in a rotating system like Earth. An object moving northward from the equator, for instance, retains its initial eastward tangential speed from the lower latitude (where the Earth's radius from the axis is larger), causing it to appear deflected eastward in the rotating frame due to the mismatch with the slower rotational speed at higher latitudes. This principle is demonstrated by the Foucault pendulum, which swings in a plane fixed in inertial space while the Earth rotates beneath it, revealing the apparent deflection over time. Similarly, the trade winds are deflected westward by the Coriolis force as they flow equatorward, contributing to the easterly surface winds observed in tropical regions. In geophysical contexts, this force plays a key role in balancing other effects, such as pressure gradients, to produce steady flows like geostrophic currents.^[22]^[20]^[21]

Pressure Gradient Force

The pressure gradient force (PGF) is defined as the force per unit mass acting on a fluid parcel due to spatial variations in pressure, expressed mathematically as \mathbf{F}_{PGF} = -\frac{1}{\rho} \nabla p, where \rho is the fluid density and \nabla p is the pressure gradient vector.^[23] This force points in the direction opposite to the pressure gradient, driving fluid motion from regions of high pressure toward regions of low pressure.^[24] In fluid dynamics, the PGF causes acceleration of fluid parcels toward lower pressure areas, serving as the primary driver of horizontal and vertical motion in both oceanic and atmospheric contexts. Vertically, in a state of hydrostatic equilibrium, the PGF balances the gravitational force, preventing net vertical acceleration and maintaining the fluid's layered structure.^[23]^[24] The horizontal component of the PGF is particularly crucial for large-scale flows, such as ocean currents and atmospheric winds, as it arises from lateral pressure differences often linked to variations in sea surface height or atmospheric thickness. For instance, in the atmosphere, a typical pressure gradient of 1 hPa over 100 km yields a PGF magnitude of approximately $10^{-3} m/s², assuming standard sea-level air density of about 1.2 kg/m³.^[24]^[25] This force acts perpendicular to isobars (lines of constant pressure), with its magnitude increasing where isobars are closely spaced, indicating steeper pressure gradients and stronger potential for fluid acceleration. In rotating systems like Earth, this direct pressure-driven flow is deflected by other forces, preventing straightforward movement along the gradient.^[23]^[25]

Mathematical Derivation

Force Balance Equation

In geostrophic currents, the steady-state balance occurs when the Coriolis force exactly counteracts the pressure gradient force, resulting in no net acceleration of the fluid parcel. This equilibrium condition is expressed in vector form as f \mathbf{k} \times \mathbf{v}_g = -\frac{1}{\rho} \nabla p, where f = 2 \Omega \sin \phi is the Coriolis parameter (\Omega is Earth's angular velocity and \phi is latitude), \mathbf{k} is the unit vector in the vertical direction, \mathbf{v}_g is the geostrophic velocity vector, \rho is the fluid density, and \nabla p is the horizontal pressure gradient.^[26]^[27] This balance implies that the geostrophic flow is perpendicular to the pressure gradient and thus parallel to lines of constant pressure (isobars), with the direction of deflection determined by the Coriolis effect—typically to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.^[28]^[26] As a result, the flow maintains a steady state without acceleration, allowing large-scale currents to persist over extended periods.^[27] The vector equation focuses exclusively on horizontal momentum components, assuming negligible vertical velocities compared to horizontal ones; the vertical force balance is separately governed by hydrostatic equilibrium, where the pressure gradient in the vertical direction balances gravity.^[28]^[27] Key assumptions underlying this balance include the neglect of frictional forces and relative curvature effects (such as those from planetary vorticity gradients), which holds for large-scale flows where the Rossby number Ro = U / (f L) is much less than 1—typically valid for horizontal scales L > 100 km and velocities U on the order of centimeters per second in oceanic contexts.^[26]^[27]

Derivation from Navier-Stokes Equations

The Navier-Stokes equations in a rotating reference frame provide the starting point for deriving the geostrophic balance, incorporating the Coriolis force due to Earth's rotation. The momentum equation for an incompressible fluid is given by

\frac{D\mathbf{v}}{Dt} = -\frac{1}{\rho} \nabla p - f \mathbf{k} \times \mathbf{v} + \mathbf{g} + \nu \nabla^2 \mathbf{v},

where \mathbf{v} is the velocity vector, \rho is the fluid density, p is pressure, \mathbf{g} is gravity, \nu is kinematic viscosity, and f = 2 \Omega \sin \phi is the Coriolis parameter with \Omega as Earth's angular velocity and \phi the latitude.^[29] For large-scale geophysical flows, such as oceanic or atmospheric currents, several approximations simplify this equation to the geostrophic balance. In the f-plane approximation, where the Coriolis parameter f is treated as constant (neglecting its latitudinal variation, \beta = [0](/page/0)), and assuming steady-state conditions where the material derivative \frac{D\mathbf{v}}{Dt} \approx 0, the acceleration terms vanish. Additionally, for large-scale motions, viscous friction (\nu \nabla^2 \mathbf{v}) is negligible, and vertical motion is small, so the analysis focuses on the horizontal components. The vertical momentum equation reduces to hydrostatic balance, \frac{\partial p}{\partial z} = -\rho g, decoupling it from the horizontal equations.^[30]^[31] Under these approximations, the horizontal momentum equations simplify to a balance between the Coriolis force and the pressure gradient force:

$0 = -\frac{1}{\rho} \nabla_h p - f \mathbf{k} \times \mathbf{v}_g,

where \nabla_h denotes the horizontal gradient and \mathbf{v}_g is the geostrophic velocity. Solving for \mathbf{v}_g yields

\mathbf{v}_g = \frac{1}{f \rho} \mathbf{k} \times \nabla_h p.

This equation describes the geostrophic current, where the flow is perpendicular to the pressure gradient, with speed inversely proportional to f.^[29]^[30] An alternative perspective on geostrophic balance arises from considering low-frequency waves in a rotating fluid, where the zero-frequency limit corresponds to a steady state. In this view, initial imbalances lead to inertial oscillations (circular motions at the Coriolis frequency f), which, through adjustment processes, decay or average to a geostrophic state satisfying the balance equation above, with no net time variation.^[32] The validity of the geostrophic approximation requires the Rossby number Ro = \frac{U}{f L} \ll 1, where U is a characteristic flow speed and L is the horizontal length scale. This condition ensures that the Coriolis force dominates over inertial accelerations, holding for synoptic-scale flows in mid-latitudes (e.g., Ro \approx 0.1) but breaking down near the equator (f \to 0) or for small-scale, rapidly evolving motions.^[33]

Properties and Behavior

Flow Direction and Speed

In geostrophic currents, the flow direction is parallel to contours of constant pressure (isobars) or, in oceanic contexts, constant sea surface height, resulting from the balance between the pressure gradient force and the Coriolis force.^[34] In the Northern Hemisphere, the Coriolis force deflects the flow such that high pressure lies to the right of the direction of motion, leading to clockwise (anticyclonic) circulation around high-pressure centers and counterclockwise (cyclonic) circulation around low-pressure centers.^[35] The thermal wind relation further governs vertical variations in direction and speed, where horizontal density gradients induce shear in the geostrophic velocity: the vertical shear ∂u/∂z and ∂v/∂z are proportional to the horizontal density gradients ∂ρ/∂y and -∂ρ/∂x, respectively, via f ∂u/∂z = (g/ρ₀) ∂ρ/∂y and -f ∂v/∂z = (g/ρ₀) ∂ρ/∂x, with f the Coriolis parameter, g gravity, and ρ₀ a reference density.^[35] The speed of a geostrophic current, denoted |v_g|, is given by the magnitude of the velocity vector satisfying the balance equation: |v_g| = \frac{1}{f \rho} |\nabla p|, where f is the Coriolis parameter (f = 2Ω sin φ, with Ω Earth's angular velocity and φ latitude), ρ is fluid density, and |\nabla p| is the horizontal pressure gradient magnitude.^[36] Equivalently, in terms of sea surface height ζ, |v_g| = \frac{g}{f} |\nabla \zeta| since |\nabla p| ≈ ρ g |\nabla \zeta| under hydrostatic approximation.^[37] For example, a sea surface height gradient of 0.1 m per 100 km at mid-latitudes (φ ≈ 45°, f ≈ 10^{-4} s^{-1}) yields |v_g| ≈ 0.1 m s^{-1}, illustrating typical speeds in moderate oceanic currents. Geostrophic speed varies inversely with the Coriolis parameter f, decreasing toward higher latitudes for a fixed pressure gradient, and inversely with density ρ, such that denser waters exhibit slower flows; it increases linearly with the pressure gradient strength |\nabla p|.^[38] In curved flows, such as those in subtropical gyres, anticyclonic circulation (clockwise in the Northern Hemisphere around high pressure) results in speeds slightly higher than the straight-line geostrophic value due to centrifugal effects enhancing the balance, whereas cyclonic flows (counterclockwise around low pressure) yield slightly lower speeds.^[39] These properties hold robustly in energetic mid-latitude regions but weaken near the equator where f approaches zero.^[38] Satellite altimetry provides a key diagnostic tool for inferring geostrophic currents by measuring sea surface height anomalies (SSHA) relative to the geoid, from which ∇ζ is computed to estimate v_g via the above relations, with global accuracy of ~0.01–0.02 m s^{-1} after corrections for mean dynamic topography.^[37] Missions like Jason and Sentinel-6 enable mapping of surface currents over periods exceeding 20 days, where geostrophic balance dominates low-frequency variability. The Surface Water and Ocean Topography (SWOT) mission, launched in 2022, provides wide-swath observations for resolving submesoscale geostrophic features.^[40]^[41]

Geostrophic Wind Relation

The geostrophic wind represents the manifestation of geostrophic balance in the atmosphere, where the horizontal component of the Coriolis force exactly counters the horizontal pressure gradient force, resulting in a steady, non-accelerating flow parallel to isobars or height contours. This balance yields the geostrophic wind velocity \mathbf{v_g} = \frac{1}{f \rho} \mathbf{k} \times \nabla p, with f denoting the Coriolis parameter, \rho the air density, \mathbf{k} the vertical unit vector, and \nabla p the horizontal pressure gradient.^[30] Unlike surface winds, which are influenced by friction, the geostrophic wind approximation holds above the planetary boundary layer—typically around 1 km altitude—where turbulent drag from the Earth's surface diminishes significantly. In this free atmosphere, geostrophic winds align closely with contours on upper-level pressure charts and drive large-scale features such as jet streams, where tight spacing of height contours indicates enhanced speeds.^[42]^[43] The vertical variation in geostrophic winds arises from horizontal temperature contrasts and is quantified by the thermal wind relation: \mathbf{v_g}(z) - \mathbf{v_g}(0) = \frac{g}{f T} \mathbf{k} \times \nabla T, where g is gravitational acceleration and T is temperature. This equation, derived by combining the hydrostatic balance \frac{\partial p}{\partial z} = -\rho g with the ideal gas law p = \rho R T ( R the gas constant for dry air) and differentiating the geostrophic wind equations with respect to height, shows that the wind shear vector is parallel to isotherms, with colder air to the left in the Northern Hemisphere.^[44] Empirical observations confirm that geostrophic winds are typically 20–50% stronger than surface winds, as the absence of frictional slowing aloft allows the full pressure gradient to accelerate the flow more effectively.^[42]^[45]

Applications and Limitations

Oceanic Currents

Geostrophic currents play a central role in the dynamics of major oceanic flows, where the balance between the Coriolis force and pressure gradient force approximates the observed circulation in the ocean interior. The Gulf Stream, a prominent western boundary current of the North Atlantic subtropical gyre, exemplifies this balance, with its swift northward flow reaching speeds of approximately 2 m/s sustained by pressure gradients arising from sharp density fronts across the current.^[46] These fronts, characterized by steep horizontal density contrasts, generate the necessary pressure differences to maintain geostrophic equilibrium, as inferred from hydrographic observations of the current's density structure. Similarly, the Antarctic Circumpolar Current (ACC), the world's strongest zonal current encircling Antarctica, is primarily driven by westerly wind stress but achieves geostrophic adjustment, resulting in a broad, deep-reaching flow with surface velocities typically ranging from 0.1 to 0.5 m/s, higher in frontal regions.^[47]^[48]^[49] This adjustment allows the ACC to transport approximately 130 Sverdrups of water, linking wind forcing to large-scale meridional structure through quasi-geostrophic dynamics.^[48] Observational evidence for geostrophic currents in the ocean relies on measurements that resolve sea surface height gradients, from which geostrophic velocities are derived as proportional to the horizontal gradient of sea surface height (∇η). The Argo float array, deployed globally since the early 2000s, provides in situ temperature and salinity profiles to compute absolute dynamic topography when combined with satellite altimetry data.^[50] Satellite missions in the Jason series, beginning with TOPEX/Poseidon in 1992 and continuing through the Sentinel-6/Jason-CS missions, with Sentinel-6A launched in 2020 and Sentinel-6B in November 2025, measure sea surface height anomalies with centimeter-level accuracy, enabling the mapping of absolute geostrophic currents across basin scales.^[51]^[52]^[53] These datasets have revealed, for instance, the time-varying structure of the Gulf Stream's meanders and the ACC's frontal variability, confirming geostrophic dominance over ageostrophic components like Ekman drift in the interior flow.^[51]^[50] In the context of basin-wide circulation, geostrophic currents dominate the interior of oceanic gyres, where Sverdrup balance governs the vertically integrated transport, relating it directly to the wind stress curl. This balance posits that the meridional divergence of geostrophic volume transport equals the Ekman pumping induced by wind curl, explaining the clockwise circulation of subtropical gyres and counterclockwise subpolar gyres.^[54] For example, in the North Atlantic, negative wind stress curl over the subtropics drives equatorward Sverdrup transport in the gyre interior, balanced by poleward geostrophic flow in the Gulf Stream, achieving a total gyre transport of about 30 Sverdrups.^[55] Such dynamics extend to the Southern Ocean, where the ACC's geostrophic component integrates wind-driven input across latitudes unconstrained by continents.^[54] Recent studies from the 2020s highlight how climate change is altering oceanic density gradients and wind patterns, thereby influencing geostrophic current speeds by 5-10% in key regions. Surface warming has accelerated upper ocean currents globally, with mean kinetic energy in the 0-200 m layer increasing by about 24% per century from 1993-2017 observations, largely attributable to enhanced geostrophic flows from thermal expansion and stratification changes.^[56] In the North Atlantic, shifts in the subpolar gyre since 2016 have intensified geostrophic branches of the North Atlantic Current, contributing to a 0.6°C warming in the upper 100 m through increased subtropical water advection.^[57] These alterations underscore the sensitivity of geostrophic balances to anthropogenic forcing, with implications for heat transport and ecosystem connectivity.^[56]

Atmospheric Flows

In the atmosphere, geostrophic currents manifest as large-scale wind patterns where the Coriolis force balances the pressure gradient force, leading to flows parallel to isobars. A prominent example is the mid-latitude westerlies, which form zonal geostrophic flows in the extratropics, typically ranging from 10 to 30 m/s in speed at upper levels, driven by the thermal wind relation arising from equator-to-pole temperature gradients. These westerlies dominate the tropospheric circulation between 30° and 60° latitude, influencing weather patterns and storm tracks in both hemispheres. Another key feature is the subtropical highs, semi-permanent anticyclones around 30° latitude where subsidence creates high pressure, resulting in clockwise geostrophic outflow in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, with winds diverging equatorward at the surface and poleward aloft.^[58] Large-scale atmospheric systems often rely on geostrophic balance for their dynamics. Rossby waves, which are planetary-scale undulations in the westerly flow, propagate as geostrophically balanced perturbations, with meridional wind reversals maintaining the wave structure through Coriolis deflection. In the Hadley circulation, the upper branch return flows from the ascending equatorial air are approximated as geostrophic, forming broad westerly jets with zonal wind speeds of 20-50 m/s that transport angular momentum poleward around 12°-30° latitude, conserving potential vorticity in the absence of significant friction.^[59] Geostrophic currents are integral to numerical weather forecasting, particularly in barotropic models that simplify the atmosphere to a single layer assuming geostrophic balance for horizontal flow predictions.^[60] Operational models like the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System and the Global Forecast System (GFS) incorporate geostrophic approximations for upper-air winds, enabling accurate medium-range predictions of jet streams and synoptic-scale features by solving primitive equations that asymptotically approach geostrophic equilibrium at large scales.^[61] Recent advances in reanalysis datasets, such as the ECMWF's ERA5 from the 2020s, have quantified the geostrophic component in extratropical storms, revealing a high degree of balance with ageostrophic errors typically under 2 m/s—corresponding to 70-90% geostrophic dominance for winds of 20-30 m/s—in mid-latitude cyclones and jets.^[62] This validation, using ERA5 alongside radio occultation observations, underscores the robustness of geostrophic theory for interpreting storm dynamics and improving forecast initialization in data-sparse regions.

References

[1]
[PDF] 2.011 Geostrophic Currents
Apr 25, 2006 · • The horizontal pressure gradients almost exactly equal the Coriolis force resulting from the horizontal currents.Missing: definition | Show results with:definition
[2]
OC2910: Physical Oceanography Basic Concepts
The geostrophic approximation is a simplification of the equations governing the horizontal components of velocity. It is valid when the largest terms in the ...Missing: definition | Show results with:definition<|control11|><|separator|>
[3]
[PDF] Ekman ≠ Geostrophic - University of Washington
© 2006 University of Washington. Time Scale of Currents. • Geostrophic current arises in 1–2 weeks. – Sea slope rises in response to steady wind. • Resulting ...
[4]
Effect of Surface Currents | manoa.hawaii.edu/ExploringOurFluidEarth
This phenomenon is known as geostrophic flow (Fig. 3.22). Geostrophic flow is the balance between Coriolis effects causing currents to form a bulge of water in ...Missing: definition | Show results with:definition
[5]
https://geo.libretexts.org/Bookshelves/Oceanography/Introduction_to_Physical_Oceanography_(Stewart)/10%3A_Geostrophic_Currents
[6]
Ocean in Motion: Geostrophic Flow Background
The horizontal movement of surface water arising from a balance between the pressure gradient force and the Coriolis force is known as geostrophic flow.
[7]
Page not found – UH Pressbooks
No readable text found in the HTML.<|control11|><|separator|>
[8]
10.8 A Closer Look at the Four Force Balances | METEO 300
Geostrophic Balance. This balance occurs often in atmospheric flow that is a straight line (R = ±∞) well above Earth's surface, so that friction does not ...Missing: analogy | Show results with:analogy
[9]
History of the Coriolis force - LEGI - UMR 5519
In 1835, Gustave Coriolis derived the expression of a force acting in rotating systems. His work was inspired by rotating devices such as waterwheels.
[10]
[PDF] MET 200 Lecture 10 Forces and Wind - SOEST Hawaii
The Geostrophic wind is flow in a straight line in which the pressure gradient force balances the Coriolis force. Note: Geostrophic flow is often a good ...Missing: banked | Show results with:banked
[11]
[PDF] William Ferrel - Biographical Memoirs
An essay on the winds and currents of the ocean. (Dated Nashville,. October 4, 1856.)' Nashville Journal of Medicine and Surgery, October and Novem- ber, 1856 ...Missing: geostrophic | Show results with:geostrophic
[12]
[PDF] Vilhelm and Jacob Bjerknes - the NOAA Institutional Repository
Jan 16, 2004 · In 1897, he developed a synthesis of hydrodynamics and thermodynamics that allowed him to propose a system for forecasting weather ...
[13]
WALFRID EKMAN (1874–1954): THEORETICAL OCEANOGRAPHER
Aug 30, 2022 · My paper examines Ekman´s early work in its contemporary context, outlines his later work (after 1923) on horizontal circulation of ocean ...
[14]
The Ekman Spiral - Currents - NOAA's National Ocean Service
The Ekman spiral, named after Swedish scientist Vagn Walfrid Ekman (1874-1954) who first theorized it in 1902, is a consequence of the Coriolis effect.
[15]
[PDF] the beginnings of numerical weather prediction and general ...
The first, by. Charney himself, was a comprehensive rationale which laid the founda tion for dynamical prediction. It justified the use of the geostrophic ap.
[16]
Ocean Circulation from Space | Surveys in Geophysics
Mar 30, 2023 · The first satellite radar altimetry missions to observe the sea surface topography and derived geostrophic currents were launched in the 1970s ( ...
[17]
50 Years of Satellite Remote Sensing of the Ocean in - AMS Journals
The development of the technologies of remote sensing of the ocean was initiated in the 1970s, while the ideas of observing the ocean from space were conceived ...<|control11|><|separator|>
[18]
[PDF] a Coriolis tutorial - Woods Hole Oceanographic Institution
The Coriolis force has a very simple mathematical form, ∝ 2Ω × V0, where Ω is the rotation vector and V0 is the velocity observed from the rotating frame. The ...
[19]
6.4 Fictitious Forces and Non-inertial Frames: The Coriolis Force
Each exhibits fictitious forces—unreal forces that arise from motion and may seem real, because the observer's frame of reference is accelerating or rotating.
[20]
[PDF] Coriolis Effect - NASA
The Coriolis “force” is an imaginary force because objects affected by it are really follow- ing a straight path. It is an apparent deflection we see from the ...<|control11|><|separator|>
[21]
The Coriolis Effect - Currents - NOAA's National Ocean Service
Because the Earth rotates on its axis, circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere.
[22]
10.3 Effects of Earth's Rotation: Apparent Forces | METEO 300
The explanation for the Coriolis force is usually broken into an explanation ... The explanation for both cases relies on conservation of angular momentum.
[23]
The Pressure Gradient Force (PGF) – Physics Across Oceanography
If the pressure varies in space within the fluid (i.e., it has a nonzero gradient), then there will be a net force on fluid parcels called the pressure gradient ...
[24]
SIO 210: Introduction to Physical Oceanography Lecture 3
Oct 7, 2002 · 4. Pressure gradient force. What is pressure? It is the Force/area any volume of fluid exerts across its boundaries on any adjacent volume. It ...
[25]
[PDF] Lecture 8. Pressure Gradient Force
Pressure varies with height too, creating vertical PGF. This balances weight of air in volume, so we normally discuss only PGF due to horizontal pres-.<|control11|><|separator|>
[26]
Geostrophic balance – Physics Across Oceanography
Geostrophic balance is the steady-state force balance between the Coriolis and pressure gradient forces, causing flow along isobars.Missing: analogy | Show results with:analogy
[27]
[PDF] Geostrophy.pdf
This additional term in the momentum equations leads to the possibility of new balances, in particular, a balance between the Coriolis force and the pressure.<|control11|><|separator|>
[28]
[PDF] The Navier{Stokes Equations in a Rotating Frame 1 Vector ...
The equations of balance of linear momentum are. @v1. @t. + v1. @v1. @x. + v2. @v1 ... Geostrophic equations. ,v2f = ,1. @p. @x. + AV. @2v1. @z2 v1f = ,1. @p. @y.
[29]
[PDF] The Geostrophic Wind
These two expressions represent geostrophic (“geo” for Earth and “strophic” for turning) balance relating the horizontal pressure and wind fields. • Letting and ...
[30]
[PDF] 3.0 DYNAMICS OF PLANETARY ATMOSPHERES 3.1.1. Equations ...
The Navier stokes equation (or “momentum equation”). If we put all the forces per unit mass together, we get a version of the Navier-. Stokes equation ...
[31]
[PDF] 4 The Shallow water system. - Staff
The zero frequency case is the time independent flow that satisfies geostrophic balance. ... These are inertial oscillations: motions for which the ...
[32]
Rossby Number - PDS Atmospheres Node
A small Rossby number indicates that the geostrophic approximation is valid ( i.e., du/dt = dv/dt = 0) and that the Coriolis acceleration, v · f, is greater ...
[33]
[PDF] a Coriolis tutorial, Part 1: - Woods Hole Oceanographic Institution
Mar 11, 2022 · northern hemisphere, high SSH is to the right of a geostrophic current (Fig.1). It would be easy to over-interpret the results from our ...
[34]
[PDF] Geostrophic balance Thermal wind Dynamic height
Oct 24, 2019 · The vertical shear in geostrophic velocity is proportional to the horizontal density derivative. Formally: - f∂v/∂z = (g/ρo)∂ρ/∂x f∂u/ ...
[35]
Geostrophy Assessment and Momentum Balance of the Global Oceans in a Tide‐ and Eddy‐Resolving Model
### Summary of Geostrophic Balance in Ocean Currents
[36]
Curved Density Fronts: Cyclogeostrophic Adjustment and ...
Oct 1, 2016 · Curvature modifies the balanced state of the system from one of geostrophic balance, where pressure and Coriolis forces exactly balance, to one ...<|separator|>
[37]
Aviso global sea surface height products
Aviso has been distributing Topex/Poseidon and ERS altimetric data worldwide since 1992. Since launches of new altimetric mission, series of products has been ...
[38]
[PDF] MSE3 Ch10 Dynamics - UBC EOAS
In regions of straight isobars above the top of the boundary layer and away from the equator, the ac- tual winds are approximately geostrophic. These winds blow ...
[39]
Constant Pressure Charts: 300 mb - NOAA
Apr 4, 2023 · This chart is primarily used to locate the jet stream. The jet stream is identified by where the wind speed is 70 kt (81 mph / 130 km/h) or greater (colored ...
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[PDF] The Thermal Wind
The thermal wind equation tells us that since there are no temperature gradients, there is no vertical shear and the geostrophic wind is independent of height.Missing: current | Show results with:current
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FORCES and WINDS
Geostrophic wind ... Friction is small over a frozen lake and strong in forest. Near the surface, friction reduces the wind speed, which reduces the Coriolis ...
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[PDF] Spatial and Temporal Variability of the Gulf Stream Near Cape ...
... Gulf Stream core speed (2 m s−1), but faster than the propagation of large amplitude Gulf Stream meanders east of 73°W where the crests and troughs can stall.
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Temporal Variability of the Antarctic Circumpolar Current Observed ...
Large-scale zonal coherence in the cross-stream sea level difference was observed, indicating a general increase in the surface geostrophic velocity of the ...
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[PDF] Wind forced variability of the Antarctic Circumpolar Current south of ...
Feb 18, 2014 · Abstract The variability of the Antarctic Circumpolar Current (ACC) system is largely linked to the atmospheric forcing.
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[PDF] Argo — Two Decades: Global Oceanography, Revolutionized
Feb 24, 2021 · In the Atlantic at 41°N the flow is weak near the coasts, so broad-scale geostrophic transport from Argo with satellite altimetry gives an ...
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[PDF] MEASURING THE GLOBAL OCEAN SURFACE CIRCULATION ...
Adding unbiased mean geostrophic current to the estimated current from merged satellite altimetry improves correlation between observed current by drifters and.
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Projected Atlantic overturning slow-down is to be compensated by a ...
Mar 24, 2023 · In summary, anticyclonic WSC provides the torque that drives the circulation of global subtropical gyres, resulting in equatorward Sverdrup ...
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[PDF] Topographic enhancement of the interior flow in the South Pacific ...
Jan 7, 2017 · Sverdrup [1947] laid the foundations for studying large-scale wind-driven circulation in the ocean interiors. The basic Sverdrup balance, for a ...<|separator|>
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Surface warming–induced global acceleration of upper ocean currents
Apr 20, 2022 · Our results show that the surface warming effect, a robust feature of anthropogenic climate change ... increase was neither observed (4) nor ...Results · Subtropical Gyres · Materials And Methods
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A shift in the ocean circulation has warmed the subpolar North ...
Feb 26, 2021 · This study documents an ongoing large-scale hydrographic change occurring within the upper layer of the SPNA: the decade-long cooling trend ...Missing: studies | Show results with:studies
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Subtropical Highs | METEO 3: Introductory Meteorology
This three-dimensional nature of the subtropical highs means that they influence wind patterns aloft, too, with their broad clockwise flow (in the Northern ...Missing: geostrophic | Show results with:geostrophic
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[PDF] ATM 241, Spring 2020 Lecture 5 The General Circulation
Definition: The geostrophic wind is the theoretical wind that results from an exact balance of pressure gradient and Coriolis force: vg = 1 f (. ∂Φ. ∂x )p.
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[PDF] 7) Numerical Weather Prediction
Grid point and spectral methods are techniques for representing information about atmospheric variables in the model and solving the set of forecast equations.
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Section 9.3 Surface wind - ECMWF Confluence Wiki
Nov 12, 2024 · Typically the winds in the boundary layer are backed and decreased from the geostrophic values through the retarding action of surface friction.
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