geostrophic wind


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geostrophic wind

[¦jē·ō¦sträf·ik ′wind]
(meteorology)
That horizontal wind velocity for which the Coriolis acceleration exactly balances the horizontal pressure force.

Geostrophic Wind

 

a horizontal, even, and straight movement of air with no force of friction and with balance in the gradient of pressure and the deflecting force of the earth’s rotation; the simplest theoretical scheme of air movement of the rotating earth. The actual wind in atmospheric layers higher than 1 km above the earth’s surface is close to the geostrophic wind. The geostrophic wind is directed along the isobar, with an area of low pressure remaining to the left of the stream in the northern hemisphere and to the right in the southern. The velocity of the geostrophic wind is proportional to the magnitude of the horizontal gradient of pressure. With equal gradients it is inversely proportional to the density of the air and the sine of geographic latitude and therefore increases with elevation and with increasing nearness to the equator.

geostrophic wind

geostrophic wind
Pressure-gradient force causes air parcel to accelerate. Coriolis begins deflecting air to the right. Coriolis increases as speed increases. Coriolis eventually balances pressure gradient forces.
That horizontal wind velocity for which the Coriolis acceleration exactly balances the horizontal pressure or gradient force.
References in periodicals archive ?
The wind forcing at a 10 m level was derived from geostrophic winds as recommended by Bumke and Hasse (1989): the geostrophic wind speed was multiplied by 0.
This feature apparently stems from the better ability of the WAM model and adjusted geostrophic wind fields to reproduce the extreme events.
The most popular way consists in the use of geostrophic wind fields that are adjusted to the 10 m level by means of a simplified procedure in which the geostrophic wind speed (usually retrieved from the Swedish Meteorological and Hydrological Institute database) was multiplied by 0.
g = [delta]], where the velocity is equal to the geostrophic wind velocity G.
The wave model was forced with wind data corresponding to an elevation of 10 m above the sea surface, constructed from the Swedish Meteorological and Hydrological Institute (SMHI) geostrophic wind database.
Figure 6 shows the 500/1000 thickness advection by geostrophic wind of 1000 hpa level in the selected case studies to represent.
Absolute vorticity advection by geostrophic wind in 500 hpa level and 1000/500 thickness advection by geostrophic wind of 1000 hpa level can interpret development or decline of the system pressure.
In particular, the abrupt change in the air flow, evaluated from geostrophic wind fields (Soomere and Raamet, 2014), signals a major change in the air pressure and upper-level wind system over the southern Baltic Sea in 1988.
The identified major regime shifts in the average air flow speed around 1988 could be related to the abrupt change in the geostrophic wind vector over the southern Baltic Proper.
The authors are most grateful to the SMHI, especially to Dr Barry Broman, for providing help in retrieving the geostrophic wind data, to the EMHI for historical wave data and weather maps provided by Ivo Saaremae, and to Inga Zaitseva-Parnaste for providing digitized wave data from Vilsandi, Pakri, and Narva-Joesuu.
The adjusted geostrophic wind data lead to about the same accuracy of reproduction of the frequency of different wind conditions.
The time series of the significant wave height and peak period were extracted from the long-term simulations of wave fields for 1970-2007 with a temporal resolution of 1 h for the entire Baltic Sea using the third-generation spectral wave model WAM [40] driven by properly adjusted geostrophic winds.