Chapter 10 - Notes Flashcards
What is Geostraphic Wind?
A wind, usually above a height of 600 meters, that blows parallel to the isobars
Geostrophic winds flow with velocities proportional to the pressure-gradient force. A steep pressure gradient creates strong winds, and a weak pressure gradient produces light winds.
Winds above a few kilometers can be considered geostrophic.
What causes Geostrophic Wind?
When the Coriolis force is exactly equal and opposite to the pressure-gradient force, the airflow is said to be in **geostrophic balance. **The winds generated by this balance are called geostrophic winds (geostrophic means “turned by Earth”).
What is Buys Ballot’s Law?
In the Northern Hemispherer if you stand with your back to the wind, low pressure will be found to your left and high pressure to your right. In the Southern Hemisphere, the situation is reversed.
This holds true for airflow aloft, but it must be used with caution when applied to surface winds. At the surface, friction and topography interfere with the idealized circulation. At the surface, if you stand with your back to the wind, then turn clockwise about 30°, low pressure will be to your left and high pressure to your right.
What are Gradient winds?
The curved airflow pattern around a pressure center resulting from a balance among pressure-gradient force, Coriolis force, and centrifugal force.
This air flows conterclockwise around Low pressure zones in the Northern Hemisphere and High pressure zones in the Southern Hemisphere.
What are Cyclones, and Cyclonic flow?
Anticyclones and Anticyclonic flow?
Cyclones are the center of a low pressure zone and the flow around them is cyclonic flow. Cyclonic flow has the sam direction of rotation as Earth: conterclockwise in the Northern Hempisphere and clockwise in the Southern Hemisphere.
Centers of High pressure are frequently called anticyclones and exhibit anticyclonic flow (opposite that of Earth’s rotation).
What is centripetal acceleration?
The inward truning of the air.
What is** **Centrifugal force?
The tendency of a particle to move in a straight line when roteted creates an imaginary outward force called centrifugal force.
How does terrain alter the angle at which air blows?
Over the relativly smooth oceon surface, where friction is low, air moves at an angle of 10° to 20° to the isobars and the speeds roughly 2/3 of geostrophic flow.
Over rugged terrain, where friction is high, the angle can be as great as 45° from the isobars, with wind speeds reduced by as much as 50%.
How does **Friction **influence a cyclone or anticyclone?
In a cyclone, in which pressure decreases inward, friction causes a net flow *toward *its center. In an anticyclone just the opposite is true.
How can **Friction **cause convergence and divergence?
- When air moves from the relatively smooth ocean surface onto land the increased friction causes an abrupt drop in wind speed. This reduction of wind speed downstream results in a pile-up of air upstream.
- When air moves from land onto the ocean, general divergence and subsidence accompany the seaward flow of air because of lower friction and increasing wind speed over the water. (If cool air movers over a comparatively warm water body, heating from below tends to destabilize the air.)
- Mountains also hinder the flow of air and cause divergence and convergence. As air passes over a mountain range, it is compressed vertically, which produces horizontal spreading (divergence) aloft. On reaching the lee side of the mountain, tha air experiences verticle expansion, which causes horizontal convergence.
Where does divergence and subsidence prevail?
Wher does convergence and slow uplift prevail?
Equatorward
Poleward
What is a Prevailing Wind?
When the wind consistently blows more often from one direction than from any other.
