lecture 6a winds and the global circulation Flashcards
cyclones and anti cyclones
Low-pressure centres, or cyclones, exhibits cloudy or rainy weather, and high-pressure centres, or anticyclones, usually bring fair weather
The cyclonic spiral is counter-clockwise in the northern hemisphere, since the Coriolis effect acts to the right (opposite in the southern hemisphere)
For anticyclones, the pressure gradient is out from the centre; this creates a divergent, outward spiralling motion (spiral clockwise in the northern hemisphere, counter-clockwise in the southern hemisphere).
Local winds can be divided into two groups:
) those that develop only in one area because a local topographic feature or body of water affects air movements (sea and land breezes).
2) winds that an area’s inhabitants consider to be distinctive, despite the fact that they may originate many hundreds of kilometres away.
thermal wind.
The pressure gradient force generated by the temperature differences between high and low latitudes is termed the thermal wind.
As the air moves, it is influenced by the Coriolis effect (deflected right in the northern hemisphere, left in the southern hemisphere).
Thus, airflow toward the poles in both hemispheres will be subject to a progressively stronger force that is directed toward the east.
The Geostrophic Wind
The Coriolis effect deflects the airflow right in the northern hemisphere and left in the southern hemisphere.
The Coriolis effect increases in magnitude as the wind gains speed, until it balances the pressure gradient force.
At that point, the sum of forces on the moving air is zero, so its speed and direction remain constant.
Consequently, the winds blow parallel to isobars (geostrophic wind).
Rossby waves
are large horizontal atmospheric undulation that are formed when polar air moves toward the Equator and tropical air moves to poleward.
polar front.
Contact zone between cold polar air and warm tropical air known as the polar front.
