Pressure Gradients develop because of unequal heating in the atmosphere
Local Wind Patterns Local Winds Santa Ana winds Sea and land Breezes Mountain and valley winds
Cyclones and Anticyclones Coriolis Effect: effect of the Earth’s rotation that acts like a force to deflect a moving object on the Earth’s surface to the right in the northern hemisphere and to the left in the southern hemisphere Acts at right angles to direction of motion Deflects to right in the northern hemisphere, left in the southern hemisphere No deflection at equator, maximum deflection at poles
Cyclones and Anticyclones Coriolis Effect Balance of Forces on a parcel of surface air: Pressure Gradient Coriolis Effect Strength increases with speed of motion Strength decreases with latitude Friction Exerted by ground surface Proportional to wind speed Acts opposite to direction of motion
Cyclones and Anticyclones Cyclone: center of low atmospheric pressure Air spirals inward (convergence) and upward Associated with cloudy, rainy weather Anticyclone: center of high atmospheric pressure Air spirals downward and outward (divergence) Associated with fair weather
ITCZ and Monsoon Circulation Monsoon: seasonal reversal of winds
Winds Aloft Pressure decreases less rapidly with height in warmer air than in colder air There is a temperature gradient from the equator to the poles So, at high altitudes there is a pressure gradient from the equator to the poles strong winds at high altitudes
Winds Aloft The Geostrophic Wind Forces acting on an upper air parcel: 1. Pressure gradient force: Moves from high pressure to low pressure 2. Coriolis force Deflects to right in NH, to left in SH Pressure gradient force balances coriolis force Wind blows parallel to isobars Geostrophic Wind: wind at high levels above the Earth’s surface blowing parallel with a system of straight parallel isobars
Winds Aloft Global Circulation at Upper Levels:
Winds Aloft Rossby Waves, Jet Streams, and the Polar Front Rossby waves: horizontal undulations in the flow path of the upper-westerlies; upper-air waves Polar front: zone where cold polar air meets warm tropical air Rossby waves: Arise in the polar front Contribute to variable weather in mid-latitudes
Flow of air along front smooth for days or weeks. Undulations begin and Become stronger. Rossby Wave forms. Warm air Pushed poleward, cold air south Waves stronger. Tongue of cold air Brough south and warm north. Tongue pinched off. Pool of cold air farther south than originally. Become cyclones of cold air Persist for days of weeks.
Polar-front jet stream Westerly; associated with Rossby waves Subtropical jet stream Westerly; above subtropical high- pressure cells Tropical easterly jet stream Runs east to west Summer only Develops in Asia
Ocean Currents Oceanic circulation: Currents exchange heat between high and low latitudes Ocean current: persistent, dominantly horizontal flow of water
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