February 25, 2013

Winds Aloft * Isobaric surfaces slope downward from the low latitudes to the pole * Atmosphere is warmer near the Equator, pressure gradients force pushes air poleward * Pressure gradient force increase with altitude, bringing strong winds at high altitudes * Friction increases from low latitude to high latitude * Decreases in upper atmosphere where wind speeds are high

The Geostrophic Wind * At high latitudes, a moving parcel of air is subjected to: Pressure gradient force and Coriolis forces. * When forces balance, air moves at right angles to the pressure gradient, parallel to the isobars, as the geostrophic wind * Winds that move bulk of our air mass around the planet * Heavy lifting of moving heat

Global Circulation at Upper Levels * General pattern global circulation at upper levels * Bands of equatorial easterly winds (result of downward air) * Bring air into the equator * Found at higher latitudes * Tropical high-pressure belts * Zone of westerly winds – come from est and blow to east * Polar lows * Lack of land mass and lack of friction fast winds speeds in southern hemisphere

Jet Streams and the Polar Front * Jet streams are streams of fast-moving air at high altitudes that occur where atmospheric temperature gradients are strong * Each hemisphere normally exhibits westerly polar and subtropical jet streams. * An easterly jet occurs in summer over Asia and Africa * Polar jet located between 35 and 65 latitude in both hemispheres * Boundary between cold polar air and warm subtropical air * Altitudes of 10 to 12 km (about 30,000 to 40,000 ft)

Disturbances in the Jet Stream * Broad wavelike undulations called Jetstream disturbances or Rossby waves * Occurs from heating and cooling * The flow of air along the polar front is fairly smooth, but then it begins to undulate * Undulation becomes stronger; disturbances in the jet stream begin to form. Warm air pushes poleward, while cold air is brought to the south. * Waves become stronger and more developed. Tongues of cold air are brought to the south where they occupy low pressure troughs * Tongues are pinched off, leaving pools of cold air at latitudes south of their original locations. Pools of cold air form cyclones that can persist

Ocean Circulation * Circulation pattern to the oceans driven by: * Differences in density and pressure * Coriolis Force * Pressure differences are created in the water because * Ocean is heated unequally * Warm water is less dense than cold water * Heat up water volume increases and ability to hold salt increases

Temperature layers of the ocean * Warm surface layer heated by the sun – low latitudes, middle latitudes in the summer * Warm layer mixed by wave action to a depth of up to 500 m (about 1600 ft.) with a temperature of 20 degrees to 25 degrees calcium (68 to 77 degrees F) * Below warm layer, temperatures drop rapidly in thermocline. * At base layer of very cold water extending to the deep ocean floor. Temperatures rang from 0 to 5 degrees calcium (32 to 41 degrees F) * Layering stable because the warm layer is less dense than the cold water and rests on top.

Surface Currents * Ocean Current – any persistent, dominantly horizontal flow of ocean water * Global surface ocean currents are dominated by huge, wind-driven circular gyres centered near the subtropical high-pressure cells * Upwelling of cold bottom water often occurs on the west coasts of continents in the subtropical zones * Current systems exchange heat between low and high altitudes

Temperature layers of the Ocean
North-south cross section of the cold ocean shows warm surface water layer disappears in Arctic and Antarctic latitudes, where very cold water is at the surfaces ….

El Nino and Enso * Normal year – low pressure dominates in Malaysia and northern Australia * El Nino year – low pressure moves east to the central part of the western Pacific * Typically, northern areas of the contiguous United States are warmer during the winter Southern areas are cooler and wetter
Deep Currents and Thermohaline Circulation
Thermohaline circulations * Dense, cold salty surface water sinks in the northern Atlantic Ocean * Generates slow bottom currents * Causes slow upwelling in the Indian Ocean, western Pacific Ocean, and along the coast of Antarctica