1. Upper-Air Winds Flow of air at altitudes above 5000 meters (16,500 ft) Flow of air at altitudes above 5000 meters (16,500 ft) Found in the upper troposphere Found in the upper troposphere A response to the temperature difference between warm tropical air and cold polar air A response to the temperature difference between warm tropical air and cold polar air Affect the formation, movement, and decay of surface cyclones and anticyclones Affect the formation, movement, and decay of surface cyclones and anticyclones Far less complex than the surface wind circulation Far less complex than the surface wind circulation

2. Poleward of 15˚-20˚ there is a pronounced westward flow of air known as the upper air westerlies Poleward of 15˚-20˚ there is a pronounced westward flow of air known as the upper air westerlies · a broad circumpolar flow of westerly winds · move much more rapidly than the surface counterparts · strongest in winter (the low-sun season) · much weaker during the summer (the high-sun season)

3. Jet streams very strong air currents very strong air currents embedded within the upper air westerlies embedded within the upper air westerlies polar jet stream polar jet stream · located where the warm tropical air meets cold polar air · located where the warm tropical air meets cold polar air · ranges from 40 to 160 km (25-100 mi) wide and… · ranges from 40 to 160 km (25-100 mi) wide and… up to 2 or 3 km (1- 2 mi) deep

4. Subtropical jet stream Subtropical jet stream · flows above the sinking air of the subtropical highs · best developed in winter when their is the steepest pressure gradient · often the subtropical jet stream completely disappears in the summer

5. Usually the upper air westerlies, and polar jet stream, flow in a fairly smooth pattern Usually the upper air westerlies, and polar jet stream, flow in a fairly smooth pattern

6. Oscillations termed Rossby waves periodically develop Oscillations termed Rossby waves periodically develop · cold polar air pushes into the lower latitudes forming troughs of low pressure · surface weather is most influenced under these conditions

7. · the oscillations can become so extreme that they become cut off · the cells eventually dissipate, and the pattern returns to normal · a complete cycle takes 4 to 8 weeks · unusually warm or cold ocean currents seem to trigger the oscillations