Class #16 Monday, October 5 Class #16: Monday, October 5 Chapter 7 Global Winds 1

Class #16 Monday, October 52 The surface winds over Earth Are very complicated because of the changing seasons, differences between land and water, and differences in latitude. Can be simplified using a conceptual model. Have been described using a 3-cell model with no land and no seasons. Only temperature differences from equator to pole are included.

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4 Complications of the real Earth Earth has seasons –The ITCZ (sometimes called the thermal equator) shifts latitude with the seasons. –The ITCZ shifts north of the equator in NH summer, and south of the equator in SH summer (NH winter) Earth has large land masses –Continents and oceans set up thermal circulations

Class #16 Monday, October 55 Observed surface pressures Vary with the seasons, requiring both a January and a July depiction Are on average high in the sub-tropics (near 30°) and near the pole Are on average low in the ITCZ and along the polar front (near 60°) In summer are high over the oceans and low over the continents (thermal lows). In winter are high over the continents and low over the oceans.

Class #16 Monday, October 56 Seasonal shifts The ITCZ, the subtropical highs, and the polar front all shift southward in NH winter and northward in NH summer. Seasonal shifts are most intense over Asia, which has the largest continental air mass. The summer monsoon is wet, with low pressure over land; the winter monsoon is dry, with high pressure over land.

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Class #16 Monday, October 515 Other monsoons Africa, North America, and Australia have monsoon-like wind patterns, particularly in the warm season.

Class #16 Monday, October 516 Winds and pressures (heights) well above the surface Pressures and heights are on average high in the tropics and decrease to lows close to the poles. Upper-level (500mb and above) winds are generally easterlies (blowing east to west) in the tropics and westerlies (blowing west to east) in higher latitudes.

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Class #16 Monday, October 520 Jet Streams Jet streams are regions of especially high wind speed in the atmosphere. In the upper-level westerlies, there can be two jet streams, the Polar front jet stream, above the polar front, and the Subtropical jet stream above the subtropical highs. Sometimes these jet streams merge into one.

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