Download Lecture 11. Climate

6/30/15 Climate and Climate Change Solving environmental problems Global warming? 1 6/30/15 Climate Is the generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years. Hadley model The Hadley model of global circulation patterns was proposed in 1735. It consists of a single wind system in each hemisphere. The tropical regions receive more heat from solar radiation than they radiate back into space, and the polar regions radiate more than they receive, Hadley theorized that warm air must therefore rise near the Equator, flow poleward at high altitudes, and lose heat to the cold air present near the poles. This cooler and denser air then descends and flows equatorward at low levels until it nears the Equator, where it is warmed and rises again. This model has been replaced by the tree-­‐
cell model. 2 6/30/15 Three-­‐cell model Three-­‐cell model Over the major parts of the Earth's surface there are large-­‐
scale wind circulations present. The global circulation can be described as the world-­‐
wide system of winds by which the necessary transport of heat from tropical to polar latitudes is accomplished. In each hemisphere there are three cells (Hadley cell, Ferrel cell and Polar cell) in which air circulates through the entire depth of the troposphere. Hadley cell The largest cells extend from the equator to between 30 and 40 degrees north and south. Ferrel cell In the middle cells, air converges at low altitudes to ascend along the boundaries between cool polar air and the warm subtropical air that generally occurs between 60 and 70 degrees north and south. The Ferrel cell moves in the opposite direction to the two other cells (Hadley cell and Polar cell) Polar cell The smallest and weakest cells are the Polar cells, which extend from between 60 and 70 degrees north and south, to the poles. Air in these cells sinks over the highest latitudes and flows out towards the lower latitudes at the surface. 3 6/30/15 Three-­‐cell model Deserts The boundary between the Hadley and the Ferrel cells is called the subtropical high or house latitude. Many deserts correlate with these latitudes (+30 degrees and -­‐30 degrees) The Coriolis effect is a deflection of moving objects when the motion is described relative to a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-­‐clockwise rotation, the deflection is to the right. Coriolis effect 4 6/30/15 Coriolis effect Winds blow across the Earth from high-­‐pressure systems to low-­‐
pressure systems. However, winds don’t travel in a straight line. The actual paths of winds—
and of ocean currents, which are pushed by wind—are partly a result of the Coriolis effect. result of Coriolis effect, hurricanes Hurricanes As in the Northern Hemisphere rotate while in the rotation counterclockwise, Southern Hemisphere hurricanes rotate clockwise. 5 6/30/15 streams are relatively narrow Jet Streams Jet bands of strong wind in the upper levels of the atmosphere. The winds blows from west to east in jet streams but the flow often shifts to the north and south. Jet streams follow the boundaries between hot and cold air Please watch online the National Geographic short documentary: http://video.nationalgeographic.com/video/101-­‐videos/global-­‐warming-­‐101 6