19.2 Pressure Centers and Winds

Pressure Centers and Winds Pressure centers are among the most common features on any weather map. By knowing just a few basic facts about centers of high and low pressure, you can increase your understanding of present and forthcoming weather. http://www.physicalgeography.net/fundamentals/images/tmw_front.jpg

Low Pressure Systems Lows, or cyclones are centers of low pressure. http://quakeinfo.ucsd.edu/~gabi/sio15/supps/low.gif http://brianmejia.files.wordpress.com/2011/05/site0-13.gif

Low Pressure Systems In cyclones, the pressure decreases from the outer isobars toward the center. http://regentsearth.com/Illustrated%20ESRT/Page%2013%20(Weather%20Map%20Symbols)/Clips/weathermap03.JPG

High Pressure Systems - Anticyclones Highs, or anticyclones, are centers of high pressure. https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQuXoU27KwFkW3Sw5LH94YuX8TwRdCc-IoJzSM50VZpo3dXBrOw

High Pressure Systems - Anticyclones In anticyclones, the values of the isobars increase from the outside toward the center https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcTpp5ymdup2OeCNamLuOW_foqWJIDR1vwl

Cyclonic and Anticyclonic Winds You learned that the two most significant factors that affect wind are the pressure gradient and the Coriolis effect. Winds move from higher pressure to lower pressure and are deflected to the right or left by Earth’s rotation.

Pressure Centers and Wind Direction When the pressure gradient and the Coriolis effect are applied to pressure centers in the Northern Hemisphere, winds blow counterclockwise around a low. Remember… in the north, low = left!!!!

Pressure Centers and Wind Direction In the northern hemisphere, winds blow clockwise around a high pressure center. Remember… In the north, High = Right https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcROwxEsWMdZPAhIU23j5lr79b1XsITYAKCW9n4nKK0Lt7k4IYUN8w

Pressure Centers and Wind Direction In either hemisphere, friction causes a net flow of air inward around a cyclone and a net flow of air outward around an anticyclone. https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcRSxf2c1P1iy-TVfzxutbvdglAiEGqa8-06lplnjwRCO9jDOrdQ https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQ7gYbGNANKjyMueFc4_C-kgdVaAAKgDRDMrHJT-eWHWrSULgWydg

Pressure Centers and Wind Direction In the Southern Hemisphere, the Coriolis effect deflects the winds to the left. Therefore, winds around a low move clockwise. Winds around a high move counterclockwise. Remember… In the south, low = right high = left

Weather and Air Pressure Rising air is associated with cloud formation and precipitation, whereas sinking air produces clear skies. Which pressure system would you predict to be associated with bad weather?

Weather and Air Pressure Which pressure system would you predict to be associated with clear weather?

Airflow Patterns, Surface and Aloft Divergent Air Aloft Convergent Air Below Convergent Air Aloft Divergent Air Below LOW PRESSURE HIGH PRESSURE

Global Winds The underlying cause of wind is the unequal heating of Earth’s surface. In tropical regions, more solar radiation is received than is radiated back to space. In regions near the poles the opposite is true— less solar energy is received than is lost.

Global Winds The atmosphere balances these differences by acting as a giant heat-transfer system. This system moves warm air toward high latitudes and cool air toward the equator.