INVESTIGATING EARTH's WEATHER The effect of the Coriolis force Nonrotating Earth launch site North Pole people Europe Africa Equator 60 45 30° 15 15 30° 45°60 target target Earth rotating 15° each hour Otoed North Pole launch site Europe l Africa Equator 75 60 45 30 150 1530 45 actual destination target actual destination 15 target Path of rotation The Coriolis force deflects the path of an object moving from a pole to the Equator It does the same to winds Encyclopaedia Britannica Inc I2
THE NATURE OF WEATHER belts surface winds blow outward toward both the Equator and the poles The Coriolis force a result of Earth's rotation deflects the winds to the right of the winds direction of motion in the Northern Hemisphere and to the left of their direction in the Southern Hemisphere This produces a belt of tropi cal easterly winds winds blowing from east to west and two belts of midlatitude west erly winds blowing from west to east one in each hemisphere Like the tropical easterlies or trade winds the surface winds from the poles are also deflected to the west Where these polar easterlies meet the westerly winds in each hemisphere at about 60° latitude a belt of low pressure girdles Earth WIND AND PRESSURE PATTERNS This arrangement of Earth s wind and pres sure belts varies somewhat with the time of the year They shift northward during the Northern Hemisphere's summer and south ward during the Southern Hemisphere's summer Both the continuity of the pres sure belts and the prevailing directions of the winds are also modified greatly by the 13
INVESTIGATING EARTH's WEATHER differing rates at which Earth s land and water surfaces exchange heat and moisture with the atmosphere Very large scale and long lasting changes in wind and pressure patterns also some times occur Most of the time for example the eastern Pacific near South America has relatively cool water temperatures and high In August 2009 a villager collects water to take to crops in a field affected by the lack of rain on in Lamongan East Java Indonesia The area had been without rain for three months as a result of El Nihio Ulet Ifansasti Getty Images 14
THE NATURE OF WEATHER pressure while the western Pacific near Australia and Indonesia has warmer water and lower pressure This results in dry condi tions in Peru and Chile and wetter weather in Indonesia and eastern Australia In some years however the pattern reverses as part of a phenomenon called El Niño Southern Oscillation ENSO which strongly affects weather in most parts of the world A buildup of warm water in the eastern Pacific then brings heavy rains to Peru while Australia experiences drought The easterly trade winds in the Pacific weaken and may even reverse The warm ocean water also strength ens winter storms that move onshore in the southwestern United States causing heavy rain in southern California and much of the southern United States 15
