• Temperatures are greatest in equatorial regions and decrease toward the poles
• Precipitation is greatest above the equatorial low pressure system
• Precipitation is least above the subtropical high pressure systems

Temperature
emperatures are greatest in the equatorial regions and decrease toward the poles. This is a direct result of the fact that more heat energy is absorbed at the equator than the poles. The mixing of ocean currents results in less extreme temperatures in oceans adjacent to land masses. High temperatures in the deserts of North Africa are not matched in relatively narrow isthmus of land that makes up Central America where temperatures are moderated by the Pacific Ocean to the west and Gulf of Mexico to the east. Likewise, the bone-chilling sub-zero cold of the Antarctic interior is not matched in the waters of the Southern Ocean where temperatures remain a few degrees above freezing.

The world's highest temperature 58^oC (136^oF) was recorded in the desert of El Azizia, Libya, north Africa. The highest temperature in North America was a few degrees less (57^oC,134^oF) and was recorded in Death Valley, California. The lowest temperature ever recorded was registered at Vostok station, Antarctica at -89^oC (-129^oF).   The lowest North American temperature recorded was -63^oC (-81^oF) at Snag, Yukon, Canada.

Global cloud cover, sea surface temperatures and land surface temperatures for the March 24, 1998. Land and ocean temperatures are highest between the tropics. Lower ocean temperatures illustrate greater mixing due to ocean currents. A current version of the image can be viewed here. Image courtesy of the Space Science and Engineering Center at the University of Wisconsin, Madison.

Click here or on the image to the right to view an animation of average monthly global temperatures for 1998 (272 kb). Images courtesy of NCDC SSMI satellite website.

Precipitation
Spatial variations in precipitation are related to variations in temperature and the global atmospheric circulation system. Precipitation is greatest where ascending moist air becomes saturated as it rises and cools. Air rises in zones of low pressure above the equatorial low and the polar front. The warmest air and greatest evaporation rates are associated with the equatorial low. Consequently,  precipitation is greatest near the equator. The high temperatures and abundance of precipitation that characterize this region support life in the tropical rain forests. The world's highest average annual precipitation was estimated as 524 inches (over 43 feet of rain, or 1310 centimeters) at Lloro, Colombia in equatorial South America.

Average global precipitation in millimeters per day (1988-1996). Greatest precipitation is concentrated over the equatorial region (central Africa, Indonesia, northern South America); least precipitation is over subtropical regions, ~30oN, S (north Africa, south Africa, Australia. Image courtesy of the Global Precipitation Climatology Project.

Precipitation is least in regions where air descending dry air becomes warmer, increasing its potential to absorb moisture. Air descends in the subtropical highs centered between 20-35^o N and S.  These areas are home to the world's major deserts (Sahara, North Africa; Gobi, central Asia; Atacama, South America; central Australia). Descending air over the South Poles creates a cold desert in Antarctica where rainfall is no more plentiful than it is in Arizona. The world's lowest average annual precipitation is 0.03 inches (0.075 cm) and occurs in Arica, Chile, in the Atacama desert. That's less than 2 inches of rain in the 59-year record of precipitation at the site.

Click here or on the image to the right to view an sequence of average monthly precipitation. Original images courtesy of the Global Precipitation Climatology Project.