13. a great continental high, occurring over Asia in winter, maintains a steady wind over the east of Asia. Heavy rains occur in the area in summer from the monsoons. Major snowfall in the Himalaya Mts. also occurs in summer. Most tertiary circulations are due to thermal effects. 1) Local cooling - a) a mountain breeze: upper areas are cooled more than lower slopes; cooler air moves down slope. b) at the edge of glaciers. 2) Local heating - valley breeze: warming on the lower slopes of valley during the day, air rises up slope. 3) Dry thermals - super-convective conditions produce "dust devils" 4) Direct thermals - these are due to simultaneous heating (land) and cooling (sea) of air (ex: sea breeze). Precipitation Most rain falls on or near the equator, then relatively small amounts of rain occur between 20-40° latitude, then rather heavy amounts fall from 40-60° latitude, followed by a sharp fall-off of precipitation toward the poles. This pattern doesn't hold completely, however. There is much variation within belts, due to: 1) seasonal shift that occurs in pressure belts 2) irregular distribution of land and sea 3) mountain ranges as barriers to air masses Precipitation is usually greater over oceans than over land for any given latitude. Only from the equator to 10°S. does more precipitation fall on land than on sea.