Major wind system that seasonally reverses its direction (e.g., one that blows for six months from the northeast and six months from the southwest). The most prominent examples occur in Africa and southern Asia. The primary cause of monsoons is the difference between annual temperature trends over land and sea. Seasonal changes in temperature are large over land but small over oceans. A monsoon blows from cold toward warm regions: from sea toward land in summer and from land toward sea in winter. Most summer monsoons produce copious amounts of rain; winter monsoons tend to cause drought.