Seasonal winds are movements of air repetitively and predictably driven by changes in large-scale weather patterns. Seasonal winds occur in many locations throughout the world. The name assigned to a particular seasonal wind—and the underlying physical forces that drive the winds—depend upon the unique geographic location.
One of the most commonly recognized seasonal winds are the monsoon winds. Although monsoons are often erroneously identified as rainstorms, they are actually a seasonal wind. A monsoon is a wind in low-latitude climates that seasonally changes direction between winter and summer. Monsoons usually blow from the land in winter (called the dry phase, because the wind is composed of cool, dry air), and from water to the land in summer (called the wet phase, because the wind is composed of warm, moist air), causing a drastic change in the precipitation and temperature patterns of the area impacted by the monsoon.
The word monsoon originates from Arabic mauzim, meaning season. It was first used to depict the winds in the Arabian Sea, but later it was extended for seasonally changing wind systems all over the world. The driving force shaping monsoons is the difference in the heating of land and water surfaces, which results in land-ocean pressure differences. On a small scale, land-sea breezes, to maintain the energy balance between land and water, transfer heat. On a larger scale, in winter when the air over the continents is colder than over the oceans, a large, high-pressure area builds up over Siberia, resulting in air motion over the Indian Ocean and South China, causing dry, clear skies for East and South Asia (the winter monsoon). The opposite of this happens with the summer monsoon in Southwest Asia. The air over the continents is much warmer than over the ocean, leading to moisture-carrying wind from the ocean towards the continent. When the humid air unites with relatively drier west airflow and crosses over mountains, it rises, reaches its saturation point, and thunderstorms and heavy showers develop.