Final answer:
Monsoons are primarily characterized by a wind system that undergoes a seasonal reversal in direction, which brings about changes in weather patterns such as the summer rains vital for South Asia's agriculture.
Step-by-step explanation:
Monsoons are characterized by a wind system that changes its direction twice each year. Specifically, in South Asia, the summer monsoon brings moist air and heavy rains as the continent heats up, causing a seasonal reversal in wind direction. This influx of moist air from the Bay of Bengal and the Indian Ocean shifts moisture-laden clouds over the land, precipitating in the form of rain which is crucial for agriculture in the region.
By contrast, the winter monsoon features cool, dry winds coming from the north, characterized by a dry season with less precipitation in most parts of South Asia. However, some areas such as Sri Lanka and southeastern India experience a rainy winter monsoon as well. The monsoon system is essential for freshwater supply and affects the livelihoods of millions of people, particularly in agricultural sectors.