NASA released a satellite time-lapse video earlier this week showing this year’s return of the monsoon rains to India. You can view it at https://www.nasa.gov/feature/goddard/nasa-sees-the-start-of-indias-monsoon-season. The official start of the monsoon season this year was June 5, a little later than usual. A strong heat wave in the days before the delayed start of the monsoon caused more than 2,300 deaths in south-central India this year. Climatologists believe that the delay in the return of the monsoon this year is linked to the El Nino which is currently occurring in the Pacific Ocean. EarthSky also had a short article on this satellite loop here.
What is a monsoon? The National Weather Service has a fairly technical description here. Wikipedia has a more expansive description. WeatherQuestions.com has a more simple definition. In general it is considered to be a seasonally changing large-scale wind pattern that is primarily driven by temperature differences between land and ocean, although recent research has brought that somewhat into question. In the cool season, the land is colder than the ocean nearby, causing a wind circulation that blows air from land to ocean near the surface. In summer, the land heats up more than the ocean and the wind is reversed, bringing humidity and rain to the land. Unlike a sea breeze, which acts over just a few miles near a coast, the monsoon depends on large land masses like portions of continents to drive the regional circulation, but the principle is the same. The failure of the monsoon in India is the major cause of drought and famine in that country. Scientists are concerned that the Indian monsoon this season may be weak and could contribute to crop failures and water shortages in that country in the next few months.
There are several other locations which also have monsoon circulations, including Southeast Asia and the Desert Southwest in North America. This year’s SW US monsoon season may have started earlier than usual due to moisture flowing into the area this week from the remains of Hurricane Blanca in the eastern Pacific Ocean.
To Indians, the monsoon is more than a shift in the wind across the Indian subcontinent; it is a change in life itself there. Or so they would tell you. If you like reading stories about science and weather, “Chasing the Monsoon” is a fascinating book about an American traveling across India waiting for the yearly monsoon to come.
