Monsoon
The monsoons are a double system of seasonal winds that travel from the sea to the land in the summer and from the land to the sea in the winter.
Historically, the monsoons were extremely important because they allowed traders and seafarers to travel from one location to another.
Monsoons can be found in the Indian subcontinent, central-western Africa, Southeast Asia, and a few other places, but the winds are strongest in the Indian subcontinent.
Monsoon
Summers in India are dominated by southwest monsoon winds.
While winters are dominated by northeast monsoons.
Southwest monsoon winds occurs as a result of an intense low-pressure system forming over the Tibetan Plateau.
Northeast monsoons is caused by the formation of high-pressure cells over the Siberian and Tibetan plateaus.
Monsoon in 2023
The onset this season was delayed by unforeseen interactions between typhoons and cyclones.
Cyclone Biparjoy was born after the onset and lingered for longer than normal to delay the arrival of monsoon over Mumbai by nearly two weeks.
For the first time in over half a century, the Mumbai saw monsoon arrive together with Delhi.
The monsoon trough thus ended up with an exaggerated curvature over northwest India.
Excess rainfall over the northern Western Ghats into northwest India.
Deficits extending in a horseshoe pattern from Uttar Pradesh into Odisha and back to the east into Chhattisgarh, Madhya Pradesh, and Maharashtra.
Extreme heat has also been reported in parts of Himachal Pradesh, even as some areas of the State received heavy rainfall.
Did climate change influence this monsoon?
With global warming, a warm and humid atmosphere acts like a steroid for the weather.
Every weather event now has some contribution from global warming.
It is not yet clear how much the current monsoon mayhem has had to do with the El Niño.
Additionally, wildfires thus far this year have burned over three-times the normal area and have also emitted about three times as much carbon dioxide. This has also had a contribution to the warming.
What are the other factors influenced this monsoon?
The Indian subcontinent is like a popcorn kettle that gets heated up as the Sun crosses over into the northern hemisphere in March.
Rainfall is like the kernels of corn popping randomly around the kettle. That is, monsoon rainfall distribution always tends to be patchy.
Excess rainfall over northwest India is consistent with the Arabian Sea having warmed by about 1.5 degrees Celsius since January.
June contributes only about 15% of the rainfall to the seasonal total.
The instabilities in the atmosphere that drive convection are not strong enough to drive large-scale rainfall during the pre-monsoon season.
Rainfall this pre-monsoon was above normal due to a combination of the warm Arabian Sea and an unusually high number of western disturbances.
As a result, soils were left moister than normal, which in turn affected the evolution of the monsoon.
However, despite averaging rainfall over a month, a season or even multiple seasons, rainfall distribution remains uneven.
Disuniform terrain and heterogeneous land-use patterns are the likely culprits.
The Atlantic Ocean and the upper atmospheric circulation also tinker with the monsoon.
The entire Atlantic Ocean has been warmer than normal since March.
While the so-called Atlantic Niño, with a warm tropical Atlantic, generally tends to suppress monsoon rainfall, it is not clear what the impacts are when the entire Atlantic is as warm as it has been this year.
The strongest winds that occur in the upper atmosphere can spontaneously break into clockwise and anticlockwise patterns, especially when they run into mountainous terrain, such as the Himalaya.
Strong clockwise winds, with air flowing out from the centre, in the upper atmosphere demand an anticlockwise circulation near the surface, in order to feed the upper-level outflow.
Such a convergence near the surface can drive excess rainfall.
Finally, the warming over the Himalaya has not been uniform either.
Some parts of the mountain chain are amplifying global warming, leading to rapid local warming.
Irregular weather patterns during the monsoon superpose on these local features as a result of the winds expanding or compressing as they race up and down the narrow valleys.
The results can be cloudbursts, heavy rains or even heatwaves — depending on the local flow patterns.
Such disparate weather patterns can occur side by side as well.
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