The Indian Institute of Science (IISc) has just published a landmark study. It studies the Boreal Summer Intraseasonal Oscillation (BSISO) and its vigorous influence on the Indian monsoon. The research emphasizes the role that cloud bands play in regulating the climate. Their movement and strength is crucial to the formation of wet spells during the monsoon season. The BSISO, which guides the transition between wet and dry spells, brings a band of clouds from the equator over to the Indian subcontinent, effectively ending dry spells.
The research serves as a reminder of just how mighty these tropical cloud arms can be. It is their strength that fuels their westward track and determines how extreme the rainfall the Indian subcontinent will receive during monsoon wet spells. In their study, researchers found that strong northward propagation of the BSISO is only present when the tropical equatorial cloud band is strong. Given enough time, previous theoretical perspectives predicted such a cloud band would move northward even if it started out weaker.
"What we have shown is that this is not the case. If the cloud band in the equator is weak to start with, then it cannot propagate north," said Aditya Kottapalli, a key researcher involved in the study.
Each summer, as blazing temperatures peak, the monsoon rains come to wash away the scorching dry season. This unusual weather pattern occurs due to the shift of cloud bands northwards from the equator. The research findings will improve climate models used to predict seasonal and sub-seasonal rainfall. This change will result in more skillful forecasts of wet spells.
Since its identification in 1979, the BSISO has been an active area of research. A new study published this week in npj Climate and Atmospheric Science uncovers some pretty thrilling news. It is evidence that air-sea interaction through the equatorial Indian ocean, rather intensely influences the genesis of wet spells over India.
"What we found is that air-sea interaction in the equatorial Indian Ocean plays a major role in driving wet spells in India. This is likely to change in the future because the atmosphere would be warmer," explained Vinayachandran, a leading researcher from IISc.
To try to get a handle on what’s causing the BSISO to move, a team of researchers took ensemble averages from some of the most skillful models. They found that background moisture—how much water vapor is present before the rains begin—will increase over most of this region. The expected increase is expected to intensify wet spells, especially in the area’s coastal plain. Overall, annual rainfall will increase by a stunning 42% to 63% across India and its surrounding oceans.