A new study by researchers at the Cochin University of Science and Technology (Cusat) has showed that Madden Julian Oscillation (MJO) can influence extreme rainfall over Kerala in the monsoon season.
MJO and its impact
MJO is an eastward propagating convective system that passes over the Indian and Pacific Oceans, with a periodicity of 30–60 days and it influences most of the tropical weather systems. “Around 70 active MJO days occurred over the equatorial Indian Ocean during 2019- 2021 in the months from June to August,” said Dr. Ajil Kottayil, scientist at the Advanced Centre for Atmospheric Radar Research, CUSAT, who led the study. K. Prajwal, research scholar in the university, and Dr. Prince Xavier of UK’s Met Office were part of the research team that analysed meteorological datasets over a period of two decades since 2000.
“MJO can cause an anomalous change in the rainfall activity over Kerala. It has both active and suppressed phases and its strong active phase over the equatorial Indian Ocean causes anomalous increased rainfall activity, the impact of which is highly devastating,” he added. The study found that active MJO phases can generate organised deep convective cloud clusters (cumulonimbus clouds) over Kerala, which can result in very heavy rainfall over a short duration of time.
Delay in withdrawal of monsoon
The extreme rainfall events occurring over Kerala coincides with the occurrence of active MJO phases over the equatorial Indian ocean. The occurrence of active MJO during September-November may have the potential of delaying the withdrawal of Indian summer monsoon, according to the researchers. Unlike extreme rainfall events associated with monsoon depressions, MJO-assisted extremes are more or less of a local nature and of lesser duration. The active MJO does not necessarily result in extreme rainfall, if its amplitudes are weak, they said.
The study has been published in Elsevier’s Atmospheric Research journal.