Inter-annual Variation of Summer Southwest Monsoon Rainfall over the Monsoon Core Region of the Eastern Bay of Bengal and its Relationship with Oceans

Abstract

Using rainfall data from the Observation and, ERA5 reanalysis of sea surface temperature, this study examined the inter-annual variation of summer southwest monsoon rainfall on the eastern Bay of Bengal (BoB) mainland Indochina regions associated with ENSO. The composite study exhibits decreased rainfall in the eastern coastal region of BoB, and an increase in the northern Indo-Myanmar region during the developing phase of El Nino, but vice versa during the decay phase. Morlet wavelet power-spectrum analysis was performed on normalized rainfall anomalies to investigate the presence of significant signals that might be embedded in the study period. Further correlation analysis demonstrates that abnormal rainfall in the above two regions is controlled by different mechanisms. The Monsoon Core region rainfall anomaly is related to local convection and water vapor flux in the developing phase of El Niño. The anomalous anticyclone circulation in the upper troposphere helps strengthen rainfall. A strong/weak Myanmar southwest monsoon (MSwM) in the developing or decaying phase of El Niño can bring excess/less moisture to wet/dry the local southwest summer rainfall. In northern Indo-Myanmar, the anomalous rainfall is not only on the intensity of the MSwM but also on the frequency of western disturbances, and further findings need to be studied.