Behaviour of Latent Heat Flux over the Bay of Bengal during Indian Summer Monsoon Deficit Period

Abstract

Variabilities of LHF and air-sea interaction processes over the Bay of Bengal (BoB) are studied on daily basis
for the June-September (JJAS) period of 1998-2010. A new criterion for the Indian Summer Monsoon (ISM)
break is considered using daily TRMM Microwave Imager (TMI) precipitation data over central India. An ISM
break is defined if the standardized rainfall anomaly over central India is less than -0.5 mm for at least four
consecutive days (following Samanta et al. 2016). The newly defined break periods match well with earlier
studies. The most intriguing result of this study is to observe the antecedents of ISM break period in 10-90 days
filtered latent heat flux (LHF) anomaly over the northern BoB. It is found that if intraseasonal LHF anomaly
over the northern BoB is less than -5 Wm-2 and continued for four consecutive days then monsoon break occurs
within next 10 days. In addition, the equatorward shift of the Inter-tropical Convergence Zone (ITCZ) few days
prior to the break, is clearly observed consistent with the presence of negative outgoing longwave radiation
(OLR) anomaly. The OLR shows a strong negative correlation with LHF over the northern BoB.