Seasonal and Interannual Variability in the Barrier Layer of the Bay of Bengal

Abstract

An objectively analyzed monthly gridded ocean analysis derived from a combination of satellite and in situ observations is used to describe the seasonal and interannual variability in the barrier layer thickness (BLT) over the maximum variance region in the BLT of the Bay of Bengal (BoB) for the period from 1993 to 2012. The northern BoB acquires a maximum variance in the BLT where a large river discharge flux was observed. The BLT showed strong seasonal variability with minima during April–May and maxima during December–February. An investigation of the variability in the BLT showed large amplitude at annual and semiannual time scales. The relationship between the BLT and the Indian Ocean dipole mode (IOD) reveals that the BLT maximum is relatively high in the negative IOD years when compared to the positive IOD years. A significant relation between the BLT and IOD is inferred with the IOD leading the BLT by 3 months and lagging by 1 month. We show that the 1 month lag in the northern BoB is mainly associated with coastally trapped Kelvin waves that radiate Rossby waves and control the BLT. However, further investigation is required regarding the temporal lead of the IOD with the BLT in the northern BoB.

Seasonal Evolution of Oceanic Upper Layer Processes in the Northern Bay of Bengal Following a Single Argo Float

“…The temperature inversions occur during winter when heating in the BL by penetrative shortwave radiation is greater than the heating of the ML by the net surface heat flux and the horizontal advection (Girishkumar et al, , hereafter GK11; GK13). The IL in the BoB also depends on the equatorial remote forcing in‐terms of the coastally trapped Kelvin waves and radiated Rossby waves (RWs; Rao et al, ; (Yu et al, ; GK11; GK13; Kumari et al, , hereafter KM18). Prasad () and Anitha et al (, hereafter AN08) used the Monin‐Obukhov length (M‐O length), which determines the relative importance of mechanical mixing (wind forcing) and surface buoyancy for analyzing stability and seasonality in the BoB.…”

Seasonal Variation of Barrier Layer in the Southern Ocean

“…The BL phenomenon suggests that the haline stratification may influence the amount of oceanic heat content available for air-sea interactions. Hence, it serves as an important blockade that prevents the cold thermocline water from entering the mixed layer and thus has significant impacts on the upper mixed layer heat content and the sea surface temperature (Foltz & Mcphaden, 2009;Pailler et al, 1999;Vialard & Delecluse, 1998a), precipitation and monsoon (Masson et al, 2005), tropical cyclones (Balaguru et al, 2012) and even El Niño (Maes et al, 2002(Maes et al, , 2005 and Indian Ocean Dipole (Kumari et al, 2018;Qiu et al, 2012).…”

Decadal Variability of the Barrier Layer and Forcing Mechanism in the Bay of Bengal

“…The resultant MLD shoaling then favors a thick BL between the bottom of the ML and top of the thermocline (Lukas & Lindstrom, 1991). The existence of such a thick BL in the BoB has been confirmed by observational studies (de Boyer Montégut et al, 2007;Girishkumar et al, 2011;Kumari et al, 2018;Sprintall & Tomczak, 1992;Thadathil et al, 2007). Particularly, Vinayachandran et al (2002) investigated the evolution of BL in the BoB during summer and emphasized the significant effect of advection on the formation and erosion of BL.…”

“…Particularly, Vinayachandran et al (2002) investigated the evolution of BL in the BoB during summer and emphasized the significant effect of advection on the formation and erosion of BL. Using a comprehensive data set, Thadathil et al (2007) reported that BLT in the BoB is the thickest in winter (December-February) and disappears in April and May (e.g., Kumari et al, 2018;Thadathil et al, 2007).…”