The role of salinity on the dynamics of the Arabian Sea mini warm pool

Abstract

Warmer (>28°C) sea surface temperature (SST) occurs in the South Eastern Arabian Sea (SEAS, 5°N–13°N, 65°E–76°E) during March–April, and is known as the Arabian Sea Mini Warm Pool (ASMWP). In this study, we address the role of salinity and the upper layer heat and salt budgets in the formation and collapse of this ASMWP. An assessment of Level 3 sea surface salinity (SSS) data from the Soil Moisture and Ocean Salinity (SMOS) satellite mission for the year 2010 shows that SMOS is able to capture the SSS variability in the SEAS. Analysis of temperature, salinity and currents from the Hybrid Coordinate Ocean Model during 2003–06, and, in situ temperature and salinity data from Argo floats during 2003–06 for the SEAS revealed that low salinity waters cap the top 60 m of the SEAS in January–February. This minimum salinity was concurrent with the formation of a barrier layer and with the time when the SEAS gained little net heat flux and the equatorward flowing East India Coastal Current (EICC) fed low saline waters into the SEAS. Subsequently, the net heat flux increased to a peak value under the increased salinity stratification, leading to the formation of the ASMWP in March–April. The ASMWP collapsed by May due to increase in SSS and the associated weakening of the salinity stratification. The monsoon onset vortex in May 2004 could be related to the minimum SSS that occurred in February 2004, followed by higher SST and heat content of the ASMWP in April 2004.

Interannual variability of the Arabian Sea Warm Pool: observations and governing mechanisms

“…This comparison suggests that the near-surface vertical haline stratification appears to play an important role in determining the amplitude of the ASWP. The recent study of Nyadjro et al (2012) over the SEAS region based on HYCOM model output and ARGO data during the period 2003-2006 also shows that the ASWP is more pronounced when near-surface salinity values are lower during the preceding winter.…”

Influence of Mesoscale Features on Mixed Layer Dynamics in the Arabian Sea

“…We used ECMWF winds, evaporation, precipitation, incoming solar radiation, and significant wave heights to be consistent with the work of Kumar and Narvekar (). For the computation of the heat budget terms following the methodology in Nyadjro et al (), outgoing longwave radiation and latent and sensible heat fluxes were also obtained from ECMWF ERA‐interim reanalysis. This product is an improved version of the previous ERA‐40 reanalysis, as it exhibits a more accurate representation of the hydrological cycle, stratospheric circulation, and temporal consistency of the reanalyzed fields (Dee et al, ).…”

“…Calculation of heat budget terms follows the methodology presented in Nyadjro et al (), which follows the work on Swenson and Hansen () and Kurian and Vinayachandran () and can be described as where T is the vertically averaged HYCOM temperature throughout the mixed layer (denoted by h ) and its time rate of change. ECMWF net near‐surface heat flux is Q s , the specific heat capacity of seawater is C p (4.0 × 10 3 J·kg −1 ·K −1 ), U and V are HYCOM zonal and meridional currents respectively, W e is the entrainment velocity, ∆T is the difference between the average mixed layer temperature and the temperature 10 m below the mixed layer.…”

“…As in Stevenson and Niiler (), W e is computed as where is the rate of the mixed layer deepening, v . ∇ h is the horizontal velocity at the base of the mixed layer multiplied by the horizontal gradient of the MLD, and w h is the vertical velocity at the base of the mixed layer (Nyadjro et al, ; Ren & Riser, ). H , the Heaviside unit function, equals 0 for a shoaling mixed layer ( and equals 1 for a deepending mixed layer .…”

Variability of sea surface salinity in the tropical Indian Ocean as inferred from Aquarius and in situ data sets

“…Sanilkumar et al (1994 analysed surface meteorological data and near-surface salinity structure in 1990 over the northern BOB during the monsoon trough boundary layer experiment and demonstrated a connection between the Indian monsoon and salinity. The link between the spatial structure of salinity over the southeastern AS and the onset of the Indian monsoon was also investigated by Masson et al (2005) and Nyadjro et al (2012), using observational data sets and numerical model simulations. Thus, a reliable estimate of SSS over the TIO at higher spatial and temporal resolutions is crucial for various applications including verification of ocean simulation and to initialize the ocean model.…”