Siddhant (Sid) Kerhalka, PhD candidate in the Tandon Lab here at SMAST, will be presenting on “Impacts of Salinity Stratification on SST in the Northern Indian Ocean Warm Pool “. This seminar will take place Tuesday February 26 in SMAST East 101-103 and on Zoom. We look forward to seeing you there!

 

Abstract:

Predicting the Indian monsoon at sub-seasonal timescales remains a challenge, hindering accurate global weather forecasting. A precursor to monsoon onset is the formation of high sea surface temperature (SST) “mini-warm pools” in the Indian Ocean during the spring inter-monsoon, characterized by intense diurnal warming, leading to formation of Diurnal Warm Layers (DWL). The spatial variability of SST and DWLs is poorly understood, despite their importance for initiating intense atmospheric convection, particularly during the Monsoon. These variations in SST can occur due to differences in river-influenced stratification, upper ocean optical properties, and air-sea fluxes. Previous high-resolution observations revealed significant (O(1°C)) SST variations over short distances (<100 km) within DWLs for diurnal timescales. Satellite data further showed similar spatial differences in monthly baseline SST increases, even with comparable wind and heat flux forcing. In this talk, we use a 1-D General Ocean Turbulence Model to investigate the role of in salinity stratification, optical properties, and air-sea fluxes in establishing spatial SST variations at diurnal and sub-seasonal timescales. Our results show that while salinity stratification plays a secondary role (12.5-25%) in daily SST variations, it becomes crucial over longer, sub-seasonal periods. A counterintuitive finding emerges: stratified waters heat more than unstratified waters under higher net heat flux conditions, but heat less under lower net heat flux. This implies that density fronts which are primarily driven by salinity can either strengthen or weaken depending on the heat flux and upper ocean optical properties. Because these SST differences occur in typically eddy-poor regions of the Northern Indian Ocean, variations in stratification become a primary driver of both diurnal and sub-seasonal SST variability. This is particularly relevant in areas with strong salinity fronts, like the Northern Indian Ocean, as SST is a critical parameter coupling atmosphere and ocean dynamics through air-sea fluxes.