Upper Ocean Temperature and Salinity Variability and Compensation in the Arabian Sea

Intraseasonal sea surface temperature (SST) and mixed layer depth (MLD) variations in the Arabian Sea are known to influence the onset and characteristics of the Indian monsoon. More recently, modeling studies have shown that resolving smaller-scale, higher-frequency variability improves monsoon forecasts. Here, we present submesoscale (~2-10 km) observations of the central Arabian Sea upper ocean evolution prior to the 2017 southwest monsoon onset. Data were collected by 2 continuously profiling ALAMO floats (deployed in close proximity) which were tracked by 2 Seagliders in a coordinated Lagrangian drift experiment completed during the NASCAar (Northern Arabian Sea Circulation – autonomous research) initiative. During the observational period, the MLD shoals rapidly following a wind shift and remains shallow under conditions of strong diurnal warming and light winds. While the shallow depth of the mixed layer is spatially uniform, temperature and salinity have significant horizontal variability. Horizontal density gradients were found to be primarily governed by temperature contributions at all resolved scales, with only partial salinity compensation observed. These results indicate that horizontal processes may be an important contributor to SST evolution in the central Arabian Sea and show the utility of autonomous platforms for observing submesoscales.