Research

Impacts of waves on air-sea momentum and heat fluxes

Momentum and heat fluxes, which are computed using COARE algorithms, are influenced by waves. This contribution is parameterized in this algorithm using wave roughness: one formula uses wind speeds while the other uses wave age and wave slopes as inputs. These formulations assumes a wind age of 1.2 (which means wind-driven short waves) and assumes wind-wave alignment. However, this assumption is often not true in presence of long waves (or swells) and during misalignment of waves and winds. In collaboration led by Dr. Hyodae Seo, we are investigating these assumptions using in-situ observations from EKAMSAT field campaign and atmosphere, ocean and wave coupled models following the approach from Sauvage et al. 2023. This work began as a collaborative project during my PhD and has since evolved into a postdoctoral appointment at UH with Hyodae, through EKAMSAT project funded by US Office of Naval Research. We are examining these cases across a range of meteorological regimes, including springtime heating, hurricanes, and the winter monsoon.

Impacts of salinity stratification in driving lateral gradients in Northern Indian Ocean

My research explores the multi-scale physical processes that govern sea surface temperature (SST) in the Northern Indian Ocean—a region where solar radiation and significant freshwater influx create a unique laboratory for air-sea interaction. Using a combination of high-resolution in-situ observations, remote sensing, and 1-D numerical modeling (GOTM), I investigate how salinity-driven stratification modulates the ocean’s response to atmospheric forcing.

Formation of Diurnal Warm Layers (DWLs) is a dominant feature in the Northern Indian Ocean, particularly under low wind speeds and high solar radiation. These features play a crucial role in atmosphere-ocean interactions. Using drifting meteorological buoys, we observed that lateral gradients in DWL evolution can be remarkably intense over distances as short as 30 km. These differences, driven by a combination of synoptic cold-pool events and mesoscale advection, significantly modify the Turbulent Kinetic energy budget and can shift DWL depths by O(10 m).

While satellite data often smooths over these features, our in-situ observations and modeling results (published in the Journal of Physical Oceanography) reveal that lateral differences in diurnal SST amplitude can reach extremes of 1.4°C. These results suggest that small-scale salinity stratification is one of the drivers of SST variability in freshwater-dominated basins.

Beyond the daily cycle, I examined how this stratification influences longer-term SST warming on intra-seasonal timescales (15–45 days), especially in context of the mini-warm pool in the Northern Indian Ocean during the Spring inter-monsoon. In research recently accepted in JGR-Oceans, we demonstrate that the impact of salinity on surface warming is not uniform; it depends heavily on the balance between net heat flux and water clarity. We derived a theoretical daily-averaged net heat flux threshold, ranging from 103 to 136 W/m², that determines whether stratified scenarios will enhance or reduce the rate of SST warming. This sensitivity to bio-optical properties and heat flux suggests that accurate monsoon and tropical cyclone forecasting requires a nuanced representation of salinity-driven stratification.

This work was done as a part of MISO-BoB and EKAMSAT projects funded by US Office of Naval Research.

Role of submesoscale processes due to interactions between Monsoon winds and cyclone wake in accelerating the wake recovery

Cold wakes generated by tropical cyclones enhance ocean productivity and influence local air-sea interactions, impacting the paths and intensities of future storms, though in-situ observations of their recovery are rare. During our 2023 EKAMSAT fieldwork, we surveyed a cold wake in the Arabian Sea, formed after Cyclone Biparjoy, using shipboard instruments about 10 days post-storm. The wake showed asymmetry, with a stronger buoyancy gradient on its eastern edge and a weaker one on the western edge, leading to differential vertical structures in temperature, salinity, and velocity. While cold wake recovery is often attributed to one-dimensional diurnal heating and cooling, our observations highlight the key role of three-dimensional submesoscale dynamics, driven by monsoon winds and submesoscale fronts. These interactions accelerated the wake’s recovery to pre-cyclone conditions in just 8 days—far faster than predicted by one-dimensional models—underscoring the importance of submesoscale processes in shaping wake evolution and future atmospheric conditions. This work was done as a part of EKAMSAT project funded by US Office of Naval Research. This work was recently published in Geophysical Research Letters.