Impact of Satellite-Derived Diffuse Attenuation Coefficient on Upper Ocean Simulation Using High-Resolution Numerical Ocean Model: Case Study for the Bay of Bengal

Abstract

Impact of satellite-derived shortwave attenuation depth and its spatial variability on the upper ocean dynamics has been studied using a numerical ocean model over the Bay of Bengal. We conducted two simulations, differing in the spatial distribution of shortwave attenuation depth for the period 2014–2015. The control run use a constant attenuation depth of 23 m (the default case for Type-I water) while the experimental run (ER) use spatially varying attenuation depths derived from daily climatology of the diffuse attenuation coefficient (${\mathrm{K}}_{\mathrm{d}}490$). Simulated parameters like sea surface temperature (SST) and mixed-layer depth (MLD) are sensitive to ${\mathrm{K}}_{\mathrm{d}}490$ that limits the penetration of downwelling shortwave radiation into the ocean. It has been found that ${\mathrm{K}}_{\mathrm{d}}490$ alters the upper ocean thermodynamics significantly. Validation has been performed using satellite, moored-buoy and profile data, for the year 2015. During spring, the errors in SST in the ER are reduced up to 35% at buoy location. The impact of improving shortwave attenuation depth is found to be maximum in the upper ocean (50–150 m). Error in simulated temperature at 100 m depth is reduced by 15% in the ER. MLD, barrier layer thickness, and the depth of 26 °C isotherm also show significant improvements in the ER.

Keywords:

• Bay of Bengal
• diffuse attenuation coefficient
• ocean dynamics
• shortwave attenuation depth
• Type-I water

Acknowledgements

Geophysical Fluid Dynamics Laboratory is thanked for providing the OGCM code. Diffused Attenuation Coefficient (K_d490) data were obtained from ftp://hermes.acri.fr/?class=archive. Temperature and salinity data from CORA were available online at https://www.seanoe.org/data/00351/46219/. GHRSST data were downloaded from https://podaac.jpl.nasa.gov/GHRSST. Temperature profile data from GTSPP were available online at ftp://ftp.nodc.noaa.gov/pub/gtspp/indian/. Dr. J. T. Farrar is thankfully acknowledged for providing the BoB mooring observations; the deployment of the Woods Hole Oceanographic Institution (WHOI) mooring. We acknowledge two anonymous reviewers for their constructive comments that helped us to improve the manuscript significantly.

Additional information

Funding

J.T.F. were supported by the U.S. Office of Naval Research, Grant N00014-13-1-0453.