Radiant heating rates and surface biology during the Arabian Sea Monsoon Experiment

Radiometric observations are carried out to estimate the net shortwave solar radiation in the upper ocean during the Arabian Sea Monsoon Experiment Phase II (ARMEX-II). Radiant heating rates in the Arabian Sea Warm Pool (ASWP) region from in situ radiometric measurements are presented for the first time. The estimated shortwave fluxes (300–700 nm) from the observed data are 101, 62, 40 and 29 W m −2 at 10, 20, 30 and 40 m depths respectively. About 5% of the surface light reaches below 50 m. Heating of the water column by penetrating solar radiation is substantial and estimated to be 0.18, 0.11, 0.08 and 0.07 ◦ Cd ay −1 in the upper 10, 20, 30 and 40 m respectively. Simultaneous observations from space-based sensors (SeaWiFS and IRS-P4 Ocean Colour Monitor) show an increase in solar absorption in regions with enhanced concentration of biologically active constituents.