Synoptic-Scale Atmospheric Motions Modulated by Spring Phytoplankton Bloom in the Sea of Japan

Atmospheric responses to biological heating caused by the spring phytoplankton bloom in the Sea of Japan are investigated. Sea surface temperature (SST) is first computed using a mixed-layer model with an ocean reanalysis product. Satellite-derived surface chlorophyll concentrations representing phytoplankton population are input to an equation for attenuation coefficients of solar radiation penetrating the mixed layer. Two sets of SST are obtained by this model, using the attenuation coefficients with and without phytoplankton. It is found that the phytoplankton bloom increases SST by up to 0.8°C by mid-May, especially in the northern Sea of Japan. Thereafter, two experiments using a regional atmospheric numerical model are conducted for April and May. One imposes SST synthesized by multiple satellite observations on the lower boundary of the model (the green case). The satellite-derived SST includes influences of biological heating by phytoplankton in the actual ocean. The other uses SST reduced by differences between SSTs computed by the mixed-layer model with and without phytoplankton (the blue case). Under modest wind conditions, extratropical cyclones east and south of the Japan Islands in the blue case develop more rapidly than in the green case. Cyclones are likely initiated by the cool and dry air mass that enhances lower-level baroclinicity above oceanic fronts. This cool and dry air mass is transported from the Sea of Japan, where SST decreases in the absence of phytoplankton. Therefore, incorporating ocean biology is potentially capable of improving regional atmospheric and ocean general circulation models.