A theoretical study of the effect of subsurface oceanic bubbles on the enhanced aerosol optical depth band over the southern oceans as detected from MODIS and MISR

摘要

Submerged oceanic bubbles, which have a much longer life span than whitecapsor bubble rafts, have been hypothesized to increase the water-leavingradiance and thus affect satellite-based estimates of water-leaving radianceto non-trivial levels. This study explores this effect further to determinewhether such bubbles are of sufficient magnitude to impact satellite aerosoloptical depth (AOD) retrievals through perturbation of the lower boundaryconditions. There has been significant discussion in the communityregarding the high positive biases in retrieved AODs in many remote oceanregions. In this study, for the first time, the effects of oceanic bubbleson satellite retrievals of AOD are studied by using a linked Second Simulationof a Satellite Signal in the Solar Spectrum (6S) atmospheric and HydroLightoceanic radiative transfer models. The results suggest an insignificantimpact on AOD retrievals in regions with near-surface wind speeds of lessthan 12 m s?1. However, the impact of bubbles on aerosol retrievalscould be on the order of 0.02–0.04 for higher wind conditions within thescope of our simulations (e.g., winds < 20 m ?1. This bias ispropagated to global scales using 1 year of Moderate Resolution ImagingSpectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer EOS(AMSR-E) data to investigate the possible impacts of oceanic bubbles on anenhanced AOD belt observed over the high-latitude southern oceans (alsocalled the enhanced southern oceans anomaly, or ESOA) by some passive satellitesensors. Ultimately, this study is supportive of the null hypothesis:submerged bubbles are not the major contributor to the ESOA feature. Thissaid, as retrievals progress to higher and higher resolutions, such as fromairborne platforms, the uniform bubble correction in clean marine conditionsshould probably be separately accounted for against individual brightwhitecaps and bubble rafts.