A unified satellite algorithm is presented to simultaneously retrieve aerosol properties (aerosol optical depth; AOD and aerosol type) and clear-sky shortwave direct radiative effect (hereafter, DREA) over ocean. The algorithm is applied to Moderate Resolution Imaging spectroradiometer (MODIS) observations for a period from 2003 to 2010 to assess the DREA over the global ocean. The simultaneous retrieval utilizes lookup table (LUT) containing both spectral reflectances and solar irradiances calculated using a single radiative transfer model with the same aerosol input data. This study finds that aerosols cool the top-of-atmosphere (TOA) and bottom-of-atmosphere (BOA) by 5.2±0.5W/m2 and 8.3W/m2, respectively, and correspondingly warm the atmosphere (hereafter, ATM) by 3.1W/m2. These quantities, solely based on the MODIS observations, are consistent with those of previous studies incorporating chemical transport model simulations and satellite observations. However, the DREAs at BOA and ATM are expected to be less accurate compared to that of TOA due to low sensitivity in retrieving aerosol type information, which is related with the atmospheric heating by aerosols, particularly in low AOD conditions; consequently, the uncertainties could not be quantified. Despite the issue in the aerosol type information, the present method allows us to confine the DREA attributed only to fine-mode dominant aerosols, which are expected to be mostly anthropogenic origin, in the range from-1.1W/m2 to-1.3W/m2 at TOA. Improvements in size-resolved AOD and SSA retrievals from current and upcoming satellite instruments are suggested to better assess the DREA, particularly at BOA and ATM, where aerosol absorptivity induces substantial uncertainty.
Bibliographical noteFunding Information:
We thank the MODIS science team for providing valuable data used in this study. We also thank the principal investigators and their staff for establishing and maintaining the AERONET sites used in this investigation. This work was supported by the Korea Meteorological Administration Research and Development Program under Grant CATER 2012-2065 . This research was partially supported by the Brain Korea 21 (BK21) program for Jhoon Kim and Jaehwa Lee.
All Science Journal Classification (ASJC) codes
- Environmental Science(all)
- Atmospheric Science