资源环境科技发展态势分析平台

Combined A-train remote sensing measurements from Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E), CloudSat, and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) are used to study MODIS liquid water path (LWP) uncertainties at high latitudes. The focus is on quantifying uncertainties due to mixed-phase clouds and solar zenith angle-dependent bias, both of which disproportionately affect the MODIS data set in the polar regions. Multisensor LWP retrievals in stratiform mixed-phase clouds show that treating mixed-phase clouds as liquid clouds result in LWP bias that is related to the ice water path (IWP) on average and reaches close to 15% at IWP of 150 g/m(2) and can reach 40% or higher when IWP is greater than 400 g/m(2). Moreover, A-train measurements and radiative transfer modeling are used to further understand the well-known yet unresolved solar zenith angle-dependent high bias in MODIS LWP. It is shown that the cloud top height variation is one of the main factors that contribute to this bias due to three-dimensional radiative interactions with cloud top inhomogeneity. Excluding only 0.5% of data points that show significant three-dimensional errors reduces the bias by 25 g/m(2) at solar zenith angle of 80 degrees and improves agreement with the AMSR-E LWP trends. Three-dimensional radiative transfer simulations confirm that cloud top inhomogeneity is primarily responsible for the solar zenith angle-dependent LWP bias as observed by the MODIS measurements. This study provides a framework to guide future improvements of MODIS LWP data set, which is a key data source to constrain climate models.