Study Of The Vertical Profile Of Cloud Water Content For Oceanic Non-raining Warm Clouds

Cloud water plays a key role in water cycle throughout the Earth. An accurate measurement of cloud liquid water path (LWP) measurement is potentially vital for many relevant studies, e.g., cloud microphysics, cloud radiative forcing and climate-modeling development. In this paper, warm cloud vertical structure is studied by cloud physical parameters retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS), the Advanced Microwave Scanning Radiometer-EOS (AMSRE) and Cloud Profile Radar (CPR).First, LWP derived from the MODIS is validated using the AMSRE retrievals for global oceanic non-raining warm clouds, with focus on the vertically homogeneous (VH) model and adiabatically stratified (AS) model of liquid water content (LWC) profile used in MODIS retrieval. With respect to AMSRE-LWP that acts as ground truth under a series of constraints, the global average of MODIS-LWPvh and MODIS-LWPas has a positive (11.8%) and negative (-6.8%) bias, respectively. Most of the oceanic warm clouds tend to have adiabatic origin and correspondingly form AS-like profiles. But the presence of drizzle and cloud-top entrainment mix seems to be the two main cause that modifies the original LWC profiles to become VH-like, which is notable for the very low clouds that have rather small thickness. These factors jointly determine the appearance of LWP profiles and in turn their spatial pattern across global oceans, with AS-like profiles dominant in the areas where non-raining warm clouds occur very frequently in the form of stratocumulus. The modified MODIS-LWP shows significant improvement compared with either MODIS-LWPvh or MODIS-LWPas . This is achieved by just using the two physically explicit models flexibly, in which the elementary MODIS retrievals of cloud top temperature (CTT), cloud optical thickness (COT) and droplet effective radius (DER) play a determinant role. A combined use of VH and AS model in the MODIS retrieval is demonstrated to be effective for improving the LWP estimation for oceanic non-raining warm clouds.Then, cloud vertical structure is studied using combined MODIS and CPR orbital datas. Warm cloud pixels are divided into isolated warm cloud and mixed warm cloud by judging the spatial continuity of the one-dimensional series of warm cloud pixel. A small number of isolated warm clouds was found, accounting for -8.8% of total warm cloud pixels. There are significant physical differences between isolated warm clouds and mixed warm clouds. Mixed warm clouds, with more cloud water and higher cloud top, seems to develop more intensively and form a deeper cloud system. Comparing the MODIS DER from three infrared channels that represent DER at distinct levels, it was found that about 60% warm clouds tend to decrease near cloud top. Mixed warm clouds show more drastic decrease than isolated warm clouds, which means stronger cloud-top entrainment effects, especially for mixed warm clouds with lower COT and higher DER. CPR reflectivity profile shows three types of structure with lowest reflectivity occurring in cloud top, but max reflectivity appearing in the middle of cloud, lower part of the cloud and cloud base. The three types of cloud profiles show different distributions and strength of radar reflectivity. It was also found that corresponding MODIS-LWP with VH assumption estimation is smaller than actual LWP.