In-cloud Vertical Structure Of Microphysical Parameters For Oceanic Non-precipitating Warm Clouds As Revealed By CPR And MODIS Measurements

By using Cloud Profile Radar(CPR/CloudSat)data from 2007 to 2009,the horizontal distributions of non-precipitating warm clouds over global oceans were examined and the vertical variation characteristics of LWC(Liquid Water Content)were analyzed for four major warm cloud types,i.e.,cumulus(Cu),stratus(St),stratocumulus(Sc)and altocumulus(Ac).It was found that among all oceanic non-precipitating warm clouds,the proportion of each type is stratocumulus(76.46%),stratus(12.48%),cumulus(7.45%)and altocumulus(3.61%).Stratocumulus plays a dominant role in the total coverage area of non-precipitating warm clouds over oceans.After the global normalization of the sample volume,there are also large differences in the spatial distribution patterns among the four types.Stratocumulus and stratus are mainly concentrated in coastal waters near the west of North America and South America continents.As a contrast,cumulus and altocumulus clouds are widely distributed on the Pacific Ocean,Atlantic Ocean and Indian Ocean,and high occurrences generally appear in the central part of each ocean.In spite of distinct formation regimes and morphologies,the vertical structures of LWC show similar patterns among the four types.From cloud bottom up to cloud top,LWC was found to increase first and then decrease.The the thickness of increasing structure and that of decreasing structure are nearly equivalent.The approximately linearly increasing structure in the lower and middle part of cloud column reflects the quasi-adiabatic growth characteristics of LWC.The upward decreasing structure near the upper part and near cloud top clearly reflects that cloud top is generally strongly affected by the intrusion of overhead dry air.The resulting evaporation of cloud water attenuates heavily downward from cloud top.The LWC vertical structure was found to be affected by cloud top height and cloud thickness.As cloud thickness increases,the upward increasing part becomes thicker,while the upward decreasing part becomes thinner.Clouds with the same thickness but different cloud top heights also have different LWC structures.Moreover,LWC structure was found to be affected by its amount.When the LWC in the cloud is higher,the increasing rate of the incremental structure of the LWC from the bottom to the middle part of the cloud becomes larger,and the decresasing rate from the middle to the top part of cloud also becomes larger.When the LWC in the cloud is lower,the vertical structure of the LWC is more susceptible to the turbulence in the cloud,which makes the relatively smooth structure of the LWC becoming a fluctuant one.This indicates that for a particular type of clouds,there are differences in the LWC structures corresponding to different stages during the cloud generation and development process.The vertical structure of DER is very similar to that of LWC structure.The DER profile after optical thickness normalization also shows to increase and then decrease from cloud bottom to cloud top.Further,the DER retrievals of MODIS are evaluated by using the CPR profile data.It was found that although the DER values of three near-infrared channels,1.6?m,2.1?m and 3.7?m,are generally higher than the CPR values,the DER vertical structure reflected by the three bands is basically consistent with that of CPR.In addition,the optical penetrating depth(OPD)and retrieval biases of the three channels of DER data of MODIS are simulated by comparing CPR DER at different level of optical depth.It was found that 3.7?m band has the minimum OPD,which is about 2.59.The OPD of 2.1?m and 1.6p?m band are comparable,10.57 and 10.76,respectively.Compared to CPR,the DER bias of MODIS was found to be related to cloud geometric thickness.The DER biases in 1.6?m and 2.1 ?m bands are very small and show little dependence on cloud thickness,while those in 3.7?m band decrease withincreasing cloud thickness.The OPD of the three bands also varies with cloud types.Both for 1.6?m and 2.1?m band,the OPD is the largest for stratus,and then followed by cumulus,stratocumulus,and altocumulus.The DER bias of stratus is the smallest.As a contratst,for 3.7?m band,the OPD is the largest for altocumulus(2.85),and then followed by cumulus(2.71),stratocumulus(2.67),stratus(2.59).The DER bias of stratocumulus is the smallest.