The Cloud Property And Vertical Structure Characteristics Of Oceanic Precipitating And Non-precipitating Warm Clouds Derived From Cloudsat/CPR And Aqua/MODIS Measurements

Clouds and precipitation are important weather phenomena,playing an important role in the global climate system.Clouds and the possibly associated precipitation events provide fresh water resources for human beings.They are therefore a very important part of the global water cycle process.The measurements-based studies on the microphysical properties and vertical structure of clouds and precipitation are critical to not only deepen the understanding of the cloud and precipitation processes,but also provide evidences for the modeling and simulation of clouds and precipitation.In this paper,we combined and collocated the Aqua/MODIS and the CloudSat/CPR data,two quasi-synchronous remote sensing data on clouds and precipitation,to conduct the comparison of cloud parameters between precipitating warm clouds and non-precipitating warm clouds,focusing on the difference characteristics of the three cloud droplet Effective Radius(Re)retrieved by exclusively using a single MODIS near-infrared channel radiance,i.e.,1.6um(R16),2.1 um(R21),or 3.7um(R37)channel.Also,the global distribution of warm cloud properties and the statistical results of the cloud property characteristics of these two types of warm clouds were analyzed.The differences of averaged radar reflectivity profiles between these two types of warm clouds were experimentally investigated.Main results of this study are as follows.The global distribution of warm cloud parameters has notable regional differences,mainly affected by the characteristics of the underlying surface,thermodynamic processes,and relevant circulation systems.In the paper,the global distribution results show that the total cloud fraction is highest over the Western Pacific Warm Pool and the Indian Ocean warm pool and the CTT is rather low,indicating the predominance of high clouds.The variances of CTT are mostly high,suggesting dramatic variations of cloud top height.This results should be attributed to the strong convective activities that caused by the unique thermodynamic conditions there.On the contrary,over the subtropical eastern Pacific Ocean near the coastlines of North America and South America,warm clouds are predominant.These typical and other similar oceanic areas have great samples of precipitating and non-precipitating warm clouds and used as target regions for investigation.The valid range of most cloud property values are similar for precipitating and non-precipitating warm clouds,including cloud top temperature(CTT),optical thickness(COT),geometrical thickness,cloud droplet effective radius(Re),cloud water path(CWP).But there is a notable difference between the averages of several cloud parameters.The COT,Re,CWP of the precipitating warm clouds is significantly larger than that of the non-precipitating ones.The exception is CTT,whose average is similar for the two types of warm clouds.For ideal stratiform cloud evolution processes,when the precipitate is absent,the high level cloud particle size is the largest,while cloud particle size at the middle level and the base level get smaller.Given precipitate onset,due to gravity-induced collision and coalescence of droplets,the base level cloud particle size would be the larger than upper levels.The three Re,i.e.,R16,R21,and R37,could be used to approximately indicate the cloud particle size at different in-cloud levels.According our statistical results,the actual situation is more complicated.There is no evident monotonous upward increasing(decreasing)of cloud particle size for non-precipitating(precipitating)warm clouds.Some hints on differences of cloud particle size vertical structure between the two types of warm cloud are derived,but still need more rigorous reexamination.The averaged radar reflectivity profiles of precipitating warm clouds and non-precipitating warm clouds are quite different.Although they both show a consistent downward radar reflectivity growth between 2km and 1km levels,while near the 1km or at lower levels,radar reflectivity of non-precipitating warm clouds tends to decrease,but that of precipitating warm clouds continues to increase.This result shows that the layer between 1km and 2km is the key height facilitating the rapid growth of the cloud droplets.