Comparisons Between Cumulus And Altocumulus On The Size And Morphology Of Cloud Entity As Well As The Mesoscale Organization Structure Of Cloud Ensemble

Cumulus(Cu)and Altocumulus(Ac)are typical cumuliform clouds with clear boundaries and distinct individual morphology,and often appear in groups at a mesoscale to form unique cloud fields.Their individual horizontal size and group organization structures play an important role in regulating the radiation flux of the region,which in turn can affect the radiation balance at a regional scale.In this study,based on the 2B-CLDCLASS-LIDAR cloud type profile data formed by CloudSat and CALIPSO joint observations,Cu and Ac cloud clusters were accurately identified,and a series of quantitative indicators were established to compare the differences in individual size and morphology as well as mesoscale organization structures between the two cloud types.The parameters for individual cloud size included width,thickness,and volume,while the morphology parameters included aspect ratio and area fraction.The cloud field mesoscale organization structure parameters used were cloud void size,overlap distance,organization index,and convective organization potential.The results are as follows:In terms of the global distribution of the frequency of occurrence of the two types of cloud clusters,there are approximately 732 Cu cloud clusters and 60 Ac cloud clusters per million square kilometers globally each year,and the frequency of occurrence of Cu cloud clusters is much higher than that of Ac,about twelve times that of the latter.Cu clouds are mainly concentrated in the low-latitude tropical ocean,the Qinghai-Tibet Plateau,and Southwest China,while Ac clouds are mainly distributed over equatorial regions and over land south of the equator.In terms of the height of the cloud clusters,the average bottom height of Cu and Ac clouds is 0.7 km and 3.5 km,respectively,with standard deviations of 0.7 km and 1.9 km.The average top height is 1.4 km and 4.8 km,respectively,with standard deviations of 1.0 km and 1.8 km.In terms of individual size,the dimensions of Ac clouds are larger than Cu clouds,with wider,thicker,and more voluminous features.Specifically,the average width of Ac and Cu clouds are 11 km and 4 km,respectively,with standard deviations of 23 km and 4 km,making the width of Ac approximately three times larger than Cu.The average thickness of Ac and Cu clouds are 1.2 km and 0.7 km,respectively,with standard deviations of 1.4 km and 0.6 km,making the thickness of Ac approximately two times larger than Cu.The average volume of Ac and Cu clouds are 59 and 11,respectively,with standard deviations of 192 and 22,making the volume of Ac approximately five times larger than Cu.In terms of shape,Ac clouds are flatter and less dense than Cu clouds.As the thickness of the clouds increases,the width and volume of both Ac and Cu clouds also increase monotonically,but the clouds become more sparse.The width and thickness of Ac clouds increase in approximately the same proportion,with little change in their flatness.Cu clouds,on the other hand,show a different trend,with a slower increase in width than thickness as the volume increases,resulting in a decrease in their flatness and a tendency towards a columnar shape.In terms of spatial organization of cloud clusters,the cloud void size is relatively similar between Ac and Cu fields,with average values of 76 km and 72 km,and standard deviations of 86 km and 78 km,respectively.However,for the overlapping distance,Ac fields have a larger overlap than Cu fields,with average values of 23.2 km and 2.9 km,and standard deviations of 42.3 km and 2.5 km,respectively.Overlapping of cloud clusters can be categorized as double-layer and triple-layer overlaps.Comparing the overlapping distances between the two types of overlaps,the doublelayer overlap distance of Ac clouds(23.6 km)is larger than the triple-layer overlap distance(18.0 km),while the difference between the double-layer overlap distance(2.9 km)and the triple-layer overlap distance(3.0 km)for Cu clouds is relatively small.For organization index,it divides cloud fields into regular,clustered,and random types by comparing the distribution of nearest neighbor distances of actual cloud clusters in the cloud field with that of nearest neighbor distances of cloud clusters in a randomly distributed field.The regular type dominates both Ac and Cu cloud fields,accounting for 86%and 87%of the total cloud fields,respectively,while the clustered type accounts for 14%and 13%,respectively.Comparing the cloud cluster number and size characteristics of regular and clustered cloud fields,it can be found that,regardless of Ac or Cu,clustered cloud fields have smaller cloud cluster numbers and sizes.In terms of convective organization potential,this parameter describes the potential for cloud clusters to interact with each other in the cloud field.The larger the cloud cluster size and the closer they are to each other,the greater the convective organization potential.The average convective organization potential for Ac and Cu cloud fields is 0.08 and 0.04,respectively,with standard deviations of 0.05 and 0.11,indicating that Ac cloud clusters are larger and more prone to clustering than Cu cloud clusters.Comparing the convective organization potential of clustered and regular cloud fields,it can be found that Ac and Cu cloud fields have greater convective organization potential and are more likely to have cloud clusters interact with each other when they are in a clustered type.