Radiative Effect And Precipitation Frequency Of Different Phases' Cloud Over The Tibet Plateau

Cloud phase as an important cloud feature plays an important role in the energy balance and water circulation system of the ground-air system.Considering the importance of the cloud phase,based on the Cloud Sat and CALIPSO joint satellite products and ECMWF-AUX dataset,we researched the cloud fraction,the distribution of cloud radiative effect,the cloud radiation contribution and the radiative heating rate of different cloud phases over the Tibet Plateau,and further studied the precipitation frequency of different cloud phases over the Tibet Plateau.In addition,this paper further analyzes the daily cycle characteristics of supercooled water clouds over the Tibetan Plateau using CATS(Cloud-Aerosol Transport System)data,and focuses on the daily variation characteristics of supercooled water clouds under four different temperature layers over the Tibetan Plateau.It also focuses on the influence of the extinction coefficient of dust aerosols in four typical regions on the daily cycle of supercooled water clouds.These results have some reference significance for the study of the change mechanism of cloud phases.The statistical results show that:(1)From the distribution of cloud cover of different cloud phases over the Tibet Plateau,there are obvious seasonal differences in cloud cover of different cloud phases.The results show that ice clouds occur more frequently during the cold season,while mixed-phase clouds,on the contrary,mainly show a greater frequency during the warm season than that during the cold season.It is worth noting that although the distribution of supercooled water clouds is relatively small in the Tibetan Plateau;However,during the warm season,the cloud distribution of supercooled water clouds in the southeastern part of the Tibetan Plateau is more compared with that of warm water clouds.(2)We can see that the radiative contributions of different cloud phases show different distribution characteristics during the cold and warm seasons.By analyzing the radiation contribution of different cloud phases,we find that ice clouds have the largest radiation contribution in the atmosphere during the cold season and occupy the main position,and the cloud radiation contribution value is over 80%;compared with the warm season,the radiation contribution of supercooled water clouds in the atmosphere is greater during the cold season,and the radiation contribution value is over 5%;on the contrary,the radiation contribution of mixed-phase clouds is relatively larger during the warm season.(3)The cloud cover,heating rate and radiative effect of different cloud phases over the Tibetan Plateau show different distribution characteristics,and precipitation frequency is no exception.Our statistical results show that precipitation over the Tibetan Plateau is dominated by ice clouds and mixed-phase clouds,and precipitation mainly occurs in the southeastern part of the Tibetan Plateau.It is noteworthy that the precipitation frequency during the warm season is higher than that during the cold season,and the precipitation frequency of supercooled water clouds is slightly higher along the southeastern coast of the Tibetan Plateau and at the great bend of the Yarlung Tsangpo River than over other regions.(4)Based on CATS data,we analyzed the daily variation of supercooled water clouds on the Tibetan Plateau,and further analyzed the daily variation of supercooled water clouds in different temperature layer ranges.The results show that the daily variation of supercooled water clouds is more obvious in the southeastern region of the Tibetan Plateau,and the cloud fraction of supercooled water clouds is more at night than during the daytime over the Tibetan Plateau region.(5)Regarding the relationship between daily cycle of the extinction coefficient of dust aerosols and the daily cycle of supercooled water cloud cover under four different temperature layers,our results show that the negative correlation between its supercooled water cloud cover and the extinction coefficient of dust aerosols is better over the Tibetan Plateau only at lower temperatures,However,the correlation coefficients between the daily variation of supercooled water cloud cover and extinction coefficient of dust aerosols over the Tibetan Plateau gradually increase with the increase of cloud top temperature,but the correlation coefficients between the daily variation of supercooled water cloud cover and extinction coefficient of dust aerosols decrease significantly,which is mainly because the daily variation pattern of supercooled water cloud cover in other temperature layers has changed,making the variation of the aerosol extinction coefficient unable to explain the daily variation characteristics of clouds.Some related studies show that the role of meteorological conditions on cloud phase is also very important.This implies that the daily cycle of supercooled water cloud cover in other temperature layers of the Tibetan Plateau may also be closely related to the meteorological conditions(e.g.,surface temperature,relative humidity in different temperature layers,and vertical velocity)of the Tibetan Plateau.In contrast,supercooled water cloud cover over other three regions generally has a good negative correlation with the daily cycle of the extinction coefficient of dust aerosols.