| East Asia is one of the typical monsoon areas,the multi-clouds in summer are the member of the mosoon system and a carrier of monsoon precipitation.Cloud is not only an important factor affecting the energy balance,but also a key process in the water cycle.It plays an important role in weather and climate change and directly affects human social activities.Compared with ground-based instrument detection,the detection of cloud systems by satellite-equipped instruments has the advantages of no geographical restrictions and detected homogenous.Therefore,using multi-source satellite instruments to observe cloud systems has become a research hotspot in the field of atmospheric remote sensing and climate change.Radar and lidar detection of cloud systems are also the latest technology in the past decade.The East Asia is a vast region with complex underlying surface conditions.Summer monsoon activities are complex and changeable,different types of cloud are formatted under the various thermodynamic and microphysical processes.Perhaps due to the limitation of observational data,scholars used to study the patterns of East Asian monsoon activities from the perspective of weather dynamics,but had limited knowledge of the cloud activities in East Asia,especially the lack of understanding of the cirrus and deep convective clouds in this region.Therefore,studying the characteristics and formation mechanism of summer cirrus and deep convective clouds in East Asia is of great scientific significance for understanding the East Asian summer weather and climate,and improving the accuracy of the precipitation forecast.The study takes East Asia(15°N-50°N,70°E-150°E)as the research area.By using spaceborne Cloud Profile Radar(CPR)and Cloud-Aerosol LIDAR with Orthogonal Polarization(CALIOP)data and other atmospheric parameter data in June-August from 2007 to 2010.We investigated the detection differences between the CPR and CALIOP instruments,and the distribution of cloud cover,vertical structure in East Asia.Mainly study the microphysical characteristics and radiative forcing of nighttime cirrus cloud in East Asia.In addition,we proposed the identification algorithm of deep convective cloud clusters and investigated the basic structural characteristics of deep convective cloud clusters over East Asia in summer.Finally,in view of the unique topography of the trumpet of the Tibetan Plateau,the characteristics of the day-night distribution of various clouds in this area in summer were studied,and the atmospheric circulation that caused these day-night differences were analyzed.The main findings are as follows:1.Revealed the difference between CALIOP and CPR cloud measurements and their radiative forcing estimation errorsSince the CALIOP and CPR are both active detection radars that are launched at the same time,and the operating time interval is within 15 S,it can be considered as synchronous dectecion in time and space,so the detection results of the two instruments can be compared with each other.Through the case studies and statistical analysis of the results of cloud cover and cloud top height over the East Asia in summer,which detected by the CALIOP and CPR.We found that CPR has poor ability to detect higher thin clouds,anvils and cloud layers with very low cloud top heights,so it will miss a large number of such clouds.The total cloud amount of East Asian detected by CPR in summer is 55.4%,which is about 20%less than that of CALIOP detection(74.6%).And the difference between the two instruments can reach more than 40%in the local areas.Because of the different detection capabilities of the two instruments for cirrus clouds,the amount of cirrus clouds detected by CALIOP(44.3%)in East Asia is about 24%more than CPR.On the ocean surface,CALIOP has a stronger ability to detect low clouds(with a cloud top height of less than 2.5 km),while CPR has a stronger ability to detect low clouds in most areas over the land.It may be due to CALIOP signal was attenuated by the clouds,the low cloud in the East Asia summer detected by CALIOP is about 0.25%lower than that detected by CPR.In addition,the average cloud top height detected by the CALIOP is about 5 km higher than that of the CPR,and in the local area the difference can reach more than 8 km.The detection results of the mean cloud amount and cloud top height around the Tibetan Plateau(TP)shows that the detection difference is smaller on the west and north sides of the TP,while it is obvious on the east and south sides of the plateau.And the difference in cloud top height will greatly affect the calculation of the radiation effect.But the sensitivity tests show that as the optical thickness increases,the effect of cloud top height on the calculation gradually decreases.Therefore,when it is necessary to accurately calculate the radiation effect of a certain cloud type,we need to consider how much error the data will bring.2.Revealed the spatial and temporal distribution and structural characteristics of cirrus and its long wave radiation effect in light time in the East Asian summer for the first timeCirrus clouds strongly influence weather and climate processes due to their effects on the radiative balance of the Earth-atmosphere system.The results show that the frequency of nighttime cirrus in East Asia in summer is about 44.9%,and the frequency at nigthttime for subvisual(??0.03),thin(0.03??<0.3),opaque(0.3??<3)and thick(?>3)cirrus are found to be 10.1%,16.6%,15.7%and 2.6%;In addition,the highest frequency(about 15%)of the cirrus are often occurs at 10.5-12.5 km;as the optical thickness increases,the height of its frequency peak also gradually increases,of which sub-visible cirrus and thin cirrus clouds occur more frequently at 10 km,opaque cirrus clouds occur more frequently at a height of 13 km,and the peak frequency of thick cirrus clouds occurs around 13.5 km.Due to the limitation of the tropopause,the top heights of cirrus clouds with different optical thicknesses are relatively close,but the height of the cloud base gradually decreases with the increase of the optical thickness.In addition,the PDF distribution of the CTH basically shows that cirrus clouds with different optical thickness basically have a bimodal structure(except for sub-visible cirrus clouds),while the PDF distribution of cloud base height has only one peak.Besides,statistics results show that the average effective particle radius and ice-water path of nighttime cirrus in East Asia in summer are 24.70 ?m and 22.33 g.m-2,respectively.Finally,the longwave radiation effect of nighttime cirrus at the TOA(34.35 W.m-2)is much higher than that of the surface(2.88 W.m-2)in summer in East Asia.And the opaque cirrus clouds contribute the most to the longwave radiation of cirrus,especially at the surface,this may primarily due to their high fractions and optical thickness appearing simultaneously.3.Proposed the identification algorithm of deep convective cloud,and exposed the spatial and temporal distribution and vertical structure of the cloud in East Asia in summerUsing the profile data detected by CloudSat,an identificaition algorithm for deep convective cloud clusters was proposed,and the structural characteristics of deep convective cloud clusters were studied in depth.The result shows that the occurrence frequency of the deep convective clouds cluster is 4.2%in East Asian in summer,which is about 2.5%lower than the results in profile units(6.7%).And the horizontal distribution of the two is significantly different,as the high-occurrence area of deep convective clouds in profile units are located near the Bay of Bengal,the trumpet of the plateau,and Japan,while the results of cloud clusters show that the high-occurrence area of deep convective cloud is located on the southern slope of the plateau and the western Pacific Ocean.In addition,the deep convective cloud clusters over the plateau are mostly shallow and with small horizontal scales,and it will have large vertical scales but small horizontal scales in the southern slope of the plateau to the Bay of Bengal,while deep convective cloud clusters near the Japanese sea are all deep and with wide horizontal scale.The vertical-scale PDF distribution of deep convective cloud clusters in East Asia has two peaks of 8.5 km and 12.5 km,and the peak of the former height is slightly larger than the latter;while the horizontal-scale PDF distribution shows that the cloud cluster with a width of 30 km has the highest frequency.Besides,the maximum frequency occurs when the total area of the cloud is 180 km2,and then with the increase of the area,the frequency of occurrence gradually decreases.In addition,the PDF distribution of the height corresponding to the maximum radar reflectivity in the deep convective clouds cluster shows two peaks of 5 km and 7 km.Finally,the distribution of liquid water in deep convective clouds is basically below 9 km.As the height decreases,its concentration and liquid water content gradually increase,and reaching a maximum at the height of 5 km,and then with the growth/drops of liquid water particles,the concentration and content of liquid water particles gradually decrease as the height decreases.4.Found the day and night differences in cloud types and vertical structures caused by the special trumpet-shaped in southern Tibetan Plateau and proposed the physical mechanism behind the phenomenonThe warm and humid summer monsoon frequently reaches the steep southern slope of the Himalayas,which is conducive to the formation of unique cloud systems.However,few studies have comprehensively evaluated the characteristics and mechanisms of cloud systems over the trumpet-shaped topography region in the southeastern Tibetan Plateau.Therefore,we investigated the occurrence frequency,vertical structures,and water path of clouds over the TST regions and their daytime-nighttime differences.Results show a marginal difference in occurrence frequency of total clouds between the daytime(95.4%)and nighttime(97%)over the TST region,while different-typed clouds exhibit various daytime-nighttime differences in frequency,vertical structures,and water path.In particular,deep convection,cirrus,altocumulus,and nimbostratus clouds tend to occur more frequently at nighttime,while stratocumulus and cumulus clouds occur more in the daytime.Multilayered clouds form more easily at nighttime,especially triple-layered clouds.The cloud top/bottom heights and liquid/ice water paths of clouds are higher at nighttime than in the daytime over the TST region,which is associated with the increase in deep convection,cirrus,and altocumulus clouds at nighttime.In general,the differences in cloud properties are mainly related to the combined effects of the TST-induced unique mountain-valley circulation,the large-scale monsoonal circulation,and the thermal difference between the day and night.These findings provide valuable observational evidence for the further understanding and accurate simulation of cloud systems over the southeastern Tibetan Plateau region. |
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