| The Yarlung Zangbo Grand Canyon（YZGC）in the southeast Tibetan Plateau（TP）is the critical region of water vapor transport over the TP.Ka-band cloud radar（KaCR）deployed at Motuo National Climate Observatory（MNCO）provides long-term measurements for the study of cloud and precipitation characteristics at the entrance of the water vapor channel.Based on the data of KaCR in 2019,the CTHs measured by the KaCR were verified through a comparison with observations from the Fengyun-4A（FY-4A）satellite at the same location,and the influence of precipitation on the cloud top height detected by KaCR was evaluated.The cloud occurrence frequency（COF）,cloud top height（CTH）,cloud base height（CBH）and thickness of cloud layer at the entrance of water vapor channel were analyzed.Finally,the cloud vertical structure in summer in Motuo was compared with that in summer in Naqu in the central TP.The main results are as follows:（1）The KaCR-obtained CTHs were generally good consistency with the FY-4A-obtained CTHs,although the KaCR slightly overestimated the CTHs of nonprecipitation clouds and underestimated the CTHs of precipitation clouds.During the observation period in 2019,The average CTHs obtained from the KaCR and from the FY-4A satellite were 6.00 and 6.02 km,respectively.In rainy season and dry season,the average deviation of the two methods is-0.39 km and 0.53 km respectively.In the case of rainfall,the meanΔCTHs were positively correlated with rain rate.The average underestimate of cloud top height by KaCR is 2 km in the case of heavy rainfall(i.e.,R=8 to 16 mm h-1).（2）Based on the analysis of the cloud characteristics of in Motuo,it is found that:（a）Cloud cover frequently occurred over Motuo with an annual mean frequency of65.3%,and single-layer clouds are dominant in Motuo,with a mean occurrence frequency of more than 80%.Clouds tended to form frequently at night and dissipate gradually in the daytime.（b）The CBH in Motuo is relatively low,and two peaks in the CBH distribution were observed in Motuo,located at 0-1 km and 2-3 km,corresponding to precipitation and nonprecipitation clouds,respectively.In addition,low and middle clouds were prevalent in Motuo for the period of observation in 2019.（c）There were two peaks,located at 0–2 km and 5–7 km,in Motuo,corresponding to nonprecipitation and precipitation clouds,respectively.The shallow clouds with thickness less than 1 km appears frequently.The daily variation of cloud thickness is similar in rainy season and dry season.The average cloud thickness is 4-5 km and 4 km in rainy season and dry season,respectively,and the variation range is about 1 km.The low value of cloud thickness appears in the afternoon.（3）In order to deepen the understanding of climate and cloud characteristics in Motuo at the entrance of water vapor channel of YZGC in southeast TP,the diurnal variation characteristics of radar echo and cloud characteristics in Motuo in summer were compared with Naqu based on the data of Ka-band cloud radar in Naqu in summer2014.The results show that:（a）In summer,the average echo characteristics of Motuo and Nagqu both have obvious diurnal cycle.The echo in Motuo has continuous and obvious melting layer with an altitude of 4 km,while that in Nagqu is not obvious with an altitude of about 1 km.The diurnal variation of precipitation in Motuo is relatively uniform,and the convective activities mainly occur from night to early morning.The strong echo in Naqu mainly occurs in the afternoon,and the convective processes were more frequent than that in Motuo.（b）The COFs of cloud cover of Motuo and Naqu both have obvious diurnal variation in summer,and show a downward trend from early morning to noon.The lowest value of Naqu appeared at 1200,while the lowest value of Motuo remained from noon to 1900,and increased rapidly at night.The highest value（70%）appeared in Motuo at night.The COF of precipitation clouds from early morning to noon in Motuo is significantly higher than that in Naqu.（c）In summer,the proportion of precipitation clouds in Motuo is significantly higher than that in Naqu,while the proportion of high clouds in Naqu is higher than Motuo.The peak value of CBH of nonprecipitation clouds in Motuo is located at 1-2 km,while that in Naqu is located at2-3 km. |
