| By using data of ground-based observations and aircraft observations during the Third Tibetan Plateau?TP?Atmospheric Sciences Experiment?TIPEX-??at Naqu in the summer of 2014,this paper studied the characteristics of convective clouds over the TP including statistical properties,daily variation and microphysical characteristics,as well as precipitation formation processes.The ground-based observations showed that the most rain events in summer over the TP were relatively weak,but higher rain rates contributed more in precipitation.The summer convections over the TP showed an obvious daily variation,and the high precipitation always occurred in the nighttime.Convective clouds were mainly initiated by solar radiation heating in the late morning,and the singular column convective clouds began to merge and reached to the highest level in the late afternoon.The convections tended to transform into stratiform clouds in the night and showed significant bright band and layered structure.Aircraft measurements showed that the maximum and mean cloud droplet concentration was 1.1×105/L and 9±10×103/L respectively,with an order of magnitude of 104/L.The larger cloud particle concentration had a maximum value of 28.82/L and an order of magnitude of 100101/L.The supercooled water content had a maximum value of 0.25 g/m3and an order of magnitude of 10-1 g/m3.The total water content had a maximum value of 1.33g/m3 and an order of magnitude of 10-1100 g/m3.The updraft had a maximum value of 4.3m/s and an order of magnitude of 14 m/s.The average cloud droplet spectrum was with multi-modal shape,which was a composition of bimodal spectra with different second modal.Larger supercooled liquid particles in convective clouds over the TP were larger cloud drops and raindrops,ice particles were consisted of mostly dense,opaque graupels,some column and plate-like ice crystals.The riming process in TP convective clouds was active.There was mixed-phase cloud process in the convective clouds over the TP.Because of the clean air,the convective clouds over the TP had lower cloud droplet number concentration,and resulted in more large cloud drops and drizzles generated from coalescence process.The glaciation process was earlier to happen because of the lower temperature of the convective clouds over the TP.The supercooled large cloud drops and drizzles contributed the rimming process to a great extent,which makes it easier to rain through mixed-phase precipitation processes,and furtherly,coupling with the strong solar heating,makes the convections over the TP frequent but weak. |
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