| The statistics of precipitation data for many years show that there is a significant heavy precipitation center in Zhejiang,Fujian and Jiangxi in the middle of June during the northward advance of summer monsoon in China.In this paper,a heavy precipitation process occurred in Zhejiang,Fujian and Jiangxi Province on June 19-20,2010 is taken as an example to analyze the precipitation budget and ice cloud thermal effects in this region.The results of synoptic weather diagnosis show that the heavy precipitation process is caused by the combination of short wave trough and stable subtropical high in the Westerlies,and the direct precipitation system is characterized by low-level shear line and cyclone;the water vapor comes from the South China Sea,and is continuously sent to Zhejiang,Fujian and Jiangxi regions by the strong low-level southwest jet;the combination of high-level and low-level jet is one of the important dynamic processes for the occurrence and maintenance of rainstorm;at 1200 LST 19 June,the short-term weakening of the low-level jet and the change of the position of the jet axis may be one of the important processes for the weakening and then strengthening of the precipitation in this case.The results of quantitative precipitation budget analysis show that the main factors affecting precipitation are water vapor convergence in water vapor budget and heat divergence in heat budget.Water vapor convergence and heat divergence are the main processes of precipitation when precipitation is strong,while when precipitation is weak,local water vapor drying and atmospheric warming become the main processes of precipitation.According to the three factors of local moisture / heat change,moisture / heat convergence and divergence and cloud condensate convergence and divergence,precipitation can be divided into eight categories,among which the precipitation intensity is the strongest when the local moisture dries up and the atmosphere warms up,the moisture convergence and heat divergence and the cloud condensate convergence,while precipitation coverage is the highest when the local atmosphere moistens and cools down,the moisture converges and heat diverges and the cloud condensate converges.The thermal effect of ice cloud includes radiation and latent heat.The comparative analysis results of sensitivity tests and control test show that the radiative effect of cloud ice is mainly reflected in heating the upper atmosphere,having little effect on the lower atmosphere,making the atmosphere more stable,restraining the ascending motion,weakening the heat divergence,and being unfavorable to the condensation of water vapor,which eventually leads to the weakening of precipitation;the radiative effect of snow and graupel is mainly reflected in cooling the upper atmosphere,and being very weak and unfavorable to the heating of low altitude,restraining the upward motions,which eventually leads to the weakening of precipitation.The latent heat process of cloud ice and snow is shown as latent heat release.The latent heat release makes the convection develop to the upper air,and causes the increase of ascending motions,and then strengthens the heat divergence,which is conducive to the condensation of water vapor,and leads to the increase of precipitation.The latent heat effect of graupel is shown as latent heat absorption,which mainly occurs in the lower troposphere,making the stratification more stable,inhibiting the development of ascending motion,and thus leading to the decrease of precipitation.Whether it is radiative effect or latent heat effect,ice clouds are very similar to cloud ice as a whole,which shows that the role of cloud ice particles plays a dominant role in the thermal effect of ice clouds. |
PDF Full Text Request