Differentiation And Analysis Of Conditional Stability And Convective Stability And Its Application To Convective Weather Forecast In Beijing And Tianjin

Conditional stability and convective stability are two concepts of stability with different physical meaning.In this thesis,through theoretical analysis,formula derivation and construction of new diagrammatic sketch,these two types of stability are systematically analyzed and explained.In particular,for the typical "conditionally stable-convectively unstable" stratification,a diagrammatic sketch of the gradual change of conditional stability of the air layer during the uplift is constructed,which gives better explanation of the convective stability.According to the diagrammatic sketch,it is found that the saturated air layer is not necessary for the uplifting air layer to become conditional unstable,and the conditional stability of the uplifting air layer depends on the height of the top of the air layer.Therefore,the uplifted height of which the air layer becomes neutral stable can be accurately calculated in theory.In this thesis,firstly,combined with case study,we analyze the changes in stability during the actual convective weather process,verifying the "conditionally stable-convectively unstable" stratification turning into conditionally unstable after being lifted to a certain level.Secondly,based on the high spatial and temporal resolution output data from WRF model,a new index,the total mean of buoyancy temperature differences,is defined to measure the overall stability of atmospheric stratification.The results show that this index can well reflect the condition of stability of the atmospheric stratification,and its change is ahead of precipitation and a negative lagged correlation has been revealed with precipitation,thus it could act as a good indicator for the occurrence of convective weather.Finally,by analyzing the 10-year air-sounding data,the climate probability and spatiotemporal variation of these two stability indices are obtained,and the characteristics of temperature and humidity distribution are then investigated to explain their variation,which helps to get better understanding of these two types of stability.