In this study,the physical meaning and generation mechanism of potential deformation(PD)are reinvestigated.A main trait of PD is that it contains deformation,which is an important factor to precipitation but not well ...In this study,the physical meaning and generation mechanism of potential deformation(PD)are reinvestigated.A main trait of PD is that it contains deformation,which is an important factor to precipitation but not well applied in precipitation diagnosis.This paper shows PD shares similar features to deformation,but contains much more physical information than deformation.It can be understood as a type of deformation of a thermodynamic-coupled vector(u*,v*).For convenient application,squared PD(SPD)is used instead for analysis.By deriving the tendency equation of SPD,it is found that whether SPD is produced or reduced in the atmosphere is associated with the angle between the dilatation axes of PD and geostrophic PD.When the angle is less thanπ2,SPD is generated.The diagnostic results during a heavy rainfall event in North China on 20 July 2016 show that the process of rapid increase in precipitation can be well revealed by SPD.The distribution of SPD becomes more organized and concentrated with increasing precipitation intensity.A diagnostic analysis of the SPD tendency equation shows that concentrated SPD is associated with the generation of SPD in the boundary layer followed by upward transport of the SPD.The concentration of SPD indicates a confluence of precipitation-favorable factors—namely,vertical wind shear and moist baroclinity,which can enhance vertical motions and thus cause an increase in precipitation.These diagnostic results further verify PD as a useful physical parameter for heavy precipitation diagnosis.展开更多
基金supported by the Strategic Pilot Science and Technology Special Program of the Chinese Academy of Sciences grant number XDA17010105the National Key Research and Development Project grant number 2018YFC1507104+1 种基金the Scientific and Technological Developing Scheme of Jilin Province grant number 20180201035SFthe National Natural Science Foundation of China grant numbers 41875056,41775140,and 41575065。
文摘In this study,the physical meaning and generation mechanism of potential deformation(PD)are reinvestigated.A main trait of PD is that it contains deformation,which is an important factor to precipitation but not well applied in precipitation diagnosis.This paper shows PD shares similar features to deformation,but contains much more physical information than deformation.It can be understood as a type of deformation of a thermodynamic-coupled vector(u*,v*).For convenient application,squared PD(SPD)is used instead for analysis.By deriving the tendency equation of SPD,it is found that whether SPD is produced or reduced in the atmosphere is associated with the angle between the dilatation axes of PD and geostrophic PD.When the angle is less thanπ2,SPD is generated.The diagnostic results during a heavy rainfall event in North China on 20 July 2016 show that the process of rapid increase in precipitation can be well revealed by SPD.The distribution of SPD becomes more organized and concentrated with increasing precipitation intensity.A diagnostic analysis of the SPD tendency equation shows that concentrated SPD is associated with the generation of SPD in the boundary layer followed by upward transport of the SPD.The concentration of SPD indicates a confluence of precipitation-favorable factors—namely,vertical wind shear and moist baroclinity,which can enhance vertical motions and thus cause an increase in precipitation.These diagnostic results further verify PD as a useful physical parameter for heavy precipitation diagnosis.
