The static balance and the geostrophic balance are the common balances in meteorology.All the synoptic systems and most of the mesoscale systems satisfy the above two balances.However,due to the strong convection and ...The static balance and the geostrophic balance are the common balances in meteorology.All the synoptic systems and most of the mesoscale systems satisfy the above two balances.However,due to the strong convection and non-geostrophic feature,many mesoscale systems usually present as static imbalance,and the quasi-geostrophic approximation is no longer attainable.This paper tried to find out a kind of balance that exists for mesoscale convective system.To do this,the concrete mathematics definitions for balance and imbalance equations were defined.Then,it is proposed that the new balance equation should include the divergence,vorticity,and vertical motion simultaneously,and the helicity equation was a good choice for the basis.Finally,the mesoscale balance and imbalance equations were constructed,as well as a new balance model that was based on the helicity,horizontal divergence,vertical vorticity,continuity,and thermal dynamic equations under same approximations.Moreover,the corresponding potential vorticity（PV）inversion technique was introduced.It was pointed out that by using the PV conservation and the potential temperature conservation,the flows of the mesoscale balance model can be deduced,and their comparison with the real fields would give the degree of the imbalance.展开更多
By using the high-resolution observation data and MM5 model simulation data,the analysis on the 12 June 2008 Guangxi flash-flood rainstorm shows that the associated major mesoscale weather system of this event is a qu...By using the high-resolution observation data and MM5 model simulation data,the analysis on the 12 June 2008 Guangxi flash-flood rainstorm shows that the associated major mesoscale weather system of this event is a quasi-stationary mesoscale vortex,which resulted from the interaction between the midlatitude synoptic-scale waves in the westerly belt and the low-latitude warm-moist flow under the terrain effect.The genesis,development,and movement of the mesoscale vortex have significant impacts on the intensity and persistence of the severe precipitation from the Guangxi flash-flood rainstorm.This vortex is characterized by the coexistence of strong vorticity and divergence with the same order of magnitude.Well organized,deep,and moist convection was observed for a long period of time,and was produced by the interaction between the mesoscale vortex and the gravity waves.The latter was generated by the terrain effect and the ageostrophic effect of high winds in the low-level jet.According to the quasi-balanced dynamical theory,quasi-balanced flow must have existed in the mesoscale motions with both divergent and rotational winds.Thus,based on the diagnosis of the quasi-balanced flow,the PV-ω inversion method is employed to analyze the organized moist convection.The results show that 50%-70% of the vertical circulation in the rainstorm areas was quasi-balanced,so the quasi-balanced flow could well reflect features of the strong vertical motions associated with the coexistence of vorticity and divergence during this event.展开更多
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2012CB417201)National Natural Science Foundation of China(91437215,41475100,and 41375052)
文摘The static balance and the geostrophic balance are the common balances in meteorology.All the synoptic systems and most of the mesoscale systems satisfy the above two balances.However,due to the strong convection and non-geostrophic feature,many mesoscale systems usually present as static imbalance,and the quasi-geostrophic approximation is no longer attainable.This paper tried to find out a kind of balance that exists for mesoscale convective system.To do this,the concrete mathematics definitions for balance and imbalance equations were defined.Then,it is proposed that the new balance equation should include the divergence,vorticity,and vertical motion simultaneously,and the helicity equation was a good choice for the basis.Finally,the mesoscale balance and imbalance equations were constructed,as well as a new balance model that was based on the helicity,horizontal divergence,vertical vorticity,continuity,and thermal dynamic equations under same approximations.Moreover,the corresponding potential vorticity（PV）inversion technique was introduced.It was pointed out that by using the PV conservation and the potential temperature conservation,the flows of the mesoscale balance model can be deduced,and their comparison with the real fields would give the degree of the imbalance.
基金Supported by the National Nature Science Foundation of China under Grant Nos. 40905022 and 40830958National Key Basic Research Program under Grant No. 2009CB421500
文摘By using the high-resolution observation data and MM5 model simulation data,the analysis on the 12 June 2008 Guangxi flash-flood rainstorm shows that the associated major mesoscale weather system of this event is a quasi-stationary mesoscale vortex,which resulted from the interaction between the midlatitude synoptic-scale waves in the westerly belt and the low-latitude warm-moist flow under the terrain effect.The genesis,development,and movement of the mesoscale vortex have significant impacts on the intensity and persistence of the severe precipitation from the Guangxi flash-flood rainstorm.This vortex is characterized by the coexistence of strong vorticity and divergence with the same order of magnitude.Well organized,deep,and moist convection was observed for a long period of time,and was produced by the interaction between the mesoscale vortex and the gravity waves.The latter was generated by the terrain effect and the ageostrophic effect of high winds in the low-level jet.According to the quasi-balanced dynamical theory,quasi-balanced flow must have existed in the mesoscale motions with both divergent and rotational winds.Thus,based on the diagnosis of the quasi-balanced flow,the PV-ω inversion method is employed to analyze the organized moist convection.The results show that 50%-70% of the vertical circulation in the rainstorm areas was quasi-balanced,so the quasi-balanced flow could well reflect features of the strong vertical motions associated with the coexistence of vorticity and divergence during this event.
