The spatial propagation of meso-and small-scale errors in a Meiyu frontal heavy rainfall event,which occurred in eastern China during 4-6 July 2003,is investigated by using the mesoscale numerical model MM5.In general...The spatial propagation of meso-and small-scale errors in a Meiyu frontal heavy rainfall event,which occurred in eastern China during 4-6 July 2003,is investigated by using the mesoscale numerical model MM5.In general,the spatial propagation of simulated errors depends on their horizontal scales.Small-scale（L 〈 100 km） initial error may spread rapidly as an isotropic circle through the sound wave.Then,many scattered convection-scale errors are triggered in moist convection zone that will spread abroad through the isotropic,round-shaped sound wave further more.Corresponding to the evolution of the rainfall system,several new convection-scale errors may be generated continuously by moist convection within the propagated round-shaped errors.Through the above circular process,the small-scale error increases in amplitude and grows in scale rapidly.Mesoscale（100 km 〈 L 〈 1000 km） initial error propagates up-and down-stream wavelike through the gravity wave,meanwhile migrating down-stream slowly along with the rainfall system by the mean flow.The up-stream propagation of the mesoscale error is very important to the error growth because it can accumulate error energy locally at a place where there is no moist convection and far upstream from the initial perturbation source.Although moist convection plays an important role in the rapid growth of errors,it has no impact on the propagation of meso-and small-scale errors.The diabatic heating could trigger,strengthen,and promote upscaling of small-scale errors successively,and provide ＂error source＂ to error growth and propagation.The rapid growth of simulated errors results from both intense moist convection and appropriate spatial propagation of the errors.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 Natural Science Foundation of China (41130964)China Meteorological Administration Special Public Welfare Research Fund (GYHY201006004)Specialized Research Fund for the Doctoral Program of Higher Education of China (20080284019)
文摘The spatial propagation of meso-and small-scale errors in a Meiyu frontal heavy rainfall event,which occurred in eastern China during 4-6 July 2003,is investigated by using the mesoscale numerical model MM5.In general,the spatial propagation of simulated errors depends on their horizontal scales.Small-scale（L 〈 100 km） initial error may spread rapidly as an isotropic circle through the sound wave.Then,many scattered convection-scale errors are triggered in moist convection zone that will spread abroad through the isotropic,round-shaped sound wave further more.Corresponding to the evolution of the rainfall system,several new convection-scale errors may be generated continuously by moist convection within the propagated round-shaped errors.Through the above circular process,the small-scale error increases in amplitude and grows in scale rapidly.Mesoscale（100 km 〈 L 〈 1000 km） initial error propagates up-and down-stream wavelike through the gravity wave,meanwhile migrating down-stream slowly along with the rainfall system by the mean flow.The up-stream propagation of the mesoscale error is very important to the error growth because it can accumulate error energy locally at a place where there is no moist convection and far upstream from the initial perturbation source.Although moist convection plays an important role in the rapid growth of errors,it has no impact on the propagation of meso-and small-scale errors.The diabatic heating could trigger,strengthen,and promote upscaling of small-scale errors successively,and provide ＂error source＂ to error growth and propagation.The rapid growth of simulated errors results from both intense moist convection and appropriate spatial propagation of the errors.
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.
