In this study, a three-dimensional mesoscale model was used to numerically simulate the well-known "98.7" heavy rainfall event that affected the Yangtze Valley in July 1998. Two experiments were conducted to...In this study, a three-dimensional mesoscale model was used to numerically simulate the well-known "98.7" heavy rainfall event that affected the Yangtze Valley in July 1998. Two experiments were conducted to analyze the impact of moist processes on the development of meso-β scale vortices(MβV) and their triggering by mesoscale wind perturbation(MWP). In the experiment in which the latent heat feedback(LHF) scheme was switched off, a stable low-level col field(i.e., saddle field—a region between two lows and two highs in the isobaric surface) formed, and the MWP triggered a weak MβV. However, when the LHF scheme was switched on as the MWP was introduced into the model, the MβV developed quickly and intense rainfall and a mesoscale low-level jet(mLLJ) were generated. The thickness of the air column and average temperature between 400 and 700 hPa decreased without the feedback of latent heat, whereas they increased quickly when the LHF scheme was switched on, with the air pressure falling at low levels but rising at upper levels. A schematic representation of the positive feedbacks among the mesoscale vortex, rainfall, and mLLJ shows that in the initial stage of the MβV, the MWP triggers light rainfall and the latent heat occurs at low levels, which leads to weak convergence and ageostrophic winds. In the mature stage of the MβV, convection extends to the middle-to-upper levels, resulting in an increase in the average temperature and a stretching of the air column. A low-level cyclonic circulation forms under the effect of Coriolis torque, and the m LLJ forms to the southeast of the MβV.展开更多
Several methods dealing with the moist adiabatic process are described in this paper. They are based on static energy conservation, pseudo-equivalent potential temperature conservation, the strict pseudo- adiabati...Several methods dealing with the moist adiabatic process are described in this paper. They are based on static energy conservation, pseudo-equivalent potential temperature conservation, the strict pseudo- adiabatic equation, and the reversible moist adiabatic process, respectively. Convective energy parame- ters, which are closely related to the moist adiabatic process and which re?ect the gravitational e?ects of condensed liquid water, are reintroduced or de?ned, including MCAPE [Modi?ed-CAPE (convective avail- able potential energy)], DCAPE (Downdraft-CAPE), and MDCAPE (Modi?ed-Downdraft-CAPE). Two real case analyses with special attention given to condensed liquid water show that the selection of moist adiabatic process does a?ect the calculated results of CAPE and the gravitational e?ects of condensed liq- uid water are not negligible in severe storms. Intercomparisons of these methods show that static energy conservation is consistent with pseudo-equivalent potential temperature conservation not only in physical properties but also in calculated results, and both are good approximations to the strict pseudo-adiabatic equation. The lapse rate linked with the reversible moist adiabatic process is relatively smaller than that linked with other moist adiabatic processes, especially when considering solidi?cation of liquid water in the reversible adiabatic process.展开更多
以第五代中尺度模式(MM5)为基础,本文对一次南京大暴雨个例进行了三组数值模拟试验,研究了模式湿物理过程参数化方案的组合对梅雨暴雨降水预报的影响.试验结果表明:模式的积云对流参数化方案的选用对南京大暴雨的预报至关重要,积云对流...以第五代中尺度模式(MM5)为基础,本文对一次南京大暴雨个例进行了三组数值模拟试验,研究了模式湿物理过程参数化方案的组合对梅雨暴雨降水预报的影响.试验结果表明:模式的积云对流参数化方案的选用对南京大暴雨的预报至关重要,积云对流参数化方案的选用比边界层参数化对暴雨数值预报的影响大;对20km模式分辨率而言,采用单一的积云对流参数化方案时,Betts-Miller方案占显著优势;模式粗、细网格采用不同的积云对流参数化方案进行组合,可以改进模式降水预报,对于60km/20km的二重嵌套网格来说,Anthens-Kuo and Betts-Miller或者Kain-Fritsch and Betts-Miller组合具有一定的优势.在此基础上,积云对流参数化方案与不同微物理过程组合可以进一步改进梅雨锋暴雨的预报,不同组合方案预报降水的中心位置和强度各不相同.另外,暴雨的分布、中心位置和强度对边界层参数化方案的选用表现出一定的敏感性.展开更多
详细阐释了对流有效位能(convective available potential energy,CAPE)的本质;提出了CAPE新的计算公式;简要介绍了与CAPE计算有关的物理过程和一些新的物理量。结合实例,用新的公式和目前通用的公式,对CAPE和对流抑制能量(convective i...详细阐释了对流有效位能(convective available potential energy,CAPE)的本质;提出了CAPE新的计算公式;简要介绍了与CAPE计算有关的物理过程和一些新的物理量。结合实例,用新的公式和目前通用的公式,对CAPE和对流抑制能量(convective inhibition,CIN)分三种情形进行对比计算:1)可逆湿绝热过程;2)假绝热过程;3)等假相当位温过程。计算结果表明,假绝热过程比可逆湿绝热过程CAPE新算法明显偏高、CIN明显偏低;MICAPS默认方法与等假相当位温过程计算结果大体相近。展开更多
In this paper, a typical mei-yu front process with heavy rainfall from June 12 to 15 in 1998 is analyzed. The results show that the mei-yu front is a front system which consists of an iso-θe dense area with strong ho...In this paper, a typical mei-yu front process with heavy rainfall from June 12 to 15 in 1998 is analyzed. The results show that the mei-yu front is a front system which consists of an iso-θe dense area with strong horizontal gradient, a deep-convective cloud tower band, a passageway transporting warm and moist air ?ow from the summer monsoon surge in the mid and low levels to the south of the mei-yu front, and a migrating synoptic scale trough to the north of the mei-yu front, which transports cold and dry air southward in the mid and upper levels. The maintenance of the mei-yu front is realized by: (1) is a positive feedback between the moist physical process enhancing frontogenesis and the development of the strong convective system in front of the mei-yu front; (2) the sustaining system to the north of the mei-yu front which is a migrating synoptic scale trough transporting cold and dry air to the mei-yu front and positive vorticity to the mesoscale system in front of the mei-yu front.展开更多
基金supported by the National Grand Fundamental Research 973 Program of China (Grant No.2015CB452800)the National Natural Science Foundation of China (Grant Nos.41275099,41205073 and 41275012)the Natural Science Foundation of the Nanjing Joint Center of Atmospheric Research (Grant No.NJCAR2016MS02)
文摘In this study, a three-dimensional mesoscale model was used to numerically simulate the well-known "98.7" heavy rainfall event that affected the Yangtze Valley in July 1998. Two experiments were conducted to analyze the impact of moist processes on the development of meso-β scale vortices(MβV) and their triggering by mesoscale wind perturbation(MWP). In the experiment in which the latent heat feedback(LHF) scheme was switched off, a stable low-level col field(i.e., saddle field—a region between two lows and two highs in the isobaric surface) formed, and the MWP triggered a weak MβV. However, when the LHF scheme was switched on as the MWP was introduced into the model, the MβV developed quickly and intense rainfall and a mesoscale low-level jet(mLLJ) were generated. The thickness of the air column and average temperature between 400 and 700 hPa decreased without the feedback of latent heat, whereas they increased quickly when the LHF scheme was switched on, with the air pressure falling at low levels but rising at upper levels. A schematic representation of the positive feedbacks among the mesoscale vortex, rainfall, and mLLJ shows that in the initial stage of the MβV, the MWP triggers light rainfall and the latent heat occurs at low levels, which leads to weak convergence and ageostrophic winds. In the mature stage of the MβV, convection extends to the middle-to-upper levels, resulting in an increase in the average temperature and a stretching of the air column. A low-level cyclonic circulation forms under the effect of Coriolis torque, and the m LLJ forms to the southeast of the MβV.
基金the National Natural Science Fourdation of China under Grant Nos.40375016 , 40428002 InnovationProject of the Chinese Academy of Sciences under Grant No.KZCX-SW-213.
文摘Several methods dealing with the moist adiabatic process are described in this paper. They are based on static energy conservation, pseudo-equivalent potential temperature conservation, the strict pseudo- adiabatic equation, and the reversible moist adiabatic process, respectively. Convective energy parame- ters, which are closely related to the moist adiabatic process and which re?ect the gravitational e?ects of condensed liquid water, are reintroduced or de?ned, including MCAPE [Modi?ed-CAPE (convective avail- able potential energy)], DCAPE (Downdraft-CAPE), and MDCAPE (Modi?ed-Downdraft-CAPE). Two real case analyses with special attention given to condensed liquid water show that the selection of moist adiabatic process does a?ect the calculated results of CAPE and the gravitational e?ects of condensed liq- uid water are not negligible in severe storms. Intercomparisons of these methods show that static energy conservation is consistent with pseudo-equivalent potential temperature conservation not only in physical properties but also in calculated results, and both are good approximations to the strict pseudo-adiabatic equation. The lapse rate linked with the reversible moist adiabatic process is relatively smaller than that linked with other moist adiabatic processes, especially when considering solidi?cation of liquid water in the reversible adiabatic process.
文摘以第五代中尺度模式(MM5)为基础,本文对一次南京大暴雨个例进行了三组数值模拟试验,研究了模式湿物理过程参数化方案的组合对梅雨暴雨降水预报的影响.试验结果表明:模式的积云对流参数化方案的选用对南京大暴雨的预报至关重要,积云对流参数化方案的选用比边界层参数化对暴雨数值预报的影响大;对20km模式分辨率而言,采用单一的积云对流参数化方案时,Betts-Miller方案占显著优势;模式粗、细网格采用不同的积云对流参数化方案进行组合,可以改进模式降水预报,对于60km/20km的二重嵌套网格来说,Anthens-Kuo and Betts-Miller或者Kain-Fritsch and Betts-Miller组合具有一定的优势.在此基础上,积云对流参数化方案与不同微物理过程组合可以进一步改进梅雨锋暴雨的预报,不同组合方案预报降水的中心位置和强度各不相同.另外,暴雨的分布、中心位置和强度对边界层参数化方案的选用表现出一定的敏感性.
文摘详细阐释了对流有效位能(convective available potential energy,CAPE)的本质;提出了CAPE新的计算公式;简要介绍了与CAPE计算有关的物理过程和一些新的物理量。结合实例,用新的公式和目前通用的公式,对CAPE和对流抑制能量(convective inhibition,CIN)分三种情形进行对比计算:1)可逆湿绝热过程;2)假绝热过程;3)等假相当位温过程。计算结果表明,假绝热过程比可逆湿绝热过程CAPE新算法明显偏高、CIN明显偏低;MICAPS默认方法与等假相当位温过程计算结果大体相近。
文摘In this paper, a typical mei-yu front process with heavy rainfall from June 12 to 15 in 1998 is analyzed. The results show that the mei-yu front is a front system which consists of an iso-θe dense area with strong horizontal gradient, a deep-convective cloud tower band, a passageway transporting warm and moist air ?ow from the summer monsoon surge in the mid and low levels to the south of the mei-yu front, and a migrating synoptic scale trough to the north of the mei-yu front, which transports cold and dry air southward in the mid and upper levels. The maintenance of the mei-yu front is realized by: (1) is a positive feedback between the moist physical process enhancing frontogenesis and the development of the strong convective system in front of the mei-yu front; (2) the sustaining system to the north of the mei-yu front which is a migrating synoptic scale trough transporting cold and dry air to the mei-yu front and positive vorticity to the mesoscale system in front of the mei-yu front.
