Using the NCAR/NCEP daily reanalysis data from 1 December 2004 to 28 February 2005, the isentropic potential vorticity （IPV） analysis of a strong cold wave from 22 December 2004 to 1 January 2005 was made. It is fou...Using the NCAR/NCEP daily reanalysis data from 1 December 2004 to 28 February 2005, the isentropic potential vorticity （IPV） analysis of a strong cold wave from 22 December 2004 to 1 January 2005 was made. It is found that the strong cold air of the cold wave originated from the lower stratosphere and upper troposphere of the high latitude in the Eurasian continent and the Arctic area. Before the outbreak of the cold wave, the strong cold air of high PV propagated down to the south of Lake Baikal, and was cut off by a low PV air of low latitude origin, forming a dipole-type circulation pattern with the low PV center （blocking high） in the northern Eurasian continent and the high PV one （low vortex） in the southern part. Along with decaying of the low PV center, the high PV center （strong cold air） moved towards the southeast along the northern flank of the Tibetan Plateau. When it arrived in East China, the air column of high PV rapidly stretched downward, leading to increase in its cyclonic vorticity, which made the East Asian major trough to deepen rapidly, and finally induced the outbreak of the cold wave. Further analysis indicates that in the southward and downward propagation process of the high PV center, the air flow west and north of the high PV center on isentropic surface subsided along the isentropic surface, resulting in rapid development of Siberian high, finally leading to the southward outbreak of the strong cold wave.展开更多
The mesoscale model MM4 is used to simulate the torrential rain associated with Meiyu front occurring on 5—6 July.1991 in the Changjiang-Huaihe Basin.Based on the outputs of the model, the cause of the mesoscale cycl...The mesoscale model MM4 is used to simulate the torrential rain associated with Meiyu front occurring on 5—6 July.1991 in the Changjiang-Huaihe Basin.Based on the outputs of the model, the cause of the mesoscale cyclogenesis on the lower troposphere is investigated in terms of the potential vorticity principle.The results show that because of the favorable pattern of moist isentropic surface,the absolute vorticity increases when cold air with high moist potential vorticity value rapidly slides down southwards along the moist isentropic surface,and then causes the cyclonic vortex development.展开更多
Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isent...Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isentropic mass circulation(IMC)perspective.Results show that the midlatitude cold surface temperature anomalies always co-occurred with the high-latitude warm anomalies,and this was closely related to the strengthening of the low-level equatorward cold air branch of the IMC,particularly along the climatological cold air routes over East Asia and North America.Specifically,the two cold surges over East Asia in early winter were results of intensification of cold air transport there,influenced by the Arctic sea ice loss in autumn.The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures(SSTs)explained the concurrent anomalous warmth there.This enhanced a wavenumber-1 pattern and upward wave propagation,inducing a simultaneous and long-lasting stronger poleward warm air branch(WB)of the IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming(SSW)event on 4 January.The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch,hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February.Results do not yield a robust direct linkage from La Niña to the SSW event,IMC changes,and cold events,though the extratropical warm SSTs are found to contribute to the February cold surge in North America.展开更多
Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical pro- files of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.After disc...Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical pro- files of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.After discussing a possible mechanism for the genesis and development of such systems and their differences from typical extratropical cyclones,a conceptual model for their activities is proposed:A weak disturbance in the mid- level of troposphere originated from around the Qinghai-Xizang Plateau may cause heavy precipitation under favourable conditions and latent heat release in the mid-troposphere leads to downward extension of cyclonic circulation and a wave on the quasi-stationary front.This weak cyclone can develop substantially and become a typical extratropical cyclone only when air from the lower stratosphere flows downslope along isentropic sur- faces into the region of interest.展开更多
By using NCAR/NCEP daily reanalysis data and the precipitation data in Liaoning routine automatic station during July 14-16,2008,the regional rainstorm weather process in Liaoning was done the isentropic analysis. Acc...By using NCAR/NCEP daily reanalysis data and the precipitation data in Liaoning routine automatic station during July 14-16,2008,the regional rainstorm weather process in Liaoning was done the isentropic analysis. According to the variation characteristics of isobar,isocratic specific humidity line and wind field on the isentropic surface,the rainstorm landing zone was gained and compared with the analysis results of isobaric surface. The results showed that the warm wet transportation belt on 330 K isentropic surface provided the rich water vapor condition for the rainstorm generation,and the distribution of air-pressure and wind field on the isentropic surface favored to understand the movement of airflow. Compared with the analysis of isobaric surface,the analysis of isobaric surface could better directly judge the landing zone of precipitation,and the forecast effect was better than the analysis forecast results of isobaric surface.展开更多
基金the National Basic Research Program of China under Grant No.2006CB403604.
文摘Using the NCAR/NCEP daily reanalysis data from 1 December 2004 to 28 February 2005, the isentropic potential vorticity （IPV） analysis of a strong cold wave from 22 December 2004 to 1 January 2005 was made. It is found that the strong cold air of the cold wave originated from the lower stratosphere and upper troposphere of the high latitude in the Eurasian continent and the Arctic area. Before the outbreak of the cold wave, the strong cold air of high PV propagated down to the south of Lake Baikal, and was cut off by a low PV air of low latitude origin, forming a dipole-type circulation pattern with the low PV center （blocking high） in the northern Eurasian continent and the high PV one （low vortex） in the southern part. Along with decaying of the low PV center, the high PV center （strong cold air） moved towards the southeast along the northern flank of the Tibetan Plateau. When it arrived in East China, the air column of high PV rapidly stretched downward, leading to increase in its cyclonic vorticity, which made the East Asian major trough to deepen rapidly, and finally induced the outbreak of the cold wave. Further analysis indicates that in the southward and downward propagation process of the high PV center, the air flow west and north of the high PV center on isentropic surface subsided along the isentropic surface, resulting in rapid development of Siberian high, finally leading to the southward outbreak of the strong cold wave.
基金Supported by the National Natural Science Foundation of China under the Projects No.49775259 and No.40075009.
文摘The mesoscale model MM4 is used to simulate the torrential rain associated with Meiyu front occurring on 5—6 July.1991 in the Changjiang-Huaihe Basin.Based on the outputs of the model, the cause of the mesoscale cyclogenesis on the lower troposphere is investigated in terms of the potential vorticity principle.The results show that because of the favorable pattern of moist isentropic surface,the absolute vorticity increases when cold air with high moist potential vorticity value rapidly slides down southwards along the moist isentropic surface,and then causes the cyclonic vortex development.
基金supported by grants from the National Key R&D Program of China(Grant No.2019YFC1510201)National Natural Science Foundation of China(Grant Nos.42075052 and 42088101)the Natural Science Foundation of Jiangsu Province(Grants No.BK20211288).
文摘Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isentropic mass circulation(IMC)perspective.Results show that the midlatitude cold surface temperature anomalies always co-occurred with the high-latitude warm anomalies,and this was closely related to the strengthening of the low-level equatorward cold air branch of the IMC,particularly along the climatological cold air routes over East Asia and North America.Specifically,the two cold surges over East Asia in early winter were results of intensification of cold air transport there,influenced by the Arctic sea ice loss in autumn.The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures(SSTs)explained the concurrent anomalous warmth there.This enhanced a wavenumber-1 pattern and upward wave propagation,inducing a simultaneous and long-lasting stronger poleward warm air branch(WB)of the IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming(SSW)event on 4 January.The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch,hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February.Results do not yield a robust direct linkage from La Niña to the SSW event,IMC changes,and cold events,though the extratropical warm SSTs are found to contribute to the February cold surge in North America.
基金This study is supported partially by National Natural Science Foundation of Chinapartially by the State Meteorological Administration Monsoon Research Funds.
文摘Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical pro- files of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.After discussing a possible mechanism for the genesis and development of such systems and their differences from typical extratropical cyclones,a conceptual model for their activities is proposed:A weak disturbance in the mid- level of troposphere originated from around the Qinghai-Xizang Plateau may cause heavy precipitation under favourable conditions and latent heat release in the mid-troposphere leads to downward extension of cyclonic circulation and a wave on the quasi-stationary front.This weak cyclone can develop substantially and become a typical extratropical cyclone only when air from the lower stratosphere flows downslope along isentropic sur- faces into the region of interest.
文摘By using NCAR/NCEP daily reanalysis data and the precipitation data in Liaoning routine automatic station during July 14-16,2008,the regional rainstorm weather process in Liaoning was done the isentropic analysis. According to the variation characteristics of isobar,isocratic specific humidity line and wind field on the isentropic surface,the rainstorm landing zone was gained and compared with the analysis results of isobaric surface. The results showed that the warm wet transportation belt on 330 K isentropic surface provided the rich water vapor condition for the rainstorm generation,and the distribution of air-pressure and wind field on the isentropic surface favored to understand the movement of airflow. Compared with the analysis of isobaric surface,the analysis of isobaric surface could better directly judge the landing zone of precipitation,and the forecast effect was better than the analysis forecast results of isobaric surface.
