In this paper,by carrying out sensitivity tests of initial conditions and diagnostic analysis of physical fields,the impact factors and the physical mechanism of the unusual track of Morakot in the Taiwan Strait are d...In this paper,by carrying out sensitivity tests of initial conditions and diagnostic analysis of physical fields,the impact factors and the physical mechanism of the unusual track of Morakot in the Taiwan Strait are discussed and examined based on the potential vorticity(PV)inversion.The diagnostic results of NCEP data showed that Morakot's track was mainly steered by the subtropical high.The breaking of a high-pressure zone was the main cause for the northward turn of Morakot.A sensitivity test of initial conditions showed that the existence of upper-level trough was the leading factor for the breaking of the high-pressure zone.When the intensity was strengthened of the upper-level trough at initial time,the high-pressure zone would break ahead of time,leading to the early northward turn of Morakot.Conversely,when the intensity was weakened,the breaking of the high-pressure zone would be delayed.Especially,when the intensity was weakened to a certain extent,the high-pressure zone would not break.The typhoon,steered by the easterly flow to the south of the high-pressure zone,would keep moving westward,with no turn in the test.The diagnostic analysis of the physical fields based on the sensitivity test revealed that positive vorticity advection and cold advection associated with the upper-level trough weakened the intensity of the high-pressure zone.The upper-level trough affected typhoon's track indirectly by influencing the high-pressure zone.展开更多
Based on the weather monitoring data,NCEP/NCAR reanalysis data and Doppler weather radar data,the circulation background,atmospheric stability and changing characteristics of radar echoes of a large-scale hail weather...Based on the weather monitoring data,NCEP/NCAR reanalysis data and Doppler weather radar data,the circulation background,atmospheric stability and changing characteristics of radar echoes of a large-scale hail weather process in Ulanqab City on July 5,2021 were analyzed.The results show that this hail weather process occurred in the summer afternoon of the hail-prone period in Ulanqab City,and was formed under the influence of upper trough and the circulation background of"two troughs and one ridge",which was conducive to the occurrence of strong convection weather.The low-level shear line provided the dynamic and water vapor conditions for the occurrence of the hail.In strong convection weather,water vapor was transported mainly from the Bay of Bengal,India and Nepal over the Himalayas.Before the occurrence of strong convection weather,water vapor transport increased significantly,and the low-level water vapor concentrated below 400 hPa,with obvious convergence and vertical transport.The characteristic parameters of radar echoes,such as combined reflectivity,vertically integrated liquid,and echo top height,increased significantly before and during the occurrence of hail,which had good indicative significance for the prediction and early warning of hail.展开更多
Based on 25-year（1987–2011） tropical cyclone（TC） best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pa...Based on 25-year（1987–2011） tropical cyclone（TC） best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence（EFC） exceeding 10 m s^（-1）d^（-1）. Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach^120 m s^（-1）d^（-1） during the extratropical-cyclone（EC） stage, an order of magnitude larger than reported in previous studies.Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear（VWS）. Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs（not in the EC stage）, it was found that environments with a moderate EFC value generally below ~25 m s^（-1）d^（-1） are more favorable for a TC＇s intensification than those with extremely large EFC.展开更多
Studies about high temperatures in China rarely touched the period beyond summer.But in September-early October 2021,a record-breaking high temperature event occurred in southern China,and affected agriculture in many...Studies about high temperatures in China rarely touched the period beyond summer.But in September-early October 2021,a record-breaking high temperature event occurred in southern China,and affected agriculture in many provinces.Both the daily maximum temperature and the number of high temperature days were the highest in September since 1951.To better understand the different features and possible causes of the extreme event in autumn from those in summer,the analysis of atmospheric circulation patterns was conducted.The western Pacific subtropical high(WPSH)was quite stronger and extended much more westward in most of the days in September 2021 than its climatology,which directly caused this unprecedented autumn high temperature event.Besides,the mid-latitude trough over the east of Japan may also play an essential role in this high temperature event.Due to the southward extension of the trough,a cyclonic circulation anomaly appeared at 850 hPa,and its northerly wind component prevailed in the west of the trough and blocked the eastward retreat of the WPSH.As a result,southern China was stably controlled by the WPSH,which led to the persistence of this high temperature event.The conclusion is further confirmed by the statistical results from the analysis of the multi-year data and analogue analysis.Compared to the previous studies,this study reveals the essential role of the mid-latitude trough and highlights the joint impacts of the WPSH and the trough in causing the unprecedented autumn high temperature event.展开更多
基金National Public Benefit(Meteorology)Research Foundation of China(GYHY201106004)National Basic Research Program"973"of China(2009CB421502)National Nature Science Foundation of China (40730948,41005029)
文摘In this paper,by carrying out sensitivity tests of initial conditions and diagnostic analysis of physical fields,the impact factors and the physical mechanism of the unusual track of Morakot in the Taiwan Strait are discussed and examined based on the potential vorticity(PV)inversion.The diagnostic results of NCEP data showed that Morakot's track was mainly steered by the subtropical high.The breaking of a high-pressure zone was the main cause for the northward turn of Morakot.A sensitivity test of initial conditions showed that the existence of upper-level trough was the leading factor for the breaking of the high-pressure zone.When the intensity was strengthened of the upper-level trough at initial time,the high-pressure zone would break ahead of time,leading to the early northward turn of Morakot.Conversely,when the intensity was weakened,the breaking of the high-pressure zone would be delayed.Especially,when the intensity was weakened to a certain extent,the high-pressure zone would not break.The typhoon,steered by the easterly flow to the south of the high-pressure zone,would keep moving westward,with no turn in the test.The diagnostic analysis of the physical fields based on the sensitivity test revealed that positive vorticity advection and cold advection associated with the upper-level trough weakened the intensity of the high-pressure zone.The upper-level trough affected typhoon's track indirectly by influencing the high-pressure zone.
文摘Based on the weather monitoring data,NCEP/NCAR reanalysis data and Doppler weather radar data,the circulation background,atmospheric stability and changing characteristics of radar echoes of a large-scale hail weather process in Ulanqab City on July 5,2021 were analyzed.The results show that this hail weather process occurred in the summer afternoon of the hail-prone period in Ulanqab City,and was formed under the influence of upper trough and the circulation background of"two troughs and one ridge",which was conducive to the occurrence of strong convection weather.The low-level shear line provided the dynamic and water vapor conditions for the occurrence of the hail.In strong convection weather,water vapor was transported mainly from the Bay of Bengal,India and Nepal over the Himalayas.Before the occurrence of strong convection weather,water vapor transport increased significantly,and the low-level water vapor concentrated below 400 hPa,with obvious convergence and vertical transport.The characteristic parameters of radar echoes,such as combined reflectivity,vertically integrated liquid,and echo top height,increased significantly before and during the occurrence of hail,which had good indicative significance for the prediction and early warning of hail.
基金jointly sponsored by the National Natural Science Foundation of China(Grant Nos.41205032,41405048 and 41375050)China Special Fund for Meteorological Research in the Public Interest(Grant No.GYHY201406008)the Guangdong Marine Disaster Emergency Response Technology Research Center(2012A032100004)
文摘Based on 25-year（1987–2011） tropical cyclone（TC） best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence（EFC） exceeding 10 m s^（-1）d^（-1）. Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach^120 m s^（-1）d^（-1） during the extratropical-cyclone（EC） stage, an order of magnitude larger than reported in previous studies.Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear（VWS）. Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs（not in the EC stage）, it was found that environments with a moderate EFC value generally below ~25 m s^（-1）d^（-1） are more favorable for a TC＇s intensification than those with extremely large EFC.
基金National Natural Science Foundation of China(42175078)Special Program for Innovation and Development of China Meteorological Administration(CXFZ 2022J030).
文摘Studies about high temperatures in China rarely touched the period beyond summer.But in September-early October 2021,a record-breaking high temperature event occurred in southern China,and affected agriculture in many provinces.Both the daily maximum temperature and the number of high temperature days were the highest in September since 1951.To better understand the different features and possible causes of the extreme event in autumn from those in summer,the analysis of atmospheric circulation patterns was conducted.The western Pacific subtropical high(WPSH)was quite stronger and extended much more westward in most of the days in September 2021 than its climatology,which directly caused this unprecedented autumn high temperature event.Besides,the mid-latitude trough over the east of Japan may also play an essential role in this high temperature event.Due to the southward extension of the trough,a cyclonic circulation anomaly appeared at 850 hPa,and its northerly wind component prevailed in the west of the trough and blocked the eastward retreat of the WPSH.As a result,southern China was stably controlled by the WPSH,which led to the persistence of this high temperature event.The conclusion is further confirmed by the statistical results from the analysis of the multi-year data and analogue analysis.Compared to the previous studies,this study reveals the essential role of the mid-latitude trough and highlights the joint impacts of the WPSH and the trough in causing the unprecedented autumn high temperature event.
