By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.s...By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.sustained rain corresponding to the ripening season of plum)in Jiangsu province.Statistic verification is conducted on the relationships between the index and the Mei-yu season in 1991–2005 to examine the impacts of the SAH characteristics index on a rain intensity index of Mei-yu and regional distribution of a characteristics index for different annual patterns of Mei-yu.Historical composite is performed of the 100-hPa circulation field for these patterns using the 100-hPa geopotential height of Northern Hemisphere from 2002 to 2005 and 45-year NCEP reanalysis to study the difference in the circulation for different patterns of Mei-yu.Diagnostic and statistic conclusions,which share much in common,have been obtained as follows.(1)The characteristics preceding to and the advancement/retreat of SAH and the movement of westerly troughs are the factors that influence the onset time of the Mei-yu season;after the Mei-yu onset,the progression/withdrawal of SAH and how farther east it extends are determining how long the Mei-yu lasts and when it ends.(2)During the Mei-yu,the general 100-hPa circulation situation and average characteristics of the SAH are well corresponding to the characteristics of the season and annual patterns of Mei-yu.In addition,the averages of the SAH ridgeline and east-extending index for June,July and the Mei-yu season have some implications to the forecast of the index of Mei-yu intensity.These conclusions can be served as powerful means in determining the starting/ending dates, duration and annual pattern of the Mei-yu season.展开更多
The eastward-moving Meiyu-Baiu frontal mesoscale vortices (MBFMVs) appear frequently and often cause heavy rainfall events along their tracks. A move-off-shore MBFMV was selected to enhance our understanding of this t...The eastward-moving Meiyu-Baiu frontal mesoscale vortices (MBFMVs) appear frequently and often cause heavy rainfall events along their tracks. A move-off-shore MBFMV was selected to enhance our understanding of this type of vortex. Synoptic analyses indicate that the MBFMV is a type of meso-α vortex and mainly occurs in the lower troposphere. A short wave trough near the coastline is highly favorable for the formation, sustainment, and displacement of the MBFMV. Vorticity budgets indicate that at lower levels of the MBFMV, convergence is the dominant factor for the increase of positive vorticity, and at high levels of the MBFMV, the vertical transportation associated with convective activities is the most important factor. The hori-zontal transportation was the main factor decreasing the positive vorticity. The land and sea environments are crucial to the evolution of the MBFMV. The characteristics of the Meiyu-Baiu Front (MBF) are also vital to the variation of the vortex.展开更多
基金Special Projects for Forecaster China Meteorological Administration(CMAYBY2011-017)
文摘By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.sustained rain corresponding to the ripening season of plum)in Jiangsu province.Statistic verification is conducted on the relationships between the index and the Mei-yu season in 1991–2005 to examine the impacts of the SAH characteristics index on a rain intensity index of Mei-yu and regional distribution of a characteristics index for different annual patterns of Mei-yu.Historical composite is performed of the 100-hPa circulation field for these patterns using the 100-hPa geopotential height of Northern Hemisphere from 2002 to 2005 and 45-year NCEP reanalysis to study the difference in the circulation for different patterns of Mei-yu.Diagnostic and statistic conclusions,which share much in common,have been obtained as follows.(1)The characteristics preceding to and the advancement/retreat of SAH and the movement of westerly troughs are the factors that influence the onset time of the Mei-yu season;after the Mei-yu onset,the progression/withdrawal of SAH and how farther east it extends are determining how long the Mei-yu lasts and when it ends.(2)During the Mei-yu,the general 100-hPa circulation situation and average characteristics of the SAH are well corresponding to the characteristics of the season and annual patterns of Mei-yu.In addition,the averages of the SAH ridgeline and east-extending index for June,July and the Mei-yu season have some implications to the forecast of the index of Mei-yu intensity.These conclusions can be served as powerful means in determining the starting/ending dates, duration and annual pattern of the Mei-yu season.
基金supported by the National Basic Research program of China (No. 2009CB421401)the National Natural Science Foundation of China (No. 40930951)
文摘The eastward-moving Meiyu-Baiu frontal mesoscale vortices (MBFMVs) appear frequently and often cause heavy rainfall events along their tracks. A move-off-shore MBFMV was selected to enhance our understanding of this type of vortex. Synoptic analyses indicate that the MBFMV is a type of meso-α vortex and mainly occurs in the lower troposphere. A short wave trough near the coastline is highly favorable for the formation, sustainment, and displacement of the MBFMV. Vorticity budgets indicate that at lower levels of the MBFMV, convergence is the dominant factor for the increase of positive vorticity, and at high levels of the MBFMV, the vertical transportation associated with convective activities is the most important factor. The hori-zontal transportation was the main factor decreasing the positive vorticity. The land and sea environments are crucial to the evolution of the MBFMV. The characteristics of the Meiyu-Baiu Front (MBF) are also vital to the variation of the vortex.
