COMPARATIVE ANALYSIS OF STATISTICAL ENVIRONMENTAL CHARACTERISTICS BETWEEN WESTERLY SQUALL LINE AND TYPHOON SQUALL LINE IN SOUTH CHINA

FANG Chong; LIN Yin-jing; CAO Yan-cha; SHENG Jie; ZHU Wen-jian

doi:10.16032/j.issn.1004-4965.2017.06.017

Abstract：20 Typical squall line processes are selected based on the March to September's thunder-gust winds and radar data in South China and the temporal distribution are analyzed.The results show that the westerly squall lines appear in spring and early summer,typhoon squall lines appear in summer,and March-April westerly squall lines begin to develop earliest in the morning and tend to weaken around noon while July-September typhoon squall lines begin to develop mostly at noon or afternoon and tend to weaken around early night.Four westerly squall line processes and four typhoon squall line processes are selected and the similarities and differences of various physical quantity characteristics are analyzed between the two types of squall line based on the NCEP data.The results show that the average 850 hPa and 500 hPa temperature difference of the westerly squall line is large,the average 925 hPa and 700 hPa temperature difference of the typhoon squall line is large;the average low-level warm advection of the westerly squall line is strong and the middle-level warm advection is not noticeable,the typhoon squall line is exactly the opposite;the change of 500 hPa average temperature advection over time is a significant negative value before the thunder-gust winds caused by westerly squall lines and the typhoon squall line is inconspicuous;for two types squall lines,200 hPa is divergent and 925 hPa is convergent,but the westerly squall lines are better defined than the typhoon squall lines;the average 925 hPa relative humidity of typhoon squall line is significantly less than the average season value and less than the 850 hPa relative humidity;there is mainly weak dry advection on 500 hPa and weak dominating advection on 925 hPa before the thunder-gust winds caused by westerly squall lines;there is significant dominatingadvection on 500 hPa and dry advection on 925 hPa before the thunder-gust winds caused by typhoon squall lines.Finally,two squall line processes are compared and analyzed.The results show that the continuous enhancement of thunderstorm high and the expansion of the cold pool lead to the continuous development of the westerly squall line,and the cyclonic shear and isobaric line front may be an important role in the generation and early development of echo.