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Lanzhou University (2019)

Preliminary Study on Moisture Sources and Physical Mechanism of Extreme Precipitation Events in the Arid Central Asia


Titre : Preliminary Study on Moisture Sources and Physical Mechanism of Extreme Precipitation Events in the Arid Central Asia

Auteur : 常石巧;

Grade : Master’s Theses 2019

Université : Lanzhou University

Résumé partiel
The arid Central Asia(ACA ;35.25-52.75°N,46.25-80°E)is the largest non-zonal arid region in the world.In the last 100 years,the precipitation in ACA represents significant regional differences,but annual and seasonal precipitation has a slightly increasing trend,especially for winter precipitation.Additionally,as a typical inland arid zone,the annual precipitation in ACA is dominated by a few extreme precipitation events.Therefore,investigating the moisture sources and underlying physical mechanisms of extreme precipitation in ACA can improve our understanding of related scientific issues and have implications for policymakers to make sustainable development strategies in the arid regions.In this study,the gridded daily precipitation from Global Precipitation Climatology Project(GPCC)during 1988-2013 and NCEP/NCAR reanalysis data are used to analyze the atmospheric circulation and moisture flux associated with extreme precipitation in different regions of ACA.Additionally,the monthly precipitation from GPCC during 1960-2013,NCEP/NCAR,and Sea Surface Temperature(SST)from NOAA are used to analyze the impacts of atmospheric circulations and SST on precipitation,revealing the possible physical mechanisms of precipitation in ACA.The main results are as follows :(1)The water vapor of summer extreme precipitation events in the north ACA is mainly transported from the Atlantic and the Arctic Ocean.The lower-and upper-level circulation anomalies provide the dynamic support for precipitation.At 200 hPa,the height anomalies represent a zonal "-+-+-" wave train pattern over Eurasia,strengthening the meridional circulations.At 500 hPa,the northerly wind anomalies on the east side of the anticyclonic circulation in Western Europe,couple with the northeasterly wind anomalies on the northwest side of the cyclonic circulation in ACA,strengthen moisture transported from the Arctic Ocean.At 850 hPa,the north ACA locate in the areas downstream of troughs,which is conducive to the southwesterly airflow transport warm humid air masses.The interactions of atmospheric circulation at different levels provide necessary dynamic conditions for extreme precipitation.(2)For the extreme fall precipitation in the north ACA,at 200 hpa,there is a meridional "+-+" wave train pattern of height anomalies extended from high latitude to low latitude over mid-latitude Eurasia.At 500 hPa,the westerly wind anomalies on the south(northwest)side of the cyclonic(anticyclonic)circulation from Western Europe to western Siberia(the Mediterranean Sea)strengthen the westerly moisture transportation from the Atlantic Ocean.At 850 hPa,the moisture from the Atlantic Ocean significantly increases because the precipitation anomalies are mainly controlled by westerlies.(3)For the extreme spring precipitation in the south ACA,the height anomalies at 200 hPa represents a strip-shaped feature.

Mots clés : the arid Central Asia; extreme precipitation events; moisture sources; Arabian Sea/northern Indian Ocean; physical mechanism;

Présentation (CNKI)

Page publiée le 21 novembre 2019