Characteristics Of Spatial-Temporal Distribution Of The Stratospheric Quasi-Zero Wind Layer In China

The characteristics of spatial-temporal distribution of the stratospheric Quasi-Zero Wind Layer(QZWL)in China are analyzed using EOF methods,Weibull distributions and other statistical methods,based on the ERA-Interim daily reanalysis data and the sounding data obtained by the L-band radiosonde sounding system in Korla,Xinjiang.The QZWL is mainly concentrated in the 70-30hpa(17-25km)height,and there is a significant difference in the distribution of the QZWL due to the different atmospheric circulation background in the low latitudes and mid-latitudes.The QZWL in mid-latitude area mainly occurs between April and September,and the starting time in the high level is before the lower level,the south before the north,and the end time is opposite.At the height of 30 and 50hPa between July and August,there will be an easterly enhancement that causes the occurrence of a discontinuity in the QZWL.Mid-latitude quasi zero wind layer mainly concentrated in the 40-50° N area,the most number of days to appear on the 50hpa,generally up to 70 days or more,can over more than 100 days in Xinjiang.Influenced by the South Asia high and the subtropical westerly jet,the QZWL on the 70hPa has a low number of days in Xinjiang.The QZWL in low latitudes is mainly influenced by the stratospheric seasonal transition and the Quasi-Biennial Oscillation(QBO),and could be classified into two categories.The north kind of QZWL is occurred at 20°N from October to April,while the south kind of QZWL occurred all year long during the westerly QBO phase,which at 5°N from May to November and combined with the north kind in the remaining time.The monthly statistical modeling indicated that Weibull distributions were a reasonable model for the wind speed data in Korla station,Haikou station and Nansha station.The specific probability wind speed predicted by the Weibull distribution and cumulative function can be used to seek the suitable airspace.The 50%cumulative probability of wind speed is lower than 5 m/s,and the 95%or 99%cumulative probability of wind speed is lower than 10 m/s at the same time,are selected as the high-quality flying area.Mid-latitude high-quality flying area mainly appeared on the 50hpa in June to September at 40° N and in May and September at 30-40° N area.Low-latitude high-quality flying area,affected by the QBO,mainly appeared on the 50hpa in November to April of next year at 20 ° N during the QBOE phase.During the QBOW phase,the high-quality flying area has more extensive distribution in 50 and 70hPa,which appear all year round at 5° N,and increased to 5-15° N in November to April of next year.