| As an important node under background of the country put forward the"great strategic concept The Belt and Road",the Hexi Corridor has an important position in the military geography.From aspect of the actual demand of military meteorological support,strong convective weather,such as thunderstorm,has an important impact on military activities such as aeronautical flight in the Hexi Corridor Region.Aim at practical demand for military meteorological support in Hexi Corridor Area,by combining station meteorological observation data,military observation data,and the NCEP/NCAR and ECMWF reanalysis data,this paper firstly analyzes climatological characteristics of thunderstorm in Gansu province in recent 33years.Then the difference of thunderstorm characteristics by local station observation data and the military observation data is investigated in three military airfields?Jiuquan,Zhangye,and Wuwei?in Hexi Corridor Region.Further,climatological characteristics of thunderstorm in these three military airfields is disclosed to represent the total situation in Hexi Corridor Region.In addition,the feature of the circulation which influencing the main modes of thunderstorm days in Gansu is concluded.And atmospheric circulation is classified for large-scale thunderstorm in Hexi Corridor Region.At last,physical elements are diagnosed during thunderstorm and rainfall without thunderstorm during 1981-2013.The main results are as follows:?1?Spatial distribution of average annual thunderstorm days present significant trend from south to north while thunderstorm days is more in the south than in the north.The area with the most and least annual thunderstorm days is in Gannan Plateau with more than forty days and Hexi Corridor with less than eight days,respectively.The thunderstorms happen in summer mostly,accounting for more than 50%of the total,and happen in the spring and autumn season the second mostly.The average annual thunderstorm days have an obviously decreasing linear trend during the recent 33 years,with the linear trend coefficient of-0.32.The results of EOF analysis show that,the first eigenvector accounts for 69.5%with decreasing tread in the all area pattern,and the area with the most obvious decreasing tread of thunderstorm days is in Gannan Plateau.The second eigenvector accounts for 11.6%with high?or low?in east and low?or high?in the west pattern,but the corresponding annual variation tendency is not obvious.The thunderstorm period decreases from south to north of Gansu province,with the longest in Gannan Plateau and the shortest in Hexi Corridor.Wavelet Analysis shows that interannual variation oscillation periods mainly exists between 1985 and 1990,with period of nearly 3a,and seasonal period of thunderstorm days is characterized as“single week oscillation”?3d and 4-7d?from June to September.?2?By comparing climatological characteristics of thunderstorm by local station observation data and the military observation data is investigated in three military airfields?Jiuquan,Zhangye,and Wuwei?,it is found that no matter for decal,interannual,or inter-seasonal variation,difference is very obvious,especially in Jiuquan.However,distinct decreased linear tendency of thunderstorm days in recent 33 years can be both found by these two data.For the seasonal variation,thunderstorm days by local station observation data are all more than that by the military observation data in Jiuquan during all months,especially the former is double times of the latter in July when the thunderstorm happen the most frequently.In Zhangye,thunderstorm days by local station observation data are 1.6 times of that by the military observation data in June.The difference is comparably small in Wuwei,which is less than 20%during all months.?3?By analyzing the three-represented military airfield in Hexi Corridor region in recent 33years,it is found thunderstorm days in Hexi Corridor region is characterized as more in decades before 1990s but less after 1990s in decals variation,as obvious decreased tendency in annual variation,and in seasonal variation as more in March-October,especially in June?29.6%?in summer?81%?.Wavelet Analysis shows that only in Jiuquan interannual variation oscillation periods mainly exists during 1995-2005 with period of nearly 3a,and seasonal period of thunderstorm days is characterized as“single week oscillation”?3d and 4-7d?from June to August.During a day,90%of the total thunderstorm happen during 13:00-24:00,and the most accounting for 31.5%happens during 17:00-19:00.The duration of more than 74%thunderstorms is 1-2 hours.The first thunder day is basically before 21st May,but the last thunder day is different in these three airfields.The occurrence of thunderstorms in the Hexi Corridor is often accompanied by weather phenomena,including rain,wind,blowing sand,sandstorm,and hail,among them the most one is rain which accounting for more than 55%of the total.?4?To research the feature of the circulation which influencing the thunderstorm days in Gansu,it is found that the meridional circulation on mid-high latitude,westerly belt and East Asian monsoon are all stronger than normal,and the convergence of the water vapor transport is also stronger in the high thunderstorm days years.But it is the reverse in the low thunderstorm days years.Besides,the circulation cause that leads to the opposite phase of average annual thunderstorm days between east and west areas in Gansu is that the western Gansu is mainly influenced by the westerly belt,but the southeast of Gansu is mainly influenced by the East Asian monsoon.So the water vapor transport over the western Gansu is very different from that over the southeast of Gansu.Moreover,the effects of dynamic and thermodynamic of Qinghai-Tibet Plateau on Northwest China also lead to the opposite phase between east and west areas in Gansu.?5?14 large-scale thunderstorm weather process in Hexi Corridor region is selected for the corresponding atmospheric circulation classification,i.e.,cold trough in upper-level,Mongolia cold vortex,the northwest flow after upper-level trough,and transverse shear line.Occurrence of thunderstorms in the Hexi corridor area must meet the requirements including unstable gas reservoir,the middle-low-level water vapor conditions,the obvious cold air invasion,and the appropriate triggering mechanism.?6?By using sounding data and reanalysis data of wind filed,physical elements during thunderstorm are diagnosed.The results show that index of SI and?35??se?can represent obvious character of stronger convective instability during thunderstorm than that during rainfall without thunderstorm,with the threshold of SI and?35??se are 3.32K-5.73K and 4.21K-7.28K in Wuwei and 0.45K-11.36K and 0.57K-14.04K in Jiuquan,respectively.Relative humidity is smaller during thunderstorm than that during rainfall without thunderstorm,showing water vapor is characterized as“dry in upper-level and wet in lower-level”during thunderstorm in July.During thunderstorm,there is obvious wind shear in middle-lower level troposphere,i.e.little change in the middle troposphere wind field and low-level westerly wind weakened or even turned to the east wind in the afternoon. |
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