Characteristics Analysis Of Atmospheric Background Field And Topographic Cloud Precipitation Process In Qilian Mountains

For the reasonable utilization of the rapid expanding of qilian mountain resources field and the atmospheric background of qilian mountain terrain cloud precipitation process have a more in-depth understanding,paper using conventional ground observation data in 2017-2019,the corresponding weather radar data and sounding data,satellite data,and ERA of 1979-2018-interim reanalysis data of high and low wind field data,to control the circulation situation of qilian mountain,high and low flow field characteristics and terrain cloud precipitation process of weather background,physical quantity field,this paper studies the changing features of radar echo,the following main conclusions:The main circulation systems controlling the Qilian Mountains are westerly circulation system,plateau monsoon system and East Asian and South Asian monsoon system.There are four types of weather patterns in favor of precipitation,namely,upper westerly trough or cold advection,Mongolian cold vortex(trough),plateau low value system(trough,shear and low vortex)and southwest airflow blocking.The surface flow field of Qilian Mountain is dominated by southwest and southeast winds,and the wind speed has been decreasing in the past 39 years.Divergence flow prevailed in the night.The divergence center was mainly located in the western section of Qilian Mountains in winter and the Middle Section of Qilian Mountains in summer.Convergence airflow prevails in the daytime,and the convergence zone is mainly located in the Middle Section of Qilian Mountains.Combined with the analysis of precipitation distribution in The Qilian Mountains,it is found that the reasons for the high precipitation in the north slope of the middle part of The Qilian Mountains are,on the one hand,that the coordination of large-scale system makes the ground convergence line maintain for a long time and the air flow continuously lift to form topographic clouds.On the other hand,after the formation of dispersed topographic clouds,they are continuously strengthened in the process of moving under the guidance of high-altitude guiding airflow.There are seven main types of surface flow fields in Qilian Mountains: northwest to northeast,southeast to south,southeast to northeast,northwest to southeast,Northeast to southwest convergent,Northeast to southwest convergent,west or southwest convergent.Precipitation process in Qilian Mountains: the upper air cold advection is forced,and the clouds mainly move to the southeast.The precipitation type in the warm area outside the subtropical high,and the clouds mainly move to the east or northeast.Low layer warm advection forced class,the clouds are mainly moving east.The scale of the topographical cloud and precipitation cloud is mainly medium.After the formation of the cloud,it passes through the mountains on the north slope of the Middle East section of Qilian Mountains during its movement,and goes through a process of strengthening and even regeneration.It reaches its maximum from the top of the mountains to the mountainside.The low-level potential function showed strong convergence before the process began.The center of the potential function strengthened after moving over the north slope of the middle part of The Qilian Mountains,indicating that the terrain cloud would be strengthened again during its eastward movement after the formation of the Qilian Mountains.Before the beginning of the process,the vertical velocity was strengthened on the north slope of the central part of Qilian Mountains,and the gradient increased with time.The central intensity was between 0.4-0.7pA /s.The large positive vertical velocity area was the area of strong updraft,and also the area where the topographical cloud developed vigorously.Precipitation process in Qilian Mountains: The evolution characteristics of reflectivity factor are as follows: the initial development height of convective cell core is about 5km from the ground,the strongest reflectivity factor is up to 45 dbz,and the echo top height is up to 10 km.Meanwhile,topographic uplift plays an important role in the formation and strengthening of echo block.The velocity field is characterized by low-level cyclonic convergence and high-level anticyclonic divergence.The positive and negative velocity pairs of monomer at the strongest stage are over 10.7m/s.When the convective monomer develops to a vigorous stage,the strong reflectivity factor profile shows & GT;The vertical depth of the convective cell core developed at 40 dbZ was up to 6km,the horizontal scale of the convective cell was up to 10 km,and the echo center of the strong reflectivity factor was nearly coincident from low to high level.