The Influence Of Kinetic Energy Change In The Entrance Region Of Asian African Jet On Drought In North China

The annual precipitation in North China is mainly concentrated in summer,and July-August is the most prone period of drought in North China,and it is interdecadal enhancement.Using the global reanalysis data provided by the European Centre for Medium-Term Weather Forecasting(ECMWF),the effects of T-N wave flux and local multiscale energy vorticity analysis(MS-EVA)on the drought in North China from 1979 to July and August 2015 were studied.The effects of warming on the location and energy balance of the jet inlet region in Western Europe were analyzed by surface temperature change.The effects of warming on the jet inlet were verified by Linear Baroclinic Mode.The following conclusions are drawn:(1)The inlet region of Asian-African rapids has obvious trend of northward uplift after1997.In August,the inlet region of the Asian-African rapids rose northward,and the North Atlantic rapids pressed south.The northward uplift of the Asian-African jet inlet is positively related to the drought in North China.When the inlet region of the Asian-African jet rises northward,the wave activity strengthens the high pressure system over the North China region.The energy on the wave is scattered to the coastal area of our country,causing the western Pacific subtropical high to weaken and retreat eastward in July and August.The warm-wet air flow of water vapor from the northwest side of the subtropical high to North China is weakened.The water vapor channels in the South China Sea and Bay of Bengal were weakened,and the drought situation in North China was strengthened.(2)The kinetic energy accumulation in the inlet region of the Asian-African jet in the whole atmosphere of July-August is mainly the kinetic energy advection transport term(QK)and the seasonal scale kinetic energy transformation term(T01).In July and August,the kinetic energy conversion term of seasonal scale increased.After 1997,the inlet region of the Asian-African jet stream showed a marked northward upward trend in July,making it easier for energy to enter the jet pipeline.In August,the northward uplift of the Asian-African jet inlet region was weak,but the energy from the North Atlantic jet exit region to the Asian-African jet inlet region was abundant.The month of July is good for energy to enter the Asian-African rapids.The energy is scattered to the downstream area,which makes theconvergence of front and back of the ridge above North China and the sinking airflow strengthen.and on the east side of the mean trough,there is strong divergence,which is not conducive to the upward movement of the airflow.The northward elevation of the Asian-African jet inlet makes the overall situation in North China unfavorable to precipitation and conducive to the continuation of drought.(3)The temperature on the left side of the entrance area of Asian-African rapids in midsummer continued to increase after 1979,and the trend of increasing temperature after1999 was more obvious.On the left side of the inlet region of the jet stream,the position of the large value zone of temperature gradient is northward when the temperature increases,and the west wind is enhanced in the left high latitude region of the inlet region.The surface warming in the inlet region of Asian-African jet is beneficial to the enhancement of kinetic energy advection transport term and seasonal scale transport term in the middle and upper layers.With the surface warming,the kinetic energy accumulation in the inlet region of the Asian-African jet increases.The position of the Asian-African jet in the entrance area is north when the temperature is increasing.The warming increases the energy accumulation in the eastern and western regions of the Atlantic,and makes it easier for the eastern and western regions of the Atlantic to diffuse energy into the Asian-African rapids.The warming is beneficial to the energy transfer to the lower reaches and promotes the drought in the lower North China region.(4)Through the simulation of non-adiabatic heating on the east coast of the Atlantic and the western part of Europe by the Linear Baroclinic Mode,the simulation results show that there is a positive height anomaly and a cyclone in the western part of Europe,the west wind is enhanced on the left side of the inlet area of the Asian-African jet,and the 20 m/s isoline U the velocity component of the Asian-African jet is raised northward.The advection transport of kinetic energy in the Asian-African rapids is mainly scattered from the eastern Atlantic and western Europe to the inlet area of the Asian-African rapids.When the inlet area of the Asian-African rapids rises to the north,the energy is more easily dispersed into the rapid flow downstream to promote the drought in North China.Based on the analysis of the northward elevation of the inlet of Asia-Africa jet caused by the warming of east coast of Asia and western Europe,the Linear Baroclinic Mode proves thatwarming is beneficial to the northward northward elevation of the jet stream,which makes the kinetic energy easy to diffuse into the downstream of the rapid flow and eventually causes drought in North China.The research in this paper reflects some causes of drought in North China,and provides the basis for exploring the mechanism of drought and the prediction of drought climate.