Characteristics Of Rossby Wave Breaking Events In The Asia-Pacific And Its Relationship With Stratosphere-Troposphere Exchange

Based on potential vorticity(PV)data on 370K potential temperature surfaces of ERA-Interim,this paper uses the method of meridional gradient reversals of PV on potential temperature surfaces to identify Rossby Wave Breaking(RWB)events in the Northern Hemisphere(NH),and analyzes the characteristics of different types of RWB events from1990 to 2018.Research shows that:(1)The frequency and average scale of AWB and CWB events in the NH have obvious seasonal characteristics:compared with winter and spring,the two types of RWB events occur more frequently,and the average scale is larger in summer and autumn.AWB events occur much more frequently than CWB events,and the average scale is also larger.For AWB events,low-PV events occur more frequently than high-PV events,and its average scale is larger.For CWB events,high-PV events occur more frequently and its average scale is larger.Transport associated with AWB events is predominantly poleward.Transport associated with CWB events is predominantly equatorward.(2)AWB and CWB events are prone to occur in areas where the jets are weak,and are generally located at the sides of the jets or at the entrances and exits of the center of the jets.In different seasons,two types of RWB events have two high-frequency centers in Asia-Pacific and North America-Atlantic regions.Compared with the center of AWB,the zonal range of CWB centers is larger and its center position is more northerly.(3)There are significant seasonal differences between AWB and CWB events in the Asia-Pacific Center(A-P)and North American-Atlantic Center(NA-A):In the four seasons,AWB events in A-P are mainly transported to the pole,and CWB events in A-P are mainly transported to the equator.The transport associated with AWB events in NA-A is symmetric in winter,spring,and autumn,but poleward in summer.The transport associated with CWB events in NA-A is equatorward in autumn and winter,but symmetric in spring and summer.(4)Combined with Aura-HIRDLS satellite observation data and FLEXPART trajectory simulation,a case analysis of a RWB event in the Asia-Pacific region was conducted,the results showes that:After the RWB occurred,the tropospheric fold zone expanded polewards and the tropospheric air masses separated from the tropical troposphere(TTL)into the subtropical stratosphere through the fold zone.42.2%of the particles in the tropospheric air masses,whose total mass is about 3.8×10¹⁴kg,completed the transport from the tropsosphere to the tratosphere(TST).The main transport path of TST:it moves quickly eastwards and polewards with the westerly wind in the horizontal direction,and rises non-adiabatically in the vertical direction.The remaining particles were quickly transported eastwards along the westerly jet,and descended in the high-altitude front area below the downstream of the jet,staying in the troposphere.There are two main source areas:one source area is northwest of the wave packet and the other is upstream of the wave packet.Particles in the northwest source area,accounting for 49.3%,completed the transport from stratosphere to troposphere(STT).Particles in the upstream source area mainly originated from the low-latitude troposphere.