CMIP6-WACCM Model Projections Of Rossby Wave Breaking Trends And Their Impacts In The Northern Hemispher

Based on CMIP6-WACCM model data,this paper estimates the distribution,frequency,and scale changes of two types of Rossby wave breaking(RWB)(anticyclonic type,AWB;cyclonic type,CWB)events in the North hemisphere near the tropopause in 2020-2099 under three emission scenarios of SSP245,SSP370,SSP585 in the future.Based on these analysis,this paper estimates further the impact of two types RWB frequency changes on the related stratosphere-troposphere meridional material exchange and surface air temperature.This study indicates that:(1)The spatial distribution characteristics of frequency of two types of RWBs are basically similar respectively under three different emission scenarios,which has a more significant longterm trend with increasing emissions.AWB has two high-frequency zones in each season: the North Pacific high-frequency zone and the North Atlantic high-frequency zone.The AWB occurrence frequency in summer in the North Pacific is significantly higher than that in the North Atlantic,while the situation is reverse in the other three seasons.The occurrence frequency of two AWB high-frequency regions will decrease in the future,with-3.45 times per decade in the North Pacific in summer under SSP585 scenario.CWB has three high-frequency zones in each season,which locates in the North Pacific,Eurasia,and the North Atlantic.The occurrence frequency of CWB is much little than that of AWB and will become increase in the future with weaker intensity,especially over land.(2)This paper analyzes the average scale changes,frequency changes,and total material transport changes of RWBs in the future in RWB high-frequency regions.The total material transport is represented by the total RWB area,which is the total area of the high and low RWB potential vortex tongues.Under the SSP585 scenario,the growth rate of total AWB area in summer in the North Pacific is 365.5 standardized grids per 10 years,which is maintly caused by decreases in its average scale and frequency of occurrence;The decrease of the total AWB area in autumn in the North Atlantic is caused by a decrease in its frequency of occurrence.The growth rates of the above three quantities of CWB in the North Pacific under SSP370 scenario are 2.2 standardized grids per 10 years,1.5 standardized grids per 10 years,and 191 standardized grids per 10 years,respectively.Under the SSP370 scenario,the growth rates of total area and frequency of CWB in the North Atlantic in summer are 116.3 standardized grids per 10 years and 1 grid per 10 years.The above three quantities of CWB in Eurasia will increase at rates of 1.9 standardized grids,1.4 standardized grids,and 203.8 standardized grids every 10 years under SSP585.(3)The net meridional material transport direction caused by RWB and its changes are analyzed by the ratio of standardized grid area occupied by high and low potential vorticity tongues.The AWB North Pacific region exhibits symmetric transport in summer.In winter,spring,autumn,it has a net polar transport under SSP245 scenario,but a net polar transport under SSP370 and SSP585 scenarios.The AWB North Atlantic region is symmetric transport in winter,spring,autumn.In summer,its net meridional material transport is towards equator under SSP245 and SSP585 scenarios,but symmetric under SSP370 scenario.For CWB,the Eurasia reginon is net transported to the pole in spring,while to the equator in the other seasons.The annual net meridional material transport direction is to the equator in the North Pacific and North Atlantic.(4)Under the SSP585 scenario,RWB frequency has most significant change.This paper evaluates the changes of RWB frequency changes on winter regional surface air temperature.The average scale of the future AWB will be smaller and the average duration will be shorter in Central Asia(40°E-80°E,35°N-65°N).The decreasing average size of the AWB results in weaker warm anomalies over Northern Europe(20°E-60°E,60°N-80°N)and weaker cold anomalies over Eastern Europe to western China(40°E-100°E,35°N-50°N).In the Northeast Pacific region(110°W-160°W,40°N-80°N),the average scale of CWB will become smaller and the average duration will become longer.The increase in the mean duration of CWB will make the associated upper trough and ridge deeper and more northwest-southeast inclined.Cold and warm air will be transported farther along the trough and ridge line,but the cold and warm air are relatively dispersed.In the northern part of the Hawaiian Islands(150°W-175°W,30°N-55°N),the cold anomaly will become weaker,but its location will extend further to the southeast.The temperature anomaly will extend further northwest from the western United States(120°W-140°W,30°N-55°N)to northwest Canada(140°W-180°W,55°N-75°N).