CMIP6-WACCM模式对北半球反气旋型Rossby波破碎趋势的预估

Projection of the trend of anticyclonic Rossby wave breaking in the Northern Hemisphere by CMIP6-WACCM

利用CMIP6中的CESM2-WACCM模式逐日资料,预估未来2020—2099年SSP2-4.5、SSP3-7.0和SSP5-8.5三种不同排放情景下北半球对流层顶附近反气旋型Rossby波破碎(Anticyclonic Rossby Wave Breaking,AWB)的空间分布、发生频率、水平尺度、对称结构及其长期趋势。总体而言,未来四个季节AWB都在北太平洋和北大西洋有高频区。夏季北太平洋高频区发生频数显著多于北大西洋高频区,其他三季相反。两高频区在三种不同情景下,AWB物质经向输送通常以对称输送为主,但北太平洋区内冬、春、秋三季在SSP2-4.5情景下AWB物质向极净输送,北大西洋区内夏季在SSP2-4.5和SSP5-8.5情景下AWB物质向赤道净输送。未来的长期趋势显示,两高频区内各季节的AWB发生频数、水平尺度和物质向极输送主要呈减小(减少)趋势,且温室气体排放量越大,减小趋势越显著。在SSP5-8.5情景下,北太平洋夏季AWB总面积变化趋势为-365.5个1°×1°标准经纬度网格/10 a,该变化由区域内AWB平均尺度减小(-2.7个标准化网格/10 a)和发生频率减少(-1.9个/10 a)共同导致;该区域的向极输送率变化率为-0.0165/10 a。北大西洋秋季AWB发生频数变化率为-2.3个/10 a,导致其总面积则以-440.4个标准化网格/10 a的速度减小。

By using daily data from the CESM2-WACCM model in CMIP6,the spatial distribution,occurrence frequency,horizontal scale,symmetric structure,and long-term trend of Anticyclonic Rossby Wave Breaking(AWB)near the tropopause in the Northern Hemisphere under three different emission scenarios:SSP2-4.5,SSP3-7.0,and SSP5-8.5 from 2020 to 2099 were projected.Overall,AWB is projected to occupy two high-frequency areas in the North Pacific and North Atlantic for all four seasons.The frequency of AWB occurrences in the North Pacific during summer is significantly higher than that in the North Atlantic,while the opposite is observed in the other three seasons.Within the two high frequency areas,symmetric transport is usually dominant for AWB material transport under the three different scenarios.However,in the North Pacific region,AWB material transport during winter,spring,and autumn tends to be poleward in the SSP2-4.5 scenario,while during summer in the North Atlantic region,AWB material transport tends to be equatorward in the SSP2-4.5 and SSP5-8.5 scenarios.There is a decreasing trend in AWB occurrence frequency,horizontal scale,and poleward transport in both high frequency areas for all seasons,with a more significant decrease in the larger greenhouse gas emissions scenarios.Under the SSP5-8.5 scenario,the total area of AWB occurrence in the North Pacific during summer is projected to decrease at a rate of-365.5 standardized 1°×1°grid cells per decade.This decrease is due to a combination of AWB average scale decreasing at a rate of 2.7 standardized grid cells/decade and the frequency decreasing at a rate of 1.9 events/decade.The trend of poleward transport rate in the North Pacific is-0.0165/decade.The trend of AWB occurrence frequency in the North Atlantic during autumn is-2.3/decade,resulting in a total area decrease rate of 440.4 standardized grid cells/decade.