The Basic Characteristics And Atmospheric Responses Of The Rotational Mode Of SST Dipole In The Subpolar North Atlantic

Except the well-known AMO(Atlantic Multidecadal Oscillation)with a period of 70 years in North Atlantic,longterm climatic records such as Central England Temperature(CET)and Greenland ice core net snow accumulation also show a significant 20 yr oscillation.Meanwhile,20-30 yr counterclockwise rotational oceanic mode in subpolar north Atlantic has been found.In this study,we analyse the basic characteristics and atmospheric responses of this rotational oceanic mode.Observational SST(ERSST),CET and Greenland ice core net snow accumulation data have been used to analyse rotational mode of SST in subpolar North Atlantic and climatic variability with 20 yr period in the vicinity,the result shows that the period of rotational mode extracted from ERSST is 40 yr.We analyse the SST rotational mode of subpolar region over North Atlantic based on SST in CCSM4(Community Climate System Model version 4)preindustrial control(piControl)simulaiton and RCP8.5 SST.The results show that the mode rotates counterclockwise with a period of 20 yr in CCSM4 piControl SST,while 30-40 yr in RCP8.5 SST.These two rotational mode of SST found in two scenarios of CCSM4 have similar mechanism and spatial pattern.Due to lack of SST with high-resolution and high-credibility before global warming period,rotational mode of SST with a period of 20 yr is unable to be extracted from observation data for SST for now.Further research is still needed to study the mechanism of prolonging period of rotational mode of observed SST.Based on the analysis to CAM4 sensitive experiment,the conclusion can be made that counterclockwise 20 yr oscillation in North Atlantic subpolar region can excite the longterm climatic record with 20 yr in the vicinity.Geopeotential height,heat flux and 2m temperature responsed to this SST dipole mode is likely to be more significant in winter.The active centers of heat flux are in North Atlantic,and active centers of SLP are in North Atlantic,North Polar region and North Pacific which demonstrate a triple mode,while the patterns of 500 hPa and 200 hPa geopotential height are similar and both in eastern North Atlantic,western Euroasia,North Polar region and eastern North Pacific.The rotational SST dipole mode in the subpolar North Atlantic can excite Arctic Oscillation(AO)/North Atlantic Oscillation(NAO)pattern in atmospheric circulation and it evolves with the evolution of the rotational mode of SST dipole in the subpolar North Atlantic.The active centers are in North Atlantic,North Polar region and North Pacific.The temperature anomalies excited by this SST mode transport up to midtroposphere and then excite corresponding geopotential anomalies which transport towards polar region.