Climate Response Projection Of Tropical Pacific And China Marginal Seas To Global Warming By Dynamical Downscaling

As IPCC AR5 reported,it’s no doublt that climate system has been warmer since the mid-20th century.Ocean plays an important role in the formation and change of climate,adjusting the heat and moisture source which influence the motion of atmosphere.Under the background of global warming,the increase of greenhouse gases concentration is nearly spatially uniform,but the response to global warming is of great difference among regions.The regional oceans display their own changes though they share the common patterns of the global mean change.The climate change projections of tropical Pacific and China marginal seas help to promote the understanding of the global climate change,and help to assessment the influence of climate change on global and China.At present,the climate change projection of tropical Pacific and China marginal seas are relatively less and of low resolution.The paper presents the climate response of tropical ocean and China marginal seas to global warming during 2080-2099 compared to 1986-2005 through dynamical downscaling using a three-dimensional ocean general circulation model(Parallel Ocean Program,POP)under the RCP4.5 and RCP8.5 scenarios.The principal conclusions are as follows:The sea surface temperature of tropical Pacific will increase.Under the RCP4.5 and RCP8.5 scenarios,the average increments are about 1.4°C and 2.6°C respectively with the largest increments lied in western equatorial Pacific and the smallest increments in the southeast subtropics.The average SST warming is greater by about 0.5° C in the northern than southern subtropics which is caused by the asymmetrical change of wind stress in the two hemispheres.In the subsurface of equatorial Pacific,the sea temperature increment is greater in the east than that in the west.The depth of equatorial thermocline is deeper in the east than that in the west,thus reducing the tilt of the thermocline between the two directions,which indicates the El nino distribution pattern will increase in the eastern equatorial Pacific in the future under the global warming.The heat content of the tropical Pacific will enhance.The largest increment is in the northern and southern subtropics,and concentrated on the surface to subsurface in the upper ocean.Under the RCP4.5 and RCP8.5 scenarios,from surface to the depth of 400 meters,the mean temperature increment is approximately 0.8°C and 1.7°C,and the heat content is about 0.15%and 0.39%larger,respectively.The equatorial currents directly driven by the trade wind will weaken due to the weakening of the equatorial trade wind under global warming.Under the RCP4.5 and RCP8.5 scenarios,the north equatorial current will reduce by about 5%and 10%respectively,and the north equatorial countercurrent will reduce by about 107%and 12.5%,and the north branch of the south equatorial current will reduce by about 16%and 24%,and the south equatorial countercurrent will reduce by about 15%and 35%,respectively.There is a little increment in the south branch of the south equatorial current and the equatorial undercurrent.The kuroshio will weaken mainly caused by the wind stress change in the north Pacific and positive anomaly of the wind stress curl due to the global warming.Under RCP4.5 and RCP8.5 scenarios,the average volume transport of kuroshio will reduce by about 12%and 15%,and the average heat transport of kuroshio will reduce by about 8%and 8.5%,respectively.There is no obvious change in the Yellow sea warm current and Taiwan warm current.The sea surface temperature of the China marginal seas will increase,the amplitude of the increment gradually enhanced with the rising of the latitude.Under the RCP4.5 and RCP8.5 scenarios,the average SST increments are about 1.5°C and 3.2°C respectively,with the largest increments in the Bohai sea and the smallest increments in the kuroshio basin.In east China sea,SST warming is principally promoted by the enhancement of heat transport by advection and the reduced release of the latent heat and sensible heat flux.In south China sea,besides the dominating contribution of net heat flux,the weakening of the upwelling caused by the negative anomaly of the wind stress curl and the enhancement of the heat transport from kuroshio intrusion also play a role to some extent.