Analysis Of Three-dimensional Temperature And Salinity Response To Tropical Cyclones In The Northwest Pacific Observed By Argo Floats

Based on the Argo profiling dataset and the tropical cyclones(TC)best track data,combined with synthetic analysis and Barne’s interpolation method,the present paper investigated the response of upper ocean temperature and salinity to tropical cyclones in the northwest Pacific.The impact of TCs’ translation speed,intensity and oceanic mixed layer depth on the TC-induced ocean temperature and salinity anomalies were also discussed.The main conclusions are as follows.For temperature,TC-induced cooling in surface layer is a funnel-shaped distribution,the amplitude and area of cooling is larger at the surface,then declines with depth,and finally vanishes at 40 m depth.The subsurface layer shows a warming trend while the deeper layer shows a cooling trend.The results of depth normalization show that the cooling amplitude is nearly the same as in the mixed layer,and the cooling area is the largest at the bottom of the mixed layer.TC-induced ocean temperature anomalies vary with the translation speed and intensity of TCs and marine environmental conditions.The sea surface cooling induced by fast-moving(weak)tropical cyclones is stronger than the slow-moving(strong)ones as a result of shallower mixed layer in the latter case.In deep(shallow)mixed layer,the entrainment rate is small(large),resulting in a weaker SST cooling.The results with depth normalization are as follows: 1)Fast-moving tropical cyclones produce weaker Ekman pumping,but their trajectories pass through a shallower mixed layer.Vertical mixing dominates the surface cooling and subsurface warming.The pumping of slow-moving TCs is stronger and has significant impact on the region near center of tropical cyclones,which produces subsurface cooling area of radius of 2R50.The entrainment is responsible for subsurface warming outside the cooling core to the contrary.2)Upwelling of cold water up to the surface under weak tropical cyclones is also weak and these TCs pass a region of shallower mixed layer.So vertical mixing significantly produces surface cooling and subsurface warming.On the contrary,the intensive pumping due to strong tropical cyclones results in a competition between the warming induced by mixing and the subsurface cooling due to the pumping.The amplitude of cooling under strong TCs is smaller than weak one;it is mainly due to the shallower mixed layer under weak tropical cyclones.3)the amplitude of surface cooling and subsurface warming are weaker(stronger and rightward-bias)in deeper(shallower)mixed layer,the difference mainly is caused by the weaker entrainment rate at the bottom of the mixed layer under the deeper one.For salinity,TC-induced salinity anomalies show a increase in mixed layer and decrease in the lower layer.A fresher salinity is pronounced on the right side of the TC track.Surface salinity anomaly distribution is the result of the combined effects of evaporation,mixing,upwelling and heavy rainfall,while decrease of subsurface comes from surface fresher water resulted by mixing.And Ekman pumping dominates the lower layer.The characteristics of TC-induced salinity anomalies are basically consistent under different translation speed,intensity of tropical cyclone and mixed layer depth.The differences are in the effected depth,amplitude,and extremum of salinity changes.1)The mixed layer beneath the fast-moving tropical cyclones is generally shallower,where a relatively higher entrainment rate brings more saltier water into mixed layer and generates a local salinity rise.Subsurface desalination maxima under the fast-moving tropical cyclone locates on left side of the track,while for the slow-moving tropical cyclones it is on right side.The rightward bias produces the tropical cyclones’ wind,causing a stronger vertical mixing and a fresher water on the right side.However,desalination maxima under fast-moving tropical cyclones are affected by the high salt Kuroshio.2)Mixed layer salinity is higher under strong tropical cyclones than the weak ones,while subsurface salinity decreases much more under weak tropical cyclones.Weak tropical cyclones tends to pass the regions of shallower mixed layer,where precipitation has a large impact on surface salinity anomalies and partly offsets the salination rate induced by vertical mixing and Ekman pumping,thus the amplitude of salination is smaller.Meanwhile,the entrainment rate is large in shallower mixed layer,bringing more freshwater into the subsurface layer and producing a larger desalination.3)The mixed-layer salination(subsurface desalination)is stronger(weaker)in regions with a deeper mixed layer than those with shallower one.The entrainment rate is weakened in the region of deeper mixed layer,so the amplitude of subsurface desalination in deep mixed layer is weaker than in shallower one.