Influence Of Precipitation On Temperature And Salinity Responses Of Upper Ocean To Tropical Cyclone

The tropical cyclones(TCs)-ocean interaction is an important process that modulates the intensity and track of TCs.As one part of the TC-ocean interaction,precipitation induced by TCs is one of the factors that affect the upper ocean thermal responses to TCs.Therefore,understanding the impact of precipitation on the upper ocean may improve the prediction of TCs.In this paper,the infrared cloud-top black body temperature,satellite precipitation and in situ oceanic observations were used to study the precipitation characteristics of TCs and the oceanic temperature and salinity responses to TCs.Combined with the ocean numerical model,the influence of precipitation on the upper ocean thermal response and dynamic processes are also studied.The main conclusions are as follows:The cloud structure and precipitation distribution of TC varied with TC intensity,and heavy precipitation were mainly distributed under the central dense cloud area and the spiral cloud belt.After Typhoon Kalmaegi(2014)and Tropical StormFung-wong(2014),the sea surface temperature(SST)decreased and sea surface salinity(SSS)increased,while in the subsurface layer,the cold and warm anomaly,as well as salty and fresh anomaly alternately appeared.The maximum of sea surface cooling during this two TCs is 2.56 °C and 1.18 °C,respectively.The SST cooling induced by Kalmaegi(2014)was stronger on the right side of the track than on the left,showing obvious asymmetric feature.In the subsurface layer,the thermal response on the right side of the track was dominated by the “heat pump” mechanism,leaving a warm and fresh anomaly;while the response on the left side was dominated by the“cold suction” effect,leaving a cold and salty anomaly.During Kalmaegi(2014)and Fung-wong(2014),there were several surface salinization processes occurred on the left side of the track,with a maximum SSS decrease of 0.278 practical salinity units(psu)and 0.773 psu.Numerical simulation results showed that TC precipitation can suppress the SST cooling and SSS increase induced by strong wind forcing,resulting in a weaker sea surface responses.Compared with the simulation case without precipitation,precipitation in the model will increase the SST at the three stations by about 0.039 °C,0.40 °C,and 0.032 °C,or 3.8%,15.1%,and 2.7%,respectively.At the same time,the SSS was reduced under the effect of precipitation by about 0.074 psu,0.152 psu,and0.078 psu,or 63.6%,52.6%,and 63.0%,respectively.The dynamic processes of horizontal advection,vertical convection,and vertical mixing are also affected by precipitation,among which the vertical mixing is most sensitive to precipitation,which is the primary process by which precipitation affects the temperature and salinity.The effect of precipitation can be divided into two parts: direct impact and indirect impact.On one hand,precipitation can directly dilute the seawater and cause a decrease in salinity.On the other hand,when salinity decreases,the ocean stratification will be enhanced,and vertical mixing will be restrained,so that the SST increases and SSS decreases,to a certain extent,suppressing the SST and SSS responses caused by wind field forcing.