Responses Of Upper Ocean To Tropical Cyclones In Northwest Pacific Ocean

Tropical Cyclones(TCs)occur frequently in the Northwest Pacific Ocean.The strong winds,heavy rains,huge waves and storm surges that accompany TCs will cause devastating damage to lives and properties in coastal areas,so TCs' landing are considered as one of the serious marine disasters affecting our country.As a strong airsea interaction process,the ocean responses and feedbacks to TCs involve dynamical,thermo-dynamical and multiple environmental processes.It will help us understand the process of air-sea interactions to carry out research on the responses of the ocean to TCs.In order to better reflect the different ocean responses on the left and right sides of TCs' path,a composing analysis method is used,in which the moving direction of TC is considered as the North direction in new coordinate system.Based on CMA's tropical cyclone database,Aviso altimetry dataset from 1993 to 2018,Sea Surface Temperature(SST)data from 1993 to 2018 and the Argo buoy data from 2006 to 2018,responses of SLA(Sea Level Anomaly),SST and 200 m temperature and salinity profiles in the upper ocean to TCs in Northwest Pacific Ocean were analyzed statistically by the composing analytical method.The duration of the upper ocean's thermal response to TCs is not consistent with that of dynamic response.The decreasing SLA continues for a longer time.Both the horizontal and vertical distributions of the upper ocean's response to TCs show an evident asymmetry pattern between left and right sides of TCs' path.The main conclusions are as follows:(1)When the TCs arrive,the sea levels in the center of the TCs decrease significantly,and the sea levels on the right side of tropical cyclone tracks increase.The sea levels deduced to a minimum value 6-7 days after the TCs' arrival,and then rise back slowly.After the TCs' pass,the center of the negative SLA gradually shifts to the left side.Both the TCs' strength and moving speed affect the spatial and temporal variations of the sea levels.The slow-moving TCs with high wind speed have a significant impact on the SLA.The maximum decrease of sea levels can approach10.93 cm for the super Typhoon.As for the effect of moving speed,the slower the TCs move,the greater the impacts on sea level height.The maximum decrease of sea level is 19.80 cm,when the moving speed of TCs are less than 5km/h.(2)When the TCs arrive,the SST in the center of TCs decrease significantly;3-4day after the TCs' arrival,the SST deduced to a miminum value,and then rise back slowly.After the passage of the TCs,the cooling center of the SST moves with the TCs.And the response of SST to tropical cyclones shows an obvious left-right asymmetric distribution.The greater the wind speed of a tropical cyclone,the greater the decrease of SST.When the wind speed is greater than 51.0 m/s,the maximum decrease of SST can reach 1.27 ° C.The slower the TCs move,the greater the impact on SST.For strong tropical storm,when the moving speed is less than 5km/h,the maximum reduction of SST is 1.97 ° C.(3)The response of temperature and salinity anomaly at the depth of 5-200 m to TCs in the Northwest Pacific from 2006 to 2018 is analyzed based on the Argo buoy data and CMA's tropical cyclone database.The results show that when TCs arrive,and after the TCs pass,the vertical structures of the temperature anomalies in the center area,the left and right area show a same pattern,can be divided into 3 depth layers: 5-40 m,40-100 m,and 100-200 m.The sea temperature anomaly presents an inverse “S”-shaped distribution of “negative-positive-negative”.In the depth range of 5-40 m,it is dominated by negative temperature anomaly,and the temperature at a depth of 5m decreases by 0.27-0.56°C;in the depth range of 40-100 m,the SST shows a positive anomaly,and the maximum temperature rise occurs at the depth of 50m;In the depth range of 100-200 m,the sea temperature represents a negative anomaly,but the decrease magnitude is small.The vertical structure of the salinity anomaly after the TCs pass can also be divided into three depth layers: 5-20 m,20-120 m,and 120-200 m,showing an "S"-shaped distribution.The salinity anomaly in the left and center areas of the TCs' path are mainly negative anomaly,while the salinity anomaly in the right area show a "positive-negative-positive" distribution pattern.The variation ranges of the temperature and salinity anomaly on the right side of the TCs are greater than those on the left side.