Study Of Coastal And Typhoon-Induced Upwelling

Upwelling is a general oceanic process and carries the colder water with high nutrients from the deep to upper layer,which can induce the sea surface cooling and facilitate the biological growth.Therefore,upwelling areas are always the important fishing grounds.Understanding the factors who could affect the formation,development,and decay of upwelling will guide the ecological conservation.In previous studies,most of researches focused on the large-span upwelling with hundreds of kilometers.However,there are less researches about the small-span upwelling within a hundred of kilometers,which would be controlled by the localized atmospheric processes.Herein,the Qingdao coastal upwelling,a small span,was investigated.The effects of variations of wind field to the Qingdao coastal upwelling would be analyzed.In addition,typhoon can change the oceanic dynamical environment within a short time and induce a strong cyclonic eddy upwelling,which could trigger the biological outbreak of algas during this period and take an effect to the localized ecological equilibrium.Herein,the 16^thh Typhoon Malakas in 2016 was investigated,which induced a cyclonic eddy upwelling to the northeast of Taiwan.The variations of oceanic dynamical environment by typhoon would be analyzed.In this paper,the satellite observations and numerical model will be employed to observe,simulate,and analyze the upwelling processes.Herein,the satellite observations include passive infrared and visible satellite data and active synthetic aperture radar?SAR?data.Then,the infrared and visible sensors include Aqua/MODIS,Terra/MODIS,Himawari-8/AHI and COMS/GOCI.The SAR sensor is ENVISAT/ASAR.The visible and infrared satellites can observe the upwelling-induced sea surface low temperature and high chlorophyll-a concentration,which would cause the low backscattering to the SAR data.For numerical model,the ROMS-WRF coupled model and ROMS-SWAN coupled model were implemented to simulate the oceanic processes.The Qingdao coastal upwelling event was observed by MODIS and ENVISAT ASAR.The satellites observations shown that a significant sea surface cooling occurred to the Qingdao coastal area on March 5,2008,which was lower than surrounding waters by about 3-4^oC and accompanied by the increase to the chlorophyll-a concentration about0.5-1 mg/m³.The sea surface cooling covered about 600 km².The ROMS-WRF coupled model was employed to simulate the oceanic process from the March 1 to 5.The model results indicated that there were two factors to induce this upwelling event:1)The vertical viscosity induced by the southeastward offshore component of wind,2)The Ekman transport induced by the northeastward alongshore component of wind.Two idealized experiments were implemented,the results suggested that the alongshore wind caused the sea surface cooling about 20%more than that caused by the offshore wind in the Qingdao coast,namely,the alongshore wind is more favorable for the upwelling than the offshore wind.The typhoon Malakas induced upwelling event to the northeast of Taiwan was observed by AHI and GOCI.The satellites observations shown that two significant sea surface cooling occurred to the northeast of Taiwan from the September 21 to 23,2016,which was lower than surrounding waters by about 3-4^oC and accompanied by the high chlorophyll-a concentration about more than 0.8 mg/m³.The ROMS-SWAN coupled model was employed to simulate the oceanic process from September 15 to 25.The model results implied that there were three cyclonic eddy upwelling areas to the northeast of Taiwan:1)The upper layer cyclonic eddy area near the northeast coast of Taiwan,the high horizontal advection and vertical viscosity by typhoon Malakas strengthened the exited eddy with the maximum vertical velocity about 9.3x10^-3 m/s,2)The deep layer permanent cyclonic eddy area near the northeast coast of Taiwan,the work of bottom pressure gradient weakened this deep eddy,3)An offshore typhoon-induced eddy area to the northeast of Taiwan,the high vertical viscosity and horizontal advection by typhoon Malakas triggered a strong upper eddy with the maximum vertical velocity about 1.92x10^-2 m/s.Meanwhile,a diurnal oscillation about 26 hours inertial period was triggered by typhoon Malakas.