The Effect Of Mesoscale Processes On The Near Inertial Internal Waves Generated By Tropical Cyclone In The South China Sea

Near-inertial internal wave(NIW)generated by tropic cyclones(TC)is an important channel to transport energy from the atmosphere to the ocean.It is reported in literature that mesoscale eddies can module the NIW energy transmission.But how the mesoscale eddies affect the NIW energy transmission is yet unclear.Since the South China Sea is one of the most active areas for the TC and mesoscale eddies in the world ocean,the thesis investigates how the cyclonic and anticyclonic mesoscale eddies affect NIW triggered by one typhoon using the insitu observational data and numerical modeling.First of all,the thesis revisits the derivation of the NIW dispersion relationship by Kunze(1985)and detects a few errors in the derivation.Secondly,in situ data from a mooring array are used to analyze the oceanic thermodynamic and dynamic responses of Typhoon Kalmaegi(2014),which passed through the center of the mooring array.The effects of the mesoscale eddies on NIWs are examined.The typhooninduced sea surface cooling is larger on the right side of the track than on the left side,and the current speed is faster on the right side.The surface ocean simultaneously shows "heat pump" and "cold suction" features.The near-inertial energy in the positive vorticity area is vertically concentrated at 200 m,but in the negative vorticity the near-inertial energy can reach 700 m while a nearly same amount of input energy from the wind at the two stations.From the comparison between vorticity,and stratification and shear at the two stations,it is inferred that if a cyclonic eddy controls the area to the right side of the typhoon track,the intensity of vertical mixing increase such that the near-inertial energy is quickly dissipated in the upper ocean and cannot be transmitted to the interior of the ocean.On the contrary,if the area to the left is controlled by an anticyclonic eddy,the vorticity is weakened after the typhoon passes,thus weakening the upper ocean mixing.In this situation,the near-inertial energy is quickly transferred to the interior of the ocean.Thirdly,the effect of different model resolutions on the vertical propagation of near-inertial internal waves is investigated.When the resolution is low,the near-inertial energy in both the positive and negative vorticity areas is concentrated at the ocean surface and cannot be transferred downward.With the increase of the model resolution,the near-inertial fluctuations in the negative vorticity area can be transmitted to the deep layers,while the area in the positive vorticity always acts on the ocean surface.Therefore,in the global air-sea coupled model,a higher model resolution is required to more accurately reproduce the energy input from the atmosphere into the ocean.