Energetic near-inertial internal waves （NlWs） were observed on the continental slope of the northern South China Sea in September 2008. Characteristics of the observed near-inertial waves were examined based on curr...Energetic near-inertial internal waves （NlWs） were observed on the continental slope of the northern South China Sea in September 2008. Characteristics of the observed near-inertial waves were examined based on current data recorded by a moored acoustic Doppler current profiler. Results of a simple slab model indicated that the NIWs were generated by the surface winds of Typhoon Hagupit. Following Hagupit＇s passage, the wave field was dominated by baroclinic NIWs. The near-inertial currents were surface-intensified with a maximum of 0.52 m/s but still reached 0.1 m/s at the depth of 210 m. Moreover, the near-inertial currents were clockwise-polarized and slightly elliptical. A depth-leading phase of the near- inertial currents was evident, which indicated downward energy propagation. However, the rotary vertical wavenumber spectra suggested that upward energy propagation also existed, which was consistent previous theoretical study. The frequency of the NIWs, modified by the positive background vorticity, was 0.714 2 cycles per day, which was 0.02f0 higher than the local inertial frequency （f0）. The near-inertial kinetic energy evolved exponentially and had an e-folding timescale of about 3 days. The vertical phase and group velocity were estimated to be 10 and 2.1 m/h, respectively, corresponding to a vertical wavelength of 340 m. The NlWs were dominated by the second mode with a variance contribution of 〉50%, followed by the third mode, while the first mode was insignificant.展开更多
The structures and characteristics of the marine-atmospheric boundary layer over the South China Sea during the passage of strong Typhoon Hagupit are analyzed in detail in this paper. The typhoon was generated in the ...The structures and characteristics of the marine-atmospheric boundary layer over the South China Sea during the passage of strong Typhoon Hagupit are analyzed in detail in this paper. The typhoon was generated in the western Pacific Ocean, and it passed across the South China Sea, finally landfalling in the west of Guangdong Province. The shortest distance between the typhoon center and the observation station on Zhizi Island （10 m in height） is 8.5 km. The observation data capture the whole of processes that occurred in the regions of the typhoon eye, two squall regions of the eye wall, and weak wind regions, before and after the typhoon’s passage. The results show that： （a） during the strong wind （average velocityˉu≧10 m s？1） period, in the atmospheric boundary layer below 110 m, ˉu is almost independent of height, and vertical velocity ˉw is greater than 0, increasing with ˉu and reaching 2–4 m s？1 in the squall regions;（b） the turbulent fl uctuations （frequency＆gt;1/60 Hz） and gusty disturbances （frequency between 1/600 and 1/60 Hz） are both strong and anisotropic, but the anisotropy of the turbulent fl uctuations is less strong;（c） ˉu can be used as the basic parameter to parameterize all the characteristics of fl uctuations;and （d） the vertical fl ux of horizontal momentum contributed by the average fl ow （ˉu＆#183; ˉw） is one order of magnitude larger than those contributed by fl uctuation fl uxes （u＆#39;w＆#39; and v＆#39;w＆#39;）, implying that strong wind may have seriously disturbed the sea surface through drag force and downward transport of eddy momentum and generated large breaking waves, leading to formation of a strongly coupled marine-atmospheric boundary layer. This results in ˉw ＆gt; 0 in the atmosphere, and some portion of the momentum in the sea may be fed back again to the atmosphere due to ˉu ＆#183; ˉw＆gt;0.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.U1133001,41030855,and 41376027)the National High Technology Research and Development Program of China(863 Program)(No.2013AA09A502)the NSFC-Shandong Joint Fund for Marine Science Research Centers(No.U1406401)
文摘Energetic near-inertial internal waves （NlWs） were observed on the continental slope of the northern South China Sea in September 2008. Characteristics of the observed near-inertial waves were examined based on current data recorded by a moored acoustic Doppler current profiler. Results of a simple slab model indicated that the NIWs were generated by the surface winds of Typhoon Hagupit. Following Hagupit＇s passage, the wave field was dominated by baroclinic NIWs. The near-inertial currents were surface-intensified with a maximum of 0.52 m/s but still reached 0.1 m/s at the depth of 210 m. Moreover, the near-inertial currents were clockwise-polarized and slightly elliptical. A depth-leading phase of the near- inertial currents was evident, which indicated downward energy propagation. However, the rotary vertical wavenumber spectra suggested that upward energy propagation also existed, which was consistent previous theoretical study. The frequency of the NIWs, modified by the positive background vorticity, was 0.714 2 cycles per day, which was 0.02f0 higher than the local inertial frequency （f0）. The near-inertial kinetic energy evolved exponentially and had an e-folding timescale of about 3 days. The vertical phase and group velocity were estimated to be 10 and 2.1 m/h, respectively, corresponding to a vertical wavelength of 340 m. The NlWs were dominated by the second mode with a variance contribution of 〉50%, followed by the third mode, while the first mode was insignificant.
基金National Key Research and Development Programs of Ministry of Science and Technology of China(2018YFC1506405,2018YFC1507404)National Natural Science Foundation of China(41275022,4167018,41975067,41675019)。
基金Supported by the National Natural Science Foundation of China(40830103 and 91215302)National(Key)Basic Research and Development(973)Program of China(2010CB951804)+1 种基金China Meteorological Administration Special Public Welfare Research Fund(GYHY201306057)Strategy Guide for the Specific Task of the Chinese Academy of Sciences(XDA10010403)
文摘The structures and characteristics of the marine-atmospheric boundary layer over the South China Sea during the passage of strong Typhoon Hagupit are analyzed in detail in this paper. The typhoon was generated in the western Pacific Ocean, and it passed across the South China Sea, finally landfalling in the west of Guangdong Province. The shortest distance between the typhoon center and the observation station on Zhizi Island （10 m in height） is 8.5 km. The observation data capture the whole of processes that occurred in the regions of the typhoon eye, two squall regions of the eye wall, and weak wind regions, before and after the typhoon’s passage. The results show that： （a） during the strong wind （average velocityˉu≧10 m s？1） period, in the atmospheric boundary layer below 110 m, ˉu is almost independent of height, and vertical velocity ˉw is greater than 0, increasing with ˉu and reaching 2–4 m s？1 in the squall regions;（b） the turbulent fl uctuations （frequency＆gt;1/60 Hz） and gusty disturbances （frequency between 1/600 and 1/60 Hz） are both strong and anisotropic, but the anisotropy of the turbulent fl uctuations is less strong;（c） ˉu can be used as the basic parameter to parameterize all the characteristics of fl uctuations;and （d） the vertical fl ux of horizontal momentum contributed by the average fl ow （ˉu＆#183; ˉw） is one order of magnitude larger than those contributed by fl uctuation fl uxes （u＆#39;w＆#39; and v＆#39;w＆#39;）, implying that strong wind may have seriously disturbed the sea surface through drag force and downward transport of eddy momentum and generated large breaking waves, leading to formation of a strongly coupled marine-atmospheric boundary layer. This results in ˉw ＆gt; 0 in the atmosphere, and some portion of the momentum in the sea may be fed back again to the atmosphere due to ˉu ＆#183; ˉw＆gt;0.
