Near-inertial waves in the wake of 2011 Typhoon Nesat in the northern South China Sea
- PDF / 1,948,791 Bytes
- 10 Pages / 595.276 x 841.89 pts (A4) Page_size
- 109 Downloads / 347 Views
Near-inertial waves in the wake of 2011 Typhoon Nesat in the northern South China Sea YANG Bing1,2,3, HOU Yijun1,2* 1
Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China Key Laboratory of Chinese Academy of Sciences for Ocean Circulation and Waves, Institute of Oceanology, Qingdao 266071, China 3 University of Chinese Academy of Sciences, Beijing 100049, China 2
Received 26 December 2013; accepted 22 May 2014 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2014
Abstract In September 2011, Typhoon Nesat passed over a moored array of instruments recording current and temperature in the northern South China Sea (SCS). A wake of baroclinic near-inertial waves (NIWs) commenced after Nesat passed the array. The associated near-inertial currents are surface-intensified and clockwise-polarized. The vertical range of NIWs reached 300 m, where the vertical range is defined as the maximum depth of the horizontal near-inertial velocity 5 cm/s. The current oscillations have a frequency of 0.709 9 cycles per day (cpd), which is 0.025f higher than the local inertial frequency. The NIWs have an e-folding time-scale of 10 d based on the evolution of the near-inertial kinetic energy. The depth-leading phase of near-inertial currents indicates downward group velocity and energy flux. The estimated vertical phase velocity and group velocity are 0.27 and 0.08 cm/s respectively, corresponding to a vertical wavelength of 329 m. A spectral analysis reveals that NIWs act as a crucial process to redistribute the energy injected by Typhoon Nesat. A normal mode and an empirical orthogonal function analysis indicate that the second mode has a dominant variance contribution of 81%, and the corresponding horizontal phase velocity and wavelength are 3.50 m/s and 420 km respectively. The remarkable large horizontal phase velocity is relevant to the rotation of the earth, and a quantitative analysis suggests that the phase velocity of the NIWs with a blue-shift of 0.025f overwhelms that of internal gravity waves by a factor of 4.6. Key words: near-inertial waves, South China Sea, Typhoon Nesat Citation: Yang Bing, Hou Yijun. 2014. Near-inertial waves in the wake of 2011 Typhoon Nesat in the northern South China Sea. Acta Oceanologica Sinica, 33(11): 102–111, doi: 10.1007/s13131-014-0559-6
1 Introduction A typhoon is an extremely high wind event which injects momentums into the oceanic surface mixed layer (SML, hereafter) during its passage for a relatively short duration (Price et al., 1994). Although the associated wind stress excites motions of the ocean on a variety of spatial and temporal scales, previous observations have suggested that the predominant oceanic response are near-inertial waves (Price, 1981; Shay and Elsberry, 1987; Shay et al., 1990; Keisuke et al., 1993; Cuypers, 2013). Near-inertial waves (NIWs, hereafter), also known as near-inertial oscillations, are characterized by the oscillating horizontal currents and vertical displacement of water particles with the frequency close
Data Loading...
