南海西北部台风激发近惯性波频移研究

doi:10.3969/j.issn.1001-909X.2023.04.002

摘要/Abstract

摘要：

近惯性波是海洋对台风响应过程中最为重要的能量传递方式之一,其频率随深度的分布会影响近惯性波能量向海洋内部传播的速度。基于台风期间南海西北部的潜标观测资料,对涡度效应和背景流引起的多普勒效应进行分析,发现背景流引起的多普勒效应是近惯性波频率“蓝移”的主要因素,近惯性波频率大于当地惯性频率,并且频率随着深度增加而增加。深度在200 m以浅,背景流多普勒效应为负;深度在200 m左右,多普勒效应趋于0;深度在230~400 m,多普勒效应为正。在230~400 m深度,背景流强度达到最大,其方向与近惯性波传播方向接近,因此由其引起的多普勒正频移也最大,观测结果显示近惯性波频率偏移也最大。该研究对加深海洋对台风响应过程的认识,特别是近惯性波在背景流结构复杂海域(如西边界流区域)的传播具有重要作用。

关键词: 台风, 近惯性波, 多普勒效应

Abstract:

Near-inertial waves (NIWs) play an important role in the response of ocean to typhoon. Their frequency varies with the depth and is the main factor in determining the propagation rate of near-inertial energy to the ocean interior. Based on the observation data from mooring, the factors affecting the blue-shift frequency of NIWs excited by typhoon were investigated in northwestern South China Sea. By analyzing the vorticity effect and Doppler effect caused by background currents, this study suggests that the Doppler effect of background currents was the main factor in the blue-shift frequency of NIWs. As depth increased, inertial wave frequencies increased. Quantitative calculations further demonstrated that within the upper 200 meters, the Doppler effect of the background currents was negative, approaching zero in depth around 200 meters. However, in the depth range of 230 to 400 meters, the Doppler effect became positive. This depth range exhibited the maximum strength of the background currents, with their direction aligned with the propagation direction of inertial waves. Consequently, the positive Doppler shift induced by the background currents was most pronounced. The results of this study are important for improving the understanding of the ocean response to typhoons, especially the propagation of near-inertial waves in areas with complex background current structure (e.g., the western boundary current region).

Key words: typhoon, near-inertial waves, Doppler effect

中图分类号:

P731.2

付殿福, 谢波涛, 黄必桂, 金魏芳, 牟勇, 蔺飞龙. 南海西北部台风激发近惯性波频移研究[J]. 海洋学研究, 2023, 41(4): 12-20.

FU Dianfu, XIE Botao, HUANG Bigui, JIN Weifang, MOU Yong, LIN Feilong. Study on frequency shift of typhoon-excited near-inertial waves in northwestern South China Sea[J]. Journal of Marine Sciences, 2023, 41(4): 12-20.

图/表 9

图1 台风“杜苏芮”路径及强度

Fig.1 The path and intensity of typhoon Doksui

图2 台风期间近惯性波在东西(a)和南北(b)方向流速分量的时间序列 (紫色三角形表示台风中心距离观测站位最近的时间。)

Fig.2 The time series of eastward (a) and northward (b) component of near-inertial waves during typhoon period (The purple triangle indicates the arrival time of the typhoon.)

图3 近惯性波谱峰频率(a)和相位(b)在深度上的分布

Fig.3 The vertical distribution of frequency (a) and phase (b) of near-inertial waves

图4 观测相对涡度和理论相对涡度分布

Fig.4 The time series of relative background vorticities from observation at mooring station and the relative theoretical vorticities

图5 台风期间观测站位背景海流东西分量(a)和南北分量(b)的分布 (竖直黑色虚线标出计算台风影响时间范围,紫色三角形表示台风到达时间。)

Fig.5 Distribution of eastward (a) and northward (b) components of the background current at the mooring station during typhoon period (The vertical black dashed lines mark the time range of typhoons impact. The purple triangle indicates the arrival time of the typhoon.)

图6 台风期间平均背景流大小(a)和方向(b)随深度的分布

Fig.6 Distribution of amplitude (a) and direction (b) for time-averaged background currents during typhoon period

图7 近惯性波引起的密度扰动与东西向流速剪切的相干谱(a)和相位谱(b) (黑色虚线表示当地惯性频率。)

Fig.7 Squared coherence (a) and phase (b) between density perturbation and shear in eastward component (The black dashed lines indicate the position of f0.)

图8 台风期间深度55 m(a),105 m(b)和155 m(c)处的近惯性流剪切矢量图

Fig.8 Shear vector hodographs of near-inertial waves at depths of 55 m (a), 105 m (b) and 155 m (c) during typhoon period

图9 近惯性波有效科氏频率与固有频率(a)和背景流引起的多普勒频移(b)在垂直方向的分布 (阴影代表置信区间。)

Fig.9 Vertical distribution of the effective Coriolis frequency and intrinsic frequency of near-inertial waves (a) and Doppler shift of the waves induced by background current(b) (The shaded areas represent confidence interval.)

参考文献 23

[1]	ROSSBY C G. On the mutual adjustment of pressure and velocity distributions in certain simple current systems, II[J]. Journal of Marine Research, 1938, 1(3): 239-263. DOI URL
[2]	GILL A E. On the behavior of internal waves in the wakes of storms[J]. Journal of Physical Oceanography, 1984, 14(7): 1129-1151. DOI URL
[3]	WEBSTER F. Observations of inertial-period motions in the deep sea[J]. Reviews of Geophysics, 1968, 6(4): 473-490. DOI URL
[4]	PRICE J F. Upper ocean response to a hurricane[J]. Journal of Physical Oceanography, 1981, 11(2): 153-175. DOI URL
[5]	PRICE J F. Internal wave wake of a moving storm.Part I: Scales, energy budget and observations[J]. Journal of Physical Oceanography, 1983, 13(6): 949-965. DOI URL
[6]	SANFORD T B, PRICE J F, GIRTON J B. Upper-ocean response to hurricane Frances (2004) observed by profiling EM-APEX floats[J]. Journal of Physical Oceanography, 2011, 41(6): 1041-1056. DOI URL
[7]	TEAGUE W J, JAROSZ E, WANG D W, et al. Observed oceanic response over the upper continental slope and outer shelf during hurricane Ivan[J]. Journal of Physical Oceano-graphy, 2007, 37(9): 2181-2206.
[8]	ZEDLER S E, DICKEY T D, DONEY S C, et al. Analyses and simulations of the upper ocean’s response to Hurricane Felix at the Bermuda Testbed Mooring site: 13-23 August 1995[J]. Journal of Geophysical Research: Oceans, 2002, 107(C12): 3232, doi:10.1029/2001JC000969.
[9]	QI H B, DE SZOEKE R A, PAULSON C A, et al. The structure of near-inertial waves during ocean storms[J]. Journal of Physical Oceanography, 1995, 25(11): 2853-2871. DOI URL
[10]	SUN L, ZHENG Q A, WANG D X, et al. A case study of near-inertial oscillation in the South China Sea using mooring observations and satellite altimeter data[J]. Journal of Oceanography, 2011, 67(6): 677-687. DOI URL
[11]	SUN Z Y, HU J Y, ZHENG Q A, et al. Strong near-inertial oscillations in geostrophic shear in the northern South China Sea[J]. Journal of Oceanography, 2011, 67(4): 377-384. DOI URL
[12]	YANG B, HOU Y J. Near-inertial waves in the wake of 2011 Typhoon Nesat in the northern South China Sea[J]. Acta Oceanologica Sinica, 2014, 33(11): 102-111.
[13]	KUNZE E. Near-inertial wave propagation in geostrophic shear[J]. Journal of Physical Oceanography, 1985, 15(5): 544-565. DOI URL
[14]	KUNZE E, SCHMITT R W, TOOLE J M. The energy balance in a warm-core ring’s near-inertial critical layer[J]. Journal of Physical Oceanography, 1995, 25(5): 942-957. DOI URL
[15]	ZHAI X M, GREATBATCH R J, EDEN C. Spreading of near-inertial energy in a 1/12° model of the North Atlantic Ocean[J]. Geophysical Research Letters, 2007, 34(10):L10609.
[16]	CHU P C, VENEZIANO J M, FAN C W, et al. Response of the South China Sea to tropical cyclone ernie 1996[J]. Journal of Geophysical Research: Oceans, 2000, 105(C6): 13991-14009.
[17]	YANG B, HOU Y J, HU P, et al. Shallow ocean response to tropical cyclones observed on the continental shelf of the northwestern South China Sea[J]. Journal of Geophysical Research: Oceans, 2015, 120(5): 3817-3836. DOI URL
[18]	GUAN S D, ZHAO W, HUTHNANCE J, et al. Observed upper ocean response to typhoon Megi (2010) in the Northern South China Sea[J]. Journal of Geophysical Research: Oceans, 2014, 119(5): 3134-3157. DOI URL
[19]	LIN F L, LIANG C J, HOU Y J, et al. Observation of interactions between internal tides and near-inertial waves after typhoon passage in the northern South China Sea[J]. Chinese Journal of Oceanology and Limnology, 2015, 33(5): 1279-1285. DOI URL
[20]	LIU J L, HE Y H, LI J, et al. Case study of nonlinear interaction between near-inertial waves induced by typhoon and diurnal tides near the Xisha Islands[J]. Journal of Geophysical Research: Oceans, 2018, 123(4): 2768-2784. DOI URL
[21]	ALFORD M H, GREGG M C. Near-inertial mixing: Modulation of shear, strain and microstructure at low latitude[J]. Journal of Geophysical Research: Oceans, 2001, 106(C8): 16947-16968.
[22]	CUYPERS Y, LE VAILLANT X, BOURUET-AUBERTOT P, et al. Tropical storm-induced near-inertial internal waves during the Cirene experiment: Energy fluxes and impact on vertical mixing[J]. Journal of Geophysical Research: Oceans, 2013, 118(1): 358-380. DOI URL
[23]	廖光洪, 袁耀初, Kaneko ARATA, 等. 吕宋海峡ADCP观测的450 m以浅水层内潮特征分析[J]. 中国科学:地球科学, 2011, 41(1):124-140.
	LIAO G H, YUAN Y C, ARATA K, et al. Analysis of internal tidal characteristics in the layer above 450 m from acoustic Doppler current profiler observations in the Luzon Strait[J]. Sci China Earth Sci, 2011, 41(1): 124-140.