Wang Wei

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  • Article
    Universal structure of mesoscale eddies in the ocean
    (John Wiley & Sons, 2013-07-30) Zhang, Zhengguang ; Zhang, Yu ; Wang, Wei ; Huang, Rui Xin
    Mesoscale eddies dominate oceanic kinetic energy at sub-inertial frequencies. Their three-dimensional structure has, however, remained obscure, hindering better understanding of eddy dynamics. Here by applying the composite analysis of satellite altimetry and Argo float data to the globe, we show that despite remarkable regional differences in amplitude, extent and polarity, etc., mesoscale eddies have a universal structure in normalized stretched coordinates. Horizontally, the associated pressure anomaly is well described by a function of the normalized radial distance from the eddy center R(rn)=(1−rn2/2)• exp(−rn2/2), whereas vertically it is sinusoidal in a stretched coordinate zs = ƒ z0 (N/f )dz, where N and f are the buoyancy frequency and the Coriolis parameter.
  • Article
    The mechanical energy input to the ocean induced by tropical cyclones
    (American Meteorological Society, 2008-06) Liu, Ling Ling ; Wang, Wei ; Huang, Rui Xin
    Wind stress and tidal dissipation are the most important sources of mechanical energy for maintaining the oceanic general circulation. The contribution of mechanical energy due to tropical cyclones can be a vitally important factor in regulating the oceanic general circulation and its variability. However, previous estimates of wind stress energy input were based on low-resolution wind stress data in which strong nonlinear events, such as tropical cyclones, were smoothed out. Using a hurricane–ocean coupled model constructed from an axisymmetric hurricane model and a three-layer ocean model, the rate of energy input to the world’s oceans induced by tropical cyclones over the period from 1984 to 2003 was estimated. The energy input is estimated as follows: 1.62 TW to the surface waves and 0.10 TW to the surface currents (including 0.03 TW to the near-inertial motions). The rate of gravitational potential energy increase due to tropical cyclones is 0.05 TW. Both the energy input from tropical cyclones and the increase of gravitational potential energy of the ocean show strong interannual and decadal variability with an increasing rate of 16% over the past 20 years. The annual mean diapycnal upwelling induced by tropical cyclones over the past 20 years is estimated as 39 Sv (Sv ≡ 106 m3 s−1). Owing to tropical cyclones, diapycnal mixing in the upper ocean (below the mixed layer) is greatly enhanced. Within the regimes of strong activity of tropical cyclones, the increase of diapycnal diffusivity is on the order of (1 − 6) × 10−4 m2 s−1. The tropical cyclone–related energy input and diapycnal mixing may play an important role in climate variability, ecology, fishery, and environments.
  • Article
    A laboratory model of vertical ocean circulation driven by mixing
    (American Meteorological Society, 2008-05) Whitehead, John A. ; Wang, Wei
    A model of deep ocean circulation driven by turbulent mixing is produced in a long, rectangular laboratory tank. The salinity difference is substituted for the thermal difference between tropical and polar regions. Freshwater gently flows in at the top of one end, dense water enters at the same rate at the top of the other end, and an overflow in the middle removes the same amount of surface water as is pumped in. Mixing is provided by a rod extending from top to bottom of the tank and traveling back and forth at constant speed with Reynolds numbers >500. A stratified upper layer (“thermocline”) deepens from the mixing and spreads across the entire tank. Simultaneously, a turbulent plume (“deep ocean overflow”) from a dense-water source descends through the layer and supplies bottom water, which spreads over the entire tank floor and rises into the upper layer to arrest the upper-layer deepening. Data are taken over a wide range of parameters and compared to scaling theory, energetic considerations, and simple models of turbulently mixed fluid. There is approximate agreement with a simple theory for Reynolds number >1000 in experiments with a tank depth less than the thermocline depth. A simple argument shows that mixing and plume potential energy flux rates are equal in magnitude, and it is suggested that the same is approximately true for the ocean.
  • Preprint
    Decadal variability of wind-energy input to the world ocean
    ( 2005-08-17) Huang, Rui Xin ; Wang, Wei ; Liu, Ling Ling
    Wind stress energy input to the oceans is the most important source of mechanical energy in maintaining the oceanic general circulation. Previous studies indicate that wind energy input to the Ekman layer and surface waves varied greatly over the past 50 years. In this study wind energy input to surface current and surface geostrophic current was calculated as the scalar product of wind stress and surface current and surface geostrophic current. The surface geostrophic current was calculated in two ways: the surface geostrophic velocity diagnosed from the TOPEX/POSEIDON altimeter data over period (1993 to 2003) or calculated from the sea surface height of the numerical model. The surface velocity was obtained from a numerical model. Estimate of wind energy input based on altimetric data averaged over the period from 1993 to 2003 is 0.84TW (1TW=1012 W), excluding the equatorial band (within ±3° of the equator). Estimate of the wind energy input to the surface geostrophic current based on the numerical model is 0.87TW averaged from 1993 to 2003, and wind energy input to the surface current for the same period is 1.16TW. This input is primarily concentrated over the Southern Ocean and the equatorial region (20°S - 20°N). This energy varied greatly on interannual and decadal time scales, and it increased 12% over the past 25 years and the interannual variability mainly occurs in the latitude band of 40°S - 60°S and the equatorial region.
  • Article
    An experimental study on thermal circulation driven by horizontal differential heating
    (Cambridge University Press, 2005-09-27) Wang, Wei ; Huang, Rui Xin
    Circulation driven by horizontal differential heating is studied, using a double-walled Plexiglas tank (20×15×2.5 cm3) filled with salt water. For instances of heating/cooling from above and below, results indicate that there is always quasi-equilibrium circulation. In contrast to most previous results from experimental/ numerical studies, circulation in our experiments appears in the form of a shallow cell adjacent to the boundary of thermal forcing. The non-dimensional stream-function maximum confirms the 1/5-power law of Rossby, Ψ ∼Ra1/5 L . Dissipation rate measured in the experiments appears to be consistent with theory. For cases of heating/cooling from a sloping bottom, circulation is similar to cases with a flat bottom; circulation is strong if heating is below cooling, but it is rather weak if heating is above cooling. Nevertheless, circulation in all cases is visible to the naked eye.
  • Article
    Climate variability in the equatorial Pacific Ocean induced by decadal variability of mixing coefficient
    (American Meteorological Society, 2007-05) Huang, Chuan Jiang ; Wang, Wei ; Huang, Rui Xin
    The circulation in the equatorial Pacific Ocean is studied in a series of numerical experiments based on an isopycnal coordinate model. The model is subject to monthly mean climatology of wind stress and surface thermohaline forcing. In response to decadal variability in the diapycnal mixing coefficient, sea surface temperature and other properties of the circulation system oscillate periodically. The strongest sea surface temperature anomaly appears in the geographic location of Niño-3 region with the amplitude on the order of 0.5°C, if the model is subject to a 30-yr sinusoidal oscillation in diapycnal mixing coefficient that varies between 0.03 × 10−4 and 0.27 × 10−4 m2 s−1. Changes in diapycnal mixing coefficient of this amplitude are within the bulk range consistent with the external mechanical energy input in the global ocean, especially when considering the great changes of tropical cyclones during the past decades. Thus, time-varying diapycnal mixing associated with changes in wind energy input into the ocean may play a nonnegligible role in decadal climate variability in the equatorial circulation and climate.
  • Article
    Dynamical roles of mixed layer in regulating the meridional mass/heat fluxes
    (American Geophysical Union, 2007-05-17) Huang, Rui Xin ; Huang, Chuan Jiang ; Wang, Wei
    The mixed layer is an important component of the oceanic circulation system. Recent progress in energetics of the oceanic circulation suggests that the amount of external mechanical energy available for mixing is directly linked to the strength of the meridional overturning circulation. Using an analytical two-dimensional model and a three-dimensional numerical model, it is shown that the meridional distribution of mixed layer depth plays an important role in regulating the meridional overturning circulation and poleward heat flux. In fact, if the mixed layer at low and middle latitudes is deeper because of increase in mechanical energy input to the turbulence in the upper ocean, the meridional overturning circulation and poleward heat flux are enhanced in a steady circulation system, and at the same time, it may take less mechanical energy to support the subsurface diapycnal mixing.
  • Preprint
    Mechanical energy input to the world oceans due to atmospheric loading
    ( 2005-08-02) Wang, Wei ; Qian, Chengchun ; Huang, Rui Xin
    Mechanical energy input to the oceans is one of the most important factors controlling the oceanic general circulation. The atmosphere transports mechanical energy to the oceans primarily through wind stress, plus changes of the sea level pressure (the so-called atmospheric loading). The rate of mechanical energy transfer into the ocean due to atmospheric loading is calculated, based on TOPEX/POSEIDON data over ten-year period (1993-2002). The rate of total energy input for the world oceans is estimated at 0.04TW (1TW=1012W), and most of this energy input is concentrated in the Southern Oceans and the Storm Tracks in the Northern Hemisphere. This energy input varied greatly with time, and the amplitude of the interannual variability over the past ten years is about 15%.