Liu Ling Ling

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Ling Ling

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Now showing 1 - 6 of 6
  • 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.
  • Preprint
    Enhancement of subduction/obduction due to hurricane-induced mixed layer deepening
    ( 2011-04) Liu, Ling Ling ; Wang, Fan ; Huang, Rui Xin
    Ventilation, including subduction and obduction, in the North Pacific is re-examined, based on SODA outputs and the Eulerian definition. The annual subduction rate averaged from 2001 to 2004 is estimated at 49.8Sv; while the annual obduction rate is 26.7Sv. Furthermore, the annual subduction/obduction rate enhancement induced by tropical cyclones in the North Pacific, defined as the difference between the annual subduction/obduction rate for the cases including the mixed layer depth perturbations induced by tropical cyclones and that for the cases without the perturbations, is estimated. Based on SODA outputs and the mixed layer deepening obtained from a hurricane-ocean coupled model, the annual tropical cyclone-induced subduction rate enhancement averaged from 2001 to 2004 is estimated at 4.4Sv and the obduction rate enhancement 5.2Sv; and such enhancement is mainly concentrated in the latitudinal band from 10°N to 30°N.
  • Preprint
    The role of diurnal cycle in subduction/obduction
    ( 2010-06-09) Liu, Ling Ling ; Huang, Rui Xin ; Wang, Fan
    The annual subduction/obduction rate can be calculated in Lagrangian and Eulerian coordinates. In previous studies such calculations were primarily focused on the case with the seasonal cycle only. By extending these calculations to the case including the diurnal cycle of mixed layer depth, the annual subduction/obduction rate can be greatly increased.
  • 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
    The global subduction/obduction rates : their interannual and decadal variability
    (American Meteorological Society, 2012-02-15) Liu, Ling Ling ; Huang, Rui Xin
    Ventilation, including subduction and obduction, for the global oceans was examined using Simple Ocean Data Assimilation (SODA) outputs. The global subduction rate averaged over the period from 1959 to 2006 is estimated at 505.8 Sv (1 Sv ≡ 106 m3 s−1), while the corresponding global obduction rate is estimated at 482.1 Sv. The annual subduction/obduction rates vary greatly on the interannual and decadal time scales. The global subduction rate is estimated to have increased 7.6% over the past 50 years, while the obduction rate is estimated to have increased 9.8%. Such trends may be insignificant because errors associated with the data generated by ocean data assimilation could be as large as 10%. However, a major physical mechanism that induced these trends is primarily linked to changes in the Southern Ocean. While the Southern Ocean plays a key role in global subduction and obduction rates and their variability, both the Southern Ocean and equatorial regions are critically important sites of water mass formation/erosion.
  • Article
    Three-dimensional structure of subduction/obduction in the North Pacific Ocean
    (American Meteorological Society, 2023-02-23) Liu, Ling Ling ; Huang, Rui Xin ; Wang, Fan
    A new three-dimensional method is proposed for calculating the annual mean subduction and obduction rate in the ocean and applied to the North Pacific Ocean. Due to the beta spiral, the subducted/obducted water at a given station can spread over/come from a wide range with different densities in the subsurface ocean. This new method can provide the three-dimensional feature of subduction/obduction and more accurate distribution of the annual subduction/obduction rate in density space. The spatial patterns of annual subduction/obduction rate obtained from both the classical and new methods are similar, although at individual stations the rate can be different; however, the new 3D method can greatly improve the density structure of subducted/obducted water mass. In spite of the assumption of idealized fluid in most previous studies, our analysis showed that subducted water masses can change their density due to diapycnal mixing, especially for water masses subducted at relatively shallow depths. In the North Pacific, the subduction process mainly takes place for about 1–2 months in most of the subtropical basin, while the time window for obduction is ∼100 days in the major obduction regions. Based on the SODA monthly mean climatology, the subducted/obducted water in the North Pacific is primarily distributed at depths of 80–120 m.