【作者】 刘玲玲；

【导师】 王伟；

【作者基本信息】 中国海洋大学 ， 物理海洋， 2008， 博士

【摘要】 由于海洋在上垫面加热和冷却,因此虽然海洋在上表面吸收很多热量,但并不能把这些热量有效的转化为机械能。为了维持准平衡态的大洋环流,需要外来机械能源来平衡摩擦和耗散所损失的能量。风和潮汐是最主要的机械能源。但到目前为止仍有一些机械能源不清楚,如热带气旋。热带气旋是中低纬度大气系统中很重要的成分,由于我们通常所用的风应力资料(如NCEP/NCAR)分辨率比较低,像热带气旋这种强烈的非线性事件都被平滑掉了,因此前面提到的风输入到海洋中的能量中并不包含热带气旋的贡献。考虑到热带气旋与海洋之间的相互作用,利用一个台风--海洋耦合模式,本文研究了热带气旋在海洋能量平衡和水团平衡中的作用。本文采用的耦合模式由两个各自测试、独立发展的模式组成:三层的海洋约化重力模式和轴对称的台风模型。本文计算了1984至2005年间约1600个热带气旋输入到海洋中的能量(包括输入到浪的能量,输入到表面流特别是近惯性流中的能量)。另外,用一个简单的平底模型估计了热带气旋导致的海洋上层重力位能增加,同时,也计算了全球大洋中由热带气旋导致的混合层加深和混合。本文的研究结果表明,当热带气旋过境时,大量的机械能被输入到海洋中。1984至2005年热带气旋输入到海洋中的年平均能量为:输入到浪1.70TW;表面流0.10TW,其中近惯性频率段0.03TW;导致的重力位能增加为0.05TW。虽然这部分能量远小于平均态风场输入的能量,但由于这部分能量主要集中在低中纬度,特别是西北太平洋和北大西洋,可能对维持大洋环流有非常重要的贡献。热带气旋是大气系统中变化最剧烈的成分,在过去的几十年由于全球增暖现象,热带气旋的活动亦增强,因此热带气旋输入到海洋中的能量也发生了很大的年际到年代际时间尺度的变化,总体上存在增大的趋势。从1984至2005年,热带气旋输入到海洋中的能量增加了19%。热带气旋输入到海洋中能量的变化主要与热带气旋的强度有关,用PDI(Power Dissipation Index)表征热带气旋的强度指数,二者的相关系数达到0.93,也就是说热带气旋输入到海洋中的能量与PDI的变化趋势基本一致。另外,热带气旋输入到海洋中能量的变化与每年热带气旋的个数也有一定的关系,但二者的相关系数仅为0.33。在低中纬度,热带气旋输入到海洋中的机械能可以有效地增加混合层的深度。最新的研究结果表明,低中纬度混合层的加深能有效地增强经向压强梯度,进而增强子午环流和向极热通量,同时使得维持次表层的跨密度面混合所需要的能量减小。1984至2005年热带气旋引起的混合层加深的体积通量为,其中在北太平洋有22.4。Qiu and Huang(1995)估计的北太平洋的subduction rate为35.2 ,obduction rate为7.8。热带气旋导致的混合层加深的体积通量大于通过subduction形成水团的50%,且远大于obduction,他们的结果显示obduction主要发生在以北地区,而热带气旋导致的混合层加深则主要集中在。该结果显示,热带气旋在区域海甚至全球海洋的水团平衡中有非常重要的作用,在讨论水团平衡时必须考虑热带气旋的贡献。热带气旋输入到海洋中的能量可以输送到大洋内部很深的地方,因此热带气旋在很大程度上增强了海洋中的局地混合。本文的结果表明,热带气旋引起了强烈的垂直混合。混合率的大小为,其最大值( )出现在西北太平洋。由于热带气旋引起的混合是高度瞬变的,且发生在强层结处的低中纬度,因此热带气旋输入到海洋中机械能对大洋环流有非常重要的贡献,能更有效地驱动大洋环流。更多还原

【Abstract】 Although oceans receive a huge amount of thermal energy, such energy cannot be efficiently converted into mechanical energy because the ocean is heated and cooled from the same geopotential level, the upper ocean. Therefore, in order to maintain the quasi-steady oceanic circulation external sources of mechanical energy are required to balance the loss of mechanical energy due to friction and dissipation. Wind stress and tidal dissipation are the primary sources of mechanical energy. However, some important sources of mechanical energy in the world oceans remain unaccounted, such as tropical cyclones. Tropical cyclone activity is a vitally important component of the atmospheric circulation system at low- and mid- latitudes. In the commonly used low spatial resolution wind stress data, such as NCEP reanalysis, these strong nonlinear events are smoothed out. As a result, their contributions to the global mechanical energy input are excluded.Using a hurricane-ocean coupled model, the important role of the tropical cyclones in the energy balance and water mass balance of the ocean is examined. The coupled model was constructed from two independently developed and tested models: a three-layer reduced gravity ocean model and an axisymmetric hurricane model. The energy input to the ocean, including the energy input to surface waves, to surface current, especially to the near-inertial motions, induced by about 1600 tropical cyclones from 1984 to 2005 were examined. Meanwhile, a simple slab model was used to estimate the increase of the gravitational potential energy in the oceanic surface mixed layer. In addition, the mixed layer deepening and vertical diffusivity induced by tropical cyclones in the world oceans are estimated.When the tropical cyclones pass through, much mechanical energy was input to the oceans. The energy input averaged over the period from 1984 to 2005 is estimated as follows: 1.70TW to the surface waves and 0.10TW to the surface currents (including 0.03TW to the near inertial motions). The rate of gravitational potential energy increase due to tropical cyclones is 0.05TW. Although the energy induced by tropical cyclones is much smaller than that induced by smoothed wind stress, most of this energy is distributed in the low- and mid- latitudes, especially in the northwest Pacific and north Atlantic, which may be very important for the oceanic general circulation.Tropical cyclones are one of the strongest time varying components in the atmospheric circulation. The activity of tropical cyclones has enhanced during the past decades, apparently due to global warming. Accordingly, both the energy input from tropical cyclones and the increase of gravitational potential energy of the ocean show strong interannual variability with an increasing rate of 19% over the past 22 years. The variability of the energy input to the ocean induced by tropical cyclones is similar with the intensity of tropical cyclones, which is denoted by PDI (Power Dissipation Index); the correlation coefficient is 0.93. The energy input is also associated with the number of tropical cyclones in each year, the correlation coefficient is 0.33.The mechanical energy input to the ocean induced by tropical cyclones can efficiently deepen the mixed layer at the low- and mid- latitudes. The deepening of mixed layer at low latitudes can enhance the meridional pressure difference and thus the overturning circulation and poleward heat flux, and decrease the energy for subsurface diapycnal mixing at the same time. The total volume flux due to mixed layer deepening in the world ocean is from 1984 to 2005, with in the North Pacific. Qiu and Huang (1995) discussed subduction and obduction in the oceans, they estimated that basin-integrated subduction rate is and obduction rate is in the North Pacific. Therefore, the total volume flux due to mixed layer deepening induced by tropical cyclones is approximately 50% of the subtropical water mass formulation rate through subduction and much larger than obduction. The obduction rate was accumulated from to ; the mixed layer deepening was distributed from to . The cyclone induced mixed layer deepening play a capitally important role in water mass balance in the world oceans, and water mass balance without taking into consideration of the contribution due to tropical cyclones may not be acceptable. 10 0N 30 0NThe energy input to the ocean induced by tropical cyclones can be transported into the ocean interior; accordingly, diapycnal mixing in the upper ocean (below the mixed layer) is greatly enhanced. Our results indicate that the vertical diffusivity induced by tropical cyclones is on the order of , with the maximum of in the western Pacific. The mixing induced by tropical cyclones varied greatly with time and took place at low- and mid- latitudes with strong stratification; the strong ocean mixing induced by tropical cyclones may play vitally important roles in the oceanic general circulation.更多还原