BAROCLINIC INSTABILITY DUE TO THERMOBARIC CONVECTION AND ITS ROLE IN FORMATION OF DEEP AND BOTTOM WATERS

本文利用一个旋转坐标系下的三维非静力模式进行了数值试验，研究了与弱层结极地海洋温压深对流有关的斜压不稳定性及其在输送过程中的作用。该模型海洋具有两层结构，冷的新鲜混合层覆盖在温暖的含盐深水单元上，如南极洲威德尔海。与基于线性状态方程的情景相比，水柱的对流翻转通过温压和二次（cabbeling）效应增强了水平密度梯度（斜压性）。如果温度（盐度）控制水密度，斜压性在翻转层的底部（表面）加强。这种强化会导致斜压不稳定或斜压不稳定的进一步发展以及更有效的垂直热量输送。在后翻转阶段，表面冷却（对流运动）有两个 ...更多信息 对斜压不稳定发展和相关热输送的相反作用。一个是由于表层对流运动引起的水平辐合流增强了斜压不稳定性，因为以前的研究报告集中在中纬度强烈分层的海洋上。当斜压性是表面加强时，观察到这一点，但当它是底部加强时，观察不到这一点。另一种是强对流运动通过不断地垂直扰动翻转层来抑制斜压不稳定。这种效应在强冷却的情况下变得显著，并且在先前研究的强分层海洋中没有观察到。因此，垂直热传输在零或低冷却速率（&lt;125 Wm2）下最有效<-2>。当斜压性初始较弱时，如在威德尔海，最有效的输送发生在25 Wim^的冷却率<-2>，这是一个可能的值在海冰覆盖下的实际情况。在实际情况下，由于水柱静稳定性的空间差异而引起的水柱的不均匀（部分）翻转是斜压不稳定发展的另一个因素。少

Numerical experiments with a three-dimensional nonhydrostatic model in a rotating frame have been executed to investigate baroclinic instability associated with thermobaric deep convection in weakly stratified polar oceans and its role in the transport processes. The model ocean has a two-layered structure with the cold, fresh mixed layer overlying the warm, saline deep water cell, such as in the Weddell Sea Antarctica. In contrast with a scenario based on the linear equation of state, convective overturning of the water column enhances the horizontal density gradient (baroclinicity) through the thermobaric and quadratic (cabbeling) effects. If temperature (salinity) controls water density, baroclinicity is intensified at the bottom (surface) of the overturned layer. Such intensification causes further development of baroclinic instability or baroclinic destabilization and more effective vertical heat transport. In the post-overturning stage, surface cooling (convective motion) has two … More oppositely-operating effects on development of baroclinic instability and associated heat transport. One is that horizontal convergent flow due to convective motion in the surface layer enhances baroclinic instability, as previous studies have reported focusing on strongly stratified oceans at midlatitudes. This is observed when baroclinicity is surface-intensified, but not when it is bottom-intensified. The other is that strong convective motion suppresses baroclinic instability by continuously homogenizing the overturned layer vertically. This effect becomes significant in strong-cooling cases, and has not been observed in strongly stratified oceans studied previously. As a result, the vertical heat transport is most effective at zero or low cooling rates (<125 Wm^<-2>). When baroclinicity is initially weak as in the Weddell Sea, the most effective transport occurs with the cooling rate of 25 Wim^<-2> which is a possible value under sea-ice cover in the actual situation. Inhomogeneous (partial) overturning of the water column resulting from spatial difference in static stability of the water column is another factor for development of baroclinic instability in the actual situation. Less