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

用旋转标架中的三维非静力模式进行了数值试验，研究了弱层结极地海洋中与热压深对流有关的斜压不稳定及其在输送过程中的作用。模型海洋具有双层结构，寒冷、新鲜的混合层覆盖在温暖、含盐的深水单元之上，例如在南极洲的威德尔海。与基于线性状态方程的情景不同，水柱的对流翻转通过热压和二次(斜压)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，倾覆层底部(表面)的斜压性增强。这种加强导致斜压不稳定或斜压不稳定的进一步发展和更有效的垂直热量输送。在后倾覆阶段，表面冷却(对流运动)有两个…在斜压不稳定的发展和相关的热量输送上有更多的相反的操作效应。其中之一是，由于表层对流运动而产生的水平辐合流加强了斜压不稳定，正如以前的研究报告的那样，重点关注中纬度的强层化海洋。这是在斜压性表面增强时观察到的，但在底部加强时观察不到。二是强对流运动使翻转的层在垂直方向上连续均匀，抑制了斜压不稳定。这种影响在强冷却的情况下变得很明显，在以前研究的强烈层化的海洋中没有观察到。因此，垂直热传输在零或低冷却速率(&lt；125Wm^&lt；-2&gt；)时最有效。当斜压性较弱时，如在威德尔海，最有效的输送发生在冷却速率为25wim^-2；这是实际情况下海冰覆盖下的一个可能的值。由于水柱静力稳定性的空间差异而导致的水柱不均匀(部分)倾覆是实际情况下发展斜压不稳定的另一个因素。较少

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