Explorations of the Annual Mean Heat Budget of the Tropical Indian Ocean. Part I: Studies with an Idealized Model
Explorations of the Annual Mean Heat Budget of the Tropical Indian Ocean. Part I: Studies with an Idealized Model
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DOI：
10.1175/jcli4157.1
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发表时间：
2007-07
影响因子：
4.9
通讯作者：
J. S. Godfrey;Ruijin Hu;A. Schiller;R. Fiedler
中科院分区：
文献类型：
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作者：
J. S. Godfrey;Ruijin Hu;A. Schiller;R. Fiedler
与观测结果相比，热带印度洋海洋环流模型（OGCM）的年平均净热通量总体上过低。在模型中，只有部分取代南向埃克曼流出的地转流入的温度低于最低海面温度 (MINSST)。观测到的热通量表明，更多的流入量比 MINSST 更冷。由于 MINSST 以下的流入只能在变热变暖后加入地表埃克曼输运，因此 OGCM 必须低估变热效应。使用矩形盒模型生成了印度洋年平均热量收支的粗略模拟，该模型在其东侧有一个位于南纬 7°–10° 处的深“印度-太平洋”差距。风应力是纬向的并且与科里奥利参数成正比，因此艾克曼输运在空间上是恒定的并且等于斯维尔德鲁普输运。对于三个实验，区域综合埃克曼输运稳定并以 10 Sv (Sv 10 6 m 3 s 1 ) 向南移动。在稳定状态下，一股 10 西弗的“印度尼西亚穿流”供给了 10 西弗的西北边界流，该流沿北纬 10° 的北部边界向东转向，为南行的埃克曼输运提供供给。大多数反热混合发生在西北角的强烈涡流内。一些地转流入的温度低于 MINSST（位于涡流的东北角）；它必须通过绝热混合升温至 MINSST。北部边界上升流超过了 10 Sv Ekman 输送带。多余的热量在涡流周围再循环时会变暖，显然为 MINSST 以下的温暖流入提供了热量。在使用“通量校正输运”（FCT）方案的实验中，涡流周围的强剪切流中发生了过热混合。然而，理查森数从未变得足够低以驱动强烈的透热混合，也许是因为（像其他已发布的模型一样）当前模型的垂直分辨率太粗糙。在三个实验中，主要混合分别是由水平扩散、虚假对流翻转和 FCT 方案调用的数值混合引起的。所有三种混合机制在物理上都是可疑的；在解决观测到的热通量与模拟热通量之间的不匹配问题之前，必须先解决此类模型问题（如果普遍存在）。然而，西边界的密度分布必须是静水稳定的，这一事实对面积积分热通量设置了下限。三个主要实验以及许多已发表的 OGCM 的结果非常接近这个下限。
Annual mean net heat fluxes from ocean general circulation models (OGCMs) are systematically too low in the tropical Indian Ocean, compared to observations. In the models, only some of the geostrophic inflow replacing southward Ekman outflow is colder than the minimum sea surface temperature (MINSST). Observed heat fluxes imply that much more inflow is colder than MINSST. Since inflow below MINSST can only join the surface Ekman transport after diathermal warming, the OGCMs must underestimate diathermal effects. A crude analog of the annual mean Indian Ocean heat budget was generated, using a rectangular box model with a deep “Indo–Pacific” gap at 7°–10°S in its eastern side. Wind stress was zonal and proportional to the Coriolis parameter, so Ekman transport was spatially constant and equaled Sverdrup transport. For three experiments, zonally integrated Ekman transport was steady and southward at 10 Sv (Sv 10 6 m 3 s 1 ). In steady state, a 10 Sv “Indonesian Throughflow” fed a northward western boundary current of 10 Sv, which turned eastward along the northern boundary at 10°N to feed the southward Ekman transport. Most diathermal mixing occurred within an intense eddy in the northwest corner. Some of the geostrophic inflow was at temperatures colder than MINSST (found at the northeast corner of the eddy); it must warm to MINSST via diathermal mixing. Northern boundary upwelling exceeded the 10-Sv Ekman transport. The excess warms as it recirculates around the eddy, apparently supplying the heat to warm inflow below MINSST. In an experiment using the “flux-corrected transport” (FCT) scheme, diathermal mixing occurred in the strongly sheared currents around the eddy. However the Richardson number never became low enough to drive strong diathermal mixing, perhaps because (like that of other published models) the present model’s vertical resolution was too coarse. In three experiments, the dominant mixing was caused by horizontal diffusion, spurious convective overturn, and numerical mixing invoked by the FCT scheme, respectively. All three mixing mechanisms are physically suspect; such model problems (if widespread) must be resolved before the mismatch between observed and modeled heat fluxes can be addressed. However, the fact that the density profile at the western boundary must be hydrostatically stable places a lower limit on the area-integrated heat fluxes. Results from the three main experiments—and from many published OGCMs—are quite close to this lower limit.