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Role of the atmospheric mean state on the initiation of the Madden-Julian oscillation in a tropical channel model

机译：大气平均状态在热带通道模型中马登－朱利安振荡开始的作用

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摘要

Tropical channel models, defined as models that are global in the zonal direction but bounded in the meridional direction, are particularly useful for simulating the Madden-Julian oscillation (MJO) and understanding its physical and dynamical basis. Influences from the extra-tropics through the lateral boundaries have been found to be essential to the reproduction of the initiation of certain MJO events. This led to a hypothesis that multi-year simulations using a tropical channel model would reproduce reasonable MJO statistics under the influence of prescribed lateral boundary conditions derived from global reanalyses. Interestingly, the MJO statistics in such a multi-year simulation by a high-resolution tropical channel model are not better than those from global climate models. The error in the atmospheric mean state is found to be a possible reason for the poor MJO statistics in the simulation. Nevertheless, even with a large error in the mean state, the multi-year simulation captures two MJO events previously found to be initiated by extratropical influences. However, the model does not reproduce a third event, whose initiation is not directly influenced by the extratropics. This implies that in the absence of dynamical interactions between the MJO and the lateral boundary conditions, the error in the meanrnstate could be sufficient to prevent the MJO initiation. To explore this third MJO event further, a series of sensitivity tests are conducted. These tests show that the simulation of this event is neither critically influenced by the cumulus parameterization employed, nor the initial conditions when the model is integrated 2 weeks prior to the MJO initiation. The model captures this event when the MJO signal is already present in the initial conditions. The use of high-resolution sea surface temperature does not improve the simulation of the third MJO event. A higher-resolution nested domain covering the Indo-Pacific warm pool region and including a cloud-system resolving domain over the Indonesian Maritime Continent has little effect on the MJO initiation over the Indian Ocean. In <2 weeks the error in the simulation is comparable to the climate error. The role of the simulated MJO on the mean state is also explored. Implications and limitations of these results are discussed.
机译：热带航道模型定义为在纬向方向上全局但在子午方向上为边界的模型，对于模拟Madden-Julian振荡（MJO）并理解其物理和动力基础特别有用。已经发现，来自温带的通过横向边界的影响对于某些MJO事件的起始再现是必不可少的。这导致一个假设，即使用热带通道模型进行的多年模拟将在从全局重新分析得出的规定的横向边界条件的影响下，重现合理的MJO统计数据。有趣的是，在高分辨率热带通道模型的多年模拟中，MJO统计数据并不比全球气候模型的统计数据更好。发现大气平均状态中的误差是模拟中MJO统计数据不佳的可能原因。然而，即使平均状态存在较大误差，多年模拟也捕获了两个先前被发现由温带影响引发的MJO事件。但是，该模型不会重现第三事件，该事件的起始不受外生性的直接影响。这意味着在MJO和侧向边界条件之间不存在动力相互作用的情况下，均值状态的误差可能足以阻止MJO引发。为了进一步探讨第三次MJO事件，进行了一系列敏感性测试。这些测试表明，此事件的模拟既不受使用的积云参数化的严格影响，也不受模型在MJO启动前2周进行集成时的初始条件的严重影响。当初始条件下已经存在MJO信号时，模型将捕获此事件。高分辨率海面温度的使用不能改善第三次MJO事件的模拟。覆盖印度洋-太平洋暖池区域并包括印度尼西亚海域上空的云系统解析域的高分辨率嵌套域对印度洋上的MJO启动几乎没有影响。在不到2周的时间内，模拟中的误差可与气候误差相媲美。还探讨了模拟MJO在平均状态下的作用。讨论了这些结果的含义和局限性。

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