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Simulations of the Madden-Julian oscillation in four pairs of coupled and uncoupled global models

机译：四对耦合和非耦合全局模型中Madden-Julian振荡的仿真

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The status of the numerical reproduction of the Madden-Julian Oscillation (MJO) by current global models was assessed through diagnoses of four pairs of coupled and uncoupled simulations. Slow eastward propagation of the MJO, especially in low-level zonal wind, is realistic in all these simulations. However, the simulated MJO suffers from several common problems. The MJO signal in precipitation is generally too weak and often eroded by an unrealistic split of an equatorial maximum of precipitation into a double ITCZ structure over the western Pacific. The MJO signal in low-level zonal wind, on the other hand, is sometimes too strong over the eastern Pacific but too weak over the Indian Ocean. The observed phase relationship between precipitation and low-level zonal wind associated with the MJO in the western Pacific and their coherence in general are not reproduced by the models. The seasonal migration in latitude of MJO activity is missing in most simulations. Air-sea coupling generally strengthens the simulated eastward propagating signal, but its effects on the phase relationship and coherence between precipitation and low-level zonal wind, and on their geographic distributions, seasonal cycles, and interannual variability are inconsistent among the simulations. Such inconsistency cautions generalization of results from MJO simulations using a single model. In comparison to observations, biases in the simulated MJO appear to be related to biases in the background state of mean precipitation, low-level zonal wind, and boundary-layer moisture convergence. This study concludes that, while the realistic simulations of the eastward propagation of the MJO are encouraging, reproducing other fundamental features of the MJO by current global models remains an unmet challenge.
机译：通过诊断四对耦合和非耦合模拟，评估了当前全局模型对Madden-Julian振荡（MJO）数值再现的状态。在所有这些模拟中，MJO向东的缓慢传播，特别是在低纬向风中，都是现实的。但是，模拟的MJO遇到几个常见问题。降水中的MJO信号通常太弱，经常被西太平洋上空的赤道最大降水不切实际地分裂成双重ITCZ结构所侵蚀。另一方面，在低纬向风中的MJO信号有时在东太平洋上太强，但在印度洋上太弱。该模型没有再现观测到的降水和与西太平洋MJO相关的低空纬向风之间的相位关系及其一般的连贯性。大多数模拟都缺少MJO活动纬度的季节性迁移。气海耦合通常会增强模拟的向东传播的信号，但在模拟之间并不一致，它对降水和低层纬向风之间的相位关系和相干性及其地理分布，季节周期和年际变化没有影响。这种不一致警告了使用单个模型的MJO仿真结果的一般化。与观测结果相比，模拟MJO中的偏差似乎与平均降水，低层纬向风和边界层水分会聚的背景状态下的偏差有关。这项研究得出的结论是，尽管对MJO向东传播的现实模拟令人鼓舞，但通过当前的全球模型重现MJO的其他基本特征仍然是一个未得到满足的挑战。

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