首页> 外文期刊>International Journal of Climatology: A Journal of the Royal Meteorological Society >Twice wind onsets of monsoon over the western North Pacific and their simulations in AMIP models
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Twice wind onsets of monsoon over the western North Pacific and their simulations in AMIP models

机译:北太平洋西部两次季风爆发及其在AMIP模型中的模拟

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摘要

The absolute angle between wind vectors is used to investigate and describe the seasonal evolutions of wind direction, which is able to indicate the abrupt seasonal shift and stable seasonal state of winds. The results show that the wind directions over the western North Pacific (WNP, 10 degrees-22.5 degrees N, 125 degrees-145 degrees E) undergo two abrupt changes and three stable states from winter to summer. Here we name the phenomenon as twice wind onsets of monsoon. The first wind onset occurs near mid-May at 15 degrees N, and the second one happens with the wind direction shifting southwesterly in mid-July and ends in late September. The variations of Outgoing Longwave Radiation (OLR) and rainfall in the northward 5 latitudes of the neighbouring region show similar abrupt features as those of the twice wind onsets. The western Pacific subtropical high (WPSH) retreats eastward in the second stable state (pentad 29 to 37), which differs from the first stable state (pentad 1 to 24). As the strong cross-equator flows from the Southern Hemisphere reach the WNP, the eastward retreat of WPSH consequently triggers the first wind onset. Then the WPSH ridge suddenly jumps to 30 degrees N and results in the second wind onset. Meanwhile, the propagation of the second wind onset is consistent with the migration of the WNP monsoon trough. Seven atmospheric general circulation models (AGCMs) of Atmospheric Model Intercomparison Project (AMIP) from Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are validated against the observations mentioned earlier. The results show that there are still notable shortcomings for the models to simulate the WNP summer monsoon, especially the twice onsets. There is no significant improvement for the simulation of multi-models ensemble mean. Only MPI-ECHAM5 captures partial characteristics of similar pattern. The poor simulation of the migration of the WPSH ridge and monsoon trough may be important factors for the shortcomings. Moreover, none of the models reproduces corresponding rainfall patterns over the WNP.
机译:利用风向矢量之间的绝对角度来研究和描述风向的季节变化,从而可以表明风的突变性和季节性的稳定状态。结果表明,从冬季到夏季,北太平洋西部(WNP,北纬10度至22.5度,东经125度至145度)的风向经历了两次突变和三个稳定状态。在这里,我们将该现象称为季风的两次起风。第一次风爆发发生在五月中旬,大约是北纬15度,第二次风爆发是在7月中旬,风向偏西南,到9月下旬结束。邻近地区北5个纬度的呼出长波辐射(OLR)和降雨的变化与两次风爆发的突变特征相似。西太平洋副热带高压(WPSH)在第二稳定状态(五单元组29至37)向东后退,该状态不同于第一稳定状态(五单元组1至24)。随着强大的赤道流从南半球到达WNP,WPSH的向东撤退因此触发了第一次风爆发。然后,WPSH脊突然跳至30度N并导致第二次起风。同时,第二次风爆发的传播与WNP季风槽的迁移一致。政府间气候变化专门委员会(IPCC)第四次评估报告(AR4)的大气模型比对项目(AMIP)的七个大气总循环模型(AGCM)已根据前面提到的观察结果进行了验证。结果表明,模拟WNP夏季风的模型仍存在明显的缺陷,尤其是两次发作。多模型集合均值的模拟没有显着改善。仅MPI-ECHAM5捕获相似模式的部分特征。 WPSH脊和季风槽迁移的模拟效果不佳可能是造成这一缺点的重要因素。此外,没有一个模型能够再现WNP上的相应降雨模式。

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