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首页> 外文期刊>Theoretical and applied climatology >Monsoon circulation interaction with Western Ghats orography under changing climate: Projection by a 20-km mesh AGCM
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Monsoon circulation interaction with Western Ghats orography under changing climate: Projection by a 20-km mesh AGCM

机译：气候变化下季风环流与西高止山脉地形的相互作用：20公里网状AGCM的投影

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摘要

In this study, the authors have investigated the likely future changes in the summer monsoon over the Western Ghats (WG) orographic region of India in response to global warming, using time-slice simulations of an ultra high-resolution global climate model and climate datasets of recent past. The model with approximately 20-km mesh horizontal resolution resolves orographic features on finer spatial scales leading to a quasi-realistic simulation of the spatial distribution of the present-day summer monsoon rainfall over India and trends in monsoon rainfall over the west coast of India. As a result, a higher degree of confidence appears to emerge in many aspects of the 20-km model simulation, and therefore, we can have better confidence in the validity of the model prediction of future changes in the climate over WG mountains. Our analysis suggests that the summer mean rainfall and the vertical velocities over the orographic regions of Western Ghats have significantly weakened during the recent past and the model simulates these features realistically in the present-day climate simulation. Under future climate scenario, by the end of the twenty-first century, the model projects reduced orographic precipitation over the narrow Western Ghats south of 16°N that is found to be associated with drastic reduction in the southwesterly winds and moisture transport into the region, weakening of the summer mean meridional circulation and diminished vertical velocities. We show that this is due to larger upper tropospheric warming relative to the surface and lower levels, which decreases the lapse rate causing an increase in vertical moist static stability (which in turn inhibits vertical ascent) in response to global warming. Increased stability that weakens vertical velocities leads to reduction in large-scale precipitation which is found to be the major contributor to summer mean rainfall over WG orographic region. This is further corroborated by a significant decrease in the frequency of moderate-to-heavy rainfall days over WG which is a typical manifestation of the decrease in large-scale precipitation over this region. Thus, the drastic reduction of vertical ascent and weakening of circulation due to 'upper tropospheric warming effect' predominates over the 'moisture buildup effect' in reducing the rainfall over this narrow orographic region. This analysis illustrates that monsoon rainfall over mountainous regions is strongly controlled by processes and parameterized physics which need to be resolved with adequately high resolution for accurate assessment of local and regional-scale climate change.
机译：在这项研究中，作者使用超高分辨率全球气候模型和气候数据集的时间切片模拟，研究了印度西高止山脉（WG）地形区域夏季季风可能响应全球变暖的未来变化。最近的过去。该模型具有约20 km的网格水平分辨率，可在更精细的空间尺度上解析地形特征，从而对印度夏季季风降雨的空间分布以及印度西海岸季风降雨的趋势进行了准真实的模拟。结果，在20公里模型模拟的许多方面似乎都出现了较高的置信度，因此，我们可以对模型预测在WG山地气候的未来变化的有效性方面具有更好的置信度。我们的分析表明，在最近的过去，西高止山脉地形区域的夏季平均降雨量和垂直速度明显减弱，该模型在当今的气候模拟中实际模拟了这些特征。在未来的气候情景下，到21世纪末，该模型预测了16°N以南的狭窄西高止山脉的地形降水减少，这与西南风和向该地区的水分输送的急剧减少有关夏季减弱意味着平均子午环流和垂直速度减小。我们表明，这是由于相对于地表较高的对流层上层暖化程度较高和较低的水平，这降低了流逝速率，从而导致响应全球变暖而增加了垂直湿静态稳定性（进而抑制了垂直上升）。增加的稳定性会减弱垂直速度，导致大范围降水的减少，这是造成WG地形区域夏季平均降雨量的主要原因。 WG上中度到重度降雨天数的显着减少进一步证实了这一点，这是该地区大规模降水减少的典型表现。因此，“对流层上部变暖效应”引起的垂直上升的急剧下降和环流减弱的影响大于“湿气积聚效应”，从而减少了该狭窄地形区域的降雨。该分析表明，山区的季风降雨受过程和参数化物理学的强烈控制，需要以足够高的分辨率解决该问题，以准确评估局部和区域尺度的气候变化。

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  • 来源
    《Theoretical and applied climatology》 |2012年第4期|555-571|共17页
  • 作者

    K. Rajendran; A. Kitoh; J. Srinivasan; R. Mizuta; R. Krishnan;

  • 作者单位

    CSIR Centre for Mathematical Modelling & Computer Simulation, NAL Belur, Bangalore 560037, India;

    Meteorological Research Institute/Japan Meteorological Agency, Tsukuba 3050052, Japan;

    Divecha Centre for Climate Change, Indian Institute of Science, Bangalore 560012, India;

    Meteorological Research Institute/Japan Meteorological Agency, Tsukuba 3050052, Japan;

    Centre for Climate Change Research, Indian Institute of Tropical Meteorology, Pune 411008, India;

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