Underlying physical mechanisms of winter precipitation extremes over India's high mountain region
Underlying physical mechanisms of winter precipitation extremes over India's high mountain region
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DOI：
10.1002/qj.4661
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发表时间：
2024-02
影响因子：
8.9
通讯作者：
Nischal;Raju Attada;Kieran M. R. Hunt;Mathew Barlow
中科院分区：
文献类型：
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作者：
Nischal;Raju Attada;Kieran M. R. Hunt;Mathew Barlow
极端降水事件（EPEs）是西喜马拉雅地区（WHR）最普遍的天气灾害之一，对生命、基础设施和农业造成广泛破坏。本研究探讨了与WHR冬季极端降水有关的天气和大尺度特征。epe被认定为超过95个百分位阈值的事件。利用第五代欧洲中期天气预报再分析中心（ERA5）和印度季风资料同化与分析（IMDAA）这两个再分析，采用复合分析来阐明有利于epe的天气条件。我们的研究结果表明，WHR的epe与副热带西风急流增强有关，其特征是比正常情况下向南转移。由于斜压不稳定的增加，对流层上层的动能增强，加强了水汽辐合和天气尺度环流，触发了深层对流，支持了epe。值得注意的是，明显的罗斯比波在西纬向下沉和区域地形的相互作用显著地调节了西部扰动（WDs）的强度。通过聚类分析，我们观察到最强的epe与对流层中上层的异常涡度以及通过增强的WDs产生的深层对流有关，这表明大尺度影响的潜在作用。利用拉格朗日方法，我们确定了阿拉伯海是西白带ep的主要水汽源。我们通过准共振放大（QRA）分析进一步探讨了大规模连接和EPEs的作用。这些发现揭示了经向温度梯度中明显的QRA指纹，以及显著放大的准平稳中纬度行星波，其特征是纬向波数6/7/8（斜压波）有助于epe。总体而言，我们的研究结果突出了冬季极端降水的潜在物理机制，强调了QRA在放大行星波和促进EPEs中的作用，强调了WHR对气候条件演变的脆弱性。
Extreme precipitation events (EPEs) are among the most pervasive weather hazards in the western Himalayan region (WHR), posing widespread damage to life, infrastructure, and agriculture. This study investigates the synoptic and large‐scale characteristics linked to winter precipitation extremes over the WHR. EPEs are identified as events surpassing the 95th percentile threshold. A composite analysis is employed using two reanalyses—the fifth‐generation European Centre for Medium‐Range Weather Forecasts Reanalysis (ERA5) and the Indian Monsoon Data Assimilation and Analysis (IMDAA)—to elucidate the synoptic conditions conducive to EPEs. Our findings suggest that EPEs in the WHR are linked to an intensified subtropical westerly jet, characteristically shifted to south than normal. Enhanced kinetic energy in the upper troposphere, attributed to increased baroclinic instability, reinforces moisture convergence and strengthens synoptic‐scale circulation, triggering deep convection and supporting EPEs. Notably, the interplay of pronounced Rossby waves sinking over the WHR and regional orography significantly modulates the intensity of western disturbances (WDs). Employing clustering analysis, we observed that the strongest EPEs are linked to anomalous vorticity in the upper to middle troposphere, together with deep convection via strengthened WDs, suggesting the potential role of large‐scale influences. Using Lagrangian method, we identify that the Arabian Sea is the primary moisture source for EPEs in the WHR. We further delved into the role of large‐scale connections and EPEs through quasi‐resonant amplification (QRA) analysis. The findings unveil distinct QRA fingerprints in meridional temperature gradients along with notably magnified, quasi‐stationary midlatitude planetary waves characterized by zonal wave numbers 6/7/8 (baroclinic waves) contributing to EPEs. Overall, our results highlight the underlying physical mechanisms for winter precipitation extremes, emphasizing QRA's role in amplifying planetary waves and promoting EPEs, underscoring the WHR's vulnerability to evolving climatic conditions.