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Sub-seasonal interannual variability associated with the excess and deficit Indian winter monsoon over the Western Himalayas

机译：与西喜马拉雅山印度冬季季风过多和不足相关的亚季节年际变化

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摘要

During the winter season (Dec, Jan., and Feb.; DJF) the western Himalaya (WH) receives one-third of its annual precipitation due to Indian winter monsoon (IWM). The IWM is characterized by eastward-moving synoptic weather systems called western disturbances. Seasonal interannual precipitation variability is positively correlated with monthly interannual variabilities. However, it was found that the monthly interannual variabilities differ. The interannual variability for Jan. is negatively correlated with that for Dec. and Feb. Because the entire seasonal interannual variability is in phase with the El Nino Southern Oscillation, it is interesting to investigate such contrasting behavior. Composite analysis based on extreme wet and dry seasons indicates that Dec. and Feb. precipitation variabilities have a high positive (low negative) correlation with eastern (western) equatorial Pacific warming (cooling), whereas Jan. precipitation variability exhibits negligible correlations. Seasonal mid/upper tropospheric cooling over the Himalayas enhances anomalous cyclonic circulation, which along with suppressed convection over the western equatorial Pacific, shifts the 200-hPa subtropical westerly jet southward over the Himalayas. Due to the upper tropospheric anomalous cyclonic circulation, mass transfer favors anticyclone formation at the mid/lower troposphere, which is enhanced in Jan. due to a wanner mid troposphere and hence decreases precipitation compared with Dec. and Feb. Additionally, a weakening of meridional moisture flux transport from the equatorial Indian Ocean to WH is observed in Jan. Further analysis reveals that mid-tropospheric and surface temperatures over WH also play dominant roles, acting as local forcing where the preceding month's surface temperature controls the succeeding month's precipitation.
机译：在冬季（十二月，一月和二月； DJF），由于印度冬季风（IWM），喜马拉雅西部（WH）的年降水量达到三分之一。 IWM的特征是向东移动的天气天气系统称为西方干扰。季节性的年际降水变化与月度的年际变化呈正相关。但是，发现每月的年际变化是不同的。 1月的年际变化与12月和2月的年际变化呈负相关。由于整个季节的年际变化与厄尔尼诺南方涛动同步，因此研究这种对比行为很有趣。基于极端湿季和干季的综合分析表明，12月和2月的降水变化与东部（西部）赤道太平洋变暖（降温）具有较高的正（低负）相关性，而1月的降水变化具有可忽略的相关性。喜马拉雅山脉上空的对流层中/上层季节性冷却增强了气旋异常循环，加上赤道西太平洋对流受到抑制，使200-hPa副热带西风急流向南移动。由于对流层高层异常气旋环流，传质有利于对流层中低层的反气旋形成。由于对流层中层的减弱，1月由于对流层中层的减弱而使反气旋形成，因此与12月和2月相比，降水减少。一月份观察到从赤道印度洋到WH的湿通量传输。进一步的分析表明，WH上的对流层中部和地表温度也起主要作用，这是局部强迫，其中前一个月的地表温度控制着随后一个月的降水。

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