Multiscale Processes Leading to Heavy Precipitation in the Eastern Nepal Himalayas
Multiscale Processes Leading to Heavy Precipitation in the Eastern Nepal Himalayas
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导致尼泊尔东部喜马拉雅山脉强降水的多尺度过程
DOI：
10.1175/jhm-d-22-0080.1
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发表时间：
2023
影响因子：
3.8
通讯作者：
Fujita Koji
中科院分区：
文献类型：
--
作者：
Hirata Hidetaka;Fujinami Hatsuki;Kanamori Hironari;Sato Yota;Kato Masaya;Kayastha Rijan B.;Shrestha Madan L.;Fujita Koji
尽管喜马拉雅山高海拔地区的暴雨过程很重要，但人们仍然不太清楚。在这里，我们研究的详细过程，造成强降雨事件，我们的雨量计网络在Rolwaling山谷，尼泊尔喜马拉雅山脉东部，使用ERA 5和区域云解析数值模拟。2019年7月8日，在东港（海拔2790米）观测到强降水（112毫米日-1）。大部分降水（81毫米）发生在当地时间1900-2300（LT）。天气尺度环境的特点是印度东北部的季风低压系统（LPS）。LPS将对流层低层的水汽向上抬升，然后在对流层中层水平输送到尼泊尔喜马拉雅山脉东部，增加了东港附近的水汽含量。强降水发生前后，东港上空有一个中尺度对流系统经过。数值模拟结果表明，到1900 LT为止，在东港上风侧山脊附近，对流层中层（约500 hPa）东南风气流与LPS共同作用下，地面热通量占主导地位，增强了对流不稳定性。地形抬升导致增强的不稳定性释放，触发了中尺度降水系统的发展。2000-2200 LT期间，东南风将降水系统推向北方，并经过东港，造成强降水。因此，我们得出的结论是，强降水来自多尺度过程，如三维水汽输送驱动的LPS和热通量的日变化，从陆面.Significance StatementPrecipitation在喜马拉雅山脉是密切相关的水文循环，洪水，滑坡灾害在南亚。因此，阐明喜马拉雅山的降水特征是重要的。这项研究探讨了导致2019年7月8日在尼泊尔喜马拉雅山脉东部Rolwaling山谷的Dongang观测到的强降水事件的多尺度过程。我们确定了新的过程产生强降水在喜马拉雅山：三维天气尺度的水汽输送驱动的季风低压系统和热通量的日变化从陆地表面的发展和运动的中尺度降水系统造成强降水的影响。这些发现拓宽了我们对喜马拉雅山强降水的理解。
The processes underlying heavy rainfall in the higher elevations of the Himalayas are still not well known despite their importance. Here, we examine the detailed process causing a heavy rainfall event, observed by our rain gauge network in the Rolwaling valley, eastern Nepal Himalayas, using ERA5 and a regional cloud-resolving numerical simulation. Heavy precipitation (112 mm day−1) was observed on 8 July 2019 at Dongang (2790 m above sea level). Most of the precipitation (81 mm) occurred during 1900–2300 local time (LT). The synoptic-scale environment is characterized by a monsoon low pressure system (LPS) over northeastern India. The LPS lifted moisture upward from the lower troposphere and then horizontally transported it into the eastern Nepal Himalayas within the middle troposphere, increasing the content of the water vapor around Dongang. A mesoscale convective system passed over Dongang around the time of the intense precipitation. The numerical simulation showed that surface heat fluxes prevailed under the middle tropospheric (∼500 hPa) southeasterly flow associated with the LPS around a mountain ridge on the upwind side of Dongang until 1900 LT, enhancing convective instability. Topographic lifting led to the release of the enhanced instability, which triggered the development of a mesoscale precipitation system. The southeasterly flow pushed the precipitation system northward, which then passed over Dongang during 2000–2200 LT, resulting in heavy precipitation. Thus, we conclude that the heavy precipitation came from the multiscale processes such as three-dimensional moisture transport driven by the LPS and the diurnal variation in heat fluxes from the land surface.Significance StatementPrecipitation in the Himalayas is closely related to the hydrological cycle, floods, and landslide disasters in South Asia. Thus, elucidating the features of precipitation in the Himalayas is important. This study explored multiscale processes leading to a heavy precipitation event that was observed on 8 July 2019 at Dongang in the Rolwaling valley of the eastern Nepal Himalayas. We identified new processes producing heavy precipitation in the Himalayas: the three-dimensional synoptic-scale moisture transport driven by a monsoon low pressure system and the effect of the diurnal variation in heat fluxes from the land surface on the development and movement of a mesoscale precipitation system causing heavy precipitation. These findings broaden our understanding of heavy precipitation in the Himalayas.