The neglected Indo-Gangetic Plains low-level jet and its importance for moisture transport and precipitation during the peak summer monsoon
The neglected Indo-Gangetic Plains low-level jet and its importance for moisture transport and precipitation during the peak summer monsoon
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DOI：
10.1002/2017gl074440
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发表时间：
2017-08-28
影响因子：
5.2
通讯作者：
Huber, M.
中科院分区：
文献类型：
--
作者：
Acosta, R. P.;Huber, M.
使用大气环流模式（AGCMs）精确模拟印度-亚洲季风（IAM）是一项具有挑战性但至关重要的工作。本研究使用再分析产品欧洲中期预报中心中期再分析，日本再分析年55，高亚洲再分析突出东风，低层障碍射流沿着印度-恒河平原（简称IG LLJ），我们确定为主要的水分输送机制的东北分支的IAM。我们发现，NCAR家庭的AGCM（社区大气模型（CAM））不捕捉这种流通，直到1/2度或更大的空间水平分辨率使用。IG LLJ的发展是由于一个以恒河盆地为中心的持续低压系统，并由喜马拉雅山脉增强。使用非绝热加热率和湿弗劳德数作为诊断，我们发现，在CAM，这分支的IAM显示两个不同的动力学制度作为分辨率的函数。在低分辨率下，喜马拉雅山附近的大气是静态不稳定的，非绝热加热很强，水汽流从阿拉伯海向西南方向移动，并在地形上移动（畅通无阻）。在高分辨率下，喜马拉雅山附近的湿静态稳定度是稳定的，非绝热加热是弱的，和流动主要进入东风从孟加拉湾和平行于地形（阻塞）。在夏季，低分辨率CAM被锁定到畅通的模式，这对解释地形季风相互作用有严重的影响。在更广泛的背景下，我们证明了超过一半的CMIP 5模型没有捕获IG LLJ，这进一步突出了整个IAM地区的模型数据不匹配。
Accurately simulating the Indo-Asian monsoon (IAM) using atmospheric general circulation models (AGCMs) is challenging but crucial. This study uses reanalysis products European Centre of Medium-Range Forecast Interim reanalysis, Japanese Reanalysis year 55, and High Asia Reanalysis to highlight an easterly, low-level barrier jet along the Indo-Gangetic Plain (referred from here as IG LLJ), which we identify as the primary moisture transport mechanism for the northeastern branch of the IAM. We show that the NCAR family of AGCMs (Community Atmospheric Model (CAM)) does not capture this circulation until 1/2 degrees or greater spatial horizontal resolution is used. The IG LLJ develops due to a persistent low-pressure system centered over the Ganges basin and is enhanced by the Himalayas. Using diabatic heating rates and the moist Froude number as diagnostics, we find that in CAM, this branch of the IAM displays two different dynamical regimes as a function of resolution. At low resolution, the atmosphere near the Himalayas is statically unstable, diabatic heating is strong, and the moisture flow is southwesterly from the Arabian Sea and moves over the terrain (unblocked). At high resolution, the moist static stability near the Himalayan Mountains is stable, diabatic heating is weak, and the flow primarily enters easterly from the Bay of Bengal and moves parallel to the terrain (blocked). During the summer season, the low-resolution CAM is locked into the unblocked mode, which has serious implications for interpreting topography-monsoon interactions. For a broader context, we demonstrate that more than half of the CMIP5 models do not capture the IG LLJ, which further highlights model-data mismatch across the IAM region.