The role of mid-tropospheric moistening and land-surface wetting in the progression of the 2016 Indian monsoon
The role of mid-tropospheric moistening and land-surface wetting in the progression of the 2016 Indian monsoon
复制标题
对流层中层湿润和陆地表面湿润在 2016 年印度季风进展中的作用
DOI：
10.1002/qj.4183
复制
发表时间：
2021
影响因子：
8.9
通讯作者：
Menon A
中科院分区：
文献类型：
--
作者：
Menon A
准确地预测印度季风是有限的了解不足的基本过程，这会导致系统的模式偏差。在这里，我们的目标是了解与季风进展相关的动力学和热力学特征，使用2016年作为代表性年份，借助气象局统一模型的对流允许模拟。模拟是在一个4 km分辨率的有限区域模式中进行的，该模式嵌套在一个较粗糙的全球模式中。影响季风向西北方向发展的两个主要过程是：（a）低层季风气流和来自西北方向的对流层中层干空气入侵之间的相互作用，以及（B）陆-气相互作用。我们发现，4公里的有限区域模式模拟对流层中层增湿，侵蚀西北干入侵，推动湿对流的北方限制西北。表层土壤湿度在季风发展的前沿也起着重要作用。与当地发病相关的暴雨湿润了土壤，降低了地表通量对土壤湿度的敏感性，并削弱了陆地对季风降雨进一步发展的影响。4 km模式与一个替代的陆面配置进行了测试，以探索其对陆面过程的敏感性。我们发现，土壤和植被的选择影响土壤水分-降水反馈的时间尺度和日对流的时间，从而影响当地的发病。我们进一步比较这些模拟与参数化对流运行在17公里的分辨率隔离对流参数化和分辨率的影响。显式对流模式较好地模拟了季风发展的动力和热力特征。
Accurately predicting the Indian monsoon is limited by inadequate understanding of the underlying processes, which feed into systematic model biases. Here we aim to understand the dynamic and thermodynamic features associated with the progression of the monsoon, using 2016 as a representative year, with the help of convection‐permitting simulations of the Met Office Unified Model. Simulations are carried out in a 4 km resolution limited‐area model, nested within a coarser global model. Two major processes thought to influence the northwestward progression of the monsoon are: (a) the interaction between the low‐level monsoon flow and a mid‐tropospheric dry‐air intrusion from the northwest, and (b) land–atmosphere interactions. We find that the 4 km limited‐area model simulates the mid‐tropospheric moistening that erodes the northwesterly dry intrusion, pushing the northern limit of moist convection northwestwards. The surface soil moisture also plays a major role at the leading edge of the monsoon progression. The heavy rains associated with the local onset wet the soil, reducing the sensitivity of surface fluxes to soil moisture and weakening the land influence on further progression of monsoon rains. The 4 km model is tested with an alternative land‐surface configuration to explore its sensitivity to land‐surface processes. We find that the choice of soil and vegetation ancillaries affects the time‐scales of soil moisture–precipitation feedback and the timing of diurnal convection, thereby affecting the local onset. We further compare these simulations with a parametrized convection run at 17 km resolution to isolate the effects of convective parametrization and resolution. The model with explicit convection better simulates the dynamic and thermodynamic features associated with the progression of the monsoon.