A case-study of land-atmosphere coupling during monsoon onset in northern India
A case-study of land-atmosphere coupling during monsoon onset in northern India
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印度北部季风爆发期间陆地-大气耦合的案例研究
DOI：
10.1002/qj.3538
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发表时间：
2019
影响因子：
8.9
通讯作者：
Barton E
中科院分区：
文献类型：
--
作者：
Barton E
本文结合研究飞机、卫星产品和模式输出的数据，介绍了季风开始期间一天的陆地-大气案例研究。独特的飞机观测揭示了由土壤湿度空间变化引起的行星边界层温度和湿度差异高达5 K和4 g/kg。发现前期降雨和灌溉都是这种大气变率的驱动因素。也有证据表明土壤水分在某些地表上引起中尺度环流。这是第一次在印度上空观察到这样的反应。土壤水分驱动的温度异常比以前在非洲萨赫勒地区的观测研究中发现的要大。此外，与萨赫勒地区不同，该地区的灌溉范围很广，对大气的影响与之前的降雨相似。这意味着灌溉实践的历史变化可能对印度季风的中尺度过程产生了重要影响。我们还研究了有关土壤湿度和云形成的证据。在较湿润的土壤上，我们观察到浅云的抑制，而深层对流的开始主要发生在受干湿土壤水分边界影响的地区。为了研究土壤水分异质性对大尺度风流的影响，对当天的三种模式描述进行了评估：欧洲中期天气预报中心的ERA - Interim和ERA5再分析，以及使用印度国家中期天气预报中心的区域对流允许统一模式生成的高分辨率（1.5公里）模拟。我们发现有证据表明，模式中的地表通量不确定性导致季风槽中出现~ 3.5 hPa异常。这确实影响了季风环流和降雨的模拟。更好地表示中尺度陆地-大气耦合可能会改善印度天气和气候模式对对流的描述。
This article presents a land–atmosphere case‐study for a single day during monsoon onset, incorporating data from a research aircraft, satellite products and model outputs. The unique aircraft observations reveal temperature and humidity contrasts of up to 5 K and 4 g/kg in the planetary boundary layer induced by spatial variations in soil moisture. Both antecedent rain and irrigation were found to be drivers of this atmospheric variability. There is also evidence of soil moisture‐induced mesoscale circulations above some surfaces. This is the first time such responses have been observedin situover India. Soil moisture‐driven temperature anomalies are larger than those found in previous observational studies in the African Sahel. Moreover, irrigation in the region is extensive, unlike in the Sahel, and has a similar atmospheric effect to antecedent rainfall. This implies that historical changes in irrigation practices are likely to have had an important influence on mesoscale processes within the Indian monsoon. We also examine evidence linking soil moisture and cloud formation. Above wetter soils we observed a suppression of shallow cloud, whilst the initiation of deep convection occurred mostly in areas affected by wet–dry soil moisture boundaries. To investigate the impact of soil moisture heterogeneity on large‐scale wind flow, three model depictions of the day are assessed: the European Centre for Medium‐Range Weather Forecasts ERA‐Interim and ERA5 reanalyses, and a high‐resolution (1.5 km) simulation generated using the Indian National Centre for Medium Range Weather Forecasting regional convection‐permitting Unified Model. We find evidence indicating surface flux uncertainties in the models lead to ∼3.5 hPa anomalies in the monsoon trough. This does affect the simulation of monsoon circulation and rainfall. Better representation of mesoscale land–atmosphere coupling is likely to improve the depiction of convection within weather and climate models over India.