Climate modeling studies in the context of Indian summer monsoon (ISM) variability have usually been performed on the seasonal and interannual timescales. The present study assesses the fidelity of the Regional Climate Model (RegCM v4.6) in capturing the subseasonal active and break spells along with the seasonal mean rainfall during the ISM season. The model fields are obtained from 24 years (1982–2005) of simulation and validated against the observations and latest reanalyzed ERA5 data products. Our analysis indicates that RegCM v4.6 fairly captures the large scale features of ISM and improvement in seasonal rainfall is noted as compared to its precedent RegCM v4.4. At subseasonal timescales, though the model captures the active and break spells of ISM, the length and frequency of these events seem inconsistent as compared to the observations. Occurrences of breaks and associated circulation features are mostly consistent but the active spells are significantly misconstrued in the model. The dry air intrusion from the western region and lack of monsoon low over the mainland and Bay of Bengal seem to suppress the precipitation in the model. This subseasonal bias might persist due to systematic errors linked to the lack of ocean coupling, inefficiency of land surface and cumulus parameterization schemes in the model. Overall, RegCM v4.6 offers improvements at seasonal timescale but needs further improvements to realistically represent the subseasonal variability of ISM.

在印度夏季风（ISM）变异性背景下的气候模拟研究通常是在季节和年际时间尺度上进行的。本研究评估了区域气候模型（RegCM v4.6）的保真度，以捕获ISM季节的次季节活跃期和中断期以及季节性平均降雨量。该模型字段是从24年（1982-2005年）的模拟中获得的，并根据观察结果和最新重新分析的ERA5数据产品进行了验证。我们的分析表明，RegCM v4.6公平地捕获了ISM的大规模特征，并且与之前的RegCM v4.4相比，注意到了季节性降雨的改善。在亚季节时间尺度上，尽管该模型捕获了ISM的主动和中断时间，但与观测值相比，这些事件的长度和频率似乎不一致。中断的发生和相关的循环特征在大多数情况下是一致的，但是活动咒语在模型中被误解了。来自西部地区的干燥空气入侵以及孟加拉大陆和孟加拉湾缺乏季风低压似乎抑制了该模型的降水。由于与海洋缺乏耦合，地表效率低下以及模型中的积云参数化方案有关的系统错误，这种亚季节偏差可能会持续存在。总体而言，RegCM v4.6在季节性范围内提供了改进，但需要进一步改进以真实地表示ISM的季节变化。来自西部地区的干燥空气入侵以及孟加拉大陆和孟加拉湾缺乏季风低压似乎抑制了该模型的降水。由于与海洋缺乏耦合，地表效率低下以及模型中的积云参数化方案有关的系统错误，这种亚季节偏差可能会持续存在。总体而言，RegCM v4.6在季节性范围内提供了改进，但需要进一步改进以真实地表示ISM的季节变化。来自西部地区的干燥空气入侵以及孟加拉大陆和孟加拉湾缺乏季风低压似乎抑制了该模型的降水。由于与海洋缺乏耦合，地表效率低下以及模型中的积云参数化方案有关的系统错误，这种亚季节偏差可能会持续存在。总体而言，RegCM v4.6在季节性范围内提供了改进，但需要进一步改进以真实地表示ISM的季节变化。