The South Asian summer monsoon provides 80% of annual precipitation to over a billion people. Among other users of water resources, the monsoon is particularly important for agriculture and power generation, itself in support of food security and employment. Accurate prediction of the amount and timing of monsoon rainfall is vital to society across many time‐scales, from daily weather forecasting up to multi‐decadal changes in the mean state. While much research continues into monsoon modelling and prediction, large model biases prevail. A key opportunity lies in better measurement and understanding of processes operating at small space and time scales, particularly interactions between the surface, boundary layer and cloud dynamics which profoundly influence monsoon convection. These processes are often parametrized in models.

It is against this background that the Earth System Science Organization (ESSO) of the Ministry of Earth Sciences (MoES), Govt. India, in collaboration with the Natural Environment Research Council (NERC), United Kingdom, funded the Drivers of variability in the South Asian monsoon programme. For NERC, this was part of a larger NERC action on “Drivers of variability in atmospheric circulation”, while for ESSO‐MoES, this activity fell under its Monsoon Mission to improve prediction of the monsoon on short‐range to interannual time‐scales.

This funding avenue provided the unique opportunity for the Indo‐UK scientific community to collaborate on a joint observational mission to India (described in Turner et al., 2020), including the first deployment of a foreign atmospheric research aircraft to the country. The INCOMPASS aircraft mission, from bases in Lucknow and Bengaluru, took place between May and July 2016 using the Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft, run jointly by NERC and the Met Office. This is a four‐engine jet aircraft, capable of carrying a large suite of instruments and up to 19 scientists on missions lasting up to 5 hours. Use of the aircraft was shared with the sister project SWAAMI (South West Asian Aerosol–Monsoon Interactions: see, for example, Brooks et al., 2019).

As described in the lead article of this Special Collection (Turner et al., 2020), the INCOMPASS field campaign is designed to better understand how an air parcel is modified as it travels towards India, crossing coastlines, mountains and a variety of land surface types and soil moisture patterns. Work motivated by INCOMPASS and published in this Special Collection has already suggested a new paradigm for the monsoon onset (Parker et al., 2016), as a tug‐of‐war between advancing tropical flow and a retreating dry intrusion emanating northwest of India. The erosion of this dry intrusion has been shown in modelling work to be aided by the detrainment of moisture from shallow convection (Menon et al., 2018), while the role of the extratropics has been further highlighted (Volonté et al., 2020), showing that monsoon progression is a jerky process.

While other monsoon processes such as ocean–atmosphere interaction have been heavily studied in the past, the role of the land surface is often overlooked. In particular, how the land surface feeds back on the progression of the monsoon through its seasonal cycle, or during monsoon variability, is ripe for study since there is a distinct lack of observations particularly related to the land surface and its role in driving convection over India. For this reason, INCOMPASS set out to plug the gap by installing a series of flux towers across the country (early results described in Bhat et al., 2020). By bringing together their outputs (e.g. latent‐heat flux) with traditional meteorological instrumentation, profiles and transects of the atmosphere overhead taken from the flight missions, INCOMPASS aims to interrogate the land–atmosphere interactions during monsoon convection.

This INCOMPASS Special Collection covers the first observational and modelling results of INCOMPASS. The process understanding developed through this work and ongoing analysis of the INCOMPASS observations will highlight the need for improved parametrizations to be developed and more observations to be assimilated in forecast models. Other work published so far in the Special Collection includes a description of the modelling and forecast tools employed in guiding the flight missions (Martin et al., 2020) and an evaluation of convective‐scale model performance in comparison to flight observations (Jayakumar et al., 2020). There is a proof‐of‐concept of the importance of mesoscale soil moisture gradients over northern India in initiating convection, based on flight observations and modelling (Barton et al., 2020), and the new identification of distinct regimes of onshore and offshore convection around the Western Ghats, based on flight and flux‐tower measurements (Fletcher et al., 2020) which could lead to new insights in forecasting.

As reported in Turner et al. (2020), INCOMPASS has highlighted the need to fully characterize the convective life cycle over India and how it changes under different conditions, whether by meteorological forcing at the large scale or by underlying surface conditions. Given the findings of strong land–atmosphere coupling in action during the monsoon, INCOMPASS has led new hypotheses to be tested on how irrigation affects the progression of the monsoon and its day‐to‐day variability. The INCOMPASS field campaign observations will serve as a starting point that, in combination with further observations and long‐term data from remote‐sensing and reanalysis products, will enable progress to be made in parametrization development and improving model biases.

南亚夏季风为超过十亿人口提供了80％的年降水量。在其他水资源使用者中，季风对农业和发电业特别重要，它本身就支持粮食安全和就业。从每日天气预报到平均状态的数十年变化，准确预测季风雨量和降雨时间对社会而言在许多时间尺度上都是至关重要的。尽管对季风模型和预测的研究仍在继续，但普遍存在较大的模型偏差。一个关键机遇在于更好地测量和理解在小空间和小规模运行的过程，尤其是深深影响季风对流的地表，边界层和云动力学之间的相互作用。这些过程通常在模型中参数化。

在这种背景下，政府地球科学部（MoES）的地球系统科学组织（ESSO）。印度与英国自然环境研究委员会（NERC）合作，为南亚季风计划的可变性驱动因素提供了资金。对于NERC，这是NERC针对“大气循环变化的驱动因素”采取的一项较大行动的一部分，而对于ESSO-Mo​​ES，这项活动属于其季风任务，目的是改善对短时到年际时标的季风预报。

这一筹资渠道为印欧科学界提供了一次独特的机会，以合作开展对印度的联合观测任务（特纳等人，2020年进行了描述），包括首次向该国部署外国大气研究飞机。INCOMPASS飞机任务于2016年5月至7月在勒克瑙和班加罗尔基地进行，使用了由NERC和Met Office联合运营的机载大气测量设施（FAAM）BAe-146飞机。这是一架四引擎喷气式飞机，能够携带一大套仪器，最多可容纳19名科学家，任务持续5个小时。该飞机的使用与姊妹项目SWAAMI（西南气溶胶-季风相互作用：例如参见Brooks）共享。等人，2019）。

如本特别收藏的主要文章所述（Turner et al。，  2020），INCOMPASS野战活动旨在更好地了解飞机在向印度行驶，穿越海岸线，山脉和各种陆地的过程中如何进行修改类型和土壤水分模式。由INCOMPASS推动并发表在本特别收藏中的工作已经提出了季风发作的新范式（Parker等人，  2016年），认为这是推进热带气流与印度西北部撤退的干侵入之间的拉锯战。这种干侵入的侵蚀已在建模工作中得到证明，这是由于浅层对流中水分的流失而引起的（Menon等人， 2018），而温带的作用被进一步强调（Volontéet al。，  2020），表明季风的发展是一个生涩的过程。

过去曾对其他季风过程（如海洋与大气的相互作用）进行过深入研究，但常常忽略了地表的作用。特别是，由于缺乏明显的观测结果，特别是与地表及其在驱动对流中的作用有关的观测资料，地表如何通过季风在整个季节周期或季风变化过程中的反馈是成熟的。印度。因此，INCOMPASS开始在全国范围内安装一系列的通量塔来填补这一空白（Bhat等人，2020年描述了早期结果）。）。通过将其输出（例如潜热通量）与传统的气象仪器，飞行任务中获取的大气开销的剖面和横断面相结合，INCOMPASS的目的是在季风对流过程中询问陆地与大气之间的相互作用。

该INCOMPASS特别收藏涵盖了INCOMPASS的首次观测和建模结果。通过这项工作以及对INCOMPASS观测值的持续分析而形成的过程理解将凸显出需要开发改进的参数化并在预测模型中吸收更多观测值的需求。迄今为止，在“特别收藏”中发表的其他工作包括对用于指导飞行任务的建模和预测工具的描述（Martin等人，  2020年），以及对流尺度模型性能与飞行观测结果相比的评估（Jayakumar等人）。。，  2020）。基于飞行观测和建模（Barton等人，2020年）以及对陆上和海上对流不同模式的新识别，印度北部中尺度土壤水分梯度在启动对流中的重要性得到了概念验证。 基于飞行和通量塔的测量结果（Fletcher等人，2020年）在西高止山脉周围， 这可能会为预测带来新的见解。

如特纳等人报道。（2020年），INCOMPASS强调了对印度对流生命周期及其在不同条件下如何变化的特征进行全面描述的必要性，无论是通过大规模的气象强迫还是潜在的地表条件。鉴于季风期间陆地与大气之间存在强烈的耦合作用，INCOMPASS提出了新的假设，以检验灌溉如何影响季风的发展及其日常变化。INCOMPASS野外活动观测将作为起点，与进一步的观测和遥感和再分析产品的长期数据相结合，将使参数化开发和改善模型偏差取得进展。