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Under the INCOMPASS project, state of the art eddy‐covariance based surface flux measurement systems were installed at eight locations across India. These sites cover different climatic conditions, land use and land cover, and water management practices. Here we present the initial analysis of the measurements taken at seven sites mainly focusing on the year 2017, quantifying for the first time the remarkable contrasts in evaporative fraction across the seasons, climate zones and land management practices of the Indian subcontinent. With the exception of Jaisalmer which is the driest of the places studied, all the sites maintain values of evaporative fraction above 0.5 after the monsoon through to November. By contrast, for those sites with natural vegetation or rain‐fed agriculture, evaporative fraction remains below 0.3 for the dry January–May period. In the middle Gangetic Plain area, irrigation and pre‐monsoon showers together maintain evaporative fraction above 0.5 between January and June. It is also observed that different variables exhibit different intraseasonal variation characteristics even at one site. Except for Samastipur which is situated in the middle Indo‐Gangetic Plains, wind speed shows spectral peak at a smaller time‐scale compared to sensible and latent heat fluxes.

The INCOMPASS field campaign combines airborne and ground measurements of the 2016 Indian monsoon, towards the ultimate goal of better predicting monsoon rainfall. The monsoon supplies the majority of water in South Asia, but forecasting from days to the season ahead is limited by large, rapidly developing errors in model parametrizations. The lack of detailed observations prevents thorough understanding of the monsoon circulation and its interaction with the land surface: a process governed by boundary‐layer and convective‐cloud dynamics. INCOMPASS used the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft for the first project of this scale in India, to accrue almost 100 h of observations in June and July 2016. Flights from Lucknow in the northern plains sampled the dramatic contrast in surface and boundary‐layer structures between dry desert air in the west and the humid environment over the northern Bay of Bengal. These flights were repeated in pre‐monsoon and monsoon conditions. Flights from a second base at Bengaluru in southern India measured atmospheric contrasts from the Arabian Sea, over the Western Ghats mountains, to the rain shadow of southeast India and the south Bay of Bengal. Flight planning was aided by forecasts from bespoke 4 km convection‐permitting limited‐area models at the Met Office and India's NCMRWF. On the ground, INCOMPASS installed eddy‐covariance flux towers on a range of surface types, to provide detailed measurements of surface fluxes and their modulation by diurnal and seasonal cycles. These data will be used to better quantify the impacts of the atmosphere on the land surface, and vice versa. INCOMPASS also installed ground instrumentation supersites at Kanpur and Bhubaneswar. Here we motivate and describe the INCOMPASS field campaign. We use examples from two flights to illustrate contrasts in atmospheric structure, in particular the retreating mid‐level dry intrusion during the monsoon onset.