1 The Regional Coupled Suite (RCS-IND1): application of a flexible regional coupled modelling framework to the Indian region at km- scale Juan M. Castillo 1 , Huw W. Lewis 1 , Akhilesh Mishra 2 , Ashis Mitra 2 , Jeff Polton 3 , Ashley Brereton 3 , Andrew Saulter 1 , Alex Arnold 1 , Segolene Berthou 1 , Douglas Clark 4 , Julia Crook 5 , Ananda Das 6 , John 5 Edwards 1 , Xiangbo Feng 7 , Ankur Gupta 2 , Sudheer Joseph 8 , Nicholas Klingaman 7 , Imranali Momin 2 , Christine Pequignet 1 , Claudio Sanchez 1 , Jennifer Saxby 5 , Maria Valdivieso da Costa 7 1 Met Office, Exeter, EX1 3PB, UK 2 National Centre for Medium Range Weather Forecasting (NCMRWF), India 3 National Oceanography Centre, Liverpool, UK 10 4 UK Centre of Ecology & Hydrology (UKCEH), UK 5 University of Leeds, UK 6 India Meteorological Department (IMD), India 7 University of Reading, UK 8 INCOIS, India 15 Correspondence to: Juan M. Castillo (juan.m.castillo@metoffice.gov.uk) Abstract. A new regional coupled modelling framework is introduced - the Regional Coupled Suite (RCS). This provides a flexible research capability with which to study the interactions between atmosphere, land, ocean and wave processes resolved at km-scale, and the effect of environmental feedbacks on the evolution and impacts of multi-hazard weather events. A 20 configuration of the RCS focussed on the Indian region, termed RCS-IND1, is introduced. RCS-IND1 includes a regional configuration of the Unified Model (UM) atmosphere, directly coupled to the JULES land surface model, on a grid with horizontal spacing of 4.4 km, enabling convection to be explicitly simulated. These are coupled through OASIS3-MCT libraries to 2.2 km grid NEMO ocean and WAVEWATCH III wave model configurations. To examine a potential approach to reduce computation cost, and simplify ocean initialisation, the RCS includes an alternative approach to couple the 25 atmosphere to a 1ower resolution Multi-Column K Profile Parameterization (KPP) for the ocean. Through development of a flexible modelling framework, a variety of fully and partially coupled experiments can be defined, along with traceable uncoupled simulations and options to use external input forcing in place of missing coupled components. This offers a wide scope to researchers designing sensitivity and case study assessments. Case study results are presented and assessed to demonstrate the application of RCS-IND1 to simulate two tropical cyclone cases which developed in the Bay of Bengal, 30 namely Titli in October 2018 and Fani in April 2019. Results show realistic cyclone simulations, and that coupling can improve the cyclone track and produces more realistic intensification than uncoupled simulations for Titli but prevents sufficient intensification for Fani. Atmosphere-only UM regional simulations omit the influence of frictional heating on the https://doi.org/10.5194/gmd-2022-7 Preprint. Discussion started: 27 January 2022 c  Author(s) 2022. CC BY 4.0 License.