The Regional Coupled Suite (RCS-IND1): application of a flexible regional coupled modelling framework to the Indian region at kilometre scale

Abstract

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 kilometre scale, and the effect of environmental feedbacks on the evolution and impacts of multi-hazard weather events. A 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 initialization, the RCS includes an alternative approach to couple the atmosphere to a lower 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, 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 boundary layer to prevent cyclone over-intensification. However, it is shown that this term can improve coupled simulations, enabling a more rigorous treatment of the near-surface energy budget to be represented. For these cases, a 1D mixed layer scheme shows similar first-order SST cooling and feedback on the cyclones to a 3D ocean. Nevertheless, the 3D ocean generally shows stronger localized cooling than the 1D ocean. Coupling with the waves has limited feedback on the atmosphere for these cases. Priorities for future model development are discussed.

Reproducible and relocatable regional ocean modelling: fundamentals and practices

“…the BoBEAS example with MPI Docker implementation). This ocean configuration is subsequently implemented in a coupled ocean-land-atmosphere regional suite (Castillo et al, 2022).…”

The Met Office operational wave forecasting system: the evolution of the Regional and Global models

“…Met Office research is also focused on delivering more accurate and comprehensive forecasts of the wider earth system (Graham et al, 2018;Tonani et al, 2019). This implies, in most cases, a need to develop more integrated systems where the different physical components (i.e., atmosphere, ocean, ice and waves) are coupled (e.g., Lewis et al, 2019;Bruciaferri et al, 2021;Valiente et al, 2021a;Castillo et al, 2022). In recent years, the Met Office has put significant effort into the development of fully coupled (atmosphere, wave, ocean and sea-ice) global and regional models and although AMM15 ocean-wave coupled system has been released, other coupled systems are still far from becoming operational.…”

“…These latest developments have facilitated the migration to version 7.12 of WW3 in wave forecasting operations and in research coupled models including Northwest European shelf (e.g., Lewis et al, 2019;Bruciaferri et al, 2021) and the Indian regional (Castillo et al, 2022) coupled wave-ocean and atmosphere-wave-ocean research systems. This paper documents the latest WW3 wave model developments introduced by the Met Office and describes the Met Office WW3 based wave operational forecasting system which includes a global model and two regional models nested one-way covering the Northwest European shelf and United Kingdom (UK) waters and the Atlantic wave ensemble.…”

Evaluation of a Mesoscale Coupled Ocean‐Atmosphere Configuration for Tropical Cyclone Forecasting in the South West Indian Ocean Basin

“…For example, the deeper mixed layer of warm‐core eddies is known to favor TC intensification (Bao et al., 2000; Chang & Anthes, 1978). Coastal effects such as the horizontal advection of warm water by coastal currents may also contribute to the fluctuation in intensity of a TC (see e.g., Castillo et al., 2022).…”

“…Coastal effects such as the horizontal advection of warm water by coastal currents may also contribute to the fluctuation in intensity of a TC (see e.g., Castillo et al, 2022).…”