Conservation of heat in the Coupled Arctic Prediction System (CAPS v1.1): comprehensive model evaluation based on the MOSAiC observations

Abstract. Atmosphere–sea ice–ocean interactions are vital to understand past and future changes of Arctic climate system. It is essential to ensure the energy closure across model components to investigate these interactions with coupled models at longer timescales. Here, we present the improved version of Coupled Arctic Prediction System (CAPS) with the conservation of heat fluxes exchanged between the atmosphere (WRF) and ocean-sea ice (ROMS-CICE) components. A set of pan-Arctic simulations covering the period of Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) was conducted with the improved CAPS. The improved CAPS significantly reduces the inconsistency in heat flux exchange between WRF and ROMS-CICE, leading to better performance in simulating Arctic sea ice conditions compared with satellite observations than its predecessor showing the drifting behaviors. The model capability of CAPS to simulate the atmosphere, ocean, and sea ice conditions in the Arctic climate system were also evaluated based on the comprehensive observations obtained from the MOSAiC drift. The assessments indicate that CAPS reproduces reasonable evolutions of Arctic conditions along the track of MOSAiC observations but accompanies with biases contributed by simulated synoptic storm systems. By applying the spectral nudging technique in the upper atmospheric levels, CAPS can better replicate the observed storm systems and reduce biases shown in the free simulation. The evaluations shown in this article also highlight the key areas for further investigations in CAPS (as well as in other numerical prediction systems) including atmospheric boundary layer processes (surface turbulent heat fluxes) and cloud processes in polar regions.