Evaluation of high-latitude temperature biases over sea-ice areas in the Korean Integrated Model (KIM)

The Korea Meteorological Administration (KMA) has been operating the Korean Integrated Model (KIM), an indigenous global numerical weather prediction system, since April 2020. In May 2025, KMA began the operational service of a high-resolution KIM, which features improved horizontal resolution to enhance overall forecast performance and prediction accuracy. Despite these technical advancements, KIM revealed continuous systematic temperature biases in the high latitudes of the Northern Hemisphere (≥70°N), particularly over sea-ice areas.

In this study, we evaluated the systematic errors of KIM by comparing its forecasted fields against ERA5 reanalysis data. We focused on the diagnostic analysis of surface skin temperature (Tsfc), 2m temperature (T2m) and lower-tropospheric air temperature to identify the specific characteristics and seasonal trends of these biases. Preliminary results showed that KIM underestimated surface temperatures over sea-ice areas throughout most of the year, although a transition to overestimation was observed during the spring period from mid-April to May. These biases suggest that the initialization and physical processes for surface conditions in the polar areas within KIM require further research and development.

To diagnose the sources of these errors, we analyzed the relationships between temperature biases and radiation/cloud-related variables using time-series analyses. The results indicated that KIM generally underestimated surface downward and net longwave radiation, while overestimating surface net shortwave radiation. In addition, cloud fraction was overestimated, whereas total cloud condensate was generally underestimated and the fraction of cloud ice was relatively large. This study aims to examine how these discrepancies in hydrometeors and radiation variables contribute to the observed temperature biases, especially over sea-ice areas. The findings from this evaluation will provide a basis for improving physical parameterizations and surface-related processes in KIM to enhance the predictive skill of the high-resolution KIM in high-latitude areas.