Refinement of coupling strength between soil moisture and latent heat flux: Effects on medium-range weather forecast and soil moisture data assimilation in the KIM system

The Korean Integrated Model (KIM), an operational global numerical weather prediction model at the Korea Meteorological Administration, has been developed during the initial phase of the Korea Institute of Atmospheric Prediction Systems (KIAPS) from 2011 to 2019. During this phase, the Noah land surface model (LSM) has been coupled to KIM, and the initial states of the land surface are being generated by a land data assimilation (DA) system based on the National Aeronautics and Space Administration (NASA) Land Information System (LIS). In the ongoing second phase of KIAPS from 2020 to 2026, the Noah-Multiparameterization (Noah-MP) LSM, designed to enhance geophysics representations, has been integrated into the KIM system and is currently undergoing further geophysical advancements.
This study examines the interaction between land surface and atmosphere in the KIM system by estimating a coupling strength between soil moisture (SM) and latent heat flux (LH) represented in LSMs. It is found that improved SM initial conditions through land DA do not ensure improving forecast fields of temperature and specific humidity in the low troposphere in some regions, particularly South Asia croplands, where typically the SM and LH coupling strength is overrepresented in LSMs. Notably, among the sub-components of LH, direct evaporation at the soil surface exhibits stronger coupling with SM than other sub-components. As the overrepresented SM and LH coupling strength may cause degraded performance of land SM DA within land-atmosphere coupled systems, here we aim to analyze and improve the SM and LH coupling representations in LSMs towards improving land DA of the KIM system. In this presentation, we will introduce the sensitivity experiments on LH-related parameters and their impacts on the SM DA performance as well as medium-range weather forecasts.

Acknowledgements. This work was carried out through the R&D project “Development of a Next-Generation Numerical Weather Prediction Model by the Korea Institute of Atmospheric Prediction Systems (KIAPS)”, funded by the Korea Meteorological Administration (KMA2020-02212).