Thermodynamic Differences Between Moderately and Extremely Long Heat Waves in South Korea

Heat waves in South Korea have become markedly longer, highlighting a need to better understand the physical mechanisms governing their persistence. Therefore, we first categorised 52 years (1973–2024) of summer heat waves into moderately long events (MLEs; 5–9 days) and extremely long events (ELEs; ≥ 10 days) based on their duration and statistical distribution. Then, we analysed each type of summer heat wave using a stage-based framework that focused on their growth, maintenance and decay stages to examine the thermodynamic evolution of these events. We found that, although both MLEs and ELEs exhibited similar initial warming driven by warm advection and adiabatic heating during the growth stage, ELEs developed distinct thermodynamic features during the maintenance and decay stages. The persistent high-pressure system over South Korea induced pronounced subsidence that sustained adiabatic warming and inhibited cloud formation, enhancing surface downward shortwave radiation and amplifying surface warming. This, in turn, depleted soil moisture, enhancing sensible heat flux through land–atmosphere interactions, thereby strengthening diabatic heating and delaying surface cooling. Those thermodynamic processes sustained ELEs, while large-scale circulation provided a dynamical background for the stagnation of the high-pressure systems. By distinguishing the thermodynamic evolution of ELEs from that of MLEs, this study provides key insights into the mechanisms driving the longer heat waves over South Korea.