Deciphering the Shift from Warm-Dry to Warm-Wet Events in Ice-Covered and Non-Ice-Covered Regions

Compound warm events exert profound impacts on environment, health, and socioeconomics. A recent study indicated a shift or transition from warm-dry events (WDEs), common in non-ice-covered areas, to warm-wet events (WWEs) in ice-covered zones. Utilizing ERA5 reanalysis data, this study determined the duration and frequency of WDEs and WWEs across ice-covered and non-ice-covered regions. A comprehensive analysis uncovers the physical mechanisms responsible for this shift and attributes it to the weakening of land-atmosphere interaction caused by ice-cover, which inhibits soil moisture feedback and reduces the intensity and duration of warm events in ice-covered areas. Both WDEs and WWEs are associated with high-pressure systems (HPs). WDEs, situated directly beneath HPs, intensify due to adiabatic warming from subsidence motions. Conversely, WWEs, located beneath the poleward fringes of HPs, emerge from advective warming and moistening associated with poleward intrusions of warm-moist air.