Contrasting Atmospheric Drivers of Greenland's Warm-Wet and Warm-Dry Extreme Events

Under the background of global warming, Greenland has experienced increasing frequency of compound extreme events, which can be categorized into warm-wet events (WWEs) and warm-dry events (WDEs). These extreme warm events over Greenland accelerate ice-sheet melting and thereby contribute to global sea-level rise. Using ERA5 reanalysis data, this study investigates the distinct mechanisms driving the WWEs and WDEs. Statistically, the WWEs occur approximately twice as often as the WDEs. The WWEs are associated with an anomalous atmospheric dipole pattern, featured as high pressure east of Greenland and low pressure to its west, enhancing moisture transport and surface downward longwave radiation. In contrast, the WDEs are governed by Ω-blocking highs, favoring increased surface downward shortwave radiation. Additionally, the jet stream configurations play a critical role in both two extreme events. Specifically, the WWEs are linked to a westward-retracted jet stream and open waveguide, facilitating Rossby wave dispersion and inhibiting persistent ridging. Conversely, the WDEs exhibit an eastward-extended jet and closed waveguide, promoting wave energy convergence and the formation of long-lived blocking highs. Our findings provide a comprehensive understanding of compound extreme events over Greenland, and support better prediction of compound events worldwide.