From snow wetting to pond formation: Stage-resolved L-band sea ice roughness during the Arctic melt season

Abstract. Arctic summer surface evolution is commonly characterized using optical melt pond fraction, but optical retrievals are limited by persistent cloud cover and cannot resolve internal snow–ice changes that occur before ponds become visible. L-band passive microwave observations are largely unaffected by clouds and respond to near-surface dielectric changes within the snow and upper ice layer, suggesting their potential to detect pre-pond surface transitions. This study examines whether small-scale L-band sea ice roughness (L-SIR), retrieved from Soil Moisture Active Passive brightness temperatures, provides a physically consistent precursor to optically detectable melt pond development. Using observations from 2017 to 2023 over a multiyear ice region in the central Arctic, we analyze the temporal ordering among the transition to positive net surface energy flux, the L-SIR transition, and melt pond formation, together with stage-dependent relationships between L-SIR and surface energy balance variables. The L-SIR transition occurs approximately two weeks after the net surface energy flux becomes positive and approximately four weeks before melt pond formation, with this ordering reproduced across years and latitudes. Correlations with surface energy variables also change systematically across three stages, shifting from a temperature-related regime to a latent heat- and longwave-associated regime during active snow ablation and meltwater redistribution, and finally to a pond coverage-related regime. These results indicate that L-SIR provides a complementary satellite-derived product for characterizing pre-pond Arctic summer surface evolution that is not captured by optical melt pond fraction alone.