The Radiative Effects of Cyclone and Anticyclone Activity Driving Arctic Sea Ice Melt Onset Patterns

Abstract:

Melt onset (MO) of Arctic sea ice signals the beginning of the summer melt season. Since 1979, observations from passive microwave satellites have shown that the timing of Arctic MO is shifting earlier in the year at a rate of ~5.7 days/decade^-1. Earlier MO lengthens the melt season – increasing the absorption of solar radiation in the ice-ocean system and contributing to declining sea ice cover. This work examines the radiative influence of synoptic-scale high and low pressure systems on the timing and spatial patterns in the spread of MO across sea ice. To quantify spatial patterns in the accumulation of MO, gridded MO dates from the Advanced Horizontal Range Algorithm (AHRA) are used to compute the accumulated area of daily MO through the annual melt season. Atmospheric and surface radiation data from the ERA5 reanalysis are used to characterize the conditions initiating different MO accumulation patterns. Enhanced cloud cover and warm air advection from cyclone activity and associated anomalous long-wave radiation is shown to produce short-lived, but wide-spread melt patterns contributing to anomalously early MO at the regional scale. Conversely, anticyclones tend to produce longer duration, sparse MO patterns associated with increased surface shortwave radiation. This work highlights the importance of spring weather conditions contributing to both anomalously early and late MO events; the effects of which propagate throughout the subsequent melt season.