Short-term variations of spaceborne microwave brightness temperature on the Greenland ice sheet during the 2012 melting season.

The accelerated melting of the Greenland ice sheet, driven by recent global warming, has attracted significant attention regarding the long-term variations in its mass balance. While several analyses have utilized snow melting indicators derived from microwave brightness temperatures observed through satellites, there is a lack of studies examining the diurnal behavior of these temperatures during the melting season. The Advanced Microwave Satellite Radiometer 2 (AMSR2) aboard the Global Change Observation Mission – Water (GCOM-W) satellite provides multiple daily observations on the Greenland ice sheet, enabling the investigation of diurnal changes in brightness temperature. This study aims to clarify the short-term relationship between snow melting and spaceborne microwave brightness temperatures during the summer of 2012, a period marked by extensive melting of the Greenland ice sheet. To examine the timing of snowmelt, snow surface temperature data collected by the Automated Weather Station (AWS) at a site on the ice sheet in north-west Greenland were utilized. The time series of snow surface temperatures from July to August 2012 were analyzed, revealing distinct patterns across three periods: Period A (early-July: snow temperature of 0°C only during the day), Period B (mid-July: snow temperature of 0°C throughout the day), and Period C (mid-August: snow temperature below 0°C all day). In the north-west regions, Snow Index (Tb18H − Tb36H: Difference in brightness temperature between 18 GHz-H and 36 GHz-H) values, indicative of snow cover, showed significantly different short-term variations between the periods. During Period A, Snow Index values were positive throughout the day and decreased towards the afternoon. In contrast, during Period B, Snow Index values were negative throughout the day, with no significant diurnal changes observed. During Period C, Snow Index values returned to positive again and, as in the previous period, no significant changes were observed during the day. These results suggest the possibility of monitoring diurnal melting with high temporal resolution through short-term variations in spaceborne microwave brightness temperature. These variations across the Greenland ice sheet, including other frequency channels, will be further discussed during the conference day.