[A-CG46] 北極域の科学

[ACG46-05] 44 years annual and geographical variations of the dark ice on the Greenland Ice Sheet

*島田 利元¹、堀 雅裕²、竹内 望³、青木 輝夫⁴ (1.宇宙航空研究開発機構、2.富山大学、3.千葉大学、4.国立極地研究所)

キーワード：グリーンランド、リモートセンシング

Dark ice distribution is a key factor of the recent albedo reduction on the Greenland Ice Sheet (GrIS) and its variability influence on the surface radiative budget and surface mass balance of the ice sheet. Satellite remote sensing is the one of the most useful tools for the widely and continuous monitoring such as the GrIS and the expansionary trend of the dark ice extent has been revealed from the analysis using MODIS satellite images (Shimada et al., 2016; Tedstone et al., 2017). Although the annual variations since 2000 are investigated, the past variations are not yet understood. In addition, the MODIS sensors carried on the Aqua and Terra platform and been used primarily for these investigations are about to end in operation because of the satellites deorbit. Therefore, it is very important to continue the legacy of past satellite observations and to connect to new sensors. In this study, we aim to investigate the annual and geographical variations in the dark ice distribution from 1979 using a long-term satellite data set. The long-term dataset of the dark ice distribution on the GrIS was developed using three optical space-borne sensors: AVHRR, MODIS and SGLI. These sensors have near-infrared wavelength band used for bare ice detection and red wavelength band used for dark ice detection. For bias correction between these sensors, the classification thresholds for AVHRR and SGLI were adjusted to MODIS based on the agreement of statistical classification results using Cohen’s Kappa coefficient. The 44 years variations of the dark ice extent using the adjusted thresholds showed positive trends in the whole region of the GrIS. In geographical comparison, the dark ice expansion was occurred in the south-western part of the ice sheet since 1980s (Left Figure). The dark ice expansion in the north-eastern and north-western part was occurred in recent 15 years, especially around 2010 to 2015 (Right Figure). These results showed that the ice sheet surface darkening is gradually expanded northward in association with surface melt acceleration. In the presentation, we will show the possible factors of the northward shift of the darkening.