[A-CG52] 北極域の科学

[ACG52-P06] 46 years annual variation of the bare ice and 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：グリーンランド氷床、衛星観測、GCOM-C

Bare ice exposure and dark ice distribution is key factors 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. The expansionary trend of the bare ice and 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. And 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 bare ice dark ice distribution from 1979 using a long-term satellite data set. The long-term datasets of the bare ice dark ice distribution on the GrIS were 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 evaluation. The 46 years variations of the dark ice extent using the adjusted thresholds showed positive trends in the whole region of the GrIS. For investigation of the phase characteristics, the study period was divided into three periods: 1979-1994 (1st period), 1995-2009 (2nd period), 2010-2024 (3rd period). In the 1st period, there was no significant trend for either bare ice or dark extent to expand. In the 2nd period, there was a significant trend for both bare ice and dark extent to expand. In the 3rd period, there was a significant trend for both to shrink. About the average values for each of the three periods, the bare ice area was smallest in the 1st period and was about the same in the 2nd and 3rd periods. The dark area was smallest in the 1st period and expanded the most in the 3rd period. Although the dark area showed a tendency to shrink in the 3rd period, there was large year-to-year variation and the behavior was unclear, so we would like to clarify recent variations by comparing with meteorological components and/or melting periods.