Shallow ice core drillings on Greenland Ice Sheet - Recent and near future activities by Japanese glaciological research projects -

第7回極域科学シンポジウム/横断セッション:[IG] アイスコア研究—これまでの成果と今後の展開12月2日（金） 国立極地研究所 2階大会議

The effects of snow grain size profile on the Greenland ice sheet snow surface melt

In July 2012, extreme surface melt events occurred on the Greenland Ice Sheet (GrIS). Generally, surface melt is physically controlled by the surface energy balance, where net shortwave radiant flux is the main energy source for melt during summer. Although (optically equivalent) snow grain size profile affects near-infrared albedo and in turn net shortwave radiant flux, its qualitative impacts on the surface melt events is unclear. In the present study we investigated effects of snow grain size profile on the surface melt event observed at the site SIGMA-A (78°03’N, 67°38’W, 1,490 m a.s.l.), which locates on northwest part of GrIS, during 30 June to 10 July 2012 through numerical studies with a physically based 1-D snowpack model SMAP. Observed snow physical state at SIGMA-A during 30 June to 13 July is indicated in Figure 1 in terms of snow grain shape profile. As shown in this figure, top melt form layers (depicted with red color) were expanded day by day as a result of surface melt during the period.First of all, we simulated temporal evolution of physical states of near-surface snowpack at SIGMA-A during 30 June to 10 July 2012 by forcing in-situ meteorological data obtained at SIGMA-A. The depth of simulated snow layer, which was characterized by a thick bottom ice formation, was 88 cm on 30 June. The initial states of snowpack were given from the snow pit observation counducted on 30 June 2012, 16:45 UTC. It was found that the simulated shortwave albedo (ctrl in Figure 2) agreed well with measurements (R2 = 0.820, root mean square error = 0.019, and mean error = 0.008).Next, we performed two sensitivity tests with SMAP, where initial snow grain size profile was modulated in order to assess its impacts on the surface energy balance. In these tests we replaced the original snow grain size profile for the top 21 cm melt form layers depicted in Figure 1 (average snow grain size was 0.6 mm) with smaller (test1) and larger profiles (test2). In test1 top 21 cm snow grain size was equally set to be 0.02 mm, which is almost the minimum value for new snow. On the other hand, in test2, 1.0 mm, which is the typical maximum value for melt form observed in seasonal snowpack in Japan, was arranged in the top 21 cm layers. Figure 2 illustrates simulated shortwave albedos for test1 and test2 cases comparing against ctrl case. Obviously, simulated shortwave albedo for test1 is higher than that for ctrl continuously, while that for test2 was kept smaller than that for ctrl. Comparing simulated results for test1 and test2 we could know how surface energy balance could be varied with snow grain size profile. Obtained average differences in simulated shortwave albedo and net shortwave radiant flux between test1 and test2 were 0.06 and 21.8 W/m2, respectively. It implies that snow grain size profile played an important role in controlling surface melt rate, which is an consequence of the surface energy balance, at SIGMA-A during 30 June to 10 July 2012.第4回極域科学シンポジウム個別セッション：[OM] 気水圏11月15日（金） 統計数理研究所 ３階セミナー室１（D305

An Utility of MDCT for Evaluation of Carotid Artery after CEA and CAS

3D-CTA by means of MDCT (multidetector-row CT) becomes an indispensable image along with a recent clinical application in the diagnosis of the cervical carotid artery stenosis and the evaluation. Then, we evaluated carotid artery after CEA (carotid endarterectomy) and CAS (carotid stenting) by using MDCT this time. Subjects were three patients, of whom one post-CEA and two post-CAS. As the evaluation of carotid artery after CEA, VR method and the MIP was evaluation almost equal to DSA. However, they are useless in patients with much calcification of the artery and post-CAS. For these cases, MPR or CPR method was able to be useful, and to evaluate in the artery enough. Although it is insufficient to the measurement of the stenosis degree and evaluation of properties of the arterial wall, 3D-CTA by means of MDCT can become image diagnosis equipment that will take the place of DSA in the future

Positive feedback effect of NIR-albedo reduction due to temperature increase on surface melting on Greenland ice sheet

第7回極域科学シンポジウム:[OM] 極域気水圏11月29日（火）国立極地研究所 2階 大会議

Analysis of shallow/deep ice core drilling data, and the future plan of intermediate depth drilling

第4回極域科学シンポジウム個別セッション：[OM] 気水圏11月15日（金） 国立極地研究所 ３階ラウン

Reconstruction of mass balance for 36 years at SIGMA-A site in the northwestern Greenland Ice Sheet

第4回極域科学シンポジウム横断セッション：[IA] 「急変する北極気候システム及びその全球的な影響の総合的解明」―GRENE北極気候変動研究事業研究成果報告2013―11月12日（火） 国立極地研究所 ２階大会議

エンダービーランド リーセル・ラルセンサン チイキ ノ チガク チョウサ ホウコク 2000-2001 (JARE-42)

第42次南極地域観測隊(JARE-42)夏隊の5名は、2000年12月18日から2001年2月18日まで、南極、エンダービーランド、アムンゼン湾内にあるリーセル・ラルセン山周辺で古地磁気学と岩石年代学の岩石試料採集、磁場探査、及び電磁探査を行った。調査にあたり、第38次隊がリチャードソン湖東岸に建設した発電棟の側に新たに居住棟を建設しリーセル・ラルセン山キャンプとした。古地磁気学調査では86地点から741試料を採集した他、帯磁率の測定や磁鉄鉱-石英片麻岩の分布も調べた。岩石年代学では珪長質片麻岩と塩基性貫入岩試料を187試料採集した。MT法による電磁探査はモレーン上の5地点とリチャードソン湖上の1地点で行い、深さ8kmから28kmで電気比抵抗が小さくなる構造を明らかにした。磁場探査は7000nTに及ぶ磁気異常が片麻岩、あるいは貫入岩の走向と平行に発達している様子を明らかにした。 63日の滞在期間中、最大瞬間風速は50.7m/sを記録したこともあったが、比較的天候に恵まれ、また、設営面での大きな事故も無く順調にキャンプの運営ができた。調査終了後、環境保全の観点から、リーセル・ラルセン山キャンプ設備をすべて撤収した他、50km西方にあるトナー島キャンプ設備も全て撤収した。Five members of the summer party of the 42nd Japanese Antarctic Research Expedition (JARE-42) stayed in the Mt. Riiser-Larsen area, Amundsen Bay, Enderby Land, Antarctica, from December 18, 2000 to February 18, 2001 for paleomagnetism, geochronology, electromagnetic and magnetic surveys. A resident hut was built beside the generator hut constructed by JARE-38 in the camp. For the paleomagnetic study, 741 samples from 86 sites were collected in addition to the data of susceptibility and distribution of magnetite-quartz gneiss. 187 samples of felsic gneisses and basic dike rocks were collected for the geochronology. The high conductivity layer between 8 and 28 km was elucidated by the magnetotelluric method applied to samples obtained from 5 sites on the moraine field and 1 site on Richardson Lake. Strong magnetic anomalies up to 7000 nT were observed along gneissosity and dike intrusions by the magnetic survey. The weather was relatively mild during 63 days, although the maximum wind speed reached 50.7m/s. The camp was maintained without major accidents or trouble. After the work was completed, the camp facilities at Mt. Riiser-Larsen and Tonagh Island were completely withdrawn for environmental protection