シラセ サイヒョウ コウコウ データ ガ シメス ナンキョク リュツォ・ホルムワン テイチャクヒョウ ノ ネンネン ヘンカ

南極リュツォ・ホルム湾において毎年ほぼ同時期,同海域を航海する砕氷船「しらせ」は,海氷モニタリング・プラットフォームに適している.同湾の海氷状況の年々変化を推測するために,1983年から2002年までの間の「しらせ」砕氷航行データを解析した.主にラミング砕氷と氷厚や積雪深との関係を調べ,ラミング一回当たりの進出距離を砕氷航行の難易度の指標とすることにより,定着氷域の変化の特徴を抽出した.ラミング時の進出距離が短い1990年代前・中期は,航海が困難で厳しい氷状を反映し,氷厚や積雪深が大きい.一方,1990年代終わりから2002年までの間は,進出距離が長い傾向にあり,湾内定着氷の崩壊・流出の頻発期とも符合していることがわかった.Characteristics of sea-ice conditions in Lutzow-Holmbukta, Antarctica, have been investigated using the ice navigation log from the icebreaker Shirase, which has made a voyage almost at the same season and in the same sailing route every year since 1983. The vessel is considered as a suitable monitoring platform for sea ice. Not only basic information such as ice thickness and snow depth, but also ramming icebreaking data have been analyzed. In particular, the penetrating distances by ramming reflect difficulty in ice navigation and show distinctly interannual variations from 1983 to 2002. The periods with longer distances are consistent with those when breakup of landfast ice occurred frequently in the bay. The penetrating distances have shown a tendency to increase since the end of the 1990s, when ice breakup has been pronounced

センジョウ カンソク データ ニ モトヅク ナンキョク リュツォ・ホルムワン テイチャクヒョウ ノ カキ ニオケル ヒョウアツ オヨビ セキセツシン ブンプ トクセイ ニツイテ

南極観測船「しらせ」船上で取得された海氷観測結果をもとに,リュツォ・ホルム湾定着氷の夏季における氷厚及び積雪深分布について考察した.ビデオ観測結果から求めた各年の全氷厚(氷厚+積雪深)確率密度分布は薄氷型と厚氷型に分けられることがわかった.また大陸沿岸から約km圏内では全氷厚及び積雪深は沿岸に向かって漸減する傾向を示した.これは北東方向の卓越風による積雪輸送によると考えられる.電磁誘導法によって観測された全氷厚分布には不連続的な変化が認められた.NOAAAVHRR画像と比較した結果,不連続の位置は定着氷流出後の再結氷域における一年氷と,未流出の厚い多年氷との境界に一致することがわかった.定着氷の流出範囲は年によって大きく変動する.流出位置が沖側に後退すると厚い多年氷域の割合が多くなり厚氷型になり,沿岸に近づくと積雪影響も相まって厚い多年氷域が縮小または消滅し,薄氷型になるというメカニズムが明らかになった.Sea ice observations have been conducted onboard the Antarctic Research Vessel Shirase" since . The authors summarize these data to investigate spatial and inter-annual variability of sea ice thickness and snow depth of the summer land-fast ice in Lutzow-Holmbukta. Probability density functions of annual total thickness (ice thickness+snow depth) derived from video observations are categorized into two types, i.e. a thin-ice and a thick-ice type. The total thickness distributions observed by the electro-magnetic inductive method have a clear discontinuity, which reects the past break-up of the land-fast ice. Thin rst-year ice develops oshore of this location, while multi-year ice mostly develops onshore. Ice thickness and snow depth gradually decrease toward the coast within about km oshore, probably due to snow drift driven by the strong northeasterly wind. It is concluded that the past breakup of the land-fast ice as well as snow depth have dominant inuence on the spatial distribution of ice thickness in Lutzow-Holmbukta. The extent of break-up varies signicantly year by year. The smaller extent enhances the development of thick multi-year ice, while the larger extent, coupled with the inuence of snow drift, enhances reduction or extinction of thick multi-year ice

Sea ice thickness measurements with electro-magnetic inductive sounder in the pack ice zone off Syowa Station

第3回極域科学シンポジウム/第35回極域気水圏シンポジウム 11月29日（木） 国立国語研究所 ２階多目的

Measurements of snow depth and sea ice thickness by electromagnetic-induction measurements observed by Japan and Australia in the Antarctic Ocean.

第2回極域科学シンポジウム/第34回気水圏シンポジウム 11月17日（木） 統計数理研究所 セミナー室

Ship-borne electromagnetic induction sounding of sea-ice thickness in the southern Sea of Okhotsk

Recent observations have revealed that dynamical thickening is dominant in the growth process of sea ice in the southern Sea of Okhotsk. That indicates the importance of understanding the nature of thick deformed ice in this area. The objective of the present paper is to establish a ship-based method for observing the thickness of deformed ice with reasonable accuracy. Since February 2003, one of the authors has engaged in the core sampling using a small basket from the icebreaker Soya. Based on these results, we developed a new model which expressed the internal structure of pack ice in the southern Sea of Okhotsk, as a one-dimensional multilayered structure. Since 2004, the electromagnetic (EM) inductive sounding of sea-ice thickness has been conducted on board Soya. By combining the model and theoretical calculations, a new algorithm was developed for transforming the output of the EM inductive instrument to ice + snow thickness (total thickness). Comparison with total thickness by drillhole observations showed fair agreement. The probability density functions of total thickness in 2004 and 2005 showed some difference, which reflected the difference of fractions of thick deformed ice

Thickness distribution, texture and stratigraphy, and a simple probabilistic model for dynamical thickening of sea ice in the southern Sea of Okhotsk

Sea ice thickness data and sea ice samples were analyzed to examine the characteristics of the ice thickness distribution and ice texture, and to understand ice growth processes in the southern Sea of Okhotsk. Ice thickness data and samples were obtained aboard the icebreaker Soya in early February, the ice growth season. Ice thickness data, which were obtained with a video monitoring system installed on the side deck of the ship each winter from 1991 to 2000 except 1995, show that the average thickness ranges from 19±7 to 55±23 cm and that it matches the characteristics of a Poisson distribution. Ice structure analysis reveals that granular texture occupies about three quarters of the total ice thickness and that the ice exhibits a layered structure with unit thickness averaging 5 to 10 cm. Stratigraphy and stable isotopic composition of the ice indicate that snow ice accounts for 10% and frazil ice accounts for 64% of the total ice thickness. This suggests that dynamic ice thickening processes such as frazil ice growth and piling up are more significant than congelation growth. On the basis of these characteristics, which resemble more those of Antarctic than Arctic sea ice, we propose a conceptual model for the ice thickening process in this region. It is shown that this model can explain the shape of the ice thickness distribution well, and is analogous with the concept of the “pancake cycle” and multiple rafting of Antarctic sea ice growth and thickening.An edited version of this paper was published by AGU. Copyright 2004, American Geophysical Union, "Journal Of Geophysical Research-oceans", Vol.10

Interannual variation of landfast ice condition in Lutzow-Holmbukta, Antarctica, derived from navigation log of icebreaker Shirase

Characteristics of sea-ice conditions in Lutzow-Holmbukta, Antarctica, have been investigated using the ice navigation log from the icebreaker Shirase, which has made a voyage almost at the same season and in the same sailing route every year since 1983. The vessel is considered as a suitable monitoring platform for sea ice. Not only basic information such as ice thickness and snow depth, but also ramming icebreaking data have been analyzed. In particular, the penetrating distances by ramming reflect difficulty in ice navigation and show distinctly interannual variations from 1983 to 2002. The periods with longer distances are consistent with those when breakup of landfast ice occurred frequently in the bay. The penetrating distances have shown a tendency to increase since the end of the 1990s, when ice breakup has been pronounced