日本地球惑星科学連合2019年大会

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[J] ポスター発表

セッション記号 A (大気水圏科学) » A-CG 大気海洋・環境科学複合領域・一般

[A-CG37] 北極域の科学

2019年5月30日(木) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:漢那 直也(北海道大学北極域研究センター)、庭野 匡思(気象研究所)、中村 哲(北海道大学大学院地球環境科学研究院)、鄭 峻介(北海道大学 北極域研究センター)

[ACG37-P16] Impact of observation-based snow/ice albedo with starting temperature of −2°C for surface melting effect on a global ocean simulation

*豊田 隆寛1青木 輝夫1,2庭野 匡思1谷川 朋範1浦川 昇吾1辻野 博之1中野 英之1坂本 圭1広瀬 成章1山中 吾郎1 (1.気象庁気象研究所、2.岡山大学大学院自然科学研究科)

キーワード:アルベド、海洋大循環モデル、北極海、南大洋、海氷モデル

Based on detailed field observations, we conducted global ocean simulation experiments with modification of starting temperature for surface melting effect from −1°C to −2°C in the snow/ice albedo parameterization. An ensemble mean field of five experiments with the modified parameterization starting from December 1989–January 1990 were compared with the original experiment. Significance of the impact of the modification was evaluated by using the ensemble spread, which measures the internal variability.

In the Arctic Ocean, the mean albedo was reduced by up to 0.015 in June–July by the modification of the parameterization (i.e. lower albedo in the ensemble mean of the modified experiements than in the original experiment), which resulted comparably from both direct effect of the modification and indirect effect via changes of the snow and ice distributions by the albedo reduction. Snow thickness on the sea ice was reduced by up to 1.5 cm in June–July but afterward impact of the modification was diminished as the snow mostly melted away. Impact of the modification on the sea ice firstly appeared in the rim regions of the snow cover with the bare ice fraction extended and, in August–September, ice thickness decreases by 1.5 cm were achieved over most of the Arctic Ocean. On the other hand, ice thickness increases were seen in some marginal ice zones, which were attributed to reduced ocean surface circulation, such as in the Beaufort Gyre, resulting from reduced surface stresses with reduced ice cover.

In the Southern Ocean, the albedo reduction by up to 0.015 in December–January resulted from comparable contributions of the direct effect of the modification of the parameterization and the indirect effect via the snow thickness decrease, as in the Arctic Ocean. In contrast to the Arctic Ocean, the decrease impact of the snow thickness by up to 2.5 cm in the Weddell Sea partly remained through year. In addition, increases of the ice thickness were widely distributed in December–January. A detailed analysis revealed that the warming effect of the albedo reduction by the modification enhanced the reduction of the sea ice concentration, in particular that of thinner ice, which weakened the ice pressure and enhanced thicker ice formation via the rheology, leading to the increases of the ice thickness. Note that thicker ice is less affected by thermodynamical melting effect than thinner ice. This thickening impact of the sea ice remained through year in the Weddell Sea. These changes by the modification of the parameterization were robust compared with the ensemble spread.

Although the above experiments and results might be rather preliminary, we believe that our demonstration of the potential impact of the new observational insight on ocean general circulation model simulations would be of value for further enhancing both observation and modelling/prediction activities and their collaborative study.