Fumio Nakazawa^1,2, *Naoko Nagatsuka¹, Kumiko Goto-Azuma^1,2, Dorthe Dahl-Jensen³, Jørgen Peder Steffensen³ (1.National Institute of Polar Research, 2.SOKENDAI (The Graduate University of Advanced Studies), 3.Niels Bohr Institute, University of Copenhagen)