|Review of the manuscript, entitled “Recent Advances in understanding the Arctic Climate System State and Change from a Sea Ice Perspective: a Review” by R. Döscher, T. Vihma, and E. Maksimovich|
I appreciate the authors’ efforts to address my comments and suggestions and to revise the manuscript. The revised manuscript has been improved on various aspects, e.g., by including earlier studies about lower latitude warm water inflow and shifting cyclones, clarifying water vapor changes and associated feedback, and providing new paragraphs of discussions and evaluations. There is no doubt I support publication of this manuscript though some weaknesses still exist, for example, the paper is still lengthy, which may prevent busy audience from reading it.
However, I would like to draw the authors’ attention and make corresponding revisions on the following key issues, which have caused confusions, in particular in young students and researchers. These issues have been discussed recently in different occasions and workshops. As a review paper, the confusing discussions about these issues may further propagation of misunderstanding or misleading.
-->1. AO and NAO: The new discussion in Section 4.1 gives an impression that the positive polarity of NAO is due to its space shifting in 1980. This is not the case. It is the phase transition that played a fundamental role in sea ice decrease. The NAO or AO went to a positive phase from the late 1980s to the mid 1990s, increasing heat transport into the Eurasian land and then the Arctic Ocean to cause sea ice decrease. NAO space shift only made an additional contribution to the role of the NAO or AO phase transition.
--><span style="font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:#00000A;mso-bidi-font-weight:bold"2. Transpolar drift stream and sea ice export: In climatology, the transpolar drift stream is a pathway of sea ice moving to Fram Strait and exports from the Arctic Ocean. The transpolar drift stream is mainly formed by the climatological Beaufort high, and its location and intensity are largely determined by the position and strength of the Beaufort high. When AO goes to a positive phase, the Beaufort high weakens. The increase in sea ice export via Fram Strait and the Canadian Arctic Archipelago is mainly due to an accumulation of sea ice on the western Arctic and an increase in sea ice outflow from these passages, rather than simply via changes in the transpolar drift. X Zhang et al. (2003) has shown this in their modeling study.
--><span style="font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:#00000A;mso-bidi-font-weight:bold"3. Second or third EOF mode: The atmospheric dynamics is generally considered as a nonlinear system. But it should not be so chaotic that, for a particular time period, its variability can be indeterminately represented by either second EOF mode or third EOF mode. Unlike AO or NAO that has the exact same expression for a long time period, the second mode or the third mode considerably changes with adding more data to the analysis sample. Also, as the authors stated, the second or third EOF mode varies with the selected analysis domain. They are therefore not robust modes representing intrinsic atmospheric variability, perhaps just a mathematic result. Discussions about physical expression of EOF can be found in North et al. (1982). So, overstatement of these modes would cause a big misleading as a review paper. Because the authors have stated these weaknesses and uncertainties of the second or third mode, it is inconsistent to continually suggest that “studies on future transformation … (such as AO, DA, …) will be essential for understanding …”. Finally, to my knowledge, I haven’t seen any studies that find transformation between these modes.
--><span style="font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:#00000A;mso-bidi-font-weight:bold"4. Sea ice export and 2007 summer low ice extent: It is well accepted that sea ice export via Fram Strait contributed to multiyear sea ice loss in the 1990s due to positive AO. However, since the mid 1990s, the sea ice export has greatly decreased though the sea ice export was slightly higher in 2007 than in 2000-2005. Summer sea ice export is only one seventh of the winter export, suggesting its contribution can be neglected in causing the great sea ice loss in 2007 summer.
--><span style="font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:#00000A;mso-bidi-font-weight:bold"5. In line 515, the authors describes “… Zhang et al. (2008) suggested a decreasing control of AO and NAO on the Arctic sea ice cover”. But the cited paper by Zhang et al. (2008) in the reference list is a case study about the 2007 summer sea ice, not about impacts of AO and NAO.
--><span style="font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:#00000A;mso-bidi-font-weight:bold"6. The following citation is duplicated in the reference list:
Screen, J. A., & Simmonds, I. (2010). The central role of …