Recent NAO move to neutral: a signal of short term Greenland extreme melt pause?
The summer NAO index is useful, when negative, in explaining extreme Greenland melting. Box et al. (2012) includes a section to that effect (see section 4.4, figure 8). The recent late July 2012 NAO index data, illustrated below, have returned to a neutral (NAO index approx. = 0) suggest the south air flow that is overheating the ice sheet has paused. Does this mean the abnormal melt year is reverting to normal melt season? I think not, because, the ice sheet reflectivity (a.k.a. albedo) remains low and there is another month-plus of time with 24 h sunlight and air temperatures are at or near melting that will allow melting to proceed in an amplified mode. What can pause the abnormal melting would be summer snowfall which would brighten the surface and insulate the melted snow below from warm air. Summer snowfall over the ice sheet is more likely with a neutral or positive NAO index.
- Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
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