| Summary: | Thesis (M.S.) University of Alaska Fairbanks, 2014 An increased warming trend over the Arctic in recent years has been documented using observations, and is expected to continue by climate model projections. This increase may shift the springtime transition time, causing an earlier onset of summer and resulting in a longer sea-ice melt and vegetation growing period over the Arctic. In this study, we investigated variability of and changes in the spring transition in a warming climate and examined attributions of various dynamic and thermodynamic processes. The results demonstrate a dramatic increase in springtime surface air temperature (SAT) over the Arctic since 1979. Physical analysis reveals an increase in poleward moisture and latent heat transport accompanied by an enhancement of cloud cover, which result in positive downward longwave radiation. A persistent increase in poleward warm air advection is also found; leading to sensible heat flux from the warmer atmosphere to the surface furthering the surface warming. Retreat of sea ice cover reduces surface albedo, making an additional contribution to the surface warming. In addition to the overall evaluation of these physical processes, composite analysis suggests that relative contributions from these processes to the increased springtime SAT vary across different geographic subregions.
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