Collaborative Research: A Heat Budget Analysis of the Arctic Climate System

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AbstractThe Arctic System can be viewed as a set of interconnected and interacting physical, biological and human components. Arguably the most integrating component of the full Arctic system is its climate system. The mean state, variability and change in the climate system exert strong controls on biological processes and human activities. Arctic climate is in turn tightly coupled to the global system. This is an effort towards synthesis of the Arctic climate system that distills the wealth of data assembled though ARCSS and other national and international efforts in a tractable, integrating heat budget framework.While the Arctic climate system is certainly complex, in its most fundamental sense it has an elegant simplicity. One can consider the system in terms of a polar cap, defined by a hypothetical wall at 70oN, and comprising two columns separated by the surface interface - an atmospheric column extending from the surface to the top of the atmosphere, and an underlying column, extending from the surface down to some depth. Changes in the heat content of the atmospheric column depend on the net flux of energy coming into its sides (the heat flux from lower latitudes), the radiation budget at its top, and net heat transfers through the surface interface. These latter transfers include processes such as sea ice growth and melt, and exchanges of sensible heat. Similarly, the underlying column gains or loses heat via fluxes into its sides and communication with the atmosphere through the surface interface. The observed mean annual cycle, variability and change in the Arctic climate system can be essentially described in terms of these interactions, reflected in familiar climate elements such as the atmospheric circulation, surface, atmospheric and upper-ocean temperatures, snow cover and sea ice conditions. While the above example considers a simple polar cap, the heat budget framework can be applied to understand regional aspects of the climate system.An advantage of this way of thinking is that it provides a common framework within which data from many sources, including atmospheric reanalyses, runs from coupled ice-ocean, land surface and global climate models, satellite remote sensing, and surface and oceanic observations, can be ingested. Different sources will give different realizations of a given budget term. This spread of realizations represents a measure of uncertainty. This group will compile gridded monthly time series of budget terms for a domain encompassing the Arctic Ocean and terrestrial drainage, emphasizing the data-rich period 1979 to present. Given the limitations of some records (e.g., observed ocean heat transports), they will also develop climatologies for simpler domains. These data sets will be applied in a series of studies, framed around key research questions, to clarify interactions shaping the annual cycles, variability and recent changes in the Arctic climate system. They will also assess consistency between recent changes and projected future states of the system.