The Properties of Mixed Phase- and Ice Clouds in the Arctic Using a Tethered Balloon System Deployed in Support of the International Polar Year (IPY)

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Over the next century, Arctic surface temperatures are predicted to rise at twice the rate of the global mean (IPCC, 2007). The role of shallow low-level clouds over the polar ice sheets is potentially quite important, since their interaction with radiative energy at both visible and infrared wavelengths can variously reduce or amplify such changes, with the net outcome being strongly dependent on the detailed microstructure of these clouds (e.g., the relative amounts and particle sizes of supercooled liquid water vs. ice within them). Recent evidence of increased spring and summer cloudiness accompanied by accelerated melt rates and associated thinning/retreat of polar pack ice lends additional urgency to our improved understanding of such linkages. The work supported here, which embodies a close collaboration between Stevens Institute of Technology and SPEC Inc., will obtain and analyze low-level measurements of microphysical and radiative properties in Arctic clouds. These uniquely detailed data will be obtained via a tethered balloon system operated in conjunction with a Norwegian-supported scientific program (THORPEX-IPY) during the 2008 International Polar Year at Ny-Alesund, located at 78 deg N in the Svalbard (formerly Spitzbergen) archipelago over an eight week period during the spring, when widespread low-level cloudcover and associated surface radiative feedbacks are favored. Observations will be obtained using a sophisticated balloon-borne cloud microphysical observing system developed by SPEC, which includes an instrument for imaging cloud particles and counting cloud droplets, a radiometer custom engineered by Stevens Technical Institute for monitoring radiative energy fluxes in the visible and near-infrared, as well as instruments required to obtain standard suite of meteorological observations. All of these data will be telemetered to a ground station in real-time. Use of a tethered-balloon platform will allow cloud structure and radiative/thermal conditions to be repeatedly and frequently profiled down to levels much nearer the surface and over far longer (~24 h) continuous periods than would be possible using research aircraft, and at considerably lower cost. This information will be input into a comprehensive radiative transfer model capable of isolating and quantifying the impact of variable cloudcover properties on the underlying ice. Through comparisons with contemporaneous ground- and satellite-based measurements, this model will be further tuned and improved to accurately represent cloud-ice interactions. A simplified version of this refined model will ultimately be incorporated into the global-scale Bergen Climate Model so as to leverage these results toward improved diagnosis of current climate conditions and more accurate long-range predictions.