Tethered Balloon Systems for Arctic Measurements in the Near-Surface Atmosphere
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AbstractIt is well known now that clouds have a particularly strong nonlinear influence on the surface energy budget in the Arctic including the timing of the onset of snowmelt. The greenhouse effect produced by low-level, thin Arctic cloud cover accelerates melting and increases the amount of open water, which absorbs more incoming sunlight than ice surfaces, setting up a positive feedback process that leads to more melting and warming near the surface. Large decreases in sea ice extent and thickness have been observed in recent years and surface temperatures have increased. Satellite monitoring of the microphysical and radiative properties of low-level Arctic stratus clouds is needed to determine the rate of ice melt and global warming. However, algorithmic retrievals from satellite observations of Arctic cloud properties are a work in progress and require long-duration in situ cloud measurements to improve their performance. Research aircraft capable of making measurements of low-level Arctic stratus clouds are costly, difficult to conduct in a Polar environment and come at a risk to human life. Tethered Balloon Systems (TBS) are now widely recognized as an emerging technology that can provide long-duration measurements of low-level Arctic stratus clouds. TBS have advantages over research aircraft in that they can conduct long-duration vertical profiles through Arctic clouds all the way to the surface; the slow impact speed negates the issue of ice crystals shattering on cloud particle probe inlets; they are cost-effective and present a low risk to human life. SPEC Incorporated developed a TBS under previous DOE SBIR funding in 2004 and successfully deployed the system to Ny-lesund (79 N. Latitude) in 2008 and the South Pole in 2009. Three articles in refereed journals have been published based on data collected from these two projects. SPEC modified the TBS to include a larger balloon with approximately twice the lift of the previous 43-m3 balloon. The new TBS was deployed to the North Slope of Alaska in October 2010 and the balloon was lost when both the primary and backup tether broke. The balloon was brought to the surface using a remotely actuated deflation system and landed in the ocean. No air traffic was interrupted and there was no loss of human life. This incident highlights the fact that we are still on a learning curve with the TBS and the causes and corrections of this incident will be a major part of the Phase I effort. In addition to developing a test cell to simulate and test loads and fatigue factors, we will upgrade some existing sensors and design new sensors in Phase I. Among the new sensors that will be designed will be a long wavelength radiometer, a large particle imager and an in situ cloud lidar that makes volumetric measurements of liquid water content, effective drop radius and extinction. Instrument designs that will be upgraded will be a cloud drop size distribution probe, cloud particle imager, cloud condensation nucleus and ice nucleus measurements. In Phase II we will purchase, fabricate and test the new winch/tether deployment system, fabricate the upgraded and new sensors, integrate the entire TBS and perform field tests. Commercial Applications and Other Benefits: Long-duration, spatially extensive datasets of in situ measurements of Arctic stratus clouds are an effective way to provide the statistical basis required to improve satellite retrievals. Development of readily deployable TBS with miniaturized sensors across the Arctic has large commercial benefit and the potential to collect a dataset with adequate statistics to improve satellite retrievals. If global climate models are improved, if public awareness is stimulated and the proper steps are taken to slow or reverse global warming, the benefit to the general public could be monumental
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