\u201cIn July 2012,\u201d Bennartz says, \u201ca historically rare period of extended surface melting raised questions about the frequency and extent of such events. Of course, there is more than one cause for such wide-spread change. We focused our study on certain kinds of low-level clouds.\u201d<\/p>\n
The University of Wisconsin, together with other institutions, maintains an atmospheric research experiment at the National Science Foundation\u2019s Summit Station, a research facility located on top of the GIS at a height of 3200 m above sea level. This experiment, which is known as ICECAPS (Integrated Characterization of Energy, Clouds, Atmospheric state, and Precipitation at Summit), provided invaluable data and insights into the different factors causing the melt event.<\/p>\n
\u201cYou can say we were really lucky to be right there when the melt happened,\u201d Bennartz continues.<\/p>\n
![\"Summit](\"http:\/\/www.ssec.wisc.edu\/news\/wp-content\/uploads\/sites\/19\/2013\/04\/icecap_565_378.jpg\")
<\/a>Low-level, liquid-bearing clouds over the Mobile Science Facility at Summit Station in central Greenland. Photo by Ed Stockard.<\/p><\/div>\n
Satellite observations show an increase in the extent of the GIS melt since at least 1979, but the July 2012 event set a new record in melt extent. Examination of long-term melt records obtained from ice-core projects at Summit Station indicate that such events occurred only about once every 150 years over the last 4000 years.<\/p>\n
\u201cThe July 2012 event,\u201d Dave Turner of NOAA-NSSL, one of the lead investigators, explains,, \u201cwas triggered by an influx of unusually warm air, but that was only one factor. In our paper we show that low-level clouds were instrumental in pushing temperatures up above freezing.\u201d<\/p>\n
Low-level clouds usually reflect solar energy back into space, while also radiating infrared energy downwards, back to the surface. That is only one element within a complex interaction of many conditions, such as wind speed, turbulence, temperature and humidity. In addition, heat transfer on the surface depends upon the snow\u2019s ability to conduct the heat received from solar radiation as well as the heat exchange between different layers of snow.<\/p>\n
When cloud thickness and temperature conditions are right, these clouds can be thin enough that, instead of reflecting most of the solar energy away from the surface, they allow some of it to pass through, while still \u201ctrapping\u201d infrared radiation at ground level. The extra heat energy available to the surface pushes temperatures above freezing. That is exactly what happened in July 2012 over large parts of the GIS.<\/p>\n
Current climate models tend to underestimate the occurrence of this particular cloud type, thus limiting those models\u2019 ability to predict cloud response to Arctic climate change and possible feedback mechanisms. By using a combination of surface-based observations, remote sensing data, and surface energy-balance models, this study not only delineates the effect of clouds on ice melting, but also shows that this type of cloud is common over both Greenland and across the Arctic.<\/p>\n
\u201cWe know that these thin, low-level clouds occur frequently,\u201d says Bennartz. \u201cOur results may help to explain some of the difficulties that current global climate models have in simulating the Arctic surface energy budget. Above all, this study highlights the importance of continuous and detailed ground-based observations over the GIS and elsewhere. Only such detailed observations will lead to a better understanding of the processes that drive Arctic climate. \u201d<\/p>\n
The research team drew together scientists from various institutions \u2014 collaborators included NOAA NSSL scientist Dave Turner, University of Colorado scientist Matt Shupe, University of Idaho professor and ICECAPS lead principal investigator Von Walden, Konrad Steffen of the Swiss Federal Institute for Forest, Snow and Landscape Research, UW-Madison research associates Nate Miller and Mark Kulie, and graduate students Claire Pettersen (UW-Madison) and Chris Cox (U-Idaho).<\/p>\n
The Summit-based ICECAPS experiment is a NSF-funded joint effort between the Universities of Idaho, Wisconsin, and Colorado, and Oklahoma, with additional contributions from NOAA\u2019s Earth System Research Laboratory (ESRL), NOAA\u2019s National Severe Storms Laboratory (NSSL), and the DOE Atmospheric Radiation Measurement (ARM) program.<\/p>\n
Additional articles can be found at:<\/p>\n
National Oceanic and Atmospheric Administration (NOAA)<\/a>.<\/p>\n National Science Foundation<\/a>.<\/p>\n Cooperative Institute for Research in Environmental Studies (CIRES)<\/a>.<\/p>\n Swiss Federal Research Institute<\/a>.<\/p>\n