Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Barrow Alaska: A Focal Point for Ice-Albedo-Transmission Feedback Studies of Arctic Sea Ice
Thomas C. Grenfell1, Donald K. Perovich2, Hajo Eicken3
1Atmospheric Sciences, University of Washington, Dept. of Atmospheric Sci., MS 351640, University of Washington, Seattle, WA, 98195, USA, Phone 206-543-9411, Fax 206-543-0308, tcg@atmos.washington.edu
2ERDC-CRREL, 72 Lyme Rd., Hanover, NH, 03755, USA, Phone 603-646-4255, Fax 603-646-4644, perovich@crrel.usace.army.mil
3Geophysical Institute, University of Alaska Fairbanks, Geophysical Institute, P.O. Box 757320, 903 Koyukuk Dr., Fairbanks, AK, 99775-7320, USA, Phone 907-474-7280, Fax 907-474-7290, hajo.eicken@gi.alaska.edu
As detailed in the SEARCH science plan, the Arctic sea ice cover has measurably decreased in thickness, extent, and seasonal duration over the last two decades. This has culminated in record or near-record fluctuations in 1998 and again in 2002 followed by a further strong melt season in 2003. Of central importance in this context are seasonal changes and short-term variability in the state of the ice cover and their effect on the interaction of solar radiation with the ice and underlying ocean. Positive feedback processes associated with decreases in albedo and increasing transmissivity act to accelerate these changes. The rates of spring warming and summer melt as well as the length of the melt season are strongly influenced by the albedo, which in turn decreases as the melt season progresses. At the same time, increased transmission provides more energy to the upper oceanic mixed layer further increasing the potential for melting at the bottom of the ice. This ice-albedo-transmission feedback plays a central role in modulating the heat and mass balance of the Arctic sea ice cover, and its effects are strongest at the ice margins where albedo contrasts are greatest. Along the coastal contact zone, the feedback processes are particularly complex due to interactions with the adjacent land surfaces. Indeed, this zone is where the summer melt is initiated and is a focal point where the feedbacks are amplified.
To understand and model the processes involved, it is necessary to determine how shortwave radiation is distributed within the ice–ocean system and how this distribution affects heat and mass balance. Analysis of this system is complicated by spatial and temporal inhomogeneity of the spring/summer ice cover, with surface conditions varying from deep snow to bare ice to melt ponds to open leads, and with ice thickness ranging from zero (open water) to ridges tens of meters thick, all within an area that is often less than one square km. Each of these categories has a different set of physical and optical properties. Treatment of the surface as a locally homogeneous medium with effective bulk optical properties represents a serious oversimplification that will significantly limit the predictive power of regional and large scale climate and dynamics models. Understanding the evolution of melt ponds and the absorption and transmission of shortwave radiation by a heterogeneous ice cover have been identified as central problems but are among the least well understood processes involved. Since these are sub-grid scale processes with respect to GCM modeling, the most efficient approach to dealing with them is to carry out surface-based process-oriented observations to determine the detailed spatial and temporal variability associated with the various surface types and develop appropriate models to apply this information on larger scales.
The coastal zone in the vicinity of Barrow, Alaska, is critically situated for studies of the processes described above. Results from a recently completed three-year observational study of heat and mass balance of the ice cover in conjunction with the interaction of solar radiation with the ice and adjacent tundra and lakes shows large lateral gradients in solar energy absorbed by the surface. This information is needed to make an accurate determination of partitioning of solar heating in this zone and provides the basis for ice-albedo feedback modeling. We will describe some modifications that will be important for generalizing to conditions attendant to increases in the length of the melt season. We propose that this type of study be continued as part of the SEARCH program and that Barrow is an area of ideally suited for these types of measurements. It offers a key scientific location in combination with superior logistics support and extensive opportunities for K-12 outreach and support of higher education.
Abstract Categories: Coastal Processes
Back to main abstract page
To view the list of records returned in your search you can use your browser's
back button, or perform the same search again:
| 