D. Andrew Rothrock

Warming of the Arctic Ocean by a strengthened Atlantic Inflow: Model results

An ice-ocean model is used to examine the behavior of the Arctic Ocean in response to recent changes in Arctic climate. The model shows that, starting about 1989, there has been a significant warming and salinification in the Arctic Ocean, in agreement with recent observations. The warming and salinification occur mainly in the upper ocean owing to a sustained increase of Atlantic inflow both at Fram Strait and, most significantly, via the Barents Sea. The increased incoming warm and salty Atlantic Water “flushes” out cold and fresh Arctic Water, thus increasing the temperature and salinity of the upper ocean and resulting in more oceanic heat flux to the mixed layer and ice cover. Concomitantly, the model shows a continuing decrease in ice volume beginning in 1987.

Extracting Sea Ice Data from Satellite SAR Imagery

With the prospect of operational satellite SARs by the end of the decade, there is a clear need to develop automated algorithms for the extraction of geophysical data about sea ice from highresolution radar imagery. To this end, we have developed techniques for distinguishing ice from open water and for resolving the details of deformation within areas 100 km square imaged by Seasat SAR. The classification of ice and open water is based on the creation of a second band of image data consisting of the local variance of the original brightness, the first band being a local average brightness. In the space of these two variables, ice and open water are separated into two distinct clusters. The deformation is found on a 3.4-km mesh by local cross correlations of the brightness. The strategy is to find a coarse displacement field with a highly averaged image, and to proceed through a hierarchy of images with increasing resolution, improving the accuracy of the displacements at each step. Comparison with manually determined displacement shows room for improvement in regions of high deformation by using smaller areas for cross correlation. The concentration and deformation data are used together to determine localized regions of the scene where open water is produced or lost.

“Eyeballing” Trends in Climate Time Series: A Cautionary Note

In examining a plot of a time series of a scalar climate variable for indications of climate change, an investigator might pick out what appears to be a linear trend commencing near the end of the record. Visual determination of the starting time of the trend can lead to an incorrect conclusion that the trend is significant when the assessment is based on standard linear regression analysis; in fact, a presumed level of significance of 5% can be smaller than the actual level by up to an order of magnitude. An alternative procedure is suggested that is more appropriate for assessing the significance of a trend in which the starting point is identified visually.

Introduction: The Alaska Synthetic Aperture Radar Facility special section

In 1985 the National Aeronautics and Space Administration (NASA) and the University of Alaska agreed to implement, at the Geophysical Institute of the Fairbanks campus, a facility dedicated to the acquisition, processing, distribution, and archival of synthetic aperture radar (SAR) data to be downlinked from satellites. Since then, the Alaska SAR Facility (ASF) has been an active part of NASAs Mission to Planet Earth. ASF Program goals were outlined by Carsey et al. [1987]. Plans were put in place to support three satellites, and the first two, the First European Remote Sensing Satellite (ERS 1) (launched in My 1991) and the Japanese Earth Resources Satellite (JERS 1) (launched in February 1992) are presently in orbit and are being supported by ASF. The third, the Canadian RADARSAT, is scheduled for launch in the spring of 1995. Future satellite missions by U.S. or foreign agencies may well be added in time.