Figure 1. The three overlapping study regions. The small region is centered on Disko Bay. The areas of the small, medium, and large regions (not including land) are: 12,400 km 2, 118,000 km 2, and 439,000 km 2. Figure 2. Left: Example of sea ice concentration (%) derived from passive microwave satellite data (SSMI) for March Right: Blow-up of the rectangle centered on Davis Strait, showing the three study regions. Each sea ice concentration grid for the Northern Hemisphere is 304 x 448 pixels with a nominal pixel size of 25 x 25 km. Figure 3. Sample chart from the Danish Meteorological Institute for March 1968 showing the ice concentration in West Greenland, as follows: Cross-hatching: 10/10; diagonal stripes: 7/10 to 9/10; vertical stripes: 4/10 to 6/10; diagonal dashes: 1/10 to 3/10; no shading: less than 1/10. The colored dots (connected by colored lines) show points that have been digitized. They delineate areas of constant ice concentration. The outlines of the three study regions are in purple (they have been overwritten in some places). Thus, for example, the green curve in Disko Bay outlines that part of the small study region for which the ice concentration is 10/10. The red curve in the lower right outlines that part of the medium study region for which the ice concentration is 1/10 to 3/10. In this way, upper and lower bounds on the ice concentration (or ice area) in each study region can be computed. This has been done for 23 charts (23 Marches) from 1953 through 1979 (four missing years: 1954, 1959, 1965, 1966). Figure 6. Left: Correlation of wintertime (Dec-Mar) sea ice concentration from SMMR & SSMI ( ) with wintertime NAO index ( ). Right: Correlation of sea ice concentration ( ) with the previous year’s NAO value ( ). Colors: dark red The correlations are generally positive in Baffin Bay, Davis Strait, and the Labrador Sea. In the un-lagged case (left), correlations are around 0.3 across a wide swath of the medium study region, while the same area in the lagged case (right) has correlations above 0.7. This suggests that last year’s NAO has predictive value for this year’s ice conditions in West Greenland. Variability of Sea Ice in West Greenland Harry L. Stern Polar Science Center, Applied Physics Laboratory University of Washington 1013 NE 40 th Street Seattle, WA USA Mads Peter Heide-Jørgensen Greenland Institute of Natural Resources c/o National Marine Mammal Laboratory 7600 Sand Point Way NE Seattle, WA USA Presented at the Workshop on Sea Ice Extent and the Global Climate System, April 2002, Toulouse, France Acknowledgements We thank the Danish Cooperation for the Environment in the Arctic (DANCEA) for funding this project. Satellite data were obtained from the National Snow and Ice Data Center in Boulder, Colorado (nsidc.org). Figure 4. The top three panels show the ice area (in thousands of km 2 ) in March in the three study regions vs. time ( ). The blue dots indicate data derived from ice charts, as in Figure 3; the black dots and red dots are from satellite data, as in Figure 2. The trends for the large, medium, and small regions are (respectively): 1.5, 3.0, 1.7 %/decade. The estimated uncertainty in the trends is about 1 %/decade. The trend in the medium region is very significant. The variability in the medium region explains most of the variability in the large region. For those two regions, notice the decadal cycle with low points in 1962, 1970, 1979, 1986, and (See spectrum in Figure 5). The fourth panel shows the winter (Dec-Mar) NAO index. Its spectrum has a weak peak at the same period as the peak in the ice area (Figure 5). The fifth panel is the near-surface sea temperature measured at Fylla Bank (63.6 o N, 52.4 o W) in early summer. It helps to explain the correlations between ice area and NAO in Table 1. References [1] Parkinson, C. L., et al., J. Geophys. Res., 104, C9, , [2] Rigor, I. G., et al., , J. Climate, 13, , [3] Hurrell, J. W., Science, 269, , A major part of the West Greenland ecosystem is covered with sea ice for about half the year. This skin of sea ice, called the West Ice, seasonally prevents fishing activities and is an important habitat for numerous birds and sea mammals and a variety of ice-associated biological activity. Parkinson et al. [1] found a trend in the wintertime sea ice extent of +7.5% per decade for for the region encompassing Baffin Bay, Davis Strait, and the Labrador Sea. The wintertime surface air temperature shows a trend of -2 o C per decade for along the west coast of Greenland north of 69 o N [2]. These regional changes in ice extent and temperature are linked to the North Atlantic Oscillation (NAO)  the difference in surface atmospheric pressure between Portugal and Iceland [3]. We examine the sea ice area in March in three overlapping study regions centered at 69 o N on the west coast of Greenland (Figure 1). The objectives are to estimate the trends in the ice cover as far back in time as possible, and to develop guidelines for a future annual assessment of the ice conditions in West Greenland. Satellite data. We use monthly gridded sea ice concentration derived from the Scanning Multichannel Microwave Radiometer (SMMR, ) and the Special Sensor Microwave Imager (SSMI, present). Figure 2 shows an example for March Chart data. From 1952 to 1980 the Danish Meteorological Institute published an annual volume called "The Ice Conditions in the Greenland Waters". Each volume contains maps of the ice concentration at the end of each month, as in Figure 3. Data for the charts came from ship and aircraft observations. We scanned the charts, digitized the contours, and computed the area of ice within each study region. Figure 4 shows the time series of ice area in March in each study region from the combined satellite and chart data sets. The ice area in the medium study region shows a significant positive trend, as well as an 8.2-year cycle (Figure 5). The winter (Dec-Mar) NAO (Figure 4, fourth panel) is highly correlated with the ice area during the satellite period, but not during the chart period (Table 1). This is explained by the relationship between the NAO and the sea temperature: positive correlation (+0.23) during the chart period and negative correlation (  0.51) during the satellite period. Figure 6 (left panel) shows the correlation of winter NAO with sea ice concentration over the whole Arctic. Blue is positive, red is negative. Correlations are moderately positive in West Greenland. In the right panel, the previous year's NAO value is correlated with the ice concentration. This boosts the correlation above 0.7 over a large area from Disko Bay toward the southwest, and suggests that next year's ice conditions in West Greenland can be predicted to some extent by this winter's NAO index. Figure 5. Top: Power spectrum of the ice area in the medium region (Figure 4, second panel). The largest power is at the longest period, but the spike at 8.2 years stands out prominently. Bottom: Power spectrum of the winter NAO (Figure 4, fourth panel), showing a weak peak at the same period. The vertical scale is linear. Table 1. Correlation of ice area with winter NAO for the chart period (left, ) and the satellite period (right, ). The difference in the correlations can be understood by considering the NAO and the sea temperature (Figure 4), which are positively correlated during the chart period (+0.23) and negatively correlated during the satellite period (  0.51). A high NAO (strong Icelandic low pressure system) was associated with low sea temperature during the later period ( ), allowing ice to advance farther south  hence high ice area and high correlation with NAO. But during the early period ( ) a high NAO was weakly associated with a high sea temperature, damping the tendency of the high NAO toward high ice area. Region Large Medium Small