Geoscience Reference
In-Depth Information
Figure 7.17.
Mean sea level pressure and anomalies (hPa) for May 1990 from NCEP/
NCAR(from Serreze et al.,
1995
, by permission of AGU).
and was characterized by extensive open water in the Beaufort and Chukchi seas.
Open water formed earlier in this region than in prior years, and September ice
extent was 25 percent less than the previous minimum over the 1953-1997 period.
The times series of Beaufort Sea ice extent at the end of September clearly shows
the year of 1998 standing out as an extreme (
Figure 7.18
). Note that ice extent was
also quite low in the preceding summer of 1997. Over the period of record exam-
ined by Maslanik et al. (
1999
),
1997
and
1998
were the only two successive years
when summer ice extent in the Beaufort Sea was at least one standard deviation
below the mean.
In a previous paper, Rogers (
1978
) diagnosed variability in ice conditions in the
Beaufort Sea from composite differences in summer-averaged sea level pressure
fields between heavy and light ice years. Light ice years are associated with positive
pressure differences over the northern Canadian Arctic Archipelago and north-cen-
tral Siberia, and negative differences over the East Siberian Sea. This strengthens
