Ensemble Predictions of Summer 2008 Arctic
Sea Ice (Model-Data Synthesis)
Significant
decline of Arctic sea ice has been detected in recent years (e.g.,
Meier et al., 2007). Perennial
ice, particularly the oldest and thickest ice within the multiyear ice
pack
(Maslanik et al., 2007), has been rapidly replaced in recent years by
thinner
first-year ice (Nghiem et al., 2007; Kwok, 2007) that is more sensitive
to
changes in atmospheric and oceanic forcing. The
decline of Arctic sea ice was particularly
dramatic during summer 2007 when Arctic sea ice extent plummeted to the
lowest
level since the 1970s (e.g., Stroeve et al.,
2008; Comiso et al., 2008).
Concurrently, there were observations of unusually warm surface
waters
in the Chukchi, East Siberian, and Beaufort seas (Steele et al., 2008),
where amplified
surface
absorption of solar energy occurred because of the disappearance of ice
cover (Perovich per. comm.;
also see Perovich et al., 2007). How
would this unprecedented decline of summer sea ice, together with
exceptionally
warm surface waters in the Arctic Ocean,
affect the ice conditions in summer 2008? To answer this
question, ensemble
predictions of arctic sea ice in summer 2008 are carried out, through a
synthesis of a model, NCEP/NCAR reanalysis data, and satellite
observations of ice concentration. The model is the Pan-Arctic Ice-Ocean
Modeling and Assimilation System (PIOMAS) that can assimilate
satellite ice concentration data. The ensemble predictions are
constructed by using the NCEP/NCAR atmospheric forcing
from 2001 to 2007 (corresponding to 7 ensemble members) and the PIOMAS
retrospectively
estimated ice and
ocean conditions at a given date of 2008 at which ensemble
predictions start. As the date approaches summer 2008, the degree of
prediction uncertainty would likely be reduced, hopefully, because of a
decreasing prediction range. Details about the ensemble prediction
procedure may
be found in Zhang
et al., 2008a.
Figure 1. This figure
shows that sea ice thickness in late
winter and early
spring of 2008 is significantly thinner than in those of 2007 in most
of the
Pacific sector of the Arctic Ocean where ice disappeared in summer
2007. Ice is also thinner in the Canadian Archipelago region (an
implication for the Northwest passage). This may indicate that the ice
is preconditioned for another radical change this summer. Should
we have anomalously strong southerly winds this summer like last
summer, that would trigger another big effect of ice-albedo feedback,
leading to a
big summer ice retreat again. Some of the effects of last summer's wind
anomaly and ice-albedo feedback may be found in Zhang
et al., 2008b.
Figure 2. This figure shows the
predicted September 2008 mean sea ice thickness from
seven individual
ensemble members, ensemble median ice thickness, and ensemble standard
deviation (SD) of ice thickness. The prediction range is 5/1 -
9/30/2008 for all seven ensemble members. Ensemble member 1
uses 2001 NCEP/NCAR atmospheric forcing over 5/1 -
9/30/2008, .... ensemble 7 uses 2007 NCEP/NCAR forcing. The observed (predicted) September 2007 (2008) ice extent is
shown in
white (black). The ensemble median is likely
to has a 50% probability of occurrence and the ensemble median ice
extent is close to that in September 2007 (Figure 2h).
Figure 3. This figure is similar to
Figure 2, but the prediction range is 4/1 -
9/30/2008. A comparison of Figure 2h and Figure 3h shows that as the
prediction range becomes
shorter, with the starting date of prediction being moved from April 1
to May 1, the
predicted summer 2008 ice
cover becomes smaller. This may indicate that the April 2008
atmospheric
and
oceanic conditions played a role in accelerating the retreat of the ice
cover, leading to a prediction of a lower summer ice extent. This is
consistent with the
finding by NSIDC scientists that April is anomalously warm over a
large area in the Arctic Ocean.
Links to Some Other Activities for Seasonal
Outlook of
Arctic Sea Ice
Work at
NSIDC.
Work
by Ron Lindsay
Work by Ignatius Rigor et
al.
Important Notice
The purpose of the seasonal predictions of arctic sea
ice is for
scientific research and education only. There
are many uncertainties with the predictions and the results must be
viewed with caution. The work is conducted at
the Polar
Science Center, Applied Physics Laboratory, University of
Washington. Support is provided by NSF and NASA.
Neither the Government nor the University of Washington nor any
individual person makes any warranty, expressed or implied, or assumes
any responsibility or liability for the use of the prediction results
or any other results in this web site.
References
Comiso,
J.C., C.L. Parkinson, R. Gersten, and L. Sock, Accelerated decline in
the
Arctic sea ice cover, Geophys. Res.
Lett., 35, L01703, doi:10.1029/2007GL031972, 2008.
Kwok,
R., Near zero replenishment of the Arctic multiyear sea ice cover at
the end of
2005 summer, Geophys. Res Lett., 34,
L05501, doi:10.1029/2006GL028737, 2007.
Maslanik,
J. A., C. Fowler, J. Stroeve, S. D robot, J. Zwally, D. Yi, W. Emery, A
younger,
thinner Arctic ice cover: Increased
potential for
rapid, extensive sea-ice loss, Geophys. Res.
Lett., 34, L24501, doi:
10.1029/2007GL032043, 2007.
Meier,
W.N., J. Stroeve, and F. Fetterer, Whither Arctic sea ice? A clear
signal of
decline regionally, seasonally and extending beyond the satellite
record, Ann. Glaciol., 46, 428–434, 2007.
Nghiem,
S.V., I.G. Rigor, D.K. Perovich, P. Clemente-Colon, and J.W. Weatherly,
Rapid
reduction of Arctic perennial sea ice, Geophys.
Res. Lett., 34, L19504, doi:10.1029/2007GL031138,
2007.
Perovich,
D. K., et al., Increasing solar heating of the Arctic Ocean and
adjacent seas,
1979-2005: Attribution and role in the ice-albedo feedback, Geophys.
Res. Lett., 34, L19505,
doi:10.1029/2007GL031480, 2007.
Steele,
M., W. Ermold, and J. Zhang, Arctic
Ocean surface warming trends over the past 100
years, Geophys. Res.
Lett., 35,
L02614, 2008.
Stroeve,
J. and others, Arctic sea ice extent plummets in 2007, EOS,
Trans. Am. Geophys. Union, 89(2),
2008.
Zhang, J.,
R.W. Lindsay , M. Steele, and A.
Schweiger, What
drove the dramatic retreat of Arctic sea ice during summer
2007? Geophys. Res. Lett., in press, 2008b.
Zhang, J., M. Steele, R.W. Lindsay, A. Schweiger, and J.
Morison, Ensemble
one-year predictions of arctic sea ice for the spring and summer of 2008,
Geophys. Res. Lett., 35,
L08502,
doi:10.1029/2008GL033244,
2008a.