Variability of the Sea Ice
Cover from AMSR andHistorical Satellite Data
Josefino C. Comiso
NASA Goddard Space Flight Center
Josefino.c.comiso@nasa.gov
JAXA/EORC AMSR/GLI Symposium
Toshi Center Hotel, 23 January 2006

Motivations for using AMSR Data
for Sea Ice Studies
We expect that the high resolution
AMSR data would enable improved flux
and air-sea ice-ocean studies.
 Wider spectral range and improved
resolution should allow for moreaccurate and less ambiguous
determination of geophysical variables.
 The data could provide the baseline
for climate change studies and themeans to evaluate historical data.
Ice
Concentration
AMSR vs SSMI
 General patterns

are basically thesame but
sensitivity to smallchanges in surface
properties are
better for AMSR.
 Area of no data(near NP) is muchsmaller for AMSR
 Sharper andimproved ice edge
characteristics forAMSRSeasonality of
the Arctic,
Antarctic andTotal Sea Ice
CoverMonthly extent,
area, andconcentrationof Arctic seaice

Ice extent
comparisons A smallbias isapparent
with AMSR
showing
less extent
than SSMI Bias issmaller inthe SHthan in theNH

Ice Edge
Characterization
 All channels fromAMSR are coherent.
The ice edge
location is almost
frequency
independent Effect of resolution
and sidelobes are
more apparent
with SSMI Errors of about 12
km is possible insome locations for
SSMI dataAnnomaly/Trend
Studies - SH
 An increasing

percentage inaverage ice
concentration isobserved As a result, thetrend in ice area ishigher than that in
ice extent

Annomaly/Trend
Studies - SH Smaller trend in

ice extent isobserved with theuse of AMSR data
instead of SSM/I
reflecting somebias
 Again, the trendsin ice area arealmost the samefor AMSR andSSMI

Unadjusted versus
adjusted
ice extent
data forSMM/IandAMSRUsing the three
years of data
overlap to adjust
SMMR andSSM/I data on amonth-by-month
basis, the trend
becomes moresimilar to theoriginal.
However, theAMSR part of
the time series ismore accurate.

Transient sensible heat polynyas

15 August – 15 September 2003 AMSR 12.5 km IC

15 August – 15 September 2003 AMSR 6.25 km IC

AMSR-E
versus Landsat

February 11, 2003a) Landsat

 Landsat data provide

information that canbe very useful in theinterpretation ofAMSR-E data The concentration of
new ice depends on
thickness and stage ofgrowth The higher resolutionof AMSR enables moredetailed comparison ofspatial featuresb) AMSR 6.25km (Daily)c) AMSR 12.5km (Daily)d) SSM/I 25km (Daily)

Blending AMSR-E to MODIS

Annomaly/Trend
Studies - NH Potential errors

associated with biases
due to different
resolution andcharacteristics ofdifferent sensors
 Ideally, a change insensor type must beavoided if possible.
However, sensors
have finite lifetimes
and new ones shouldtake advantage of
new technologies

Anomaly/TrendStudies - NH Long term studies

requires consistency
checks speciallyduring periods ofoverlap
 Use of AMSR provides
a means of improving
accuracy in trend
analysis but biases
should be removedfirst Ice area values are
more stable becauseof less dependency toice edge location

2002 perennial ice using 89 GHz IC Data

2005 perennial ice using 89 GHz IC Data

The perennial ice cover using AMSR-E data
- last 4 years
Statistics:A (1979-1982)
is 6.33 x 106km2
A (2002-2005)
is 4.95 x 106km2
δA is 1.38 x
106 km2 or
9.9%/dec

5-year mean in summer extent and area
(1980 to 2005)
 Big change every

10 years Phase shift
towards a later
date of summer
minimum
 Big drop during
the summer andautumn in 2005

Yearly Arctic Ice
Cover during
Maximum Extents
1979-2003
Arctic Extents and Areas
during Ice Maxima

Arctic Perennial Ice, 1979 to 2005

Retrieved Multiyear Ice in Winter vs Perennial
Sea Ice Extent and Area

• Extents are pretty similar in magnitude but variability is not the same
• Area are very different – this is mainly in part because of different
signature of the 2nd year floes• Trends are similar but not of the same magnitude because of thevariable contribution of the 2nd year ice cover.

Extents

Per Ice Area
MY ice Area

Polar AmplificationFeedbacks
 Ice-Albedo

Feedback –relevant
to retreating
perennial ice coverand also over land
 Cloud feedback –positive ornegative,depending on theheight of clouds
 Other feedbacks
are mainly positive

5.4%/deca) Yearly Melt (1982 to 2005)
Ice Sheet Melt Area (x106 km2)

Area of melt increased
dramatically (IR data)
in Greenland during
the last four years.
Impacts on sea level isa concern (up to 7 m).

< 1 week of melt
< 2 weeks of melt

3.8%/decYearb) 1992c) 2002d) 2005

9G3f

Since the satelliteera, global surface
temperature has
been going up
almost consistently.
We now know that2005 is thewarmest year sincemoderntemperature
measurement
techniques havebeen implemented.

Summary and Conclusions
 AMSR provides the expected improvements inthe large scale characterization of the sea icecover.
 AMSR shows spatial details of the ice cover thathave never been observed before and will
enable more accurate heat flux, polynya, andOdden studies .
 AMSR provides better ice edge and divergence
information and has the potential of improving
the accuracy of long term variability and trend
estimates in the ice cover AMSR could rightfully serve as the baseline for
future sea ice studies.