Arctic
summer time
The short summer of 2004
Norbert
Untersteiner
Sydney Chapman Professor
University of Alaska Fairbanks
and
Professor Emeritus, Atmospheric Sciences and Geophysics
University of Washington, Seattle, WA
Background
Since 2002, the multi-agency USA-Japan joint project
entitled "North
Pole Environmental Observatory" (NPEO) has deployed Web
Cameras along with the automatic stations and instrumentation
that provide valuable air/ice/ocean datasets. Instruments
included short-wave and long-wave radiometers for down-welling radiation,
air temperature, wind direction and velocity, atmospheric pressure,
ice temperature, and ocean temperature and salinity to 250 m depth.
The Web Cam images show the installations and some scenery throughout
the entire summer, from the beginning of snow melt to freeze-up
in autumn and the onset of darkness.
Observations from the North Pole in summer 2004
Like the previous
two summers, the summer of 2004 appeared also somewhat unusual.
After a brief warm spell on 5 June, surface air temperatures
reached the usual near-zero degrees on 12 June, perhaps a week later
than climatology. Significantly later than climatology, the snow
began to appear water-logged toward the end of June, but the first
melt ponds do not appear until 7 July.
After that, melting seemed to progress rapidly, with
ponds developing steep and even undercut margins. The webcam images
suggest that total pond area reached a maximum on about 15 July.
Shortly thereafter (16-17 July) several images show a thin skim
of ice on the pond surfaces. This is a common occurrence in the
Arctic late summer, caused by clearings of the usually overcast
sky. During these, usually brief, events the increase in direct
radiation from the sun is not sufficient to compensate for the loss
of IR radiation from the low stratus clouds, and the result is a
negative surface heat balance and the formation of a skim of ice
on water that is almost at the freezing point. A striking demonstration
of the inverse relationship of diownwelling long and short wake
radiation can be seen on 9 and 17 May when changes between overcast
and clear sky caused short and long wave radiation to change in
opposite direction by as much as 150 W / sq.m.
Between 20 July and 10 August, the solar
radiation records shows several extremely high short-lived peaks
of up to 500 W / sq.m Such high numbers are possible when the sun
shines through a large opening in the sky and a great deal of additional
radiation is reflected from the clouds surrounding the opening.
The first signs of freeze-up occur as early as 7 August
(Fig. 5) , and by 19 August all ponds visible in the webcam images
are covered with ice and new snow (Fig 6).Sonar
devices at the four buoy sites (Borneo, Jamstec, IABP-NORTH,
IAPB-South) indicate an amount of surface melt between 15 and 35
cm. The lone ablation stake shown in the images of web cam #2 (Fig
6,7) indicates a surface mass loss of 20 cm . As in commonly observed
in thick ice, bottom accretion continues through June and amounts
to about 10 cm.
Comparison of Arctic summertime
in 2002, 2003 and 2004
The summers of 2002, 2003, and 2004, as observed by the Web Cams,
were very different (below). The onset of melting is typically in
early June, but occurred in late July in 2002, and late June in
2003 and 2004. The Web Cam images show very limited melt pond coverage
in 2002, but widespread melt pond coverage in 2003 and 2004. In
2003, the melt ponds were widespread by July 4, but diminished in
late July, and then reformed in mid-August. This was not observed
in the other years. Freezeup began in late August in 2002, Sept
7 in 2003, and in mid-August in 2004.
Summary of Arctic Summertime 2004
Despite the small number of ice thickness measurements that are
available, it seems highly likely that the summer loss of ice in
2004 was anomalously small and that the 2004 melting season was
unusually short.
Difficulty of Summertime Observations at the North
Pole
To appreciate the value of these data and images, we
should bear in mind that the proverbial "inaccessibility of
the frozen Arctic Ocean" due to cold and darkness applies to
the mild summer even more than to the cold and dark winter. During
the long and mild days of summer melt snow and ice, the surface
becomes littered with ponds and potholes, and the transportation
of people and equipment is limited to the most difficult and expensive
modes, i.e. helicopters and ice-breaking ships. It is for these
reasons that all-year manned drifting ice stations, and hence summertime
data, have been at a premium in the history of US arctic research.
While the Soviet Union maintained 30 such stations between 1952
and 1991, the US scientists were able to acquire only four sets
of summer data, two from the International Geophysical Year 1957
and 1958, one year from the Arctic Ice Dynamics Joint Experiment
in 1975, and one year from SHEBA in 1998.
The extraordinary value of the web cam pictures
is illustrated by the preceding samples. This technology
is clearly producing a large amount of information at a very low
cost and the current projects are only a beginning. Fish-eye lens
cameras pointing to the zenith can be employed to observe cloud
amount. A camera could be used to measure accumulation/ablation
by taking pictures of suitably marked stakes, a method that would
yield more representative values than those from a sonic device
that looks at a single point. Cameras could also be used to take
pictures of radiometers and other instruments to determine whether
their readings are compromised by rime deposition.
More Information
The puzzling summer
of 2003
What
changes have occurred in Arctic sea ice volume and dynamics over
the past 50 years?
North Pole Web Cam home page
Moods of the North Pole (selected images) for 2002,
2003 and 2004
North
Pole Environmental Observatory
North Pole Weather
Data
NOAA Arctic Theme
Page
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