Production of HPP
21. REAL-TIME SATELLITE INFORMATION Garen Garrity
21.4 Sea Ice Information .1 Sea Ice Edge
Using the SSMII data and the NASA Team algorithm, the sea ice edge defined as the 10 % ice concentration for a 25x25 km grid spacing with an accuracy of +I- 6%
is shown in Table 1. The following table shows the sea ice edge at the various longitudes near the ship during the cruise.
Table 1 : Sea Ice Edge at Locations of Interest During this Cruise for Bird and Mammal Research
21.4.2 Sea Ice Visual Observations
The visual sea ice observation program is not complete due to darkness, and the fact that the ship tended to move during the night, with station stops in the day. This varied however, thus observations were made providing a record of major
changes in sea ice conditions as the ship progressed through the ice. Visual observations are difficult due to viewing the sea ice as one would view the cloud Cover. The closer to the horizon one looks, one tends to overestimate the sea ice concentrations. Thus, the observations are descriptive more than quantitative.
Satellite derived concentrations are quantitative for first year, old ice and total ice, and were provided to the public (Messe 11), the Captain and transferred
electronically to the senior scientist as a colour image on a regular basis during the time spent in the sea ice. Products were distributed to those requesting a copy.
These Images would be too expensive to include in the cruise report, thus individuals who require quantitative sea ice inforrnation should contact the e-mail address: icedoctors@iqs.net. The NASA Team algorithm would be used, thus a 25x25 km averaged sea ice concentration area, however, a 12.5x12.5 km can be obtained, but with more effort due to interpretation requirements.
The sea ice conditions presented below shows typical variability of a sea ice edge from a young ice regime, to first year ice, with old ice (fresh ice) small floes
intervening from the ice berg graveyard near Neumayer (AtkaBay). The most appropriate way to present these general sea ice conditions is to be descriptive.
Satellite information can augment this description by quantifying the sea ice information as a percent of ice covering the ocean surface. Only the visual
observations can estimate the amount of new versus young sea ice, which was the dominant case at this time of ice formation.
Note that general observations such as air temperature, wind speed etc can be obtained from the ship's data (Poldat), thus can augment the sea ice environment if necessary by the User.
April 12 68 49s 5W Dusk to Dark (1 600.. .UTC)
On route to Neumayer, with off shore winds at 8 knots and -30C at the station. A typical sea ice edge was encountered as a pancake ice regime, increasing in concentration southward to 69 10' 6W. Pancake ice concentration varied between 0-1 00% in bands, thus the SSMII NASA Team satellite algorithm missed the 10%
sea ice edge, due to the 25x25 km resolution at this position. The 12.5x12.5 km resolution could be used to define an ice edge more accurately, under most circumstances, but not all. There was 62 nm (1 16 km) of sea ice from the ice edge at 8W to the shelf ice at Neumayer.
April 14 70 27s 8 18W Visibility < (less than) 1 km (0800 UTC)
High winds at 21.1 mls, direction 83 degrees (deg) caused ice pressure to build up. The easterly winds caused little pressure for navigation purposes since the sea ice was only 50 cm thick, 100% concentration, 50% rafting and 50% ridging. This could be a potential situation for krill to hide. The ship waited for the storm to pass.
April 14 70 14s 8 20W Dark (1 900-2000 UTC)
Evidence in the sea ice structure showed that it had been under pressure recently.
Ice type was grey to grey-white, a maximum thickness of 30cm. Concentration was1 OWo with 10 cm of Snow and 0-60% ridging (i.e. variable). Winds remained high, 19 mls form 92 deg. The tide removed pressure from the ice, counteracting andlor stronger effect than the wind. For the SSMII satellite foot print (grid spacing of 25x25 km) the ice concentration was 75%.
April 15 70 10s 7 22 W Visibility 2 km (0800-0900 UTC)
Winds increased to 22.5 mls from 99 deg
.
The ice concentration and ice types varied considerably as compared to previous observations: Open water 10%, white nilas 5%, grey to grey-white ice 1574, and first year 70%.April 15 70 10s 7 27W Stopped (1000 UTC)
The ship stopped due to high winds and incompatible tides for the day. First year ice was prominent at 100%.
April 16 69 59s 7 48W (0800-0900 UTC)
The floe size became recognizable at 1-3 m (minimum) with a grey-white sea ice concentration of 75% and 5 cm of Snow cover. Beginning of the first year ice pack.
April 16 70 9 s 6 54W Visibility 4 km with low winds, 3.2 mls.
The ice floes were <I m in size being 40% grey ice, 5% dark nilas and 5% Open water. The remainder was brash ice.
April 16 70 13s 6 52W (1 130-1230 UTC)
There was a station at 1300 UTC, where the sea ice concentration was typically 15% grey ice and 85% brash with none of the floe sizes > (greater than) 1 m. The SSMII showed 95% ice cover (recall, the concentration if for a larger area than the eye can observe).
April 17 69 58s 6 18W Excellent visibility
-
Day long ice station The sea ice was relatively thin for an ice station where the tides tend to putpressure On the ice by the late afternoon, early evening. Grey-white ice (maximum 30 cm, no ridging or rafting included) with a concentration of 95% the remainder being 5% Open water. Floe size generally 100-1 000 m.
April 18 69 48s 3 47W (0800-0900 UTC)
Floe size near 3 m on average. Dark nilas at 10% with the remaining 90% grey and grey-white ice.
April 18 69 54s 3 36W (0900-1 000 UTC)
The pancake ice was well developed and frozen together with a low concentration of 10%. Dark nilas at 25% and greylgrey-white ice at 65% concentration. The grey- white floe size did not change from the above.
April 18 70 3 s 3 14W (1000-1 100 UTC)
Floe sizk had increased to 10 m with 90% grey-white ice, 5% white nilas and 5%
dark nilas.
April 18 69 51 S 3 4W (1 100-1 130 UTC)
There was a trace of dark nilas, with evidence of past pressured young ice. The floe size of 100% greylgrey-white ice was 25% rafted and floe size averaging 3 m.
April 18 69 51 S 3 4W (1 130-1200 UTC)
There were many (relative to other areas during this cruise) seals and whales observed at this position with brown ice occupying 5% of the sea ice. The floe size was < 1 m at least 30 cm thick (greylgrey-white) (50%) and pancake ice (5O0/0), well established, thus frozen together into an ice sheet. The first year ice type was rafted 25%, thus providing a thickness > 30 cm. The rafting may provide an area for krill to live in harmony, and predators enjoy the idea of a good feast.
April 18 69 3 9 s 3 8W (1200-1330 UTC)
Typical ice edge with swell overtaking the sea ice. The pancake ice was variable, again typical of an ice edge, with 80-1 00% ice concentration. Thus, the floe size was < 1 m. The SSMII showed 80-90% ice Cover.
April 19 70 13s 6 13W (0800-0900 UTC)
An ice station with a variable polynya (small) with time covered with 5% grease and slush ice, 5% water and later in the day 5% dark nilas. There was 5% white nilas at the edges of the 3O0I0 grey ice and grey-white ice areas.
April 20 69 52s 6 W (0800-1200 UTC)
The floe size was decreasing with time with a trace of old fresh ice. Typical compact ice edge with 25% brash ice and 75% greylgrey-white ice 25% rafted.
April 20 69 7.5s 4 1 W (1600 position) (1200-1600 UTC)
There was a sudden decrease in sea ice conditions at 1500 UTC where bands became more apparent. There was 85% pancake ice and 15% Open water before the bands were more prominent at the ice edge. The ice floe size decreased considerably at the 1500 UTC change over of ice conditions. The floes were C 1 m. The SSMII shoed 7O0I0 ice cover.
The SSMII ice cover calculated using the NASA Team algorithm showed different ice concentrations than from visual observations due to: 1) human error in estimated sea ice concentrations from a ship, and 2) the orbit time did not necessarily occur at the time of the visual observation which was averaged over various time periods.
There were a total of 561 good satellite overpasses archived in TeraScan forrnat during this cruise.
APPENDIX 1