This is the next in a quasi-weekly series of diaries on the Northern Hemisphere Arctic sea ice melt season. I write these in memory of Johnny Rook, who passed away earlier this year. He was the author of the blog Climaticide Chronicles.
A week of slowly accelerated melting, though nothing like the ice melt in most of July. The Barrow AK web cam from Friday 21 August is shown below. Cloudy, a little bit of green on the ground in the foreground, and the ocean clear of ice as far as one can see.
The temperature at 21 UTC (13 ADT) was 53°F, dewpoint 40°F, winds southeast at 5 kts. The high on 21 August was 60°F with a low of 44°F; a trace of liquid precipitation was recorded.
More below.
Sea Ice Extent and Concentrations
I thought it would be educational to annotate the Arctic sea ice extent graphic I usually put up (which I didn't do last week), with the forecasts for minimum sea ice extent I covered in a diary dated 19 July 2009. You can view it for yourself below.
I placed a horizontal line at 6 million km2 so I could figure out the level as of 22 August: it appears to be about 5.8 million km2. I also put a semi-transparent blue box to cover the range of forecasts for sea ice minimum that were reported on in July, based on June 2009 data. These range from 4.0 mm km2 to 5.2 mm km2.
Further insight can be obtained from a mid-month report done the by the National Snow and Ice Data Center (NSDIC), which I diaried without graphics (or much notice, in fact) on 19 August. Apparently, the large scale circulation changed in such a way to preserve Arctic basin sea ice; the exit through the Fram Strait (between Greenland and Svalbard to the east) was essentially not being used since late July 2009. The ice instead was being pushed toward the Siberian coast, where the water is colder and the ice would be slower to melt.
The table below shows 22 August 2009 sea ice concentration (upper left), 15 August 2009 concentration (upper right), and 22 August 2008 sea ice concentration (lower left). I've annotated the current sea ice concentration to show where there has been sea ice loss in the last week. There hasn't been anything perceptible in the way of gain, and losses are limited generally to the Bering/Chukchi Sea sector of the Arctic Ocean basin.
22 August 2009 | 15 August 2009 |
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22 August 2009 | 22 August 2008 |
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Compared to last year, there's somewhat more ice than in 2008 in the Fram Strait for the reasons stated above; and in the area north of the Canadian Northwest Territory and in the East Siberian Sea. Less ice than last year is found in the Laptev Sea and north of AK into the Arctic Ocean proper.
Current Weather
The weather at 06 UTC on 23 August 2009 is shown below, courtesy of the University of Cologne, Germany. I've contoured areas that are 0°C or below (at contour intervals of 3°C) so it's easier to see where the weather is below freezing.
Much of the central Arctic Ocean basin is at or below freezing; areas near Greenland are colder yet, at about −3 to −5°C.
The drift buoy where the NOAA north pole web cam is (about 84.2°N and near 0°W) stands at +0.5°C; another buoy almost exactly at the north pole presently has a temperature of −2.6°C.
2009 Arctic Sea Ice Minimum
The minimum sea ice extent from year to year depends on a few things: the amount of solar input (based on cloudiness), the winds and how they break up, disperse, or push together the ice, and the temperature anomalies. Once the sun begins to set, melt does continue for a little while as temperatures are affected by the amount of open ocean available and the water temperature anomalies.
As we've seen this year, the sea ice has been very sensitive to wind circulation and temperature anomalies. This year, if we go back to the July pattern of winds pushing ice through the area east of Greenland, we may still get significant ice loss. At present, however, I will go with an amateur prediction of minimum sea ice extent occurring in about 3 weeks, at the top end of the forecasts shown in the graphic above (or about 5.2 million km2.
Sea Surface Temperature Anomalies
The sea surface temperatures (SSTs) are indicative to an extent of the amount of heat content is being held in the upper ocean, though a more accurate measure would be an average temperature anomaly of the upper mixed ocean layer times its depth. What do the SSTs show us now?
Below is the latest 1/8° by 1/8° analysis of SST for the earth's northwestern quadrant as of 12 UTC 23 August 2009. The north coastline of AK and western Canada, where there is water rather than ice, is well above normal in many areas; on the order of 5-6°C (equal to 9-11°F). This has been the case the last few summers, with early ice melt and solar energy thus being available for directly warming the ocean.
Also in the northwestern quadrant you can see the impact of Hurricane Bill on SSTs in the Atlantic along its path (cooler water upwells beneath the cyclonic circulation of the storm); also, the above normal temperatures of El Niño can be seen along the eastern equatorial Pacific ... about 1-3°C above normal over a large stretch of equatorial ocean.
In the earth's northeastern quadrant from the same time shown below, SSTs are once again well-above normal between the Arctic sea ice field and much of the Arctic coastline of Asia and Europe. This is especially pronounced on the central Siberian Arctic coast, where temperatures are as much as 8°C (14°F) above normal. Remember that water has a very high heat capacity and takes some time to cool; a factor that will delay refreezing to some extent. This was true last year as well, however, and refreeze took place at a very fast pace.
An extra treat: 1900-2008 seasonal sea ice extent
As an extra treat, below is the graphic of seasonal sea ice extent, courtesy of University of Illinois Urbana-Champaign (UIUC), for fall, winter, spring, and summer seasons from 1900-2008.
Some things are very obvious here with the data:
- There are a couple of discontinuities in the data, the first in 1950s and the second in 2007 with the record minimum.
- All show a downward trend, though the winter season had an interruption in same in the late 90s to early 2000s.
- Summer has shown the biggest impact, with winter the least. This makes sense with thinning ice; think about how quickly a thin sheet of ice will melt compared to an ice cube, for example. Thin ice can also be more easily torn up by wind and wave action, beyond the lower volume of ice that, all else being equal, can be melted more quickly.
Data from before 1950 comes from ship observations at the edge of the Arctic sea ice field. From 1950-1979 we have those obs plus the submarines of the Cold War; from 1979 to the present we have satellite observations using microwave imagery to distinguish sea ice and see through the frequently cloud-covered Arctic basin, especially in the summer season. How these different observational data sets are blended together would be a diary in itself, and perhaps beyond the scope of what I write here.