27 December, 2002

On the road again

Date: 12/27/02

Latitude: 86° 58’ 44” S

Longitude: 107° 56’ 19” W

Time of Observations: 7:00 p.m. local time

Temperature: -25 C / -13 F

Wind speed: 10 knot

Wind Chill: -36 C/ -33F

Wind direction: Westerly

Meters of ice collected: 506 m

By Gordon Hamilton

The day after the day after Christmas -- what some us call December 27. We woke early this morning to witness a bank of fog come rolling in over camp. Being close to the summit of Hercules Dome, it’s not unusual for local patches of fog to form in calm conditions. By the time we had eaten our breakfast mcmuffins, the fog had shrouded our camp in a cold white haze.

Today is our traverse day, and because we had done most of our packing last night there was not a lot to do before we were able to leave. The final sleds were arranged in the trains and the tractor engines were warmed and, a couple of hours after breakfast, we were on our way. So far progress has been good and we are currently about 50 km from our camp at Hercules Dome. Our only slowdown came near the start of the travel day when we had fog conditions; the small droplets of moisture in the air freeze and form something called diamond dust. Because diamond dust is so fine it clogs up the engine cooling grills on the tractors and causes the engines to overheat. It means we have to stop and brush away the diamond dust periodically. When it’s bad, the stops come every 1 km or so, which really slows progress. Luckily, now that we are farther from the summit of the dome, the fog and diamond dust have dissipated.

Apart from the diamond dust, the travel has been uneventful. Riding in the Blue Room takes some getting used to because there are no large windows so we can see when we might hit a bump or sway from side to side. Although the surface of the ice sheet looks flat, it is actually composed of lots of little bumps and ripples formed by blowing snow. These features are called sastrugi. Every time our sled slides over a sastrugi the Blue Room shakes from side to side, as do the other buildings on sleds. The tractor drivers, on the other hand, have cushioned seats and get a much smoother ride. A bad travel day is when the sastrugi are spaced closely together. Luckily today has been relatively smooth for the most part.

Sastrugi form when snow being blown across the surface by the wind gets trapped by an obstruction (like an existing sastrugi). They always form with their long axes parallel to the wind direction. The region we are traveling across now is dominated by katabatic winds (currents of cold air that follow the slope) from East Antarctica. Because we are driving into the dominant wind direction, we encounter most of the sastrugi lengthwise. That makes for a much smoother ride compared to crossing sastrugi sideways.

Sastrugi make for uncomfortable travel conditions, but they can actually be quite useful for some purposes. Whenever we arrive at a new ice core site, we use the sastrugi orientation to determine the prevailing wind direction bringing snow to that site. Pilots of the Twin Otter aircraft (that our roving team member Leigh Stearns has been using for the past week to revisit sites from previous ITASE field seasons) use sastrugi directions to assess wind patterns when coming in to land at remote ice sheet sites.

And so the ride goes on… Markus and Susan are driving the lead train at the moment and have probably reached disk 7 of the Harry Potter CD set that ITASE investigator Deb Meese sent to the field for us to listen to on the long drives. Lynn is driving the second tractor, doing his best to give those of us in the Blue Room a smooth ride. Blue is working on shallow radar and GPS profiling, having just taken over from Jim who worked the first 6 hour shift. Andrea is knitting, Mark and Paul are watching a movie and the rest of the team seem to be in la-la land.