30 September, 2010 Halley
The month of September, so often associated with dew on the ground, the rustle of crisp leaves and woodsy aromas back home in the UK, brings a starkly contrasting ambience to our little corner of the Brunt Ice Shelf. The days are hastily gaining length, with smaller and smaller windows to enjoy views of the Milky Way in the night sky, although these give way to some truly magnificent sunrises and sunsets. Outdoor activity steps up as vehicles are gradually de-winterised, and we catch our first clear glimpses of features around the ice shelf such as the northern headlands, the MacDonald Ice Rumples and even features in the Hinge Zone looking south, towards the continent.
Base life began in true Halley style with a fancy dress party to celebrate my twenty-fourth birthday. Eleven cartoon characters descended upon one of the finest selections of party food ever to adorn a pool table, and then continued onto a friendly competition at the local bowling alley.
Having demonstrated a somewhat formidable partiality towards Tracker Bars over the course of winter, I was duly delighted when presented with nothing less than a Tracker Bar-clad chocolate cake.
As the wintering meteorologist and electronics engineer, I look after scientific equipment not only on base but also at remote sensing sites in the field. As the daylight returns, off-base travel is possible once again, and the Field Assistant Ed and I took the opportunity to visit a field site early in September. The site, DD10, is home to part of an experiment that uses GPS receivers to track how the ice shelf is moving, and had stopped sending data back to base.
In order to travel safely and notice tell-tale signs of crevassing, it is important for the contrast of the snow surface (i.e. the ability to discern surface features) to be sharp, which requires the absence of low thick cloud. Unfortunately, these conditions are often coincident with cold nights, as there is no insulating cloud layer to reflect escaping radiation, so we had to wait several hours after sunrise before the skidoo engines had warmed up to the point at which they would start, about −35°C.
On our first attempt to reach the site, which is approximately 12km (or a 1 hour skidoo journey) away from base, the contrast deteriorated to such an extent that we had to turn back before reaching our destination. A few days later, we made a successful second attempt, testing the power systems and restarting the experiment.
The following day marked the start of my winter trip. All winterers at Halley have two holidays, one week at the start of winter and one at the end. If weather conditions permit, people almost always take the opportunity to travel to interesting sites on the ice shelf, such as the coast (10km from base), the MacDonald Ice Rumples (20km) or the Hinge Zone (40km).
On my first winter trip (during March), I was fortunate enough to spend fourteen days in the Hinge Zone as part of the intrepid Sledge Bravo party, the latter nine spent laid up in the tent waiting for an early onset of unfavourable weather to clear before making a speedy retreat back to base. While the weather this time round did not lend itself to a long expedition, we were glad to make it out for an overnight stay at Windy Caboose as well as a day trip to the Rumples.
On the final day of our trip, we had to perform some emergency oil line repairs on my skidoo, for which the emergency medical supplies box came in surprisingly handy.
The Hinge Zone was also revisited during the course of September.
Back on base, construction had started on one of the most intriguing projects that the Brunt Ice Shelf has seen in recent years. With an ambitious floor plan of 2 metre diameter, this structure was located east of the Simpson Science platform.
Sadly, a bout of severe weather caused serious structural damage, rendering the project unsalvageable before the start of summer. Plans for a second attempt during summer are already in the pipeline.
During September, Halley saw the most spectacular polar stratospheric clouds observed so far this year.
High enough to be strongly illuminated by the sun when it is still below the horizon, the clouds pictured form at heights from 15km to 25km in the stratosphere, much higher than clouds usually occur. These particular clouds (Type I) signify temperatures below −78°C, although weather balloon radiosondes often measure temperatures as low as −90°C during the winter.
Type I Polar Stratospheric Clouds play a crucial role in the destruction of ozone during the Antarctic ozone depletion season. During the winter, a regular circulation known as the circumpolar vortex forms around the continent, isolating air masses in the stratosphere. With little influx of warmer air from lower latitudes, temperatures tend to drop very low, leading to the formation of stratospheric clouds. These provide surfaces for chlorine compounds such as Hydrogen Chloride (HCl) and chlorine nitrate (ClONO2) to release chlorine monoxide (ClO). When sunlight returns in the Antarctic spring, this ‘active chlorine’ catalyses ozone destruction reactions, causing the Antarctic ozone hole.
Nacreous clouds are also stratospheric, and are characterised by pastel colours. This picture was taken one hour after the previous picture.
Other activities in September included rigging a radio antenna after repairs performed by our Comms Manager Ian, and restocking the BART (Balloon and Radiosonde Terminal) with helium for balloon launches during summer.
We also enjoyed some of the last sunsets of the winter.