Equinox and shorter days bring interesting light effects. We also debrief you on work and play this week at Davis.

Sky and the seasons

As the meteorology tech guy, the first thing I'll be talking about is the weather. This Wednesday (20th March) is equinox. This means that the days and nights are of equal length, and the days are fast becoming shorter. On equinox the sun will rise in due east and set in due west, and from then until the next equinox in September the sun will be in the northern half of the sky, skimming closer and closer to the horizon until it doesn’t rise at all (in June).

We are definitely feeling the chill. The weather through the summer seemed to hover around freezing, but now it is common to see temperatures of minus ten to fifteen degrees Celsius. On the second of March we had grease ice forming on the bay. At first I thought it would be blown out by the next wind, but this was two weeks ago and we have had pretty light winds since then. So now the ice is getting thicker and thicker, and it’s easily enough to support the weight of an elephant seal. They have a little gap in the broken pancake ice by the beach but it will be interesting to see how much longer they can keep it open for.

Another interesting thing is the optical phenomena we have seen. Now the sun is setting, and lower in the sky, the ground is beginning to cool, and as a result the surface temperatures can be several degrees colder than the air a few hundred metres up. This is known as a temperature inversion. Funnily enough it tends to happen on the clear sunny days, as cloud can act as a blanket and give warmer temperatures. On a few of these days the temperature differentials have been so strong that the light actually bends slightly, towards the colder denser air on the surface. This results in a superior mirage, meaning the image you see is above where it really is.

On the other hand, when the sun sets over the ocean the light often passes over a warmer layer of air over the ocean surface. The sea water maintains a temperature of minus one point eight Celsius, so that is actually often warmer than the cold air coming from the ice plateau. As a result air is bent upwards, and this can be a good thing when you are trying to see a green flash. A green flash happens for only a few seconds, just after sunset. It is the last of the sun’s rays refracting around Earth’s surface, just like in a prism. I've only ever seen it once before, on the ship out of Hobart, but this one on 14 March went for probably three to five seconds and about half of a dozen of us saw it. I managed to get a photo but really, you had to be there!

Finally something to look out for at sunrise or sunset is the solar pillar. This is a vertical beam of light above the sun, caused by reflections off ice crystals in the atmosphere. We've all seen it a few times, and it can often be seen for up to half an hour or so. It is always good to have a camera close at hand. 

Getting out for a walk

For many of us, getting out and about and seeing the scenery is a highlight of the Antarctic experience. In the last week of February, four of us walked out to Watts hut. Since so far I've had a knack of having my trips during the good weather, conditions were perfect and the travel was straight forward. Nevertheless, we were all pretty tired when we arrived at the hut.

The following weekend another party went to Brookes hut. They left Davis under broody, overcast skies with a stiff breeze blowing and on their first evening they had a surprise snow dump which kept them hut-bound for the next day of below average weather.

Last weekend, a third party planned a trip to Watts hut. They wisely moved their trip back a day while we had a dump of snow and as it turned out, the next day was absolutely perfect with sunny skies and the wind dropping away to nothing. The extra snow did pose some problems though, particularly for the last couple of kilometres which took them four hours! It just goes to show that the Vestfold Hills can have tricks up their sleeves.

Meanwhile Pat and I did a day walk and since the weather was so fantastic, I dragged Paul out again for another day walk the next day while our friends at Watts hut recharged their batteries. When they finally made it back to base, their trip leader read a humorous passage I’d printed from Big Dead Place (stories about the US Antarctic base at McMurdo). It was comparing today’s expeditioner with the hardy souls of old, who would “never question the expedition leader, and will follow the leader into the middle of nowhere for no particular reason, but will do so boldly”. At that point Mark (on the Watts hut trip and having serious problems climbing up the stairs on his return) let out a chuckle!

Getting out to do work

Another thing we try and get done while the weather is nice is ‘outside work'. In the last week, Rich and Gavin helped me get the AWS (automatic weather station) performance checks done. This ensures the accuracy of our meteorological records and is done at least every six months. Bob also did work on his antennas, including the Digisonde antenna which sends up HF radio waves to measure what is reflected at different frequencies.

Other work we do is more reactive, when something happens and we have to respond. This week we had a mishap which lost us 60,000 litres of water. Normally we only run our reverse osmosis water treatment plant in the summer. But before the station tarn freezes altogether, we were able to bash through the ice on top and refill the tanks, which will last us through the winter and leave some for when the summer crew arrive. No need to shower with a friend just yet.

Nick Neynens