In my early teens, I wanted to be a meteorologist. Mostly this was because I found weather thrilling – living at the interface of the Great Basin and Rocky Mountains, the weather, when it happened, usually was thrilling – but learning about the principles and patterns of weather systems was fascinating in its own right. Back before the Weather Channel had any programming more mainstream than the local forecast, I would watch it for fun, and in the long unstructured days of summer would follow the development of tropical storms the way others might follow a soap opera. The only downside to this interest (aside from the number of ads for orthopaedic beds) was the regular disappointment, in the winter, that we didn't get the forecast amount of snowfall.
Any intent to pursue this interest professionally petered out within a couple of years. It was one of the many scientific disciplines which was really fun to learn about, but daily practice mostly involved solving complicated equations, and that was not going to work for me. The summer I was 14, I caught the animation bug, and never really looked back. I could not have imagined that my animation career, and where it led me, would bring me to a place where all my meteorological dreams would come true.
It had been proposed that I go for one last visit to Cape Evans on Saturday, December 7th. The day was clear, the forecast promising, and the sea ice still in decent shape. We suited up and packed the sledge to go, but then one of the snowmobiles wouldn't start. When impromptu snowmobile maintenance failed, the fault was called in to the maintenance people, and we went and got an early hot lunch instead of eating a cold late one at our destination. By the time the problem (spark plugs) had been fixed, the weather was obviously turning, and we called off the trip.
That ended up being a very good decision, because that afternoon a surprise storm rolled in, and by the time I was up and about the following morning, more snow had piled up than had been dropped by any other storm in my time there. I got a taste of what the early explorers meant when they wrote that the weather was 'thick as a hedge' – it really was like walking through a leafy hedge, the air so dense with snowflakes that you almost couldn't inhale without sucking them in. Long-timers were commenting that they'd never seen snow pile up like this. And it kept snowing.
On one of my first nights there, I attended a science lecture by one of the meteorology research teams – not the day-to-day, observing-and-forecasting meteorologists, but a group looking at big-picture, model-building stuff. Their presentation was on the difficulty of measuring precipitation in Antarctica: Because it's always windy, not only is it hard to get the snowflakes into the gauge, but it's practically impossible to know what is new precipitation and what is old snow being blown there from perhaps hundreds of miles away. "It's a signal vs. noise problem," as they put it. They showed a number of ingenious automated weather stations they'd designed to calm the wind immediately around the gauge, and how Antarctica had laughed at them and found an easy way around their ingenuity. It's very difficult to forecast precipitation when you can't build up an accurate record of what has fallen in the past, or when you can't cross-check your forecast with what actually did happen. At present, models run entirely on the amount of moisture in the atmosphere (detectable by satellite) and make their best guess, based on that, how much might reach the ground.
Antarctic snow is very light. Melted down, you get only a small fraction of its volume in water. Commuters and teenage weather enthusiasts care about accumulation totals; meteorologists are much more interested in the amount of moisture ('Snow Water Equivalent') and not how deep the snow is. Knowing Antarctica was a desert, I was surprised how many days there were snowflakes falling from the sky, but moisture-wise they were purely decorative. Even the barely-precedented accumulation on 8 December was fluffy like down; you could shuffle your feet through it and feel hardly any resistance. Most of the snow in Antarctica doesn't stay accumulated; either it blows somewhere else, or it evaporates back into the air, a process called sublimation.
The day-to-day observing-and-forecasting meteorologists at McMurdo, who had not been represented in the talk, take regular observations from their many exciting instruments, and twice a day send up a weather balloon to get a picture of what's happening at higher levels. The balloon launch is just an ordinary part of the job for them, but is great fun for non-meteorologists, so they allow people to come down and set it loose at the designated time. These are coordinated with meteorological stations around the world, and therefore are always at 11:30 AM and PM, McMurdo time. I was usually busy for the morning launch, and usually asleep (or trying to be) for the night one. But this Sunday I had nothing going on, and thanks to the prompting of my coordinator, in whose company I was eating brunch, I made it to the meteorologist's eyrie in time to join in the fun.
Back in Olden Times, the hydrogen-filled silk balloon would carry up a little box with instruments that recorded temperature, altitude (via pressure), and wind direction. This was attached to the balloon by a slow match, which would sever the connection after a specified time, and trigger the release of a parachute to ease the instrument box's descent. The box held one end of a long red thread, and the other was held by someone on the ground; when the box fell, the thread could be followed to retrieve the box and its precious data. Many a polar diary tells of following the thread over rocks and pressure ridges until losing it in bad light, or finding that it had broken, but a few instrument boxes were retrieved, and Simpson, the meteorologist, worked their observations into his surprisingly accurate models.
Nowadays, the balloon is latex, filled with helium instead of hydrogen, and the instrument box radios its much wider range of data back to base in real time. As the balloon rises, external air pressure decreases, and its internal pressure expands the balloon's skin until it finally pops. No one tries to retrieve balloon or instrument. I'm not sure how it factors into the Antarctic Treaty's imprecation to pack out what you pack in, but there seems to be an agreement amongst meteorologists around the globe that the small amount of e-waste from twice-daily balloon launches is just regrettable collateral damage against the greater good of accurate models and forecasts.
The instrument box, or 'radiosonde', comes sealed tight in plastic. Once unwrapped, it's put into a 100% humidity tank to check the calibration:
Then it's taken down to the launch pad to get hooked up with a balloon. The balloon launch area is essentially a garage on the bottom level of the building that houses the sewage treatment plant, so I got to see that on the way, which was a nice plus. (No, really, it was. It didn't even smell that bad.) Down here are the helium canisters and the very high-tech equipment of a brass stand and a cup-hook screwed into the side of a workbench.
The balloon is hooked up to a canister and filled until it just lifts the brass stand off the tabletop. This indicates exactly the amount of helium that will lift the balloon at a rate of 300 metres per minute.
Waxed twine is then tied very securely around the neck of the balloon, with a loop sticking out. This loop is hooked onto the cup hook, keeping the balloon anchored and leaving both hands free, so they can attach a clip with a spool of plastic line very securely to the neck.
The radiosonde will hang from this line. The instrument itself is is encased in styrofoam, and guest launchers get to write a personal message on it. You know me, one-track mind ...
Then, just before the balloon is released, current conditions on the ground are noted, to give a starting place for the readings that come off the radiosonde. For example, the instrument measures wind speed with an accelerometer, which measures changes in its motion, not an anemometer, with measures the wind speed directly, so the wind speed on the ground has to be subtracted from its data.
Then it was out into the McMurdo snow globe to let the balloon go ...
The meteorologist, who took the picture of me, apologised that the conditions were such that the balloon didn't really show up in the photo, but I assured him that a grey-on-grey photo of launching a weather balloon in a freak record snowstorm was immensely more satisfying to me, personally, than a postcard-perfect snapshot of sending an ivory balloon into a clear blue sky.
(BAS has put together a fun little interactive page about releasing weather balloons, if you'd like to see it done on the other side of Antarctica, in the sunshine, and with a different accent.)
Sunday, December 8th was supposed to be my penultimate day at McMurdo. I was booked onto the flight leaving on the 10th – the return flight of the C-130 arriving on the evening of the 9th – and I knew that I'd be spending most of the 9th in a flurry of packing, cleaning, and goodbyes. The 8th was the last day I could really enjoy, and enjoy it I most certainly did.
As so often happens in Antarctica, the weather forced a change of plans. The dump of snow at the airfields, and the sastrugi carved by the wind afterwards, put them out of action until they could re-pack and re-groom the landing strips. No plane would be landing on the 9th, and therefore no homeward flight departing on the 10th. I was given a few more precious days on the Ice.
McMurdo is a scientific outpost, filled with rational, objective people, but it was funny how often news of my weather delay got the response "They want you to stay!" with no ambiguity about who They might be. So, whoever it was who pulled the strings to send a teenage fantasy's surprise snowstorm: Thank you. It was the finest early Christmas present a girl could ask for.