Going back in time

Upper air observations in Antarctica in 1969

I was one of three meteorologists in the tenth South African team to Antarctica in 1969. Our base was on the ice shelf in Queen Maud land, at about 70S and 01W. The base was 12 meters below the surface because of the accumulation of snow.

As South Africa is generally a hot and dry place, living on ice for a year with temperatures down to –50C was a new and fascinating experience for us. We were enchanted by ice bergs, penguins, aurora, crevasses, overland expeditions, going out with the huskies, blizzards, and so forth. As meteorologists, our task was obviously to make meteorological observations.

We carried out routine surface observations, and an upper-air sounding every night at 00:00Z. Upper-air observations made by our first team on the ice in 1959 got off to a bad start – they only had sufficient balloons for a month. Even today, almost 50 years later, the same problem persists; we always seem to have a shortage of radiosondes.

We used the (then) new transistorized Vaisala RS13 radiosondes and were very proud that we were not using RS12s with old-fashioned valves any more.

Not for the impatient
Pressure, temperature and humidity were recorded by a Vaisala AR13 receiver.

There are probably not many readers who remember the lengthy preparation procedure for radiosondes in those days. A few days before the release, the humidity hair element had to be conditioned by placing a damp cap over the humidity sensor. Then the sensor was repeatedly tested in a mixing hygrostat at different percentages of humidity to obtain a calibration curve. Calibration curves for pressure and temperature were provided by the factory. After at least two tests for pressure and temperature, a scale was drawn on the plotting aerogramme for the three (PTU) elements. Each instrument had its individual aerogramme on which the data was plotted, and where all the computations were made during the sounding.

Winds were received by an RT16 radio theodolite. The less said about this – the better. The RT16 had a small CRT screen with a flashing circle which had to be tuned until it was flat and quadrants were plotted and, well, make one mistake and you struggled for the rest of the night. Sometimes winds were recorded by optical theodolite observations, but this was not really a feasible option. One could not stand outside, track a balloon and write down azimuth and elevation every minute for very long. And we could only track the balloon optically during the few summer months when it wasn’t dark at night.

Safety officers’ nightmare
Our balloon room was a grotto which would have made the hair of any self-respecting safety officer stand up straight. The balloon room was also about 12m below the surface, just like the rest of the base. The temperature inside varied between –10C to –15C.

Hydrogen was produced by a low pressure hydrogen generator. About an hour before launch we had to check that there was water available and that the water pipes were not frozen. The balloon was soaked in a bucket with warm diesel, with the belief that it would make the rubber soft and pliable, and hopefully achieve better heights. We poured a mixture of caustic soda and aluminum chips into the generator, and slowly fed some water into the monster. This usually produced hydrogen which filled the balloon. When the balloon reached the required filling weight, the mixture inside the generator was simply dumped on the ice through a hole in the floor. The still active and very hot mixture would simply melt a hole for itself into the ice – still producing hydrogen on its way down. This hole in the ice never filled up. One of the observers said that it will eventually melt through 200m of ice to the sea below and we will be able to catch fresh fish in the balloon room every morning.

Now; enter Mr. Safety inspector. He would have found no “Danger Hydrogen Flammable” or “No open flame” notices. There was a fire extinguisher which did not work because it was frozen. There was no first aid kit, and it never occurred to us to use protective gloves or goggles. Nor was there any fire alarm. We did not even know of the existence of a hydrogen alarm.

Heat for the balloon room was provided by a ventilator from the generator room right next to the balloon room. So air containing hydrogen could move freely between the two rooms. The diesel mechanics next door, as we know, love to do things that make sparks like grinding and welding. When the mechanics fixed things in the cold, sparks usually flew around with great abundance. Just outside the door of the balloon room were 400 drums, which contained the base’s supply of diesel. All this while there was an active chemical reaction producing hydrogen into the atmosphere - and we were concerned about crossing crevasses on field expeditions...

Second and third soundings provided exciting times because then the generator was hot and the reaction took place very quickly, with a very fast increase in pressure inside the tank. Happily – and miraculously – there was never a serious incident.

This situation was rectified when a new base was built in the late 1970s. The upper-air facility was then made a stand-alone building away from the main buildings of the base. Just as well - just before this base was due to be decommissioned in the late 1990s, static between the observers’ anorak and the balloon caused an explosion. The 20-year-old walls of the balloon room simply folded outwards, and the roof went through the hole in the ozone – it was never seen again. The observer was protected from the flames by his protective Antarctic clothing. The only injury he suffered was that his year’s growth of beard was instantly burnt away.

Releasing the precious balloon
But returning to 1969, and the filling of the balloon: with the balloon now filled, it required three people to get it and the attached radiosonde into the air in one piece. One guy was down below inside the balloon room and he would slowly let it rise attached to a string up the 12m high shaft. The top of the shaft was covered by two large horizontal sliding doors which had to be opened manually. Outside, one guy would take control of the balloon and the other would take the radiosonde. Meantime, the person at the bottom would rush to the met office to check the signals and start the receivers when the balloon was released.

After releasing the balloon, the two guys outside had to shut the sliding doors properly, otherwise the whole shaft could have filled with snow. That’s a mistake you don’t want to make.
The RS13s had, I believe, a 12 meter antenna, which made launches in strong winds a very chancy business. When winds reached 35 – 40 knots we did not even try. The balloon would simply stay low and our precious radiosonde would be destroyed against the sastrugis.

Careful manual work
Two guys were needed to carry out the sounding, one to track and calculate PTU and the other for tracking and calculating winds. They tracked, plotted and calculated all the values by hand and by using various slide rules and tables. Then, when the balloon burst and the calculations were done, the two guys changed positions – each one checked the calculations of the other. The upper-air codes were also compiled manually and it was typed on a telex paper punch tape to be sent out during the next radio schedule. The duration of the sounding from release until coffee time was a very busy two hours.

The average heights we achieved varied between 22 hPa in summer, dropping to 76 hPa in winter, which was better than most of the other nine South African upper-air stations at the time.

Compared to what we had in 1969, the modern upper-air receivers and radiosondes are a joy to use. But what great memories and stories have the old nuisances provided me with!

Author: Johan van der Merwe, South African Weather Service, Pretoria, South Africa