The ’s at Rothera Point, Adelaide Island, . Photo: Pete Bucktrout, www.photo.antarctica.ac.uk British Antarctic Survey on the Progress in upper air data collection

Although the main principles remain unchanged, radiosonde sounding has developed significantly over the years. Comparing the routines involved at the end of the 1970s and the situation now provides some insights into the changes that have taken place in almost three decades. In the following, two meteorologists describe their experiences with the British Antarctic Survey operating on the Antarctic Peninsula.

20 179/2009 Faraday, now called Vernadsky, and Rothera. Radiosonde sounding had to carry a radar target as well as at Faraday in 1980 the heavy sonde. Launching the sonde was a Mike Brettle, Faraday, 1978 – 1980: My labour-intensive affair needing the first job out of university in 1977 was whole met team. In the sonde room, as a meteorologist/physicist with one person would be needed on the British Antarctic Survey (BAS). the sonde receiver and another, the This included two winters at one of wind man, on the radar controls. their Antarctic stations. I was sent to Outdoors, someone would be Faraday on the Antarctic Peninsula responsible for guiding the radar where a major part of my duties with a kind of gun sight arrangement involved the daily radiosonde ascent. and someone, usually the night met, Preparations for flying the radio- would launch the balloon. sonde started the night before. One of In any kind of wind it would take the jobs of the meteorologist on night two people to launch the balloon duty was to prepare the radiosonde – one to actually let the thing go for the following morning’s ascent. before it disintegrated, and another The radiosondes at that time person energetic enough to stand were polystyrene devices about the downwind at the full extent of the size of shoeboxes and not especially suspension string and start running, reliable. They had to be assembled or more often, wading through snow, and tested with their humidity downwind to give the sonde a chance sensor, which in those days was of getting airborne without hitting a carbon hygristor about half the the ground. size of a credit card. The night met The knack was to give the sonde was wise to get this task completed a sideways push before it was early in the night because of the high snatched out of your hand. With failure rate. The next duty, before any luck this would give the sonde waking his colleagues, was filling the a conical pendulum motion keeping balloon. We had a sizeable balloon it above the ground. Meanwhile, shed and a hydrogen generator. the radar aimer would follow the The balloons were large by modern radar target as long as he could, standards, about 1500g, because they the radar itself following his move-

179/2009 21 miscounting the pressure switches or other errors was huge. After a radiosonde balloon burst, there would be a rush to complete the TEMP message combining the sonde data with the radar wind data. The wind man had selected his own significant points and now had to give wind data for the tropopause and other levels needed from the sonde data. Geopotential heights had to be calculated by iteration from the surface using a tephigram (thermo- dynamic diagram) to approximate the hydrostatic equation (one of the most important equations in meteo- rology) over small intervals. The TEMP message finally came together. It was sent out via Purple skies behind the Piggot platform, Halley Research Station. To help predictions of climate a communications station in Port change, BAS meteorologists look at the formation and properties of Antarctic clouds as part of a wider study of interactons between the atmosphere, sea-ice and the oceans. Photo: Miriam Stanley, Falkland Islands, by Morse Lorwerth, www.photo.antarctica.ac.uk code in the first instance. For this we needed our wireless operator. As the sending of the 1200GMT meteoro- ments. Indoors, the wind man had to was then simply read off as the vector logical codes was his first job of the lock onto the target manually. This between the two successive minutes. day, he would normally blunder from involved staring at a CRT display, a The knack here was to keep ahead the bunkroom in his pyjamas straight bit like an oscilloscope trace, and of the radar and its nagging beeps. into the radio shack. moving a box, representing the This was not an easy task, especially This whole process took two radar range gate, back and forth at long ranges when the radar was hours or more and involved 4 or to trap a spike in the trace repre- liable to lose its lock and need to be 5 people. The potential for human senting the target. As soon as this manually brought back on target. error was enormous. We were very was achieved, he pressed a button Plotting all the winds ten degrees out careful to check for these before and then hopefully the radar would or accidentally missing minute data we passed the message to the radio follow automatically. If the balloon were also common problems on the shack. was lost from sight before lock, the wind computation. There was also a lot of potential wind man would have to control the Meanwhile two met men for mechanical error. A foot getting azimuth and elevation of the radar in worked at the sonde receiver. The tangled with the balloon string was an attempt to find it. sonde output appeared on a chart the most common, but the equip- Assuming all went well at launch recorder. As the sonde ascended, ment often seemed designed to invite and the radar could track the balloon, an aneroid capsule connected via stupid mistakes, such as sending the real work began. The radar had an arrangement of levers switched the sonde away fixed on transmit- no memory or electronic output. the sonde transmitter output ting humidity only or with the radar Instead, once a minute, it would beep between temperature and relative target upside down. and momentarily freeze three digital humidity. By counting the number Getting the sonde away in a displays showing slant range, azimuth of switches that had occurred, it strong wind and getting the radar to and elevation. The wind man then was possible to derive the pressure track it to an extreme range was a wrote these down and converted the at any point. Selecting points for matter of pride, as was a complete range and elevation to distance, using a TEMP (the code for a pressure, CLIMAT TEMP statistics message at tables, and plotted them on a huge temperature, humidity and wind the end of the month. sheet of paper. A large, snooker-sized report) message was a matter table dominated the sonde room, with of drawing connecting straight Soundings at Halley a kind of protractor-ruler arrange- pencil lines along the chart, so and Rothera in 2006 ment. This allowed the wind man to that temperature and RH (relative plot the balloon location minute by humidity) did not deviate too far Cathy Moore, Halley and Rothera, minute. Wind speed and direction from these lines. The potential for 2000-present: My first job out of

22 179/2009 university in 2000 was also as a We fill the balloons with helium At Halley, the balloon launching meteorologist/physicist with the while inside the hanger and, when process is very similar to Rothera, British Antarctic Survey. I first spent full, open the hanger doors, then but there is a specially designed two winters at the Halley Station on walk out and let go of the balloon balloon launching facility. This is a the Brunt and now spend with the sonde attached to the fancy name for a shipping container the summer months at the Rothera bottom. The string then unwinds on raised up on steel legs, but it does station on the Antarctic Peninsula. At the top of the sonde until it is a clear the job well. Halley has about 1m both stations, launching radiosondes distance from the balloon. of snow accumulation a year, so all is a main part of the met observer’s We then let the computer system buildings would be buried if they job. do the processing of the data in the were not annually raised on their At the Rothera station, the work hanger. We can see the data coming legs above the surface. The container begins after the morning forecaster’s in by remotely connecting to the has doors opening at either end to brief for the pilots. The whole computer from the met room back allow shelter from the wind when radiosonde ascent process requires in the main building. The program launching the balloon. However, as only one person, so the on-duty met calculates the winds and plots the it can be about 4 – 5 m above the person takes a baked balloon from temperature and humidity. It plots surface, in strong winds of around our oven and takes a walk over to the the significant points, but needs 50kts, the balloon often goes down aircraft hanger on the far side of the checking, and we often add more before going up again! It also gives station (across the runway). We use points if necessary. The TEMP the met person a feeling of slight 350g balloons and we bake them at message is calculated automatically sea-sickness as the building sways 60oC for 24 hours before launch, as and we then email it directly to the in the wind. Halley has just started this makes the balloon material more Met Office in Exeter, UK. The profile using the newer Vaisala Radiosonde pliable and increases the height they is also directly used by the forecaster RS92. These give more accurate eventually reach. at Rothera in the summer. humidity measurements as they use In the hanger we have a small The whole balloon launching two sensors, heating one to remove heated container where we prepare process seems much simpler than it condensation while the other takes the sonde and check it for accurate used to be, although we still have to measurements, and then swapping temperature, pressure and humidity. contend with the Antarctic weather between the two during the ascent. The sondes are Vaisala Radiosonde conditions, which can’t be improved There are a few other difficulties RS80s, which use GPS wind finding by the latest technology! Many hours met people at each station have to and transmit the signal back to a are still spent chipping out doors overcome. At Halley, sometimes we receiver on the hanger roof. This from the ice or shovelling snow away had to battle against the blowing makes the calculation of wind to be able to launch the balloons. snow in high winds. Some days speed and direction all a matter of And lots of fun is had struggling you would not even be able to see computer processing of the GPS posi- with unwieldy balloons in 40 or 50kt beyond the end of your arm. At tions as the balloon rises. winds! Rothera, during the winter months, seals can sometimes be found near the base. They can be very grumpy if stumbled over by an unsuspecting met person early in the morning in the darkness! At both stations, in the cold months, a tried and tested technique is to dip the balloons, up to the neck, in a mix of aviation fuel and oil for about 15 minutes and then hang them to dry. This makes the balloons reach much higher altitudes during the very cold winter months.

Further information: www.vaisala.com/weather/ products/soundingequipment

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