The crew at Greenland’s Summit Station recently launched a tandem balloon to gather data for two ongoing research projects.
Polar Field Services (PFS): Was this the first ever tandem launch?
Heather Moe (HM), Summit Science Tech: No, this is not the first year that we have done tandem launches; they have been used over the last few years when conditions allow. It is useful to have two simultaneous data sets, and also conserves helium and balloon supplies. The techs use this approach when the conditions allow (requires warmer temps and more light); usually the first tandem launch is in the spring and we go back to single launches in the fall when it begins to get dark. One balloon carries both payloads.
PFS: What time of day did you launch?
HM: The ICECAPS launches are constrained time wise to be launched so the data matches with other meteorological launches around the world centered at 12 and 24 UTC. And the NOAA sondes contain liquid, so freezing is an issue. They need to be launched during the warmest part of the day. During the winter, that means the two project restraints don't allow us to combine balloon launches. But once it’s warm (enough) and consistently sunny, we can move the NOAA balloon launch to match the IceCap's.
PFS: What is the benefit of a tandem launch?
HM: The benefit for tandem launches for NOAA is that the ICECAPS sonde has a much better pressure sensor allowing the NOAA data to be corrected to make a more accurate ozone measurement.
PFS: How did you connect the two?
HM: As for combining the two, the ICECAPS sonde was attached by a string to the bottom of the NOAA Sonde, which is the bigger styrofoam box with lots of orange duct tape. The ICECAPS sonde is the smaller plastic sonde dangling below.
PFS: Did you have to make any alterations?
HM: Other then attaching the string through the styrofoam box to hang the ICECAPS sonde, the only other change was altering the frequency that the NOAA sonde transmitted on back to camp.
Both sondes default to the same rough frequency so one or the other needs to be changed so that they don't stomp on each other.
PFS: How high did the balloon go?
HM: It made it to roughly 37,300m and which is at an atmospheric pressure of 3.1 Hectopascal (hPa). another unit of measurement for pressure. One hPa is equivalent to 1 millibar (mb). Our rough pressure at the surface here is 670 mb and the balloon went up to 3 mb. Pressure at sea level is usually somewhere around 1,000 mb.
PFS: Is that a record?
HM: I don’t know what the record for balloon height is here. Lately with the NOAA balloons, we have been getting bursts at pressures around the low teens or high single digits. This was definitely the highest for our phase. The measure for success is different for IceCaps vs NOAA. On the NOAA side, we want the balloon to go to at least 22,000m to be considered a success and always want as high as possible. At 22,000m, the balloon typically gets through the bulk of the ozone layer.
PFS: What was the size of the balloon when it burst?
HM: These are just rough numbers but it is about 6 feet in diameter when we launch and grew to about 33 feet in diameter when it burst.