Ground Blizzard

On Saturday, we had another visit to do work on an AWS site. The site was Linda AWS, which is located about 40 miles to the southeast of McMurdo Station on the Ross Ice Shelf. The work to be done was to raise the station, similar to what I described in an earlier post for Ferrell AWS. The flight was by a Kiwi (New Zealand) helicopter. The New Zealand base (Scott Base) is about 3 km from McMurdo. Their helicopter operations are based out of McMurdo and their helos are used by the US Antarctic Program when not being used by the Antarctic New Zealand program. The flight to Linda AWS was fairly routine and it took about a half hour. While flying we could see blowing snow on the surface and that it was likely very windy.

When we got out of the helicopter the wind speed was measured at about 20-23 mph and the temperature was 3F. The snow was blowing at the surface. These were much different conditions than what we had the last two days out in the field where the wind was basically calm. One of the big advantages of having calm to light winds is you don't have to worry about blowing snow. The tool bags, orange duffel bags, and other equipment are quickly filled with snow as the wind finds any cracks and openings. The annoying part is that once the snow gets in, then things get wet and staying warm is much more difficult when things are wet. Whenever you are placed in the field, without the helicopter/airplane staying with on site, you are required to have a "survival bag", VHF radio for local radio comms, and a satellite phone. The survival bag is a large duffel bag with a tent, two sleeping bags, food, and other supplies to live for three days in the field. Before the helicopter departs, we are supposed to establish radio communication with the helicopter and Mac Ops (the radio operations center in McMurdo). It took awhile to establish the radio comms, but once we did communicate with Mac Ops, the helicopter left and it was time to start the field work.

Linda AWS shortly after we arrived. The blowing snow at the surface can be seen with the "fuzzy" conditions near the ground. The solar panel had become unattached during the past year and was hanging by the cable.

The first decision that was made was that there was no need to raise the AWS equipment. The current site had the wind instrument 10 feet above the surface and that is still at a reasonable height. This was also a good thing because adding an additional 7 foot tower section in 20+ mph winds would have been challenging. We also needed to do some maintenance work in remounting the solar panel, which had become undone since the last visit, and to troubleshoot a problem with the pressure sensor. After working for about an hour, we realized that the winds had increased. The winds were now about 30 mph and the depth of the blowing snow had increased substantially. When we landed we were able to see the landmarks Minna Bluff and White Island in the distance. Those sites were no longer able to be seen. Without the necessary time for the station raise, the work that we had finished, and the deteriorating conditions, we decided it would be wise to radio Mac Ops and request that the helicopter return early to pick us up. Besides, the 30 mph winds were making doing anything to the AWS very difficult. 30 minutes later we heard back from Mac Ops and the Kiwi helicopter would soon be launching to pick us up.

Dave calling to Mac Ops using the VHF radio requesting that the helicopter pick us up earlier than planned.

While waiting for the helicopter, the decision was made to do some small tasks to make things a little safer. The winds were now 30-32 mph with gusts to 35. We collected all of the gear and bags together to ensure that if the conditions got worse we would still be able to find everything. This was especially true with the survival bag. We then piled all of the gear into a wall to serve as a wind barrier. I figured since we'd be waiting for awhile, there was no reason to stand around in the wind. Such a strong wind can oftentimes cut through your clothing and is not the best condition to stand around in if you can avoid it. The pile of gear made a great wind barrier and we settled down by sitting on the snow, out of the wind, waiting for the helicopter.

Looking downwind as the survival bag about 100 feet from the AWS. The survival bag was where the helicopter landed to drop us off for the work on Linda AWS.

Dave waiting behind the wind barrier as we waited for the helicopter to pick us up after serving Linda AWS. Notice the depth of the blowing snow as well as the limited horizontal visibility.

There was one other time where I was dropped off by a helicopter and the conditions deteriorated from a perfect day to light snow. Shortly after we were picked up the helicopter pilot said another 30 minutes and we might not have been picked up and we would have had to use the survival bag. Given the poor conditions that we were experiencing on Saturday, the thought of the helicopter not being able to pick us up was real. It is hard to say what the visibility was because there were no landmarks to see, except for 10+ miles away, which were definitely not visible. I would estimate the visibility at the surface was around 100-200 m. However, this was a ground blizzard caused by blowing snow at the surface. Above the surface, it was blue skies. The key is that the helicopter pilot needs to be able to make out the horizon and roughly identify the surface. The same Kiwi pilot that dropped us off is the pilot that came to pick us up, which means he knew exactly where we were and what we looked like. Fortunately, there were no problems with the helicopter landing. The helicopter landed, kept the blades running, and we broke down our wind barrier and loaded everything into the helicopter. I was amused that before the pilot got back into this seat, he took out his camera to get a few photos. Naturally, I had even more respect for the pilot as he clearly realized this was some great weather and it was worthy to capture in pictures. In the end, we were on the ground for about an hour and a half after we called Mac Ops to send the helicopter. Once back in the air it was a fairly routine flight back to McMurdo.

Picture of the horizon during the ground blizzard at Linda AWS. The discernible surface at the center of the picture is the result of the wake zone due to my wind block. Similarly, the line on the left side of the picture is the downwind calm zone from the wind barrier.

One of the upsides to this experience is that the winds that I experienced can be loosely defined as a part of the Ross Ice Shelf air stream, or the RAS. My PhD dissertation was an observation and modeling study of the RAS. I now have firsthand experience of what I studied for years while working on my PhD. From my research, I also know that what I experienced is very tame, especially in comparison to the conditions during the winter months.