Field Work

I am back in Christchurch. I left on a C-130 flight operated by the New Zealand Air Force this morning. Clearly, I have fallen behind my posts. I am going to play a little catch up with a couple posts sharing events from the past week and then a final post to close out the season. A few weeks ago I wrote a post on our field work at Tall Tower and labeled it "Part 1". A friend reminded me that I never followed up with that post and overall I have not written much about the field work from this field season. In this post I'll go through two trips in a 10 day period of the field season.

As an opener, it is fitting for me to provide a quick summary and purpose of the work in Antarctica. I am here as part of a project funded by the Office of Polar Programs of the National Science Foundation with a focus on measuring precipitation in Antarctica. This is the second of three fields seasons and this year the concentration is on the maintenance and repairs of the Antarctic Precipitation Systems (APSs). While something as simple as measuring precipitation (snowfall) seems basic it is actually very difficult to do in Antarctica. This is even more true when it is attempted to be done remotely and with the requirements to be run on batteries during the long polar night. The instrument at the focus of the measurements is a weighing bucket precipitation gauge. The gauge collects the snow and has a sensitive scale that weighs the collected snow providing a liquid water equivalent measurement. The gauge by itself can have a difficult time collecting the snow if it is unshielded and there is any level of wind. We have installed a wind shield around the precipitation gauge that is designed to slow the horizontal motion of the precipitating snow so that it is able to be collected in the bucket. In addition to this instrument configuration, we also have instruments to measure particles in the air, wind speed, temperature, measurement of the height of the snow surface, an instrument for particle size and velocity, and a webcam. All of this data is collected by a datalogger and we are able to communicate to the datalogger through an internet connection to McMurdo and then radio communications from McMurdo to the APS sites. This comms configuration allows us to monitor and analyze the observations year-round from Colorado.

Friday, November 23, 2018

This trip was our return trip to Tall Tower. Because of the great weather during our first visit, the amount of work that needed to be completed was somewhat limited. We had removed the datalogger and the instrument to measure particle size and speed and they were re-configured in the lab in McMurdo. We re-installed the two pieces of equipment and verified that things were running correctly. Some other small repairs were done to the instruments and precipitation wind shield. Lastly, at the end of a field visit, I take a series of photos, to capture the status and condition of the instruments, and a series of measurements of the height of the instruments to the surface. This final survey was completed and we were ready to fly onto the next APS site.

The next site to visit is the Lorne APS site. This site is approximately 50 miles to the southeast of McMurdo Station. Typically, the transportation to get to this site is by helicopter. However, we had sufficient time in our day that it was an easy stop on the return flight from Tall Tower. I should add that the conditions at both Tall Tower and Lorne were not as nice as they were on the initial visit to Tall Tower. The winds were around 18-20 knots and the temperature was about 16F. Those are far from horrible conditions but not the beautiful conditions that we've had so many other times during this field season. At Lorne we did similar maintenance and repairs to the site as we had done previously at Lorne and Phoenix APS sites.

One unique part of the visit to Lorne was the removal of a power system (solar panels, batteries, cases) for an instrument that had been installed at Lorne seven years ago. As I described previously, the sites on the Ross Ice Shelf generally have snow accumulation of approximately 1-2 feet per year. That means that over the past seven years the power system for this instrument has been progressively getting buried. We we were at the site a year ago and there was only about 12" above the surface. It was agreed that we would remove this power system on this field visit and return it back to McMurdo. Most all of that work was done by the two field engineers with UNAVCO and the two Twin Otter pilots. They spent about three hours digging a hole down about seven feet to remove the large power system.

Frequently, whenever it is available, we are asked by various support and logistics coordinators for us to bring people from town with us into the field. Officially the trips are referred to as "morale trips" to boost the experience and morale of workers that do not get to leave McMurdo. More frequently they are referred to as "boondogglers" as they get to experience and see a part of Antarctica that they are supporting in their work in town, but they rarely get to see directly. On this trip we had two boondogglers. They were told that they would need to be able to shovel snow. The two boondogglers started to help with the digging out of the power system at Lorne and then Scott and I each used one of them to help us with the work we were doing on the APS instruments. This day in the field will likely be one of the highlights of their season in Antarctica and fun photos are often a part of the trip.

Wednesday, November 28, 2018

When we left the Lorne APS site on the previous visit we had hoped that we had completed all of the necessary work on the APS system, but we were not entirely certain. After getting back to the lab in McMurdo it was realized that a few of the instruments were not working as expected. Fortunately, a return trip to Lorne was also needed to install a GPS receiver, which is being provided by UNAVCO. We once again traveled by Twin Otter as there was Twin Otter availability and the helicopters were still busy catching up from the late start to the season. We also took two more boondogglers with us. When we got to the APS site we were hoping that a quick fix was going to solve the problem with the  three instruments. The expected quick fix was not the problem. Within about 15 minutes we were able to identify a wiring issue and that fixed two of the instruments. The third instrument was more difficult. We ended up spending over an hour troubleshooting the instrument, which measures particle size and speed, to diagnose the problem. Such an in-depth level of analysis is best avoided when doing work in the field, especially on this day with 20 mph winds. In the end, it was determined that the instrument was not communicating with the datalogger and it was pulled to be further investigated in the lab. We would later determine that instrument could not be fixed during this field season and will be returned to Colorado.

We were able to get back to McMurdo in time for a late lunch. That also meant there was more time to get some work done during the day. Earlier in the season we had completed all of the work at the Phoenix APS site except for the re-installation of the webcam and tightening of guy cables. These are two fairly easy tasks to complete so we took a fat-tire truck, required for driving on the snow roads, and drove the 45 minutes to Phoenix Airfield, the location of the Phoenix APS. For local trips we do not have to go through the boondoggler system. I knew of a dining assistant (DA) who had the day off so she came along with us for the quick visit. The work at Phoenix APS took the expected 15 minutes and then on the return back to McMurdo we also stopped at the Willie Field APS site for some quick tests. Overall, it was a busy day of running around and seeing three of the four APS sites.

The Story of a DFIR

The last 10 days have been far busier than I anticipated. The weather for this field season, since I arrived, has been spectacular with mostly sunny to sunny days on nearly every day and warm temperatures. The result of that has been a continuous run of field work. We did two flights on the Friday before the Thanksgiving Saturday celebration. That Sunday evening we went into the field to one of the local sites for two hours, and returned that next morning for a long day at the site. On Wednesday we had a flight to Lorne APS in the morning and in the afternoon we took a quick drive to the Phoenix APS. Then on Friday we had a long afternoon with a crew of five at the Willie Field APS. The good news is that we are very close to being done with the field work. The bad news is that it has been a week since I have written a post.

The Double Fence Intercomparison Reference (DFIR) shield is the World Meteorological Organization standard for providing a shield around a precipitation gauge measuring snow. As a part of this project, we included a DFIR shield so that we could compare the measurements made with our Antarctic-focused wind shield and precipitation gauge design. The thinking is that we'd be able to develop a function that indicates the multiplier, in relation to wind speed, to be applied to our shield and gauge design to that of the DFIR.

The construction of the DFIR at the Willie Field APS site in November 2017 with the assistance of two carps.

The DFIR is a large and cumbersome shield to assemble. This is why we had no intentions of installing a DFIR at all four sites. Instead, we constructed the DFIR setup at the local Willie Field APS site so that it would be near to town to support the construction and maintenance of the DFIR. Part of the DFIR was constructed in Colorado before being shipped to Antarctica. Other parts and the assembly of the DFIR was done a year ago in McMurdo at the Carpentry shop. We also had two "carps" in the field with us for an entire day installing the DFIR. The finished DFIR has an appearance similar to that of a snow fence. The top of a DFIR "picket" was 78" above the surface and the outer shield has a diameter of 40 feet. The finished product looked great.

The finished DFIR at the Willie Field APS site in November 2017. The top of the shield is 78 inches above the surface and the diameter of the outer ring is 40 feet. 

During this past February we were seeing in the observations exactly what we had hoped to see. The plot below shows the three different precipitation gauges (we also installed one with the Antarctic double-shield at the same height as the DFIR) at the Willie Field APS site. The plot below shows the three different rates of accumulation depending on the wind shield and height configuration for the precipitation gauge.

A plot of precipitation accumulation at the Willie Field APS for early February 2018. The three different lines show the different rates of accumulation dependent on the different precipitation shield design and height above the surface.

However, as the austral spring turned to winter, something odd happened in the observations. The accumulation in the DFIR precipitation gauge (solid blue line) increased much more dramatically than the others. By mid-March, the DFIR gauge leveled off at values greater than 110 mm (liquid water equivalent), meanwhile the other two precipitation gauges were in the 60s. From afar in Colorado, this seemed really odd. The observations did not match what we were expecting. In fact, there was even some question if the instrument was failing. Adding to the drama, in mid-August the precipitation gauge, with the Antarctic double-shield at the lower height, had a similar characteristic to that of the DFIR in March.

The odd behavior of the DFIR shielded precipitation gauge (solid blue line) in March 2018.

The mystery was solved with some photos provided to us a few days before we arrived in McMurdo. It was also confirmed in our first field visit to the Willie Field APS site. We found the DFIR wind shield, installed at a height of 78 inches, to be nearly completely buried. I expected the Willie Field site to have an annual accumulation of 1-2 feet and now it was over 3 feet at the instrument tower and over six feet at the DFIR. In the end, we created our own snow drift and it resulted in a dome of snow centered around the DFIR and extending to our other instrument locations.

The buried DFIR shield and precipitation gauge at the Willie Field APS site in November 2018.

This also presented a big question as to what do we do now. Initially, there were naive thoughts that we would dig it out. The more we thought about it, and showed the photos around town, that idea quickly disappeared. In fact, the photos for the DFIR getting buried have been a big hit around town, including many senior support personnel. Thoughts were put into an operation that could remove a move a much larger quantity of snow. Along the way, we also agreed that we did not want to install the DFIR again for another year. The chances of it burying again, as well as all of the effort to install it again, were not appealing. Instead we came up with a modified experimental design for the site.

After discussions among various support work centers around town, the implementer for our project was able to put a plan together. We were going to get a bigger shovel to assist us. The plan was for a bulldozer to work during the night shift, Sunday evening after Thanksgiving, to clear the snow away from the outer ring and to push the snow away from the DFIR. The work that we had to do Sunday evening was to finish digging out the instrument cable and to provide instructions to the bulldozer operator.

The bulldozer clearing away the snow from the outer ring of the DFIR shield.

The finished work by the bulldozer removing the snow from the outer ring of the DFIR.

We returned the next morning and were greeted by an excavator to finish the work with us. The bulldozer and done a great job in clearing the snow away from the outer fence. We had to dig down at the joints for each outer section and unscrew each section and then carry each section to the truck. After doing that for all 16 outer sections, the excavator started doing the major work. The excavator progressively removed the snow that had accumulated between the outer and the inner DFIR shields. Once that was done, we had to remove the sections from the inner DFIR shield. Then the excavator had to remove the snow leading to another shield and finally the instrument. Fortunately, the excavator operator was amazing in his operation of the excavator and he was able to gently carve away at the snow with the giant bucket. It was a master piece of work. Eventually we reached the precipitation gauge at the center and removed all of the remaining hardware and the installation tower. The entire day with the excavator took six and a half hours, and that included our lunch break. It was amazing to have the assistance and support of the bulldozer and the much, much bigger shovel of the excavator. I don't know how else it would have gotten done.