Initial Visit to Two APS Sites

When this project was initially proposed, a focus was placed on having two of the Antarctic Precipitation Sites (APSs) within range of being able to drive to the sites. One of the main reasons for this is that it is considerably easier to visit a site by truck or mattrack (a truck with tracked wheels) than by helicopter or Twin Otter airplane. We benefitted from that close proximity last year as we did many visits to the Phoenix and Willie Field sites as we constructed the precipitation systems and made the final engineering decisions and tests. Similarly, the nearby locations benefitted us today as we were able to take the mattrack to visit the same two sites and do an initial evaluation of how the sites survived the Antarctic winter. Two colleagues visited the sites a week ago and had sent us pictures so what we saw was not a complete surprise but it was still different to actually see the sites.

Willie Field APS - Drifting and Accumulation

The obvious feature that is immediately apparent from the Willie Field site is the significant accumulation of snow at the site. In this region of Antarctica, past experience with automatic weather stations is that the area gets about one to two feet of snow accumulation each year. The ice sheets in Antarctica accumulate snow each year and the ice sheets are slowly pushed out towards the ocean. Eventually, the ice sheet calves off into icebergs and drifts away in the ocean. I was expecting this same 1-2 feet of accumulation at Willie Field. Instead, we found about 25-38 inches of accumulation. The range is because the Double Fence Intercomparison Reference (DFIR) shield resulted in significant drifting and accumulation and that accumulation varied throughout the installation. You can roughly think of the DFIR as two rings of wooden snowfences surrounding the precipitation gauge. At installation, not quite a year ago, the top of the DFIR was 78" above the snow surface. There is now only 3" of the DFIR above the snow surface (over six feet of accumulation at the DFIR). In looking at the past observations, it appears that already in mid-March the snow had accumulated to the point where the drifting snow filled the bucket of the precipitation gauge. I've include some photos from a year ago and now to show the changes due to accumulation. The initial task will be to dig out the DFIR and then we'll decide what we should do for this upcoming year.

Phoenix APS - A Wind Shield In Trouble

The good news from the Willie Field APS location is that the wind shields surrounding the precipitation gauges were in very good condition. The double-ring wind shield is designed to slow the winds and increase the ability of the gauge to catch the snow. However, that also means that the wind shields are encountering the significant winds of Antarctica and can take a beating. The wind shields at Willie Field APS survived and looked good. In mid-August, I viewed a video clip of the Phoenix APS site and saw that one of the corners had become disassembled and it was flapping in the wind. I contacted a colleague who was in McMurdo at the time and they visited the site to do a repair hoping to keep the shield intact. Sometime in the last couple weeks, the wind shield at Phoenix had significantly come apart at multiple points and was barely staying together. That is the condition that we found the wind shield today. We lowered the shield and spent about an hour putting it back together and the shield was able to return to much closer to the original condition than I ever imagined with such minimal effort. We'll be going back to this site to do some reinforcing of the joints, and other final details, before raising the wind shield back into place.

Conclusions

Some of the unknowns of this field season were what condition would we find the APS sites and what work will need to be done to repair the sites for a second year of observations. Today, we were able to take an initial visit to two of the sites and I'd classify the results as mixed. There are big questions as to how we'll dig out the DFIR and what we'll do with it for next year. Yet the overall repairs that need to be done seem reasonable. We will now make some decisions on how to go forward with these two sites and then start planning for what we can expect for the two sites accessible by helicopter and Twin Otter airplane.