Dude ... where's my shield?

Now that training is out of the way, we have been able to make it to two of our sites: Willie and Phoenix. As I alluded to in one of my prior blogs (and as you likely surmised from the title of this post), we had some surprises that awaited us. I'll start with Willie. As some of you might recall from my posts last year, Willie is our premier site because of its close proximity to McMurdo (it's the closest of the four sites) and because of it hosts three precipitation gauges instead of one. One of those gauges was surrounded by a Double Fence Intercomparison Reference (DFIR), and the other two were surround by a type of double Alter shield. We use shields around the gauges to slow the wind so the snow falls more vertically into the gauge instead of blowing past it. The DFIR is considered the standard but it's large ... 40 feet in diameter to be exact. The double Alter shields are smaller (with a maximum of 8 feet in diameter) and we installed both types of shields at Willie to see how the accumulations in the gauges compared between the different types of shields. I should also state that the DFIR stands about six feet tall but our standard gauge heights (for the gauges at the other sites) were about 13 feet, which created a challenge to design something that could be installed at that height and not blow away in the wind. Willie has a gauge installed at the 13-foot height, as well as a gauge in the DFIR at the 6-foot height, and we installed the third gauge at Willie with a double Alter at the same height as the DFIR so we could more easily compare the two types of shields without having to deal with the difference in height as an additional unknown variable in the comparison.

I'll start with a couple of pictures of the sites as they were deployed last year.

The DFIR shield at Willie as seen in 2017.

Full view of the Willie site with the two double Alter shields on the left and right and the DFIR in the distance.

I will draw your attention to a few things in the pictures. First, you'll notice the height of the flags above the ground, and the wires draped between them. At the (brilliant) suggestion of Thomas (who works for UNAVCO and helps provide ground assistance), we strung all the cables between the flag poles so they wouldn't get buried in the snow, thus requiring us to dig them out a some later point. Secondly, you'll notice the height difference between the double Alter shields (which I explained earlier) and the height of the DFIR shield. Lastly, notice the sky ... the mostly clear, blue, sunny sky with only a few wisps of clouds around Mt. Erebus. Ok, Got it? Great! Fast forward to the present.

Remember the picture with the DFIR? (Yes, you can scroll up if you need to revisit it, no one but your computer will know you are cheating). Here's a picture of the DFIR taken from a somewhat similar position as the picture from last year.

The 2018 view of the DFIR with Mt Erebus in the background.

Yes, that's right. The DFIR is now a whopping 3 inches tall! Some might argue that we've done an excellent job of creating a scale model of Mt. Erebus (seen in the distance in the background), complete with the central dome but I can assure you that was not our intent. So what happened? Wasn't the title of my talk that many of you attended "Catching snow in the world's southernmost desert"? What kind of desert gets six FEET of precipitation over a year? To begin, anecdotally we have heard that McMurdo had a snowier winter than usual. That being said, they did not have a six-foot-snowier-than-usual winter. What happened was that the site likely got more along the lines of 1.5 to 2 feet of snow (as opposed to the usual 1 foot of snow we were expecting), which brought the snow level up nearly to the bottom of the shield. At that point, snow wasn't able to blow as freely beneath the shield and the shield started acting more like a snow fence, piling all the snow inside the shield. So just how much snow is piled inside the shield you ask? Well, doing some simple math, there is approximately 10,000 cubic feet of snow inside the shield. How much snow is that? Well, it covers a volume about 450 times as big as a hot tub, or 2,000 times as big as a standard bathtub, or about 4,500 times as big as a car gas tank, or about 6,000 times as big as a beer keg (I see many of you took note of this comparison), or 200,000 times as big as the human stomach (sorry, it's almost dinnertime here) ... anyway, you get the idea. When viewed from a distance, it's clear we formed our own snow dome that extended a ways out. Far enough out, in fact, that it impacted our other sensors ... such at the instrument tower.

The instrument tower at Willie.

If you look closely at the bottom of the tower, below the white box to the left, you'll see a metal arm that disappears into the snow. At the end of that arm, buried just below the surface, is the snow depth sensor. Below that (completely buried) is our particle detection sensor, which has been reporting that its viewing area is blocked since August. We had originally thought the sensor was broken, but no, it's simply buried. Also of note in this picture is the flags. Our attempts to keep the wiring above the snow failed and we spent about 30 minutes with 4 of us digging most of them out again.

The shorter double Alter was also somewhat impacted by our snow dome, but to a lesser degree. It's not completely buried, but it will be soon if we don't raise it this season.

The shorter double Alter gauge ... now much shorter.

 Just how low is the shield? I use myself for a reference here.

Me ... after managing to get inside the shield.

So, what are we going to do? Well, we can't just leave the shield buried (that would be a violation of the Antarctic treaty) so we have to figure out a way to get it out. How, you ask?

Tools available for digging out the shield.

Yes, you guessed correctly. We are going to pick up the phone in the picture above and call for help. (Surely you didn't think I was going to use the shovel and throw 6,000 kegs worth of snow over my shoulder, did you?) The current plan is to partially dig out each post (about a foot and a half down), undo the guy wire connected to it, and then have FleetOps bring out a large tractor with a blade to dig out around the shield. Each section can then be dismantled individually and the outer posts removed, the same can be done with the inner shield until we eventually get to the gauge itself. Whether we set it up again depends on the condition of the shield post-removal. Curious how the gauge held up? I was at least able to find the top of it.

The gauge at the center of the DFIR.

It's not all doom and gloom at Willie though. The tall double Alter is still standing and in actually quite good condition. In fact, it endured over 100kt winds many times throughout the winter and held up without much problem so our overall design is good! It's doubtful we'll have to do much to it to get it ready for another winter season.

Next, we drove on to Phoenix (the Antarctic airfield, not the city in Arizona) to survey that site. We could tell after landing at Phoenix on our first day here that something was not right with the shield as we could see it leaning in the distance. When we got close, something definitely was not right with the shield.

The double Alter at Phoenix Airfield.

Inside view of the Phoenix double Alter shield.

Clearly that's not at all how the shield is supposed to look. A couple of the set screws were missing and I suspect it only took one or two of them to come loose for the whole shield to start coming apart over time in the strong winds. In one of my earlier blogs, I posted a picture from the shield back in August, which showed it was coming apart then. We had a couple of people from the base here go out and attempt to stabilize it. If you look close at the picture, you'll notice a cargo strap between two poles near the center horizontal bars halfway up the posts. They put that in to keep the poles from completely separating, which definitely helped. Our fear was that the shield was a total loss and we would have to (at minimum) take the entire thing down and (hope to) rebuild it. After discussion with the other members of our team that day, I was able to convince them to lower it and attempt to just put it back together in place. Nothing had actually blown away or fallen off the shield and after a mere hour, with lots of finagling and maybe a couple of mumbled curse words, we had the entire thing pieced back together again, ready to be raised back into place.

The repaired double Alter shield.

We are making some additional modifications to the shield to reinforce it for the coming winter but what I had envisioned being at least a days worth of work was thankfully done in an hour. Other than the shield, the rest of the Phoenix instruments appear to be fine. There was less snow at Phoenix than at Willie and while some of the lower sensors on the tower will need to be raised, the site overall is mostly ready to go for the next winter. I got this nice shot of the instrument tower with an awesome halo around the sun in the background.

Phoenix instruments complete with a halo.

Our hope is to make it to Tall Tower at some point soon as the Twin Otter aircraft are being under-utilized right now and they don't have a lot of people requesting flights at the moment. You'll recall my comment on the earlier pictures of how clear and blue the sky was. We haven't really seen blue skies yet this year and weather has been mostly cloudy and windy/snowy. The forecasts are indicating this should change and our fingers are crossed it will. I'll sign off of this post with a few other random pictures. Most posts to come with details on Tall Tower and this years adventure down the ob tube!

Another view of the buried DFIR with Ross Island in the background. McMurdo is just outside of the photo on the left.

It may be 24 hours of daylight here, but the shadows can still be long, even in the middle of the day.

Scott Base - The New Zealand (or Kiwi) base just on the other side of Ob Hill from McMurdo. It's easily identifiable with its lime green buildings.