The IceCube Construction Season

ARIANNA is not the only experiment with a successful construction season. IceCube also had a great season. They deployed 20 strings into the South Pole ice (beating their goal), and finished a week early.

This is a very impressive achievement. 2500 meter deep (1 1/2 miles), 60 cm (about 2 feet) diameter holes are drilled in the ice, and strings (cables) of 60 optical modules are lowered into the hole. The photo above shows the drill head, which is moved from hole to hole. The holes are drilled with a water jet that shoots 200 gallons/minute of water at 88 degrees (Centrigrade) through a 1.8 cm (about 3/4 inch) diameter nozzle at a pressure of 200 pounds per square inch.
Drilling each hole takes about 40 hours, plus another 12 hours for deploying the strings. This photo shows a DOM being lowered down the hole.




LBNL postdoc Lisa Gerhardt has just returned from the South Pole, where she worked on testing the deployed strings. She kept a nice blog. Laura Gladstone (U Wisconsin) also kept a blog of her trip. There are accounts of past trips (with tons of pictures) elsewhere. In view of all of these other accounts, I will be brief and end here.

[n.b. These two photos are from my 2006 trip]

Global Warming in Antarctica?

Several people have asked me about the 'warm' weather that I experienced, and whether this was due to global warming. Others have asked about my photos of liquid water (e. g. above). Is this due to global warming? Did I see global warming in Antarctica?

I've hesitated to answer these questions here, because these are not simple ones. However, with the caveat that I am NOT an expert on climatology, let me tell you what I know.

The evidence for global warming is very clear.

The carbon dioxide levels in the atmosphere have risen to levels far beyond anything seen at least since the last Ice Age, and very probably for the last 400,00 years. For the purposes of considering the future of humanity, I don't think that we need to go any further back. This increase is clearly due to human activity.

Global temperatures are rising, and the last 50 years have been the warmest in centuries. There are many many places where one can compare photos of glaciers taken 50-100 years ago with recent photos; the differences are dramatic. A quick google search found examples from Glacier National Park, elsewhere in North America , and even from Africa's Mt. Kilamanjaro. One can debate temperature trends, the effect of heat islands, etc., but it is clear that these glaciers have formed over long periods, and are now rapidly disappearing. Further, they are far from cities or other local heat sources.

These examples are all from the Northern hemisphere or equatorial region (Mt. Kilamanjaro is 3 degrees south of the Equator). In Antarctica, the evidence is less dramatic, but there are clear signs of thinning glaciers.

Of course, one can find contrary evidence. In McMurdo, I heard a talk about exploring the dry valleys; the speaker pointed out one location where there is now apparently much more ice than in 1904, when Scott visited the site. On balance, however, there is much more evidence for global warming than against it.

That said, what I observed was not evidence of glacial warming. The temperatures during my visit were well within the expected range. The water pools were not anomalies; the snow around McMurdo always melts on hot summer days, forming small freshwater pools. Global warming is real, but one needs careful, long-term study to observe the effects - one visit to an area is not enough.

Anybody who wants to learn more about global warming should visit the website of the International Panel on Climate Change (IPCC). Their reports (available on the website) discuss an enormous volume of climatological data drawn from many sources. Notwithstanding an occasional gaffe, their carefully worded conclusions represent the views of the vast majority of climate scientists.

Looking at the Data

It's been several weeks since I posted. The major reason for the gap is that my father passed away in early January, and it's been tough. I'm very glad that this didn't happen while I was in Antarctica.

In the past few weeks, we (the royal we - mostly, it has been Steve Barwick, Jordan Hanson, Lisa Gerhardt and Ryan Nichol) have been looking at the data, which is flowing smoothly through the internet link. Mostly, things look very good, and the station continues to work well. This data falls into two classes: housekeeping data, relating to station performance, and triggered data, collected when the antennae see something).

Lisa Gerhardt posted some of the early (through early January) housekeeping data on the web Please remember that not all of this data has been calibrated yet. The temperatures in particular seem low. That said, a few trends are clear. One is that the wind kicked up shortly after we left (starting around Dec. 26th), and again in early January. So, there may be hope for the wind generator. A second is that the diurnal (day-night) variations are present, but small.

The antenna data is harder to describe here, but we are also making progress. Some background might be helpful here. We collect data (and call it an event) whenever the signals on two of the four antennae are above an adjustable threshold. These signals could come from background noise, natural sources, or man-made sources. When a trigger occurs, we record the data for each antenna for 60 nanoseconds (billionths of a second). This may seem like a short interval, but a real neutrino event should produce a pulse that is less than a few nanoseconds long.

One thing that jumped out early was that the trigger rate was partly periodic. We saw triggers every 60 seconds, as expected, These are the 'heartbeat' pulses that we create to check the detector. But, we also see other, unexpected periodic signals. Sometimes, triggers are separated by almost exactly 6 seconds - pretty clearly, a man-made source. The rate of these pairs varies over 24 hours, and we suspect that it comes from the switching power supplies that power the internet hardware. If so, this will disappear when the internet equipment is removed. We also see other events not related to these periodic signals. These might be 'thermal noise' the irreducible background associated with random noise due to molecular motion, etc. This thermal noise provides the 'natural' limit to detector performance. There are ways to reduce it (better antenna, lower noise preamplifier, etc.), but this thermal noise limit is our immediate goal.