Hunting sprites

Well we are now out of the frozen north, and down at Langmuir Laboratory in Socorro New Mexico. We are looking for sprites using our high speed camera. I will try to post a summary of the Toolik experiment, and introduce the sprite work later this week.

Waiting for the weather to clear

Unfortunately it has been snowing a good bit here. We had clear skies Wednesday evening, but the aurora was very quiet. Thursday and Friday night it snowed. Today I walked up to the mailbox on the haul road. We typically leave candy bars in the mailbox, and the truckers will stop, take the candy bars, and leave us yesterday's paper which they bring up with them on the haul road from Fairbanks. Today I left them a snickers bar as you can see.

It is finally starting to clear off today. As I walked up, the sun was hitting the Brooks range, so I have included that picture as well. The light here is really fantastic, and is constantly changing. Yesterday we had pretty much white out conditions, but today we have a bit of sun to the south. Hopefully it will finish clearing, and we will be able to get some observing in.

Other research around camp

It started clearing off today, so hopefully we will get some decent data tonight. Since the weather was turning nice, I decided to walk around and see what other research is going on. I found UAF graduate student Laura Brosius drilling holes in the 4.5 ft thick ice that covers Toolik Lake. A picture of her and Shelby, who is a staff member at the station, lifting the ice auger out of the hole they drilled in the ice is shown to the right. Laura works for Dr. Katey Walter, who is in the Water and Environmental Research Center at UAF. Their work has to do with methane gas that comes out of lakes in Alaska and Russia caused by thawing permafrost and other mechanisms. Meeting other scientists and finding out what they do is half the fun of these field expeditions.

First results

We had snow last night and it is still snowing today, so I sat down and analyzed some of the high speed photometer data from Monday evening. The Interplanetary Magnetic Field (IMF) was nicely southward from about 04-08 UT, see the attached plot from the ACE website.

The ACE spacecraft is between the Earth and the sun, and measures the IMF orientation, as well as the solar wind speed and density. When the IMF is southward, it can "cancel" out the magnetic field of the earth which points northward. Magnetic fields can store energy (inductors are an example of this), and when the Earth's magnetic field "reconnects" with the IMF, some of the magnetic field energy is released into kinetic energy of the particles. This increase in kinetic energy results in increased aurora.

It turns out that the energy is not distributed evenly around the auroral oval when the IMF turns south. Rather, the most likely place to see an increase in auroral activity is on the opposite side of the earth from the sun. At Toolik Lake magnetic midnight is about 11:30 UT, so the aurora we were looking at was pre magnetic midnight.

At around 08:00 UT on Monday 4 March 2008, we were looking at a quiet arc that was in the magnetic zenith. The magnetic zenith is the location where the magnetic field comes straight into the Earth. At Toolik this happens at about 203 degrees Azimuth (with 0 degrees being magnetic north), and 80 degrees elevation. This means we were looking straight up the magnetic field line.

We took regular fram rate (30 frames a second) video with a Watec Supreme camera that is not intensified, as well as high speed video with a Phantom 7 camera with a VideoScope intensifier. Additionally we had a 16 channel multi anode photometer from Hamamatsu that we digitize at 20,000 samples per second. This photmeter is an easy way to look for high speed flickering in the aurora. We take the digitized time series output of the photometer, and turn it into a spectrogram, which shows power at different frequencies as an image.

The spectrogram shown to the right comes from pixel number 8 (the center pixel in the linear array of 16 pixels). The data were taken at 0801UT. The top panel in the image shows the digitized output, while the bottom panel shows the spectrogram. In the spectrogram, increasing frequency in Hertz is long the y axis, while time runs along the x axis. the color bar is in dB, with reds and yellows being higher power than blues. As you can see, there is quite a bit of power down around 5-10 Hz. In the first ~15 seconds of the spectrogram, there is also power at higher frequencies, 50-80 Hz. The eye can detect frequencies up to about 10-15 Hz, so the lower frequencies are what are seen by the eye in the Watec images.

Each file is 30 seconds long, and takes the computer a bit over 30 seconds to write to disc. So the next file was about a minute later at 08:03 UT. The spectrogram for channel 8 is shown to the left, and you can see the higher frequencies have disappeared, leaving the lower "narrow band tone" at around 8-9 Hz. A little later in the spectrogram the higher frequencies are seen again, but weaker than they were in the first spectrogram.

This is very similar to what Hans and I published in a Geophysical Review Letters article back in 1998.

We hope to obtain optical observations of flickering aurora at the same time that Jim LaBelle's Dartmouth group measures radio frequency auroral roar.

Observatory pictures

Attached find two photos of the observatory setup. You can see that we have a small plywood box that has plexiglass dome on it for an observatory. The mountains in the background are the Brooks Range. Inside the observatory, we have two high speed cameras, and a high speed photometer.

The funny looking "pink" things on the front of the cameras and photometer are really Kodak #32 magenta filters. They let through both blue and red, but block out green light. The four prominent wavelengths in the aurora are 427.8, 557.7, 630.0, and 750-850 nm. The first and the last emissions are prompt emissions from Nitrogen, and have very short lifetimes. Since we are looking for fast changes in inensity of the auroral light, we want the cameras to be looking at the prompt emissions. The middle two emissions are from Oxygen, and have longer lifetimes. Looking at the light from these will smear out the response we are looking for, so we filter out the bright 557.7 nm forbidden Oxygen line with the magenta filter.

Does anyone know why the lifetime of the Oxygen is longer? If you do not, you can look up the answer in a quantum mechanics book. I have set the permission on the blog so anyone can make comments, so if you have any questions don't hesitate to ask.

Setting up at Toolik

We set up all day Saturday. Here is a picture of Hans Nielsen working on the all sky camera that the Geophysical Institute runs here at Toolik. Hans is the associate director for the institute, and still does research! He is a real inspiration as a scientist.

The allsky data can be found here. Basically the all sky uses a fish eye lens, and focusses the entire sky into a single picture frame. It is very useful for telling what the overall auroral conditions are at a site. Typically, North is at the top of the picture, and east is to the left. Imagine you are laying on your back looking up, and your head is towards the north; this is the orientation of the image in the northern hemisphere.

We had a good aurora last night, fairly early in the evening. We had been setting up all day long, and got the high speed photometer and one of the high speed cameras working. The computer that runs the other camera did not like the cold outside in our little observatory, and we had to bring it back in to warm up. Last night is was about -30 degrees F outside, but the inside of our dome was staying around +30. Unfortunately we have to open the dome all the time to set the equipment up, and the temeprature fell enough that the one computer complained. We will try setting it up in the daylight today. It is at least sunny today, and is a bit warmer out. I will take pictures of our setup after we get everything working and upload them.

Adigan Pass

Adigan pass along the Dalton Highway seems from another world. All the trees have been left south of you, and the scenery is a mixture of shadow and light. Here is a photo of one of the hills off to the east side of the road taken on 29 Feb 2008 around 4:30 pm local time. We were about 10 miles south of Adigan when I took this picture. The shadows on the hills were extremely striking. We are now safe and sound in Toolik, and tomorrow set up the high speed cameras and photometer.

On the road to Toolik

We drove north 380 miles along the Dalton Highway today on our way to Toolik Lake. The trip took us about 9 hours. The drive is truely incredible. You see every type of scenery imaginable. Here is a picture of trees covered in frost above the Yukon river that I took in January of 2007 on my trip to Toolik.

And here is the picture!

This is a 2 second exposure with a Nikon D-100 using a 20mm lens. The green auroral emission from the forbidden Oxygen line is very apparent.

Why go to Toolik Lake?

I am going to Toolik Lake to study the aurora. If you want to know a bit more about the aurora, you can look here. People who study space physics are interested in the aurora, because it is the most obvious manifestation of the interaction between the solar wind and the magnetic field of the Earth. I personally like studying the aurora not only becuase it is interesting science, but becuase it is beautiful.

I am going to Toolik Lake to study a particular type of aurora called flickering aurora. As the name implies, flickering aurora visibly changes intensity in time that the eye can see. I have previously studied flickering aurora at Poker Flat Research Range in Alaska, but I moved to Toolik Lake so I could search for links between flickering aurora and VLF auroral roar. More on this next post. For now, here is a picture of the aurora taken from Toolik Lake in 2007 by my friend Dirk Lummerzheim.

Getting Ready to go to Toolik Lake

I am currently getting ready to travel to Toolik Lake, in Alaska. While there I will be studying the aurora. This week I spent time packing all the gear, and getting it sent off to the Geophysical Institute at the University of Alaska, Fairbanks. When I get back to work at the Air Force Academy, I will post some pictures from the trip to Toolik last year.