- Observations of coincident EMIC wave activity and dusk-side energetic electron precipitation on 18–19 January 2013 - Blum, L.W., A.J. Halford, R. Millan, J.W. Bonnell, J. Goldstein, M. Usanova, M. Engebretson, M. Ohnsted, G. Reeves, and H. Singer, (2015) GRL
Writing it out like that makes it some how look all the more official.
This paper is one of my favorites as it has some of my favorite people on it. My undergraduate advisor, my current advisor, the guy who convinced me to stay in the field when I was sure I was leaving, and a few of there good friends. It has sentimental value. But beyond that, it has some great results. We looked once again at electromagnetic ion cyclotron (EMIC) waves and relativistic electron precipitation. You might be spotting a theme here. I tend to look at EMIC waves a lot. It was my PhD thesis after all. But they are just so very cute. They are the smallest wave lengths in ULF frequency range, which is like calling the the runt of a great Dane litter small.
But that's besides the point. These waves are theoretically one of the best candidates for the mechanism that precipitates relativistic (very high energy) electrons from the radiation belts. There are other processes which are also theoretically able to do this. So why do we say that EMIC waves are the best candidate? Well I'm sure if you asked others they may disagree with that statement. We claim they are because when you look at the time scales that the different wave-particle interactions occur over, EMIC waves are the fastest. Why would others say they aren't? Even though EMIC waves may be associated with very fast time scales for pushing the electrons out of the radiation belts and into the loss cone, they aren't around as often as some of the other waves, and they appear to be very very localized. It becomes a question of The Tortoise and the Hare. Which process will ultimately push more energetic electrons out of the radiation belts, the fastest or the one that's around the most? We're still debating that.
So how does this paper fit into that question? One of the parts of that question is determining when, where, and under what conditions does this wave occur. Here we showed two relativistic electron precipitation (loss of high energy electrons - to keep the dog theme going say the Jack Russell terriers of the electrons in the radiation belts) events which occurred near the same magnetic field line as the EMIC waves in space. This event occurred in the recovery phase of a geomagnetic storm. However, the storm was relatively small and seemed to perhaps fully recovered by this point. There was also a pressure pulse. A shock wave from the Sun hit the Earth right before this event. Some of the waves appear to have started with this, but we only see the electrons falling into the atmosphere as the pressure plus starts to subside. Maybe this has something to do with it, but we think we have a better explanation.
During both of the intervals where we have the waves and the electron precipitation at the same time, there was a substorm. Substorms are relatively smaller (at least smaller than geomagnetic storms) releases of built up energy in the magnetosphere. These typically occur at least once to three times a day. However, there have been periods of weeks without a substorm. Since they occur so routinely and frequently, it's worth going to the arctic circle (say near Kiruna Sweden) to watch the aurora. You are almost guaranteed to see one a night. That said, don't come at the moment for the aurora as it's daylight/twilight for most of the night.
However, this could be quiet important. There's no reason that EMIC waves and substorms couldn't be related, but we haven't found this type of correlation on a statistical scale yet. But this is one piece of evidence that perhaps EMIC waves may be generated by and precipitate electrons during substorms, a common phenomena.
More work needs to be done, as always, but this little paper is perhaps one more piece of the puzzle.
And just because I can't have a post without a photo. We saw a moose yesterday while working on HiT&MIS, and auroral imager which can see the aurora during the day... Thus why we took it with us to Kiruna for the third BARREL campaign.