In this new paper, "Simulation of ULF Wave Modulated Radiation Belt Electron Precipitation During the 17 March 2013 Storm", Thiago (Brito et al) traces test particles through a modeled magnetosphere during a geomagnetic storm. What this translates to... We modeled the Earth's magnetosphere under storm time conditions. As the modeled magnetosphere is unable to include higher frequency waves, such as EMICs and Whistler mode Chorus which are typically considered the waves which push particles into the atmosphere, we can see the sole effect of the longer period ULF waves. In order to see how particles - in this case electrons - will be affected by the ULF waves, we put some into the simulation and follow them as they move around the magnetosphere during the storm. This allows us to see what fraction of the electrons were lost to the atmosphere and how many stayed trapped as they interacted with the Pc4-5 waves.
What we found: The ULF waves were able to cause precipitation of electrons with pitch angles near the loss cone.
What does this mean: ULF waves are likely affecting the resonances of these other waves, but they themselves can also precipitate particles that are near the loss cone! These higher frequency waves can effect particles that are deeper in the trapped population, but once they diffuse closer to the loss cone, both the higher frequency waves and the ULF waves can work together to scattering them into the upper atmosphere.
Why should you care: This is another small step in learning more about the dynamics of the outer radiation belt. This process could help explain what is observed both in space and in the ground. Understanding the dynamics of the system and the relative importance of source and loss mechanisms will help us to one day be able to predict space weather! As with most science though, this is one small step that is now in the literature and will be tested by others and ourselves.
From working on this paper, a few of us got together and wrote a successful grant to further this research question - "How do ULF waves affect radiation belt particles". Over the next three years we hope to identify time periods where BARREL saw electron precipitation with temporal structures with the same periodicity as these Pc 4-5 waves. We've already found a few (as can be seen in the paper), but there are many more. Through careful study of each event period, we hope to be able to test the model against the data. It's great when we can learn new physics through modeling, or through data analysis, but we truly test our understanding by comparing model and data results together. If the model show that too few electrons are precipitated, then we know that we need at least one more loss mechanism. If too many electrons are precipitated, then we know that the model doesn't quiet describe the correct physics in the system. By probing the events, we'll hopefully be able to improve the current models as well as our understanding of how Pc 4-5 ULF waves affect the radiation belts!
It's going to be a fun three years :). Who wouldn't want this job, you get to work with good friends, look at interesting questions, and find out a little bit more about the world we live in.
Now on to writing up the next paper.