The Storm that fizzled and what we learned from it.
BARREL (theĀ Balloon Array for Relativistic Radiation belt Electron Losses) was designed to study the loss of electrons from the Earth's radiation belts to the upper atmosphere. However,Ā BARREL, this relatively tiny balloon mission compared to the big satellite missions, can also see other sources of X-rays. In fact, at the beginning of January 2014, BARREL observed portions of the entire solar storm process. First, BARREL was able to observe the X-rays produced at the active region of the Sun from a solar flare. The mission then inferred and studied the impact of theĀ solar energetic particle event on the EarthĀ (this is theĀ space weather many worry about for astronauts). Approximately two days later, when the shock produced by thisĀ coronal mass ejectionĀ arrived at the Earth, BARREL, theĀ Van Allen Probes, and other spacecraft in the heliospheric fleet saw the magnetosphere become compressed. This led to the generation ofĀ chorus wavesĀ and the loss of radiation belt electrons from the magnetosphere into the Earth's atmosphere.Ā
In other words... We saw the whole shebang. We saw the start of the active region on the Sun and its ultimate effects on the Earth. And the crazy thing, this was a very, very small geomagnetic event that we almost didn't bother looking at. However, this little event allowed us to see very clearly how interconnected the Sun-Earth system is - even when it's not all that stormy.Ā
This event has just been published in theĀ Journal of Geophysical Research: Space PhysicsĀ if you are interested in reading more about it. We also have a paper on the solar energetic particle event, which we'll save for another post.Ā
So why should you care, besides the fact that this is just so cool? It's another step in learning how competing source and loss processes work in the Earth's radiation belts. Understanding how the radiation belts change will help us protect satellites in this region of space (and there are many of them). Protecting satellites is becoming increasingly important as we move into solar max and our technology becomes more dependent on them. As an easy example - think of using GPS and navigating a new city without it! Driving in a new place with small tiny roads - like in Coimbra, Portugal would be even more terrifying!Ā
Why do you care if you are a space physicist? Because this is an event where we had a fantastic conjunction of instrumentation that captured a large portion of the entire process! THEMIS was situated near noon and saw the magnetopause pushed inside its orbit. BARREL had three balloons up, which mapped to a box about 2 L wide (a measure of distance from the Earth, roughly 1L = 1Earth Radii at the magnetic equator), and 2 hrs MLT long. What is Magnetic Local Time? Think of the area of space around the Earth as a clock; looking at the Sun is noon, looking away from the Sun behind the Earth is midnight, then dawn and dusk are decided by the Earth's rotation.
The figure below shows (not to scale, at least for the Sun's relative location to the Earth) where the Van Allen Probes (triangles labeled A and B), the GOES satellites (circles G15 and G13), and then three of the BARREL balloons mapped out to the magnetosphere (Diamonds labels 2K, 2X, and 2L which is slightly covered by G13).Ā
The Van Allen probes saw an electric field impulse caused by the solar storm hitting the Earthās magnetosphere, which transported particles earthward and toward a trapped population. Some of the particles do get lost to the atmosphere as they move Earthwards (towards a large loss cone).
Chorus waves were observed outside theĀ plasmasphereĀ and appeared to be active over the time frame when precipitation was inferred at BARREL payloads 2K and 2L. Chorus waves can pitch angle scatter these ~100 keV electrons into the loss cone.Ā
Having the array of payloads aloft allowed us to see the effects of chorus waves relative to the electric field impulse on the precipitation of the electrons. Although the electric field impulse was observed at Van Allen Probe A, which was very close to BARREL payload 2X, little to no precipitation was observed at this location. The electric field impulse may precipitate some electrons, but the chorus waves were more effective over this short and small event.Ā
This is such a neat little event; it was so much fun to work with all my co-authors on it. We pulled on a wide area of expertise and many different data types. This was necessary to get the complete picture of the event, although sometimes a bit overwhelming. But in the end, it was oh-so satisfying!Ā