Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Properties of the Fast Forward Shock Driven by the July 23 2012 Extreme
  Coronal Mass Ejection   Late on July 23, 2012, the STEREO-A spacecraft encountered a fast forward
shock driven by a coronal mass ejection launched from the Sun earlier that same
day. The estimated travel time of the disturbance ($\sim 20$ hrs), together
with the massive magnetic field strengths measured within the ejecta ($>
100$nT), made it one of the most extreme events observed during the space era.
In this study, we examine the properties of the shock wave. Because of an
instrument malfunction, plasma measurements during the interval surrounding the
CME were limited, and our approach has been modified to capitalize on the
available measurements and suitable proxies, where possible. We were able to
infer the following properties. First, the shock normal was pointing
predominantly in the radial direction (${\bf n} = 0.97 {\bf e}_r -0.09 {\bf
e}_t -0.23 {\bf e}_n$). Second, the angle between ${\bf n}$ and the upstream
magnetic field, $\theta_{Bn}$, was estimated to be $\approx 34^{\circ}$, making
the shock "quasi-parallel," and supporting the idea of an earlier
"preconditioning" ICME. Third, the shock speed was estimated to be $\approx
3300$ km s$^{-1}$. Fourth, the sonic Mach number, $M_s$, for this shock was
$\sim 28$. We support these results with an idealized numerical simulation of
the ICME. Finally, we estimated the change in ram pressure upstream of the
shock to be $\sim 5$ times larger than the pressure from the energetic
particles, suggesting that this was not a standard "steady-state" cosmic-ray
modified shock (CRMS). Instead it might represent an early, transient phase in
the evolution of the CRMS.

10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas