Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Height of Shock Formation in the Solar Corona Inferred from Observations
  of Type II Radio Bursts and Coronal Mass Ejections   Employing coronagraphic and EUV observations close to the solar surface made
by the Solar Terrestrial Relations Observatory (STEREO) mission, we determined
the heliocentric distance of coronal mass ejections (CMEs) at the starting time
of associated metric type II bursts. We used the wave diameter and leading edge
methods and measured the CME heights for a set of 32 metric type II bursts from
solar cycle 24. We minimized the projection effects by making the measurements
from a view that is roughly orthogonal to the direction of the ejection. We
also chose image frames close to the onset times of the type II bursts, so no
extrapolation was necessary. We found that the CMEs were located in the
heliocentric distance range from 1.20 to 1.93 solar radii (Rs), with mean and
median values of 1.43 and 1.38 Rs, respectively. We conclusively find that the
shock formation can occur at heights substantially below 1.5 Rs. In a few
cases, the CME height at type II onset was close to 2 Rs. In these cases, the
starting frequency of the type II bursts was very low, in the range 25 to 40
MHz, which confirms that the shock can also form at larger heights. The
starting frequencies of metric type II bursts have a weak correlation with the
measured CME/shock heights and are consistent with the rapid decline of density
with height in the inner corona.

15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th