Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Strength and Radial Profile of Coronal Magnetic Field from the
  Standoff Distance of a CME-driven Shock   We determine the coronal magnetic field strength in the heliocentric distance
range 6 to 23 solar radii (Rs) by measuring the shock standoff distance and the
radius of curvature of the flux rope during the 2008 March 25 coronal mass
ejection (CME) imaged by white-light coronagraphs. Assuming the adiabatic
index, we determine the Alfven Mach number, and hence the Alfven speed in the
ambient medium using the measured shock speed. By measuring the upstream plasma
density using polarization brightness images, we finally get the magnetic field
strength upstream of the shock. The estimated magnetic field decreases from ~48
mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can
be described by a power law in agreement with other estimates at similar
heliocentric distances.

35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin