Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence of solar-cycle related structural changes in the solar
  convection zone   While it has been relatively easy to determine solar-cycle related changes in
solar dynamics, determining changes in structure in the deeper layers of the
Sun has proved to be difficult. By using helioseismic data obtained over two
solar cycles, and sacrificing resolution in favour of lower uncertainties, we
show that there are significant changes in the solar convection zone, and
perhaps even below it. Using MDI data, we find a relative squared sound-speed
difference of $(2.56\pm 0.71)\times 10^{-5}$ at the convection-zone base
between the maximum of solar Cycle~23 and the minimum between Cycles~23 and 24.
The squared sound-speed difference for the maximum of Cycle~24 obtained with
HMI data is $(1.95\pm 0.69)\times 10^{-5}$. GONG data support these results. We
also find that the sound speed in the solar convection zone decreases compared
to the sound speed below it as the Sun becomes more active. We find evidence of
changes in the radial derivative of the sound-speed difference between the
solar minimum and other epochs at the base of the convection zone implying
possible small changes in the position of the convection-zone base, however,
the results are too noisy to make any definitive estimates of the change.

17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
23
The categories of this paper are: solv-int