Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time variability of high energy cosmic rays   Our model involving cosmic ray acceleration in supernova remnants has been
used to predict cosmic ray intensities over long periods of time on a
statistical basis. If, as is highly probable, extensive air showers caused by
PeV cosmic rays are needed to initiate terrestrial lightning then past dramatic
changes in PeV intensities may have had important biological effects.
  The model has been used to estimate the manner in which the PeV cosmic ray
intensity at Earth has varied over the past tens of thousand years.

4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex