Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Intermediate-term periodicities in soft X-ray flare index during solar
  cycles 21, 22 and 23   We have analyzed the intermediate term periodicities in soft X-ray flare
index ($FI_{SXR}$) during solar cycles 21, 22 and 23. Power spectral analysis
of daily $FI_{SXR}$ reveals a significant period of 161 days in cycle 21 which
is absent during cycle 22 and 23. We have found that in cycle 22 periodicities
of 74 and 83 days are in operation. A 123 day periodicity has been found to be
statistically significant during the part of the current solar cycle 23. The
existence of these periodicities has been discussed in the light of earlier
results.

19
The categories of this paper are: eess
3
The categories of this paper are: physics
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th