Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Drop of solar wind at the end of the 20th century   Variations in the solar wind (SW) parameters with scales of several years are
an important characteristic of solar activity and the basis for a long-term
space weather forecast. We examine the behavior of interplanetary parameters
over 21-24 solar cycles (SCs) on the basis of OMNI database
(https://spdf.gsfc.nasa.gov/pub/data/omni). Since changes in parameters can be
associated both with changes in the number of different large-scale types of
SW, and with variations in the values of these parameters at different phases
of the solar cycle and during the transition from one cycle to another, we
select the entire study period in accordance with the Catalog of large-scale SW
types for 1976-2019 (See the site http://www.iki.rssi.ru/pub/omni, [Yermolaev
et al., 2009]), which covers the period from 21 to 24 SCs, and in accordance
with the phases of the cycles, and averaging the parameters at selected
intervals. In addition to a sharp drop in the number of ICMEs (and associated
Sheath types), there is a noticeable drop in the value (by 20-40%) of plasma
parameters and magnetic field in different types of solar wind at the end of
the 20th century and a continuation of the fall or persistence at a low level
in the 23-24 cycles. Such a drop in the solar wind is apparently associated
with a decrease in solar activity and manifests itself in a noticeable decrease
in space weather factors.

28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol