Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Turbulence in the Sub-Alfv\'enic Solar Wind   Parker Solar Probe (PSP) entered a region of the sub-Alfvenic solar wind
during encounter 8 and we present the first detailed analysis of low-frequency
turbulence properties in this novel region. The magnetic field and flow
velocity vectors were highly aligned during this interval. By constructing
spectrograms of the normalized magnetic helicity, cross helicity, and residual
energy, we find that PSP observed primarily Alfvenic fluctuations, a
consequence of the highly field-aligned flow that renders quasi-2D fluctuations
unobservable to PSP. We extend Taylor hypothesis to sub and super Alfvenic
flows. Spectra for the fluctuating forward and backward Elsasser variables are
presented. The observed spectra are well fitted using a spectral theory for
nearly incompressible magnetohydrodynamics assuming a wave number anisotropy.
The density spectrum is a power law that resembles neither the Elsasser spectra
nor the compressible magnetic field spectrum, suggesting that these are
advected entropic rather than magnetosonic modes and not due to the parametric
decay instability. Spectra in the neighboring modestly super Alfvenic intervals
are similar.

22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat