Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measures of Scale Dependent Alfv\'enicity in the First PSP Solar
  Encounter   The solar wind shows periods of highly Alfv\'enic activity, where velocity
fluctuations and magnetic fluctuations are aligned or anti-aligned with each
other. It is generally agreed that solar wind plasma velocity and magnetic
field fluctuations observed by Parker Solar Probe (PSP) during the first
encounter are mostly highly Alfv\'enic. However, quantitative measures of
Alfv\'enicity are needed to understand how the characterization of these
fluctuations compares with standard measures from prior missions in the inner
and outer heliosphere, in fast wind and slow wind, and at high and low
latitudes. To investigate this issue, we employ several measures to quantify
the extent of Alfv\'enicity -- the Alfv\'en ratio $r_A$, {normalized} cross
helicity $\sigma_c$, {normalized} residual energy $\sigma_r$, and the cosine of
angle between velocity and magnetic fluctuations $\cos\theta_{vb}$. We show
that despite the overall impression that the Alfv\'enicity is large in the
solar wind sampled by PSP during the first encounter, during some intervals the
cross helicity starts decreasing at very large scales. These length-scales
(often $> 1000 d_i$) are well inside inertial range, and therefore, the
suppression of cross helicity at these scales cannot be attributed to kinetic
physics. This drop at large scales could potentially be explained by
large-scale shears present in the inner heliosphere sampled by PSP. In some
cases, despite the cross helicity being constant down to the noise floor, the
residual energy decreases with scale in the inertial range. These results
suggest that it is important to consider all these measures to quantify
Alfv\'enicity.

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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
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The categories of this paper are: adap-org
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: cond-mat
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph