Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observational Test of Stochastic Heating in Low-$\beta$ Fast Solar Wind
  Streams   Spacecraft measurements show that protons undergo substantial perpendicular
heating during their transit from the Sun to the outer heliosphere. In this
paper, we use {\em Helios~2} measurements to investigate whether stochastic
heating by low-frequency turbulence is capable of explaining this perpendicular
heating. We analyze {\em Helios~2} magnetic-field measurements in low-$\beta$
fast-solar-wind streams between heliocentric distances $r=0.29$ AU and $r=0.64$
AU to determine the rms amplitude of the fluctuating magnetic field, $\delta
B_{\rm p}$, near the proton gyroradius scale $\rho_{\rm p}$. We then evaluate
the stochastic heating rate $Q_{\perp \rm stoch}$ using the measured value of
$\delta B_{\rm p}$ and a previously published analytical formula for $Q_{\perp
\rm stoch}$. Using {\em Helios} measurements we estimate the `empirical'
perpendicular heating rate $Q_{\perp \rm emp} = (k_{\rm B}/m_{\rm p}) B V
(d/dr) (T_{\perp \rm p}/B)$ that is needed to explain the $T_{\perp \rm p}$
profile. We find that $Q_{\perp \rm stoch} \sim Q_{\perp \rm emp}$, but only if
a key dimensionless constant appearing in the formula for $Q_{\perp \rm stoch}$
lies within a certain range of values. This range is approximately the same
throughout the radial interval that we analyze and is consistent with the
results of numerical simulations of the stochastic heating of test particles in
reduced magnetohydrodynamic turbulence. These results support the hypothesis
that stochastic heating accounts for much of the perpendicular proton heating
occurring in low-$\beta$ fast-wind streams.

25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ