67 research outputs found
Interplay between intermittency and dissipation in collisionless plasma turbulence
We study the damping of collisionless Alfv\'enic turbulence by two
mechanisms: stochastic heating (whose efficiency depends on the local
turbulence amplitude ) and linear Landau damping (whose
efficiency is independent of ), describing in detail how they
affect and are affected by intermittency. The overall efficiency of linear
Landau damping is not affected by intermittency in critically balanced
turbulence, while stochastic heating is much more efficient in the presence of
intermittent turbulence. Moreover, stochastic heating leads to a drop in the
scale-dependent kurtosis over a narrow range of scales around the ion
gyroscale.Comment: 15 pages, 3 figures, accepted to JP
The statistical properties of solar wind temperature parameters near 1 AU
We present a long-duration (10 years) statistical analysis of the
temperatures, plasma betas, and temperature ratios for the electron, proton,
and alpha-particle populations observed by the \emph{Wind} spacecraft near 1
AU. The mean(median) scalar temperatures are
12.2(11.9) eV, 12.7(8.6) eV, and
23.9(10.8) eV. The mean(median) total
plasma betas are 2.31(1.09),
1.79(1.05), and 0.17(0.05). The mean(median) temperature ratios are
1.64(1.27),
1.24(0.82), and
2.50(1.94). We also examined these parameters during time intervals that
exclude interplanetary (IP) shocks, times within the magnetic obstacles (MOs)
of interplanetary coronal mass ejections (ICMEs), and times that exclude MOs.
The only times that show significant alterations to any of the parameters
examined are those during MOs. In fact, the only parameter that does not show a
significant change during MOs is the electron temperature. Although each
parameter shows a broad range of values, the vast majority are near the median.
We also compute particle-particle collision rates and compare to effective
wave-particle collision rates. We find that, for reasonable assumptions of wave
amplitude and occurrence rates, the effect of wave-particle interactions on the
plasma is equal to or greater than the effect of Coulomb collisions. Thus,
wave-particle interactions should not be neglected when modeling the solar
wind.Comment: 23 pages, 3 figures, 6 tables, submitted to Astrophys. J. Suppl. on
Jan. 30, 201
Proton and Alpha Driven Instabilities in an Ion Cyclotron Wave Event
Ion scale wave events or "wave storms" in the solar wind are characterised by
enhancements in magnetic field fluctuations as well as coherent magnetic field
polarisation signatures at or around the local ion cyclotron frequencies. In
this paper we study in detail one such wave event from Parker Solar Probe's
(PSP) fourth encounter, consisting of an initial period of left-handed (LH)
polarisation abruptly transitioning to a strong period of right-handed (RH)
polarisation, accompanied by clear core-beam structure in both the alpha and
proton velocity distribution functions. A linear stability analysis shows that
the LH polarised waves are anti-Sunward propagating Alfv\'en/ion cyclotron
(A/IC) waves primarily driven by a proton cyclotron instability in the proton
core population, and the RH polarised waves are anti-Sunward propagating fast
magnetosonic/whistler (FM/W) waves driven by a firehose-like instability in the
secondary alpha beam population. The abrupt transition from LH to RH is caused
by a drop in the proton core temperature anisotropy. We find very good
agreement between the frequencies and polarisations of the unstable wave modes
as predicted by linear theory and those observed in the magnetic field spectra.
Given the ubiquity of ion scale wave signatures observed by PSP, this work
gives insight into which exact instabilities may be active and mediating energy
transfer in wave-particle interactions in the inner heliosphere, as well as
highlighting the role a secondary alpha population may play as a rarely
considered source of free energy available for producing wave activity
The In Situ Signature of Cyclotron Resonant Heating
The dissipation of magnetized turbulence is an important paradigm for
describing heating and energy transfer in astrophysical environments such as
the solar corona and wind; however, the specific collisionless processes behind
dissipation and heating remain relatively unconstrained by measurements. Remote
sensing observations have suggested the presence of strong temperature
anisotropy in the solar corona consistent with cyclotron resonant heating. In
the solar wind, in situ magnetic field measurements reveal the presence of
cyclotron waves, while measured ion velocity distribution functions have hinted
at the active presence of cyclotron resonance. Here, we present Parker Solar
Probe observations that connect the presence of ion-cyclotron waves directly to
signatures of resonant damping in observed proton-velocity distributions. We
show that the observed cyclotron wave population coincides with both flattening
in the phase space distribution predicted by resonant quasilinear diffusion and
steepening in the turbulent spectra at the ion-cyclotron resonant scale. In
measured velocity distribution functions where cyclotron resonant flattening is
weaker, the distributions are nearly uniformly subject to ion-cyclotron wave
damping rather than emission, indicating that the distributions can damp the
observed wave population. These results are consistent with active cyclotron
heating in the solar wind
Signaling in Secret: Pay-for-Performance and the Incentive and Sorting Effects of Pay Secrecy
Key Findings: Pay secrecy adversely impacts individual task performance because it weakens the perception that an increase in performance will be accompanied by increase in pay; Pay secrecy is associated with a decrease in employee performance and retention in pay-for-performance systems, which measure performance using relative (i.e., peer-ranked) criteria rather than an absolute scale (see Figure 2 on page 5); High performing employees tend to be most sensitive to negative pay-for- performance perceptions; There are many signals embedded within HR policies and practices, which can influence employees’ perception of workplace uncertainty/inequity and impact their performance and turnover intentions; and When pay transparency is impractical, organizations may benefit from introducing partial pay openness to mitigate these effects on employee performance and retention
The Temperature, Electron, and Pressure Characteristics of Switchbacks: Parker Solar Probe Observations
Parker Solar Probe (PSP) observes unexpectedly prevalent switchbacks, which
are rapid magnetic field reversals that last from seconds to hours, in the
inner heliosphere, posing new challenges to understanding their nature, origin,
and evolution. In this work, we investigate the thermal states, electron pitch
angle distributions, and pressure signatures of both inside and outside
switchbacks, separating a switchback into spike, transition region (TR), and
quiet period (QP). Based on our analysis, we find that the proton temperature
anisotropies in TRs seem to show an intermediate state between spike and QP
plasmas. The proton temperatures are more enhanced in spike than in TR and QP,
but the alpha temperatures and alpha-to-proton temperature ratios show the
opposite trends, implying that the preferential heating mechanisms of protons
and alphas are competing in different regions of switchbacks. Moreover, our
results suggest that the electron integrated intensities are almost the same
across the switchbacks but the electron pitch angle distributions are more
isotropic inside than outside switchbacks, implying switchbacks are intact
structures but strong scattering of electrons happens inside switchbacks. In
addition, the examination of pressures reveals that the total pressures are
comparable through a switchback, confirming switchbacks are pressure-balanced
structures. These characteristics could further our understanding of ion
heating, electron scattering, and the structure of switchbacks.Comment: submitted to Ap
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