136 research outputs found
Correcting Parker Solar Probe Electron Measurements for Spacecraft Magnetic and Electric Fields
The spacecraft body of the Parker Solar Probe may interfere with electron measurements in two ways. The first is the presence of several permanent magnets near the Solar Probe Analyzers (SPAN) instruments. The second is the widely varying spacecraft potential. We estimate the effect of these interferences by performing particle tracing simulations on electrons of various energies using a simplified model of the spacecraft potential and measurements of the magnetic fields. From this we can (1) estimate the individual and combined fields of view of the SPAN‐E instruments, (2) identify regions of phase space that may be highly distorted, and (3) simulate measurements of the velocity distribution function. We compute density, temperature, and bulk velocity moments of the measured distribution functions and find that a correction table derived from the particle tracing results can be incorporated in the computation to greatly decrease the errors caused by the spacecraft potential and magnetic fields. Similar tables could be computed for a wide range of spacecraft potentials and applied during the processing of actual SPAN data.Key PointsSpacecraft‐produced electrostatic and magnetic fields likely interfere with the collection of PSP SPAN‐E dataThese fields are modeled in order to estimate how electron measurements might be affectedA technique for correcting electron measurements using these results is presentedPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151982/1/jgra55211.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151982/2/jgra55211_am.pd
Global Magnetospheric Response to an Interplanetary Shock: THEMIS Observations
We investigate the global response of geospace plasma environment to an interplanetary shock at approx. 0224 UT on May 28, 2008 from multiple THEMIS spacecraft observations in the magnetosheath (THEMIS B and C) and the mid-afternoon (THEMIS A) and dusk magnetosphere (THEMIS D and E). The interaction of the transmitted interplanetary shock with the magnetosphere has global effects. Consequently, it can affect geospace plasma significantly. After interacting with the bow shock, the interplanetary shock transmitted a fast shock and a discontinuity which propagated through the magnetosheath toward the Earth at speeds of 300 km/s and 137 km/s respectively. THEMIS A observations indicate that the plasmaspheric plume changed significantly by the interplanetary shock impact. The plasmaspheric plume density increased rapidly from 10 to 100/ cubic cm in 4 min and the ion distribution changed from isotropic to strongly anisotropic distribution. Electromagnetic ion cyclotron (EMIC) waves observed by THEMIS A are most likely excited by the anisotropic ion distributions caused by the interplanetary shock impact. To our best knowledge, this is the first direct observation of the plasmaspheric plume response to an interplanetary shock's impact. THEMIS A, but not D or E, observed a plasmaspheric plume in the dayside magnetosphere. Multiple spacecraft observations indicate that the dawn-side edge of the plasmaspheric plume was located between THEMIS A and D (or E)
Measurements of Forbush decreases at Mars: both by MSL on ground and by MAVEN in orbit
The Radiation Assessment Detector (RAD), on board Mars Science Laboratory's
(MSL) Curiosity rover, has been measuring ground level particle fluxes along
with the radiation dose rate at the surface of Mars since August 2012. Similar
to neutron monitors at Earth, RAD sees many Forbush decreases (FDs) in the
galactic cosmic ray (GCR) induced surface fluxes and dose rates. These FDs are
associated with coronal mass ejections (CMEs) and/or stream/corotating
interaction regions (SIRs/CIRs). Orbiting above the Martian atmosphere, the
Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has also been
monitoring space weather conditions at Mars since September 2014. The
penetrating particle flux channels in the Solar Energetic Particle (SEP)
instrument onboard MAVEN can also be employed to detect FDs. For the first
time, we study the statistics and properties of a list of FDs observed in-situ
at Mars, seen both on the surface by MSL/RAD and in orbit detected by the
MAVEN/SEP instrument. Such a list of FDs can be used for studying
interplanetary CME (ICME) propagation and SIR evolution through the inner
heliosphere. The magnitudes of different FDs can be well-fitted by a power-law
distribution. The systematic difference between the magnitudes of the FDs
within and outside the Martian atmosphere may be mostly attributed to the
energy-dependent modulation of the GCR particles by both the pass-by ICMEs/SIRs
and the Martian atmosphere
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
Turbulence Transport Modeling and First Orbit Parker Solar Probe (PSP) Observations
Parker Solar Probe (PSP) achieved its first orbit perihelion on November 6,
2018, reaching a heliocentric distance of about 0.165 au (35.55 R).
Here, we study the evolution of fully developed turbulence associated with the
slow solar wind along the PSP trajectory between 35.55 R and 131.64
R in the outbound direction, comparing observations to a theoretical
turbulence transport model. Several turbulent quantities, such as the
fluctuating kinetic energy and the corresponding correlation length, the
variance of density fluctuations, and the solar wind proton temperature are
determined from the PSP SWEAP plasma data along its trajectory between 35.55
R and 131.64 R. The evolution of the PSP derived turbulent
quantities are compared to the numerical solutions of the nearly incompressible
magnetohydrodynamic (NI MHD) turbulence transport model recently developed by
Zank et al. (2017). We find reasonable agreement between the theoretical and
observed results. On the basis of these comparisons, we derive other
theoretical turbulent quantities, such as the energy in forward and backward
propagating modes, the total turbulent energy, the normalized residual energy
and cross-helicity, the fluctuating magnetic energy, and the correlation
lengths corresponding to forward and backward propagating modes, the residual
energy, and the fluctuating magnetic energy
ISS Space Plasma Laboratory: An ISS instrument package for investigating the opening/closing of solar and heliospheric magnetic fields
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140428/1/6.2014-1422.pd
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
Switchbacks, microstreams, and broadband turbulence in the solar wind
Switchbacks are a striking phenomenon in near-Sun coronal hole flows, but their origins, evolution, and relation to the broadband fluctuations seen farther from the Sun are unclear. We use the near-radial lineup of Solar Orbiter and Parker Solar Probe during September 2020 when both spacecraft were in wind from the Sun's Southern polar coronal hole to investigate if switchback variability is related to large scale properties near 1 au. Using the measured solar wind speed, we map measurements from both spacecraft to the source surface and consider variations with source Carrington longitude. The patch modulation of switchback amplitudes at Parker at 20 solar radii was associated with speed variations similar to microstreams and corresponds to solar longitudinal scales of around 5°–10°. Near 1 au, this speed variation was absent, probably due to interactions between plasma at different speeds during their propagation. The alpha particle fraction, which has recently been shown to have spatial variability correlated with patches at 20 solar radii, varied on a similar scale at 1 au. The switchback modulation scale of 5°–10°, corresponding to a temporal scale of several hours at Orbiter, was present as a variation in the average deflection of the field from the Parker spiral. While limited to only one stream, these results suggest that in coronal hole flows, switchback patches are related to microstreams, perhaps associated with supergranular boundaries or plumes. Patches of switchbacks appear to evolve into large scale fluctuations, which might be one driver of the ubiquitous turbulent fluctuations in the solar wind
Small-scale Magnetic Flux Ropes in the First two Parker Solar Probe Encounters
Small-scale magnetic flux ropes (SFRs) are a type of structures in the solar
wind that possess helical magnetic field lines. In a recent report (Chen & Hu
2020), we presented the radial variations of the properties of SFR from 0.29 to
8 au using in situ measurements from the Helios, ACE/Wind, Ulysses, and Voyager
spacecraft. With the launch of the Parker Solar Probe (PSP), we extend our
previous investigation further into the inner heliosphere. We apply a
Grad-Shafranov-based algorithm to identify SFRs during the first two PSP
encounters. We find that the number of SFRs detected near the Sun is much less
than that at larger radial distances, where magnetohydrodynamic (MHD)
turbulence may act as the local source to produce these structures. The
prevalence of Alfvenic structures significantly suppresses the detection of
SFRs at closer distances. We compare the SFR event list with other event
identification methods, yielding a dozen well-matched events. The cross-section
maps of two selected events confirm the cylindrical magnetic flux rope
configuration. The power-law relation between the SFR magnetic field and
heliocentric distances seems to hold down to 0.16 au.Comment: Accepted by ApJ on 2020 Sep 1
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