138 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 SPANâE 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 PointsSpacecraftâproduced electrostatic and magnetic fields likely interfere with the collection of PSP SPANâE 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
Whistler mode waves upstream of Saturn
Whistler-mode waves are generated within and can propagate upstream of
collisionless shocks. They are known to play a role in electron
thermodynamics/acceleration and, under certain conditions, are markedly
observed as wave trains preceding the shock ramp. In this paper, we take
advantage of Cassini's presence at ~10 AU to explore the importance of
whistler-mode waves in a parameter regime typically characterized by higher
Mach number (median of ~14) shocks, as well as a significantly different IMF
structure, compared to near Earth. We identify electromagnetic precursors
preceding a small subset of bow shock crossings with properties which are
consistent with whistler-mode waves. We find these monochromatic,
low-frequency, circularly-polarized waves to have a typical frequency range of
0.2 - 0.4 Hz in the spacecraft frame. This is due to the lower ion and electron
cyclotron frequencies near Saturn, between which whistler waves can develop.
The waves are also observed as predominantly right-handed in the spacecraft
frame, the opposite sense to what is typically observed near Earth. This is
attributed to the weaker Doppler shift, owing to the large angle between the
solar wind velocity and magnetic field vectors at 10 AU. Our results on the low
occurrence of whistler waves upstream of Saturn also underpins the
predominantly supercritical bow shock of Saturn.Comment: Published in Journal of Geophysical Research: Space Physics (January
2017) 21 pages, 4 figure
A comparison of the impacts of CMEs and CIRs on the Martian dayside and nightside ionospheric species
Measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN)
spacecraft, orbiting Mars are used for investigating the impact of coronal mass
ejections (CMEs) and corotating interaction regions (CIRs) on Martian
ionospheric species. We have chosen 15 CME and 15 CIR events at Mars from the
existing catalogs. We have extensively analyzed Martian dayside and nightside
profiles of ionospheric species during each of the CME and CIR events. We have
selected the disturbed orbit plasma density profiles which are beyond the quiet
time mean profile during each event. The primary focus of this paper is to
provide a comparative average scenario of the variation of Martian ionospheric
species during CME and CIR events between 150-500 km altitudes. A significant
difference can be observed in the profiles of Martian dayside and nightside
ionospheric species (O+, O2+, CO2+, NO+, C+, N+, & OH+) during CMEs and CIRs.
The difference is more prominent on the nightside in comparison to the dayside
ionosphere. We have observed that the plasma densities were lower during CIRs
compared to CMEs. During CIRs, the nightside ion density is one order of
magnitude less (above 250 km) in comparison to CMEs. The mean peak altitude and
density of the lighter ions (O+, C+, N+, & OH+) were at lower altitudes during
the CIRs compared to CMEs. Therefore, this study suggests that the impact of
CIRs on the Martian ionospheric species is more prominent compared to CMEs
Thank You to Our 2018 Peer Reviewers
On behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union (AGU), and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2018. Reviews of Geophysics is the top rated journal in Geophysics and Geochemistry and it could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate the time spent reading and commenting on manuscripts, and we are very grateful for your willingness and readiness to serve in this role. Reviews of Geophysics published 20 review papers and an editorial in 2018, covering most of the AGU Section topics, and for this we were able to rely on the efforts of 85 dedicated reviewers from 20 countries. Many reviewers answered the call multiple times. Thank you again. We look forward to a 2019 of exciting advances in the field and communicating those advances to our community and to the broader public
Solar Wind Electron Interaction with the Dayside Lunar Surface and Crustal Magnetic Fields: Evidence for Precursor Effects
Electron distributions measured by Lunar Prospector above the dayside lunar surface in the solar wind often have an energy dependent loss cone, inconsistent with adiabatic magnetic reflection. Energy dependent reflection suggests the presence of downward parallel electric fields below the spacecraft, possibly indicating the presence of a standing electrostatic structure. Many electron distributions contain apparent low energy (<100 eV) upwardgoing conics (58% of the time) and beams (12% of the time), primarily in regions with non-zero crustal magnetic fields, implying the presence of parallel electric fields and/or wave-particle interactions below the spacecraft. Some, but not all, of the observed energy dependence comes from the energy gained during reflection from a moving obstacle; correctly characterizing electron reflection requires the use of the proper reference frame. Nonadiabatic reflection may also play a role, but cannot fully explain observations. In cases with upward-going beams, we observe partial isotropization of incoming solar wind electrons, possibly indicating streaming and/or whistler instabilities. The Moon may therefore influence solar wind plasma well upstream from its surface. Magnetic anomaly interactions and/or non-monotonic near surface potentials provide the most likely candidates to produce the observed precursor effects, which may help ensure quasi-neutrality upstream from the Moon
Appreciation of Peer Reviewers for 2017
On behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union, and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2017. The journal could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate all that you do, and we are very grateful for your willingness and readiness to serve in this role.Plain Language SummaryOn behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union, and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2017. The journal could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate all that you do, and we are very grateful for your willingness and readiness to serve in this role. Reviews of Geophysics published 29 review papers, a commentary and an editorial in 2017, covering most of the AGU Section topics, and for this we were able to rely on the efforts of 99 dedicated reviewers. Many reviewers answered the call multiple times. Thank you again. We look forward to a 2018 of exciting advances in the field and communicating those advances to our community and to the broader public.Key PointThe Reviews of Geophysics Editors thank all the peer reviewers from 2017Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147789/1/rog20174.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147789/2/rog20174_am.pd
Impact demagnetization of the Martian crust: Current knowledge and future directions
The paleomagnetism of the Martian crust has important implications for the history of the dynamo, the intensity of the ancient magnetic field, and the composition of the crust. Modification of crustal magnetization by impact cratering is evident from the observed lack of a measurable crustal field (at spacecraft altitude) within the youngest large impact basins (e.g., Hellas, Argyre and Isidis). It is hoped that comparisons of the magnetic intensity over impact structures, forward modeling of subsurface magnetization, and experimental results of pressure-induced demagnetization of rocks and minerals will provide constraints on the primary magnetic mineralogy in the Martian crust. Such an effort requires: (i) accurate knowledge of the spatial distribution of the shock pressures around impact basins, (ii) crustal magnetic intensity maps of adequate resolution over impact structures, and (iii) determination of demagnetization properties for individual rocks and minerals under compression. In this work, we evaluate the current understanding of these three conditions and compile the available experimental pressure demagnetization data on samples bearing (titano-) magnetite, (titano-) hematite, and pyrrhotite. We find that all samples demagnetize substantially at pressures of a few GPa and that the available data support significant modification of the crustal magnetic field from both large and small impact events. However, the amount of demagnetization with applied pressure does not vary significantly among the possible carrier phases. Therefore, the presence of individual mineral phases on Mars cannot be determined from azimuthally averaged demagnetization profiles over impact basins at present. The identification of magnetic mineralogy on Mars will require more data on pressure demagnetization of thermoremanent magnetization and forward modeling of the crustal field subject to a range of plausible initial field and demagnetization patterns.United States. National Aeronautics and Space Administration (NNG04GD17G)United States. National Aeronautics and Space Administration (NNX07AQ69G)United States. National Aeronautics and Space Administration (NNX06AD14G
Making waves: Mirror Mode structures around Mars observed by the MAVEN spacecraft
We present an in-depth analysis of a time interval when quasi-linear mirror
mode structures were detected by magnetic field and plasma measurements as
observed by the NASA/Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft.
We employ ion and electron spectrometers in tandem to support the magnetic
field measurements and confirm that the signatures are indeed mirror modes.
Wedged against the magnetic pile-up boundary, the low-frequency signatures last
on average 10 s with corresponding sizes of the order of 15-30 upstream
solar wind proton thermal gyroradii, or 10-20 proton gyroradii in the immediate
wake of the quasi-perpendicular bow shock. Their peak-to-peak amplitudes are of
the order of 30-35 nT with respect to the background field, and appear as a
mixture of dips and peaks, suggesting that they may have been at different
stages in their evolution. Situated in a marginally stable plasma with
1, we hypothesise that these so-called magnetic bottles,
containing a relatively higher energy and denser ion population with respect to
the background plasma, are formed upstream of the spacecraft behind the
quasi-perpendicular shock. These signatures are very reminiscent of magnetic
bottles found at other unmagnetised objects such as Venus and comets, also
interpreted as mirror modes. Our case study constitutes the first unmistakable
identification and characterisation of mirror modes at Mars from the joint
points of view of magnetic field, electron and ion measurements. Up until now,
the lack of high-temporal resolution plasma measurements has prevented such an
in-depth study.Comment: 37 pages, 11 figures, 1 tabl
Using machine learning to characterize solar wind driving of convection in the terrestrial magnetotail lobes
In order to quantitatively investigate the mechanism of how magnetospheric convection is driven in the region of magnetotail lobes on a global scale, we analyzed data from the ARTEMIS spacecraft in the deep tail and data from the Cluster spacecraft in the near and mid-tail regions. Our previous work revealed that, in the lobes near the Moonâs orbit, the convection can be estimated by using ARTEMIS measurements of lunar ionsâ velocity. Based on that, in this paper, we applied machine learning models to these measurements to determine which upstream solar wind parameters significantly drive the lobe convection in magnetotail regions, to help us understand the mechanism that controls the dynamics of the tail lobes. The results demonstrate that the correlations between the predicted and measured convection velocities for the machine learning models (>0.75) are superior to those of the multiple linear regression model (âŒ0.23â0.43) in the testing dataset. The systematic analysis shows that the IMF and magnetospheric activity play an important role in influencing plasma convection in the global magnetotail lobes
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
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