Engineering topics

Andersson, Laila

Publications and source records attributed to Andersson, Laila.

7 records

NASA NTRS2018

MMS Observations of Electrostatic Waves in an Oblique Shock Crossing

High-resolution particle and wave measurements taken during an oblique bow shock crossing by the Magnetospheric Multiscale (MMS) mission are analyzed. Two regions of differing magnetic behavior are identified within the shock, one with active magnetic fluctuations and one with laminar interplanetary magnetic field topology. A prominent reflected ion population is observed in both regions. The active magnetic region is characterized by large-amplitude (>100 mV/m) electrostatic solitary waves, electron Bernstein waves, and ion acoustic waves, along with intermittent current activity and localized electron heating. In the region of laminar magnetic field, ion acoustic waves are prominently observed. Solar wind ion deceleration is observed in both regions of active and laminar magnetic field. All observations suggest that solar wind deceleration can occur as a result of multiple independent processes, in this case current and ion-ion instabilities.

Goodrich, Katherine A.↗

NASA NTRS2018

MAVEN Case Studies of Plasma Dynamics in Low‐Altitude Crustal Magnetic Field at Mars 1: Dayside Ion Spikes Associated With Radial Crustal Magnetic Fields

We report for the first time, simultaneous ion, electron, magnetic field vector and electric field wave measurements made possible by Mars Atmosphere and Volatile EvolutioN, during ion energy flux spikes in low‐altitude radial crustal magnetic fields on the Mars dayside. Observations show energetic electrons and ions (E > 25 eV) precipitating on magnetic field lines assumed as closed. Ions (E < 1.4 keV) display broad velocity distributions toward Mars, showing ions flowing from higher altitude possibly after magnetic reconnection or loss cone filling from pitch angle scattering effects. Precipitating ions (E < 1.4 keV) show nonadiabatic features depending on ion mass and energy and returning ions (E < 1.4 keV) show evidence of conserving the first adiabatic invariant in a mirror field. We observe magnetic field perturbations up to 60 nT, electric field wave amplitudes up to 38 mV/m, and brief periods of peaked electron spectra. At ∼175 km and at times Mars Atmosphere and Volatile EvolutioN is below the mirroring altitude of electrons, we observe mirroring and transverse heating of H+ ions alongside increased electric field wave amplitude fluctuations. It suggests field aligned potential drops result from different mirror altitudes of ions and electrons. Ions E > 1.4 keV (O+) occur as injected accelerated ion beams and ions heated after energization or deceleration. Energy dispersed kilo‐electron‐volt ions suggest a selection effect in radial magnetic fields for lower‐energy Marsward ions, compared to reflection of higher‐energy anti‐Sunward ions. Precipitating kilo‐electron‐volt ions show energy deposition rates of 3.6 ×10(exp -6) W/sq m and sputtering escape rates from precipitating O+ ions of 1.5 ×10(exp 5)/(sq cm.s) and 2.1 ×10(exp 6)/(sq cm.s) are calculated.

Plasma Dynamics↗

NASA NTRS2016

Photoelectrons and Solar Ionizing Radiation at Mars: Predictions Versus MAVEN Observations

Understanding the evolution of the Martian atmosphere requires knowledge of processes transforming solar irradiance into thermal energy well enough to model them accurately. Here we compare Martian photoelectron energy spectra measured at periaps is by Mars Atmosphere and Volatile Evolution MissioN (MAVEN) with calculations made using three photoelectron production codes and three solar irradiance models as well as modeled and measured CO2 densities. We restricted our comparisons to regions where the contribution from solar wind electrons and ions were negligible. The two intervals examined on 19 October 2014 have different observed incident solar irradiance spectra. In spite of the differences in photoionization cross sections and irradiance spectra used, we find the agreement between models to be within the combined uncertainties associated with the observations from the MAVEN neutral density, electron flux, and solar irradiance instruments.

solar ionizing↗

NASA NTRS2016

Electron Energetics in the Martian Dayside Ionosphere: Model Comparisons with MAVEN Data

This paper presents a study of the energetics of the dayside ionosphere of Mars using models and data from several instruments on board the Mars Atmosphere and Volatile EvolutioN spacecraft. In particular, calculated photoelectron fluxes are compared with suprathermal electron fluxes measured by the Solar Wind Electron Analyzer, and calculated electron temperatures are compared with temperatures measured by the Langmuir Probe and Waves experiment. The major heat source for the thermal electrons is Coulomb heating from the suprathermal electron population, and cooling due to collisional rotational and vibrational CO2 dominates the energy loss. The models used in this study were largely able to reproduce the observed high topside ionosphere electron temperatures (e.g., 3000 K at 300 km altitude) without using a topside heat flux when magnetic field topologies consistent with the measured magnetic field were adopted. Magnetic topology affects both suprathermal electron transport and thermal electron heat conduction. The effects of using two different solar irradiance models were also investigated. In particular, photoelectron fluxes and electron temperatures found using the Heliospheric Environment Solar Spectrum Radiation irradiance were higher than those with the Flare Irradiance Spectrum Model-Mars. The electron temperature is shown to affect the O2(+) dissociative recombination rate coefficient, which in turn affects photochemical escape of oxygen from Mars.

magnetic topology↗

NASA NTRS2000

Electromagnetic Waves and Bursty Electron Acceleration: Implications from Freja

Dispersive Alfven wave activity is identified in four dayside auroral oval events measured by the Freja satellite. The events are characterized by ion injection, bursty electron precipitation below about I keV, transverse ion heating and broadband extremely low frequency (ELF) emissions below the lower hybrid cutoff frequency (a few kHz). The broadband emissions are observed to become more electrostatic towards higher frequencies. Large-scale density depletions/cavities, as determined by the Langmuir probe measurements, and strong electrostatic emissions are often observed simultaneously. A correlation study has been carried out between the E- and B-field fluctuations below 64 Hz (the dc instrument's upper threshold) and the characteristics of the precipitating electrons. This study revealed that the energization of electrons is indeed related to the broadband ELF emissions and that the electrostatic component plays a predominant role during very active magnetospheric conditions. Furthermore, the effect of the ELF electromagnetic emissions on the larger scale field-aligned current systems has been investigated, and it is found that such an effect cannot be detected. Instead, the Alfvenic activity creates a local region of field-aligned currents. It is suggested that dispersive Alfven waves set up these local field-aligned current regions and in turn trigger more electrostatic emissions during certain conditions. In these regions ions are transversely heated, and large-scale density depletions/cavities may be created during especially active periods.

Andersson, Laila↗

NASA NTRS2000

Electron Signatures and Alfven Waves

The electron signatures which appear together with Alfven waves observed by the Freja satellite in the auroral region are reported. Precipitating electrons are detected both with and just before the wave. The observed Alfven waves must therefore be capable of accelerating electrons to higher energies than the local phase velocity of these waves in order for the electrons to move in advance of the wave. The characteristics of such electrons suggest electrons moving infront of the wave have characteristics of origin from warmer and lower density plasma while the electrons moving with the wave have characteristics of cooler and denser plasma. The pitch angle distribution of the electrons moving with the wave indicates that there is continuous acceleration of new particles by the wave, i.e. a propagating Alfven wave is the source of these electrons . A simple model of a propagating source is made to model the electrons that are moving in advance of the wave. Depending on whether accelerated electrons leave the wave above or below the altitude where the Alfven wave has the highest phase velocity, the detected electron signatures will be different; electron dispersion or potential drop like, respectively. It is shown that the Alfven wave acceleration can create electron signatures similar to inverted-V structures.

Andersson, Laila↗

NASA NTRS2000

Freja Studies of the Current-Voltage Relation in Substorm-Related Events

Field-aligned currents and electrostatic potentials play important roles in the coupling between the magnetosphere and the ionosphere. If one assumes that the ionosphere-magnetosphere potential difference is mainly due to the mirror force, one can use the single particle adiabatic kinetic theory to describe the system. From this theory, a linear relationship j(sub II) = KV between field-aligned current density j(sub II) and potential drop V along the same field line can be derived, provided that the potential drop is not too large and not too small. With rare exceptions, observational tests of this relation have mainly concentrated on quiet magnetospheric situations, with acceleration voltages V approx. less than 5 kV. Here we use observations from the Freja satellite of precipitating auroral electrons at 1.700 km altitude to study substorm related events, with acceleration voltages up to 20 keV. The observations are found to be consistent with a linear current-voltage relation even i n these conditions, although with values of the field aligned K lower than previously reported (1-5 x 10(exp 11 S/sq m). This can be explained by lower densities and higher characteristic electron energies in the magnetospheric source region of the precipitating electrons. We analyze the data by three different methods, which are all found to be in general agreement. The results are in agreement with a previous study, where the spectra of precipitating electrons --were indirectly inferred by inversion of data from the EISCAT incoherent scatter radar, thereby validating the use of radar data for studies of auroral electrons. Comparisons with previous studies are made, emphasizing the dependence of the results on the type of auroral structure and magnetospheric conditions.

Olsson, A.↗