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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
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NASA NTRSDate not supplied

The Electron Heat Fluxes Associated with Electron Precipitation in the Region of Diffuse Aurora

Electron heat flux that comes from the magnetosphere to the upper ionospheric altitudes controls the value of electron temperature in the core plasma, and, as a result, the total electron density content that is required for different kinds of space weather applications. Knowing the thermal electron heat flux at the upper ionospheric boundaries is the Achilles' heel of all ionospheric models. Such a thermal heat flux setting is especially difficult to justify in the region of the diffuse aurora that is connected to a large energy reservoir of electrons with energies of a few kiloelectron volts, the Earth's plasma sheet, where magnetosphere-ionosphere coupling processes are strongly interconnected. We use the simulated heat flux provided by SuperThermal Electron Transport (STET) code to estimate electron temperatures at the upper ionospheric altitudes and compare these results with corresponding observations from the Defense Meteorological Satellite Program satellite during Saint Patrick's Days 2013 and 2015 Geomagnetic Storms.

George V. Khazanov↗
NASA NTRS2022

A 2D Kaleidoscope of Electron Heat Fluxes Driven by Auroral Electron Precipitation

Electron heat flux is an important value for ionospheric space weather modeling networks. Utilizing the 2D array of Time History of Events and Macroscale Interactions during Substorms all-sky-imager (ASI) observations, Gabrielse et al. (2021, https://doi.org/10.3389/fphy.2021.744298) described a new method that estimates the auroral scale sizes of intense precipitating electron energy fluxes and their mean energies during two substorms on 16 February 2010. These parameters in combination with SuperThermal Electron Transport code were used to develop a new methodology to calculate electron thermal fluxes from data inputs in 2D during one of the substorms at 09:40:00 UT across Canada and Alaska. To test the effect of various precipitation lifetimes on electron heat flux values, boxcar averages ranging from 0 to 900 s were applied to the ASI data. These data are then combined with the newly developed kinetic simulation to determine the thermal fluxes associated with the observed diffuse and discrete precipitation.

Electron precipitation in aurora↗
NASA NTRSDate not supplied

How Auroral Electron Precipitations Contribute to the Formation of Electron Heat Fluxes to the Ionosphere?

Electron heat fluxes (also called electron thermal fluxes) in the ionosphere are carried by thermal electrons whose energy is below a few eV. Electron heat fluxes greatly impact on electron temperature, which is a fundamental parameter in the ionospheric dynamics. At the high latitude in the auroral regions electron heat flux is originated dominantly from the magnetosphere through high-energy electron energy fluxes. High-energy electron fluxes in the diffuse auroral region can undergo multiple backscatters between the magnetically conjugated regions of both hemispheres, and different kind of wave-particle interactions along the magnetic field line. High-energy electron fluxes in discrete auroral region can be trapped below the auroral acceleration region and can also undergo backscatter and multiple reflection. These processes, in turn, amplify super-thermal electrons (<~500-600 eV) that dominantly form electron heat fluxes through Coulomb collision between thermal electrons. Such electron heat fluxes play an important role to determine electron temperature profile in the ionosphere, which is one of the key parameters that controls the ionospheric dynamics. Thus, it is necessary to include electron heat flux as a topside energy input in all global ionospheric models. We demonstrate all above results based on Superthermal Electron Transport (STET), Superthermal Proton, Electron and Atomic Hydrogen tRansport in the Ionosphere and Thermosphere (SPEAH-RIT), and Comprehensive Inner Magnetosphere and Ionospheres (CIMI) codes developed at NASA Goddard Space Flight Center.

George V. Khazanov↗
NASA NTRS1994

Perpendicular electron heating by absorption of auroral kilometric radiation

We investigate the possibility of perpendicular heating of electrons and the generation of '90 deg -electron conics' by particle diffusion in velocity space due to wave-particle interaction with intense auroral kilometric radiation. This interaction is made possible by the downward shift in the R-X cutoff below the electron cyclotron frequency that occurs in the presence of warm plasma. We stimulate this condition and solve the diffusion equation using a finite difference algorithm. The results show strong perpendicular electron heating and indicate that the main characteristics of an electron conic distribution can be reproduced under these conditions.

Morgan, D. D.↗
NASA NTRS1998

Conditions for Aeronomic Applicability of the Classical Electron Heat Conduction Formula

Conditions for the applicability of the classical formula for heat conduction in the electrons in ionized gas are investigated. In a fully ionised gas ( V(sub en) much greater than V(sub ei)), when the mean free path for electron-electron (or electron-ion) collisions is much larger than the characteristic thermal scale length of the observed system, the conditions for applicability break down. In the case of the Venus ionosphere this breakdown is indicated for a large fraction of the electron temperature data from altitudes greater than 180 km, for electron densities less than 10(exp 4)/cc cm. In a partially ionised gas such that V(sub en) much greater than V(sub ei) there is breakdown of the formula not only when the mean free path of electrons greatly exceeds the thermal scale length, but also when the gradient of neutral particle density exceeds the electron thermal gradient. It is shown that electron heat conduction may be neglected in estimating the temperature of joule heated electrons by observed strong 100 Hz electric fields when the conduction flux is limited by the saturation flux. The results of this paper support our earlier aeronomical arguments against the hypothesis of planetary scale whistlers for the 100 Hz electric field signal. In turn this means that data from the 100 Hz signal may not be used to support the case for lightning on Venus.

Cole, K. D.↗
NASA NTRS2023

Thermal Electron Heat Fluxes Associated with Precipitated Auroral Electrons During the Saint Patrick's Days 2013 and 2015 Geomagnetic Storms

The Rice Convection Model-Equilibrium (RCM-E) and SuperThermal Electron Transport (STET) are combined to investigate electron heat flux formation in the region of the diffuse aurora for the geomagnetic storms of 17 March 2013 and 17 March 2015. The primary electron precipitation into the atmosphere resulting from wave particle scattering in the magnetosphere are simulated by the magnetically and electrically RCM-E during these two geomagnetic storms. The primary precipitating electron fluxes are modified by the STET model by taking into account atmospheric backscatter processes. The modified electron energy fluxes and their mean energies are coupled to the STET code to calculate electron thermal fluxes associated with diffuse aurora on a global scale. We use the simulated heat flux to estimate electron temperatures at the upper ionospheric altitudes and compare them with corresponding observations from the Defense Meteorological Satellite Program satellite.

George V. Khazanov↗
NASA NTRS1983

Thermal electron heating rate: A derivation

The thermal electron heating rate is an important heat source term in the ionospheric electron energy balance equation, representing heating by photoelectrons or by precipitating higher energy electrons. A formula for the thermal electron heating rate is derived from the kinetic equation using the electron-electron collision operator as given by the unified theory of Kihara and Aono. This collision operator includes collective interactions to produce a finite collision operator with an exact Coulomb logarithm term. The derived heating rate O(e) is the sum of three terms, O(e) = O(p) + S + O(int), which are respectively: (1) primary electron production term giving the heating from newly created electrons that have not yet suffered collisions with the ambient electrons; (2) a heating term evaluated on the energy surface m(e)/2 = E(T) at the transition between Maxwellian and tail electrons at E(T); and (3) the integral term representing heating of Maxwellian electrons by energetic tail electrons at energies ET. Published ionospheric electron temperature studies used only the integral term O(int) with differing lower integration limits. Use of the incomplete heating rate could lead to erroneous conclusions regarding electron heat balance, since O(e) is greater than O(int) by as much as a factor of two.

Hoegy, W. R.↗
NASA NTRS1984

Thermal electron heating rate - A derivation

The thermal electron heating rate is an important heat source term in the ionospheric electron energy balance equation, representing heating by photoelectrons or by precipitating higher energy electrons. A formula for the thermal electron heating rate is derived from the kinetic equation using the electron-electron collision operator as given by the unified theory of Kihara and Aono. This collision operator includes collective interactions to produce a finite collision operator with an exact Coulomb logarithm term. The derived heating rate O(e) is the sum of three terms, O(e) = O(P) + S + O(int), which are respectively: (1) primary electron production term giving the heating from newly created electrons that have not yet suffered collisions with the ambient electrons; (2) a heating term evaluated on the energy surface m(e)/2 = E(T) at the transition between Maxwellian and tail electrons at E(T); and (3) the integral term representing heating of Maxwellian electrons by eneegetic tail electrons at energies ET. Published ionospheric electron temperature studies used only the integral term O(int) with differing lower integration limits. Use of the incomplete heating rate could lead to erroneous conclusions regarding electron heat balance, since O(e) is greater than O(int) by as much as a factor of two. Previously announced in STAR as N84-15941

Hoegy, W. R.↗
NASA NTRS1994

Regulation of the solar wind electron heat fluxfrom 1 to 5 AU: Ulysses observations

In this study we use observations from the three-dimensional electron spectrometer and magnetometer aboard the Ulysses spacecraft to examine the solar wind electron heat flux from 1.2 to 5.4 AU in the ecliptic plane. Throughout Ulusses' transit to 5.4 AU, the electron heat flux decreases more rapidly (approximately R(exp -30)) than simple collisionless expansion along the local magnetic field and is smaller than expected for a thermal gradient heat flux, q(sub parallel e) (r) = - Kappa(sub parallel) del(sub parallel) T(sub e)(r). The radial gradients and magnitudes expected for a number of electron heat flux regulatory mechanisms are examined and compared to the observations. The best agreement is found for heat flux regulation by the whistler heat flux instability. The upper bound and radial scaling for the electron heat flux predicted for the whistler heat flux instability are consistent with the observations.

Scime, Earl E.↗
NASA NTRS2022

Electron Heat Fluxes Generated by Intense Whistler Waves at the Upper Ionospheric Altitudes

Magnetospheric whistler waves, chorus and hiss, can't provide the resonance heating of the core electron plasma population. However, these whistler-mode branches, can implicitly participate in the heating processes of the core plasma thermal electron population by triggering the electron precipitation over a broad energy range from the magnetosphere and subsequent atmospheric ionization processes leading to the production of superthermal electron population. These superthermal electrons play a large role in the magnetosphere-ionosphere-atmosphere energy interplay with participation of both magnetically conjugate hemispheres, and their Coulomb interaction with background magnetospheric thermal electrons. Using strong hiss and chorus wave events measured by the Van Allen Probes and SuperThermal Electron Transport code, we evaluate the formation of electron heat fluxes at the upper ionospheric altitudes and discuss their consequences on the formation of electron temperature. It is found that chorus and hiss waves that initiate the precipitation of magnetospheric electrons with energies below 30 keV and the follow-up production of secondary electrons play an important role in the energy balance of ionosphere-magnetosphere system.

Magnetospheric whistler waves as an implicit sourc↗
NASA NTRS1987

Strong electron heating at the earth's bow shock

The paper reports on two sets of bow shock crossings observed by the ISEE 1 and ISEE 2 spacecraft, in which very large electron temperature increases were found. When the two sets of shocks with the large electron heating were compared with the rest of the 52 bow shock crossings of the compiled series, these sets were found to correlate with an unusually high upstream solar wind flow speed. The highest correlation was found between the amount of electron heating, expressed by the difference in temperature between the downstream and upstream electrons (rather than their ratio), and the total change in the bulk flow energy per particle across the shock. The results suggest that the appropriate quantity to consider in studies of electron heating at shocks is the temperature difference rather than the temperature ratio. The latter can be artificially elevated by low upstream temperatures.

Thomsen, M. F.↗
NASA NTRS2017

Electron Heating at Kinetic Scales in Magnetosheath Turbulence

We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earths magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.

Chasapis, Alexandros↗
NASA NTRS1987

Electron heating by ion acoustic turbulence in simulated low Mach number shocks

Explicit and fully electromagnetic particle-in-cell simulations of perpendicular, collisionless, and nominally subcritical shocks are performed in one and two spatial dimensions using the code wave. Shock parameters are chosen to maximixe the growth rates of the current-driven ion acoustic instability in the shock. Electron heating by ion acoustic turbulence is observed at the shocks, at rates in agreement with second-order Vlasov theory predictions. However, the amount of resistive electron heating is small and ion reflection provides the major source of dissipation. Strictly resistive shocks do not exist for the parameters suitable for explicit particle codes running on today's supercomputers, because the plasma convects through these shocks so quickly that current-driven instabilities have little time to be amplified and to heat the electrons resistively. This effect is primarily a result of the relatively small values of omega(pe)/omega(ce) that can be analyzed.

Tokar, Robert L.↗
NASA NTRS1992

Diagnostics of electron-heated solar flare models. III - Effects of tapered loop geometry and preheating

A series of hydrodynamic numerical simulations of nonthermal electron-heated solar flare atmospheres and their corresponding soft X-ray Ca XIX emission-line profiles, under the conditions of tapered flare loop geometry and/or a preheated atmosphere, is presented. The degree of tapering is parameterized by the magnetic mirror ratio, while the preheated atmosphere is parameterized by the initial upper chromospheric pressure. In a tapered flare loop, it is found that the upward motion of evaporated material is faster compared with the case where the flare loop is uniform. This is due to the diverging nozzle seen by the upflowing material. In the case where the flare atmosphere is preheated and the flare geometry is uniform, the response of the atmosphere to the electron collisional heating is slow. The upward velocity of the hydrodynamic gas is reduced due not only to the large coronal column depth, but also to the increased inertia of the overlying material. It is concluded that the only possible electron-heated scenario in which the predicted Ca XIX line profiles agree with the BCS observations is when the impulsive flare starts in a preheated dense corona.

Emslie, A. G.↗
NASA NTRS2007

Self-consistent Model of Magnetospheric Ring Current and Propagating Electromagnetic Ion Cyclotron Waves. 2. Wave Induced Ring Current Precipitation and Thermal Electron Heating

This paper continues presentation and discussion of the results from our new global self-consistent theoretical model of interacting ring current ions and propagating electromagnetic ion cyclotron waves [Khazanov et al., 2006]. To study the effects of electromagnetic ion cyclotron wave propagation and refraction on the wave induced ring current precipitation and heating of the thermal plasmaspheric electrons, we simulate the May 1998 storm. The main findings after a simulation can be summarized as follows. Firstly, the wave induced ring current precipitation exhibits quite a lot of fine structure, and is highly organized by location of the plasmapause gradient. The strongest fluxes of about 4 x 10(exp 6) (cm(raised dot) s(raised dot) sr(raised dot) (sup -1)) are observed during the maill and early recovery phases of the storm. The very interesting and probably more important finding is that in a number of cases the most intense precipitating fluxes are not connected to the most intense waves in simple manner. The characteristics of the wave power spectral density distribution over the wave normal angle are extremely crucial for the effectiveness of the ring current ion scattering. Secondly, comparison of the global proton precipitating patterns with the results from RAM [Kozyra et al., 1997a] reveals that although we observe a qualitative agreement between the localizations of the wave induced precipitations in the models, there is no quantitative agreement between the magnitudes of the fluxes. The quantitative differences are mainly due to a qualitative difference between the characteristics of the wave power spectral density distributions over the wave normal angle in RAM and in our model. Thirdly, the heat fluxes to plasmaspheric electrons caused by Landau resonate energy absorption from electromagnetic ion cyclotron waves are observed in the postnoon-premidnight MLT sector, and can reach the magnitude of 10(exp 11) eV/(cm(sup 2)(raised dot)s). The Coulomb energy degradation of the RC H(+) and O(+) ions maximizes at about 10(exp 11) (eV/(cm(sup 2) (raised dot) s), and typically leads to electron energy deposition rates of about 2(raised dot) 10(exp 10) (eV/(cm(sup 2)(raised dot)s) which are observed during two periods; 32-48 hours, and 76-86 hours after 1 May, 0000 UT. The theoretically derived spatial structure of the thermal electron heating caused by interaction of the ring current with the plasmasphere is strongly supported by concurrent and conjugate plasma measurements from the plasmasphere, ring current, and topside ionosphere [Gurgiolo et al., 2005]. Finally, the wave induced intense electron heating has a structure of the spot-like patches along the most enhanced density gradients in the plasmasphere boundary layer and can be a possible driver to the observed but still not explained small-scale structures of enhanced emissions in the stable auroral red arcs.

Khazanov, G. V.↗
NASA NTRS1987

Electron heating in a Monte Carlo model of a high Mach number, supercritical, collisionless shock

Preliminary work in the investigation of electron injection and acceleration at parallel shocks is presented. A simple model of electron heating that is derived from a unified shock model which includes the effects of an electrostatic potential jump is described. The unified shock model provides a kinetic description of the injection and acceleration of ions and a fluid description of electron heating at high Mach number, supercritical, and parallel shocks.

Ellison, Donald C.↗