AURORA on Earth

Photo Credit: Jouni Jussila, Finland

 

 

Bibliography - Abstract


Marina Galand

AURORA on Earth

Photo Credit: Jan Curtis, UAF, GI

 

ABSTRACT OF SCIENTIFIC PUBLICATIONS IN REFEREED JOURNALS

Galand M., D. Lummerzheim, A.W. Stephan, B.C. Bush, and S. Chakrabarti, Electron and proton aurora observed spectroscopically in the far ultraviolet, J. Geophys. Res., 107(A7), 10.1029 /2001JA000235, 2002.

The only way to get a global, instantaneous picture of the energetic particle input over the auroral oval is through spectral imaging. The major driver of auroral emissions in the high latitude ionosphere is overall electron precipitation. However, for certain locations and times, such as the equatorial edge of the evening auroral oval, proton precipitation can be the major energy source, and thus the primary contributor to auroral emissions.
Using kinetic transport models to describe the transport of energetic particles in the atmosphere, we analyze UV spectra from the STP78-1 satellite mission during magnetically disturbed conditions (Kp=6) in the evening sector of the auroral oval. We discuss the contribution of protons and electrons to the auroral emissions. The energy flux of the incident protons is inferred from the H Lyman a emissions, after removing the H geocoronal background induced by solar radiation. Both the mean energy and energy flux of electron precipitation are inferred from non-H emissions (NII 108.5 nm, N2 135.4 nm, and OI 135.6 nm), after removing the contribution of proton precipitation. From the latitudinal distribution of the incident energy flux, the location of the electron and proton aurorae is discussed. The estimation of the particle characteristics allows one to infer the Pedersen and Hall electrical conductances induced by particle precipitation. For the studied substorm period, energetic protons contribute significantly to the Pedersen conductance, about 25-30% overall of the total particle-induced conductances and much more at the equatorward edge of the midnight aurora. Because protons and electrons do not interact in the same way with the atmosphere, our study shows that, while analyzing auroral spectra and studying the state of the ionosphere, it is crucial to separate electron and proton components of the precipitation. The method described to disentangle the relative contribution of precipitating electrons and protons may be applicable to the UV data of the upcoming TIMED and DMSP missions.



Galand M., and S. Chakrabarti, Auroral processes in the solar system, Refereed Monograph Chapter, in "Atmospheres in the Solar System: Comparative Aeronomy" (AGU Monograph 130), edited by M. Mendillo, A. Nagy, and H. Waite, AGU Press, Chapter I.4, p.55-76, 2002.

Studies of the aurora constitute a fundamental component of geophysical research. The observational, theoretical, and modeling advances achieved in understanding terrestrial auroral activity mark a high point in space science and, in particular, in defining linkages between energetics, dynamics, and coupling within the solar wind-magnetospheric-atmospheric system. One of the major achievements of space age technology has been the detection of auroral emissions on other solar system bodies. While the mechanisms
responsible for auroral structure on other worlds involve the same basic physics operating on Earth, the settings are of vastly different scale and with sources often unique to each site. Defining an aurora as any optical manifestation of the interaction of extra-atmospheric energetic electrons, ions, and neutrals with an atmosphere, we review the observational inventory of aurora in the solar system and discuss the different steps used for modeling auroral processes. Aurora offers us a unique and extremely valuable remote sensing of magnetic field configuration and is a tracer of plasma interactions. It is an indicator of the atmospheric composition and energy source and can be used for remote sensing of the characteristics of the incident energetic particles. The diversity of magnetic field geometries, plasma interactions, energy sources, and atmospheric constituents, all make comparative auroral studies a rich field, which should lead us to further understanding of interactions taking place at different solar system bodies.




Galand M., Introduction to the special section: proton precipitation into the atmosphere, J. Geophys. Res., 106, 1-6, 2001.

See short introduction



Galand M. and A.D. Richmond, Ionospheric electrical conductances produced by auroral proton precipitation, J. Geophys. Res., 106, 117-125, 2001.

From incoherent scatter radar observations and space-borne particle detector data, it appears that energetic proton precipitation can sometimes, for some locations, be a major source of ionization in the auroral ionosphere and contribute significantly to the electrical conductances. Here we propose a simple parameterization for the Pedersen and Hall conductances produced by proton precipitation. The derivation is based on a proton transport code for computing the electron production rate and on an effective recombination coefficient for deducing the electron density. The atmospheric neutral densities and temperatures and the geomagnetic-field strength are obtained from standard models. The incident protons are assumed to have a Maxwellian distribution in energy with a mean energy <E> in the 2-40 keV range and an energy flux Q0. The parameterized Pedersen and Hall conductances are functions of <E> and Q0, as well as of the geomagnetic-field strength. The dependence on these quantities is compared with those obtained for electron precipitation and for solar EUV radiation. To add the contribution of proton precipitation to the total conductances for electrodynamic studies in auroral regions, the conductances produced by electron and proton precipitations can be combined by applying a root-sum-square approximation.



Galand M., T.J. Fuller-Rowell, and M.V. Codrescu, Response of the upper atmosphere to auroral protons, J. Geophys. Res., 106, 127-139, 2001.

A three-dimensional, time-dependent, coupled model of the thermosphere and ionosphere has been used to assess the influence of proton auroral precipitation on Earth's upper atmosphere. Statistical patterns of auroral electron and proton precipitation, derived from DMSP satellite observations, have been used to drive the model. Overall, electrons are the dominant particle energy source, with protons 
contributing ~15% of the total energy. However, owing to the offset of the proton auroral oval toward dusk, in certain spatial regions protons can carry most of the energy. This is the case particularly at the equatorward edge of the dusk sector and at the poleward edge of the dawn sector of the auroral oval. The increase in Pedersen conductivity raises the average Joule heating by ~10%, so raising the E and F region temperature by as much as 7%. The enhanced E region ionization also drives stronger neutral winds in the lower thermosphere through ion drag, which alters the temperature structure through transport, adiabatic heating, and adiabatic cooling. The neutral wind velocity modifications in the E region can reach 40% in some sectors. In addition, the upwelling of neutral gas raises the N2/O ratio, depleting the F region and so reducing the ion-drag driven winds in this region. This study illustrates the modest yet significant impact of auroral proton precipitation on the upper atmosphere.



Lummerzheim D., M. Galand, J. Semeter, M.J. Mendillo, M.H. Rees, and F.J. Rich, Emission of OI(630 nm) in proton aurora, J. Geophys. Res., 106, 141-148, 2001.

A great red aurora occured over southern Canada and central Maine on 11 April 1997, producing a brightness of OI(630 nm) of several kR, which lasted for several hours. Two passes of the DMSP F12 satellite occurred during this time, and optical data were obtained from four COTIF (CEDAR Optical Tomographic Imaging Facility) sites. The DMSP F12 particle spectrometers observed proton precipitation south of the electron aurora with energy fluxes of several mW m-2. Tomographic inversion of the COTIF optical observations gives the altitude profile of emissions along a magnetic meridian. We combine all available data using an ionsopheric auroral model. Our analysis shows that the model produces the observed auroral brightness from the proton precipitation alone.



Lummerzheim D., and M. Galand, The profile of the hydrogen Hb emission line in proton aurora, J. Geophys. Res., 106, 23-31, 2001.

Models of hydrogen-proton transport in proton aurora predict the line profile of the hydrogen emissions from specified incident proton precipitation. We are using a model that includes collisional angular redistribution which leads to upward moving proton and hydrogen fluxes. For ground-based observation in the magnetic zenith, this causes a small Doppler broadening towards the red in the line profile. The precipitating energetic hydrogen atoms are responsible for the prominent Doppler shift towards the blue. The resulting line profile has thus both, a widenend red and a windened blue wing. Using a spectrometer with sufficient spectral resolution to distinguish the red-shifted wing of the line from the instrumental line broadening we obtain Hb line profiles (486.1 nm). Comparing the predicted line shapes to our observations, we find the red-shifted wing due to upward moving hydrogen as predicted by the angular redistribution in the model calculations. The shape of the blue shifted wing, rather than the location of the peak of the blue shifted line profile, is a suitable indicator of the mean energy of the precipitating proton flux.



Galand M. and D. Evans, Radiation damage of the proton MEPED detector on POES (TIROS/NOAA) satellites, NOAA Technical Report OAR 456-SEC 42, February 2000.

The Medium Energy Proton and Electron Detector (MEPED), aboard the polar-orbiting, low-altitude, POES (Polar Operational Environmental Satellite) and measuring protons in the 30 keV-6 MeV energy range, undergoes damage over time. During all phases of solar activity, its response in auroral latitudes decreases as much as 90% over time. This decrease is caused by radiation damage. The 90° detector observes larger fluxes of protons which mirror at or below the satellite than the 0° detector which observes smaller fluxes of auroral precipitating protons in the loss cone. For this reason the 90° detector suffers from radiation damage much faster than the 0° detector. In addition, the damage effects can be seen earlier, when the satellite is launched near solar maximum, and damage effects during major magnetic storms can be observed in the data. The high radiation dose the MEPED instrument undergoes over the years causes the formation of a dead layer in the silicon structure and a partial charge collection. As a result, the energy of the incident proton, as well as the particle flux, is underestimated in auroral regions. This shift in energy is dependent on the proton energy. In addition, even though the protons measured by the MEPED instrument contribute to the damage, they are not the only ones. Further investigation must be undertaken concerning the particles responsible for the damage in order to correlate the shift in energy with the total counts of particles. In the meantime, one can bypass the damage effect by rejecting data obtained in the late life of the satellite, the period of rejection varying from one satellite to another.




Galand M. and A.D. Richmond, Magnetic mirroring in an incident proton beam, J. Geophys. Res., 104, 4447-4455, 1999.

We point out that the influence of magnetic-field non-uniformity on redirecting the pitch angle of a particle is independent of the particle's charge and thus is identical for protons and neutral hydrogen atoms. Under certain circumstances one can then speak of  "magnetic mirroring" of hydrogen atoms as well as of protons. In the case of an energetic proton beam incident on the upper atmosphere, the study of the influence of magnetic field on both protons and H atoms can be relevant to inferring information about proton aurora from measurements of upgoing energetic particles observed
from space. In a model that here neglects collisional angular redistribution of the particles, the total particle and energy albedos are approximately independent of the 
energy of the incident particles and of the atmospheric temperature. However, the separate proton and H atom albedos have a strong dependence on the incident energy. We also reinvestigate how to handle energy conservation properly in the presence of a nonuniform magnetic field, to provide a good validation for proton transport models. 



Galand M., J. Lilensten, D. Toublanc and S. Maurice, The ionosphere of Titan: ideal diurnal and nocturnal cases, Icarus, 140, 92-105, 1999.

We have solved a stationary Boltzmann transport equation to describe the ionosphere of Titan in two simple cases. The first one deals with the satellite being outside the Kronian magnetosphere on the dayside of Saturn, which happens under strong solar wind conditions. In that case, the main energy source of ionization is the solar photons. We show the effect of the photoionization and the secondary ion production for a solar zenith angle of 45 deg. The electron production peaks at 25 electrons s-1 cm-3 around 1000 km. We estimate the electron density from a comprehensive chemical code. This electron density is then compared with the one computed from a simple recombination model. Finally, we determine the intensity of nitrogen emissions, which are compared to the Voyager 1 measurements.
In the second case, the satellite is inside Saturn's magnetosphere. We show the effect of the ionization due to electron precipitation at night, above the polar regions. The input electron flux is measured by the Voyager probes, gathered from several instruments on board. A simple Kappa distribution is given to model a mean electron flux precipitating on Titan. We show that the electron production ranges between 1 to 5 electrons s-1 cm-3 between about 550 and 650 km. The electron production due to the photoionization above the pole is evaluated and compared to the effect of the kronian electron precipitation. 



Galand M., R. Roble and D. Lummerzheim, Ionization by energetic protons in Thermosphere-Ionosphere Electrodynamics General Circulation Model, J. Geophys. Res., 104, 27,973-27,990, 1999.

Originating in the magnetosphere and precipitating into the high-latitude ionosphere, energetic protons in the keV energy range are a common auroral phenomenon and can represent an important energy source for the auroral atmosphere. In global models describing the ionosphere-thermosphere interaction, keV protons have always been neglected or treated as if they were electrons. Here we investigate the effect of keV protons on both the ionospheric and thermospheric composition in the E region on a planetary scale.  We present a parameterization of electron and ion production rates induced by an incident proton beam as a fast computational scheme for use in global
models.  The incident proton beam is assumed to have a Maxwellian distribution with characteristic energies between 1 and 20 keV.  The parameterization is validated against a full proton transport code. By including these parameterized electron and ion production rates in a one dimension-in-space (1D-in-space) Thermosphere- Ionosphere Global Mean Model, we show that proton precipitation can cause a significant enhancement of the electron density, the major ion (O2+ and NO+) densities, and the nitric oxide density.  As a result, the conductivities in the E region are also greatly increased.  Using the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM), we show that the proton precipitation, when added to the normal electron aurora, causes a large increase (up to 70%) in electron, O2+ and NO+ densities over much of the auroral oval. The NO density is affected in a larger area owing to the long lifetime of NO on the nightside. This first study of the influence of protons on a planetary scale clearly shows the significant impact that auroral keV protons can have on the ionospheric and thermospheric composition and the need to include proton precipitation in global models.




Galand M., J. Lilensten, W. Kofman and D. Lummerzheim, Proton transport model in the ionosphere: 2. Influence of magnetic mirroring and collisions on the angular redistribution in a proton beam, Ann.Geophys., 16, 1308-1321, 1998.

We investigate the influence of magnetic mirroring and elastic and inelatic scattering on the angular redistribution in a proton/hydrogen beam by using a transport code in comparison with observations. H-emission Doppler profiles viewed in the magnetic zenith from ground exhibit a red-shifted component which is indicative of upward fluxes. In order to determine the origin of this red shift, we evaluate the influence of two angular redistribution sources which are included in our proton/hydrogen transport model. Even though it generates an upward flux, the redistribution due to magnetic mirroring effect by protons is not sufficient to explain the red shift. On the other hand, the collisional angular scattering induces a much more significant red shift in the lower atmosphere. The red shift due to collisions is produced by < 1keV protons and is so small as to require an instrumental bandwidth < 0.2 nm. This explains the absence of measured upward proton/hydrogen fluxes in the Proton I rocket data because no useable data concerning protons < 1 keV are available. At the same time, our model agrees with measured ground-based H-emission Doppler profiles and suggests that previously reported red shift observations were due mostly to instrumental bandwidth broadening of the profile. Our results suggest that Doppler profile measurements with higher spectral resolution may enable us to quantitify better the angular scattering in proton aurora.



Lilensten J. and M. Galand, Proton/electron precipitation effects on the electron production and density above EISCAT and ESR, Ann. Geophys., 16, 1299-1307, 1998.

The suprathermal particles, electrons and protons, coming from the Sun and precipitating into the high-latitude atmosphere are an energy source for the Earth's ionosphere. They interact with the ambient thermal gas through inelastic and elastic collisions. Most of the physical quantities perturbed by the precipitation, such as the electron production rate, may be evaluated by solving the stationary Boltzmann transport equation, which yields the particle fluxes as a function of altitude, energy, and pitch angle. This equation has been solved for the three different suprathermal species (electrons, protons, and hydrogen atoms). We first compare the results of our theoretical code to a coordinated DMSP/EISCAT experiment, and to another approach. Then, we show the effects that pure proton precipitation may have on the ionosphere, through primary and secondary ionization. Finally, we compare the effects of proton precipitation and electron precipitation in some selected cases above EISCAT (Tromso) and ESR.



Galand M., J. Lilensten, W. Kofman and R.B. Sidje, Proton transport in the ionosphere, 1: multi-stream approach of the transport equations, J. Geophys. Res., 102, 22 261-22 272, 1997. 

The suprathermal particles, electrons and protons, coming from the magnetosphere and precipitating into the high-latitude atmosphere are an energy source of the Earth's ionosphere. They interact with ambient thermal gas through inelastic and elastic collisions. The physical quantities perturbed by these precipitations, such as the heating rate, the electron production rate, or the emission intensities, can be provided in solving the kinetic stationary Boltzmann equation. This equation yields particle fluxes as a function of altitude, energy, and pitch angle. While this equation has been solved through different ways for the electron transport and fully tested, the proton transport is more complicated. Because of charge-changing reactions, the latter is a set of two-coupled transport equations that must be solved: one for protons and the other for H atoms. We present here a new approach that solves the multistream proton/hydrogen transport equations encompassing the collision angular redistributions and the magnetic mirroring effect. In order to validate our model we discuss the energy conservation and we compare with another model under the same inputs and with rocket observations. The influence of the angular redistributions is discussed in a forthcoming paper.




ABSTRACT OF THESIS


Galand M., Transport des protons dans l’ionosphère aurorale, Thèse de 3ème cycle (Ph.D.), Spécialité Astrophysique et Milieux Dilués, Univ. Joseph Fourier, Grenoble, France, 1996.

The suprathermal electrons and protons coming from the Sun and precipitating into the high latitude atmosphere are an energy source of the Earth's ionosphere. These particles interact with the ambient thermal gas through collisions. The Boltzmann equation providing particle fluxes in altitude, energy, and pitch angle allows one of the most complete descriptions of the transport of these particles. We demonstrate it again in the dissipative case, the most general one, and we propose an original resolution of transport equations of protons and hydrogen atoms: these equations are coupled via charge-changing reactions. This resolution based on the introduction of dissipative forces to describe the energetic degradation of precipitating particles allows to take into account the angular redistributions of collisionnal or magnetic origin, neglected until now. Nevertheless their effect has been observed from ground on the H atom emissions as the red shift of the magnetic-zenith Doppler profile attests it. The resolution adopted here is validated by comparison with another model in the classical case of no angular redistribution. The influence of magnetic mirroring effect is discussed: this effect does not seem sufficient to explain alone the observed red shift. The collisionnal angular redistribution has then to play a significant role. At last a comparison of our model with Proton I rocket data is proposed.


RELATED WEB SITES

Proton aurora into the atmosphere

Comparative Aeronomy in the Solar System


If you would like a reprint of one of these papers, please contact:
Marina Galand at m.galand at imperial.ac.uk
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