AURORA on Earth
Photo Credit: Jan Curtis, UAF, GI
into the Atmosphere
CEDAR 1999 PROTON Workshop
AURORA on Earth
Photo Credit: Jan Curtis, UAF, GI
Originating in the magnetosphere, energetic protons in the keV energy range represent an important energy source upon the high latitude atmosphere. Their interaction with the ambient neutral species makes them a significant source of ionization; it also leads to the auroral emissions, especially to H emissions, a typical signature of proton precipitations.
In 1994 Roger Smith had organized the "Proton Aurora Workshop". This meeting had focused on the observations and interpretation of the proton aurora signatures in the dayside and nightside aurora. It had addressed the aeronomical problems associated with the proton aurora, and the need of combined experiments between space and ground and of theoretical results for the exploitation of the proton aurora data.
Since this initial proton workshop, considerable progress has been made in proton studies. As for the proton aurora observations from ground, optical instruments with much better resolution are now available. The data obtained have a resolution good enough to be analyzed by models, which are today more comprehensive and so more suitable for such an analysis. Optical instruments aboard existing and future satellites are going to reinforce the H emission observation database: the harvest is expected to bring a better global picture of the proton oval.
Using proton transport code, combined observations between a satellite measuring the incident proton flux and ground-based instruments (radar, optical) have helped in the understanding of proton aurora data and have also shown the major role protons play in the auroral ionosphere. Using global models it has been possible to show the effect of proton precipitations on both the ionosphere and the thermosphere. Recent rocket campaigns in coordination with ground-based instruments have allowed to validate the proton models and to progress in the analysis of proton aurora.
Today, it is not only time to have an overview on all the progress made since the last proton workshop. The present workshop is also intended to stimulate more interactions between people interested in proton aurora issues. We would like especially to provoke and encourage discussions concerning issues which are relevant to several aspects of proton precipitation, such as the characteristics of the incident proton fluxes deduced from satellite observations or the possibility to infer these fluxes from H emission observations from ground or space.
* Introduction of workshop
* Direct measurements of H+/H flux
- Satellite observations
- Rocket campaigns
* Indirect measurements: H emissions
- From ground
- From space
* Summary and perspectives
Workshop Report (full)
Participants: 21 attendees
Marina Galand gave a short introduction of the interaction of proton precipitation with the atmosphere. Note that H emissions are a typical signature of proton precipitation.
Roger Smith gave us an overview of the 1994 CEDAR "Proton Aurora Workshop":(1) Van Zyl reported that there is too little lab data concerning cross section and energy loss associated with energetic protons and H atoms. [Marina Galand had contacted Van Zyl before this present proton workshop but he is now retired and he had no new data to present.]
(2) Protons can be used as signature of magnetospheric regions or processes:
- inner edge of the plasmasheet,
- proton velocity filter in the cusp (DMSP particle obs.),
- H arcs observed during the onset of a storm.
The observations can be made via the measurements of H emissions but need to be spectral and not just photometric. As for the other auroral emissions, they are induced by both protons and electrons as illustrated by Roger. The variablity in time and space can be important.
(3) As for modeling, the spreading of the beam induced by the neutral path of the incident protons was poorly known. But Dag Lorentzen using his Monte Carlo code can now evaluate this extend of the beam.
(4) Need a set of observations (optical, particle detector, radar) and need more interaction between observations and modeling.
2. Direct measurement of H+/H flux
2.a- Satellite observations (J. Sharber, M. Codrescu)
* TED and MEPED aboard TIROS, SSJ aboard DMSP, MEPS/PEM aboard UARS and electrostatic analyzer aboard FAST.From these particle flux observations one can obtain information about the energy/pitch angle distribution of the incident protons.
- Marina Galand presented spectra of auroral protons from UARS from Jim Sharber.
The data show clearly a high energy tail: the distribution is more kappa-like than Maxwellian which was used to date in modeling study.
* From these data, statistical patterns can be derived which are very useful to have a global picture of the incident particles over the auroral ovals.
- Mihail Codrescu showed patterns derived from the TED data (low energy particles below 20 keV aboard TIROS) adding both electron and proton information (see http://www.sec.noaa.gov/pmap for daily results from Dave Evans). These patterns are function of the activity index deduced from the total hemispheric power (electron + proton). Mihail is actually deriving independant patterns for electrons and protons from the TED data. Such patterns will be used for defining the boundary conditions for 3D study (see 4.).
- Mihail has already derived patterns for the medium energy population (30 keV< E < 6MeV) using the MEPED data from TIROS. These patterns are function of medium energy particle index. You can find information of these patterns as well as the daily characteristics of high energy protons at: http://sec.noaa.gov/~codrescu/part.html.
Westward curvature drift for protons, eastward for electrons.
Need to investigate further the percentage of energy flux carried by protons. But be careful when comparing proton and electron energy flux input. One of the main goals is to deduce ionization induced by these particles and protons are more efficient to produce electrons than incident energetic electrons.
2.b- Rocket campaign (C. Deehr (presented by R. Smith))
- Dayside campaigns to study a region of Earth's atmosphere that is directly exposed to the solar wind and to investigate the cause of a plasma fountain.
Focus: thermal and low energy electrons and ions observed at 10 magnetic local time.
* SCIFFER campaign (January 25, 1995, rocket launched from Andoya, Norway)
Anticorrelation between electron and proton precipitations.
No energetic proton detector aboard (E<500 eV).
* CAPER campaign (January 21, 1999, rocket launched from Andoya, Norway)
Velocity filter observed on proton flux data (E<7 keV) [energy dispersion of protons along the convection line]. H emissions observed from ground too low to get significant information.
What do we need more for campaign focusing on proton precipitation?
- High energy proton spectra
- Incoherent scatter radar measurements from ground
- H emission observations from space
3. Indirect measurements: H emissions
3.a- From the ground (C. Deehr (presented by R. Smith)) [Halpha, Hbeta]
What is the interest of observing H emissions from the ground?
H emissions used as an ionospheric signature of magnetospheric processes or regions.
Protons can provide more reliable information from the magnetosphere compared to electrons because they carry more momentum and are less influenced before reaching the E-region.
- At nightside, H emissions expanding polarward at the onset of a substorm
- At dayside, H emissions observed from the ground confirming the velocity filter process first observed with DMSP particle data.
- Story of a CME's reaching the Earth's magnetosphere (compression of the magnetosphere at dayside and then perturbation along the tail observed using meridian scanning photometers)
3.b- From space (L. Paxton, G. Romick) [H Lyman alpha, Halpha]
What is the interest of observing H emissions from space?
As particle detector provides information only along the track of the satellite, an information over the auroral oval can be only on a statistical point of view.
H emission images from space are the way to get a global picture of proton activity during a given magnetic event. As underlined from ground-based observations, the variability of proton precipitation in intensity, energy, and location, can be important during magnetic activity.
* Larry Paxton showed spectroscopic observations of the stronger H emissions, H Lyman alpha, from space (STP78-1, MSX). At dayside it is important to substract the geocoronal component to the total emission to get the auroral emission. H alpha and H beta not chosen because lower intensity and backscattered too hard on dayside.
* Larry also spoke about the future missions: GUVI on TIMED (May 2000) and SSUSI on DMSP (2001) will observe H Lyman alpha, similar instruments scanning from horizon to horizon. These data of not too high resolution will be mainly used to indicate where/when major proton precipitation occurs over the auroral oval. So, when/where it is the case, be careful for analysis of non-H auroral emissions.
- Data obtained are available, collaborations if any is interested.
- Validation of the analysis of H Lyman alpha:
DMSP (not before 2001) will have both a particle detector and a spectrographic imager in UV.
3.c- Inversion to infer information about precipitating protons (D. Lummerzheim)
* Dirk Lummerzheim presented ground-based observations:
Hbeta is not very bright (30-40 R), so spectrometric analysis is a challange.
Dirk has fitted the observed spectra as a function of 5 parameters (background, red/blue halfwidths, blue shift, intensity). The blue halfwidth seems to be a relevant parameter to use to infer information on the characteristic energy of protons.
- Need to validate the analysis with combined particle observations from space.
- Need to get the analysis automatic
4. Modeling (B. Basu, D. Decker, J. Jasperse, M. Galand)
* Bamandas Basu presented an overview of the proton transport code.
Three schools: Code solving Boltzmann equations, Continuous slowing down code, Monte Carlo code. Good agreement between these three approaches in H+/H fluxes.
- From them one can deduce the ionization rate or optical emissions.
- Coupling with electron transport code for more comprehensive study of aurora.
- Analysis of DE2 upward electron flux has shown that the data seem to be sensitive to high energy protons and that the incident protons seem to have a high energy tail (corroborates the result from J. Sharber, see Sec. 2-a). The ionization rate and emission rates are sensitive to this high energy tail.
- Lessons learned: if the physics of the problem is understood, the modeling capability is limited by uncertainties in the inputs (cross sections and incident proton flux). Need lab measurements (but sometimes not possible) and in situ measurements.
* Marina Galand presented a combined space/ground-based observations analysed using an electron/proton transport code. This study allows to show the major effect protons can play on the electron density in high latitudes. Moreover, introducing in TIE-GCM a parameterization of the electron/ion production rates derived from a proton transport code, the effect of protons on both the thermosphere and the ionosphere have been evaluated on a planetary scale. At nightside for medium magnetic conditions, the increase in density of the electrons, of the major ions in E-regions (O2+ and NO+) and of NO is more than 60 %.
It appeared clearly that all these different aspects of proton precipitations are interconnected. The statistical model developed by M. Codrescu will be used in the planetary scale modeling initiated by M. Galand. H Lyman alpha observations can be better analysed with simultaneous ground-based H emissions observations with higher resolution or particle detector data from space. As mentionned already in the 1994 workshop, we need more cross section measurements or/and in situ observations.
Three related main points of focus in the future:
- to learn more about incident protons (in energy and pitch angle distribution as well as location and energy carried compared to that of electrons),
- to continue to investigate and evaluate the role protons play as an energy input and a source of ionospheric perturbations,
- to work further on the analysis of auroral emissions, especially the H emission Doppler profile, which allows to get valuable information on magnetospheric processes from the ground and to infer information of the proton inputs in a large field of view from space.
Finally, I would like to thank all the speakers and the attendees.
I hope we will have fruitful collaborations which will lead to a better understanding of auroral protons and of their interaction with the atmosphere.
What next after this workshop? Perhaps a special issue (JGR Special Proton Section).
If you have any comment on this page, please contact:
Marina Galand at mgaland at bu.edu.
For more information about the CEDAR 2000 workshop and other CEDAR related topics, visit the CEDAR Homepage.