The SEVEM Project: Statistical ELF and VLF Environment Models

The SEVEM Project:

Statistical ELF and VLF Environment Models

Fabien Darrouzet - Joseph Lemaire - Andrew Orr Fabien.Danouzet@bira-iasb.oma.be

Belgian Institute for Space Aeronomy (IASB-BIRA) Avenue Circulaire, 3

Brussels, I 180, Belgium

ABSTRACT

There is currently a lack of ELF (Extremely Low Frequency) and VLF (Very Low Frequency) electromagnetic wave models for the terrestrial magnetosphere. Therefore, at the Belgian Institute for Space Aeronomy, using 'archived' and ' new ' satellite magnetospheric data, we are creating a ' global' statistical map of these kinds of waves, i.e. the creation of Statistical ELF and VLF Environment Models (SEVEM).

We present here the first step of our project: the SEVEM Web site (http://www.magnet.oma.be/ seven';).

SEVEM contains a catalogue/table of missions/satellites in the terrestrial magnetosphere , which are, or have been, equipped to measure fluctuations of low frequency electromagnetic waves. Based on this survey, we have been able to select the most relev ant data sets from which we can create a database of electromagnetic magnetospheric data.

Using this database and the corresponding observations of the CLUSTER mission, we plan to create a 'global' map (the primary objective of this project) of ELF and VLF electromagnetic waves in the magnetosphere.

KEYWORDS

Electromagnetic, Magnetosphere, Models , Waves, SEVEM.

INTRODUCTION

At the Belgian Institute for Space Aeronomy, we initiated the SEVEM project (Statistical ELF and VLF Environment Models). The statistical 'global' maps, we plan to create, of spatial and frequency distribution of ELF and VLF electromagnetic waves in the magnetosphere will have at least two uses : I) to evaluate quantitatively the importance of pitch angle scattering by wave interaction with energetic particles trapped in the geomagnetic field and 2) to evaluate the e lectromagnetic noise levels in different frequency ranges (useful when designing antennae for future space missions).

Our study requires the creation of a database using electromagnetic magnetospheric data from 'o ld ' missions in parallel with ' new ' missions (CLUSTER and DEMETER). Since the data from CLUSTER and DEMETER are not yet available, the first step was therefore to identify all 'old' magnetospheric missions and satellites that carried instrumentation (radio antenna e and/or fluxgate magnetometers) to measure the ambient low frequency electromagnetic environment in space. This resulted in a catalogue called SEVEM (Survey of ELF and VLF Waves in the Magnetosphere at http://www.magnet.oma.be/sevem/ )

This site contains a comprehensive study of relevant missions, presenting, orbital parameters, description of experiments, location and format of data, contact addresses, etc. The SEVEM Web site is invaluable in identifying appropriate 'old' missions since the se lection process involves several different criteria, e.g.

duration of mission, availability and locati on of data , frequency range of instruments , etc. For instance,

104 SPACE SCIENTIFIC RESEARCH fN BELGIUM / VOLUME 2 SPACE SCIENCES PART 2

based on this s urvey, we have selected e lectric and magnetic data from the Viking miss ion as the first one to work with. T he Viking data set has been chosen as I) it is a relatively recent mission and therefore more read ily available, 2) the wave instruments have a wi de frequency range, 3) the data are arch ived at the French data center CDPP (Ce ntre de Donnees de la Physique des Plasmas) and 4) the PI (prin cipa l investigator) of the V4L low frequency wave experiment, G. Gustafsson, su pported th is initiative (as a Co-I of our project he offered his collaboration in th e analysis and interpretation of this data). We plan to bu ild statistical maps of the ELF, VLF and plasma wave distribution in th e mag netosphere, and to develop empirical and statistical models of the 3-d imens iona l distribution of wave parameters such as amplitud e, spec tra, and polarisation, as a fun ction offTequency.

THE SEVEM WEB SITE

The SEVEM Web s ite is a large table/catalogue that:

• I dentifies past and current satell ites that have made , or are making, wave measurements in the magnetosphere.

• Provides bibliographical information about wave instruments aboard satell ites, e.g. antennas and magnetometers.

• Provides bibliographical references co ncerning the ava ilab le data .

• Provides information on the ava ilability a nd geograph ica l location of the arch ived data.

T he survey involved a hundred magnetospheric satellites. For each one, information was grouped into two categories:

• Satell ite information (names, project manager, space agency, lifetime, etc).

• Orbital informat ion (type of orbit, apogee, perigee, orbita l period, etc).

Add itionally, SEVEM provides various hyperlinks to information on the acro nyms used and on the wave experiments carri ed (Tabl e I).

PI of the experiment Prelim inary results Institute of the PI (country) Measured data

E-mai l of the PI Data range

Type of experiment Sens itivity

Bibliographical references Time reso lution Link(s) to Web site(s) Sampli ng rate Start experime nt operation Data format and support

End experiment operation Location of the data L ifetime of the experiment References about the data

Highest data rate High-resolut ion data

Table 1: List of the entries available for each wave experiment.

T he Web site provides a search e ngin e to select relevant missions according to criteria such as I) type of experiment, 2) wave frequency range, 3) period of observat ion, 4) inst itute invo lved, 5) country involved and 6) data center. It also provides diagrams of the frequency range covered for each sate llite data set (e lectric or magnetic instrument). Figure 1 illustrates such a diagram.

Another plot displays the period of time over which data was collected. T hanks to this information it is a

re latively easy task to identitY the mission /satellite data sets, which can be used to bui ld a database of the

e lectromagnetic ELF and VLF environment in the terrestrial magnetosphere.

CHAPTER 3 : PLASMA PHYSICS 105

In the future the SEVEM Web site will contain an updated list of institutes and laboratories that are currently exploiting, or have exploited, a data set to produce statistical maps or models of the ELF and VLF wave environment.

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THE SEVEM PROJECT

Current statistical studies of ELF and VLF electromagnetic waves in the magnetosphere are, at best, focused on limited regions of the magnetosphere and/or under specific geomagnetic activity conditions . For example, Meredith

uses CRRES satellite data to map the distribution of electron cyclotron harmonic (ECH) wave amp I itudes in the equatorial region 3.8 < L < 7. Green and Boardsen

present a simi lar statistical study, using Hawkeye satellite data, to map the latitudinal distribution of plasma wave nonthennal continuum radiation (at frequencies of 23 .7 kHz, 31.1 kHz and 56 kHz). And Parrot

using Aureol-3 satellite data, maps ELF and VLF emissions (at frequencies of 800 Hz, 4.5 kHz and 15 kHz) at low altitudes onto a ' world map '.

The creation of a statistical (also referred to as empirical) global map of ELF and VLF electromagnetic

waves in the entire magnetosphere region is ultimately the objective of the SEVEM project. The maps will

depend on geomagnetic parameters, such as, Kp, Ost, solar cycle, solar wind parameter, etc, allowing, for

example, behaviour under quiet/disturbed geomagnetic conditions to be analysed . This will allow the

creation of many new models of the magnetosphere, being readily available for producing graphs,

histograms, statistical data (mean and standard deviation), etc.

106 SPACE SCIENTLFIC RESEARCH IN BELGIUM / VOLUME 2 SPACE SCIENCES PART 2

The statistical maps and models will have many uses, for example:

• Eva luate the electromagnetic noise level in different frequency ranges (useful w hen designing antenna for future space missions).

• As a comprehensive input for radiation belt models, al lowing the importance of wave-part icle interactions as a so urce and loss of energetic particles trapped in the Van Allen radiation belts to be evalua ted.

• To complement standard radiation belt models (such as the AE-8 and AP-8 empirica l models mapping the flux of radiation belt electrons and protons) or more recent empirical models of the Earth 's outer space environment.

T he resu lting mode ls will be made avai lab le through SPENVIS (the SPace ENVironment Information System at http: //www.spenvis .oma.be/spenvis/).

The internationa l model ling effort and validation will be coordinated by VERSIM (VLF/ELF Remote Sensing of Ionospheres and Magnetospheres at http: //www.nerc-bas .ac.uk/pub li c/uasd/ versim.htm l).

The Commission H (Plasma Waves) of URSI (Union Radio Science International) supports this modelling activ ity of the ELF and VLF wave environment. A recommend ation supporting the SEVEM initiative has been passed at the URS I 1999 General Assemb ly in Toronto (the fu ll text of this recommendation

availabl e at htt p://www .magnet.oma.be/sevemiURSI-Recommendation.html).

CONCLUSION

The first step of the SEVEM project was the creation of a comprehensive Web based cata logue providing the results of a survey of all magnetospheric satel lites instrumented to measure ELF and VLF electromagnetic waves. Orbital parameters, description of experiments, bibliographical references concern ing the experime nts and preliminary results, geographica l location of arch ived data sets, links to useful Web sites, etc, are ava il ab le on this sight.

Th is survey is especial ly useful for the selecti on of appropriate 'old ' missions from which to bui ld a database of the electromagnetic low freq uency environment for th e terrestria l magnetosphere. Statistical global maps and models of ELF and VLF waves in the magnetosphere w ill be developed by exam ining and analysing the database.

The Viking data set will be the first data set that we wi ll exp loit at the Belgian Institute for Space Aeronomy in col laboratio n with the Center for Space Radiation at the Un iversite Cathol ique de Louvain.

FUNDING SOURCES

The research presented in this paper has been founded by ESA/ PRODEX CLUSTER-2 (covering the time period 01109/ 1998 through 31112/2000) and by ESAIPRODEX SEVEM (covering the time period 01 /0112001 through 3111212002).

REFERENCES

Darrouzet, F., and J. Lemaire, Survey of ELF and VLF experiments in the magnetosphere, Proceedings of Cluster 1 1 Workshop on Multiscale/Multipoint Plasma Measurements, London, ESA SP-449, 307-310, 2000.

2 Meredith , N. P., R. B. Horne, A. D. John stone, and R. R. Anderson, The temporal evo lution of electron distributions and associated wave activity following substorm injectio ns in the inner magnetosphere, Journal of Geophysical Research, 105, 12907-129 1 7, 2000.

3 Green, J. L., a nd S. A. Boardsen, Confinement of nonthermal continuum rad iat ion to low latitudes, Journal of Geophysical Research , 104, 10307-10316, 1999.

4 Parrot, M., World map of ELFIYLF emissions as observed by a low-orbiting satell ite, Annales

Geophysicae, 8, 135- 14 6, 1990.

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BIBLIOGRAPHY Conference paper

Darrouzet, F., and J. Lemaire, Survey of ELF and VLF experiments in the magnetosphere, Proceedings of

Cluster II Workshop on Multiscale/Multipoint Plasma Measurements, London , ESA SP-449,

307-310, 2000.