Adv. Space Res. Vol. 8, No. 9—10, pp. (9)333—(9)342,1988 0273—1177/88$0.00+ .50Printedin GreatBritain. All rights reserved. Copyright© 1989 COSPAR

INFERRING FIELD-ALIGNED CURRENTSYSTEMS AND OTHER IONOSPHERICQUANTITIES FROM GROUND-BASEDARRAYS: A REVIEW

Y. KamideFaculty of Science, Kyoto SangyoUniversity, Kita-ku, Kyoto 603, Japan

ABSTRACT

This paper aims at discussing new techniques for the use of ground—basedmagnetometers todetermine the three—dimensional current system that links electrically the magnetosphere andthe ionosphere These ‘remote sensing” techniques are designed to deduce electrodynaxnicfeatures at high latitudes. In the updated schemes, several different types of measurementscan be incorporated: electric fields from radars and polar—orbiting satellites, conductivi—ties from radars, and the auroral distribution from satellites, as well as magneticperturbationsat the ground at satellite heights.

INTRODUCTION

Magnetic field perturbations recorded on the earth’s surface contain the effects of a vari-ety of different source currents flowing in outer space and the induced current flowingwithin the earth’s interior. In the past, it was not possible to determine uniquely theseparate effects of ionospheric, field—aligned, and magnetospheric currents from groundmagnetometer observations alone, because the magnetometer recorded a complicated superposi-tion of all these currents. During the last decade, however, several computational tech-niques, called the magnetogram—inversion methods, have been developed to obtain the globalpattern of the electric fields and currents and Joule heating in the high—latitude iono-sphere, thus enabling us to sense the state of the ionosphere and the magnetosphereas wellas their electrodynamic coupling: see recent reviews by Gla~meier/1/ and Kamide /2/. Oncewe understand the origins of ground magnetic perturbations in terms of various source cur-rents, the ground—based observations have a great advantage over rocket and satellitemeasurements, since variations in the geomagnetic field can be monitored continuously at alarge number of fixed points at the earth’s surface, making the quantitative separation ofspatial and temporal changesrelatively easy.

The algorithm of the magnetogram—inversionmethod has now been enormously improved, suchthat simultaneous more direct or in situ measurements of electric fields, conductivities,and field—aligned currents by satellites and radars can be incorporated into the scheme.This paper shall demonstrate that it is essential to combine measurementsfrom ground—basedarrays and those from satellite and radar techniques, since the in situ observations eachtypically cover only a small portion of the entire magnetosphere—ionospheresystem, theelectrodynamic state of which is highly variable. Owing to recent progress in satellite—viewed auroral images in the UV and X—ray ranges, it has become possible to estimate‘instantaneous” patterns of the ionospheric electrodynamic quantities over the entire polarregioi with a time resolution of severalminutes.

WHAT MAGNETOGRAM-INVERSION SCHEMES CAN DO

Figure 1 shows a block diagram, outlining the physical processes occurring in the earth’smagnetosphere—ionospheresystem. One of the points emphasized by this diagram is that groundmagnetic perturbations recorded at high latitudes are, under certain approximations /3/, thedirect effects of two dominant currents, the ionospheric “horizontal” current and the“vertical” current flowing along magnetic field lines. Kisabeth /4/ has attempted toseparate quantitatively the ground magnetic effects from these two currents, while others/5,6,3/ have developed more advanced techniques in which not only currents but also electricfields in the ionosphere can be determined primarily from ground—based magnetic records. Infact, many recent studies, coinciding with the rapid progress in the systematic data—gathering program during the 1976—1979 IMS (International Magnetospheric Study) period, haveproven that these“remote sensing” schemes are quite powerful in estimating electromagneticquantities on a global scale, thus providing basic information for numerical modeling ofmagnetosphericplasmaprocesses/7/.

It must be noted, however, that, unlike rocket and satellite measurements, the derivation ofionospheric parameters using the magnetograni—inversionscheme is not based on in situ data,

(9)334 Y. Kamide

M ~ h Magnetospheric Magnetospheric Magnetosphericagne OSP ere electric field particle distribution electric Current

Auroral particles

IonosphericIonosphere Electric field conductivity

Electric current eia~ednt

Ground Ground magneticperturbations

Fig. 1. Schematic diagram showing electrodynamic coupling between the earth’s magnetosphereand the ionosphere. Ground—based magnetometer data are assumed to record the combinedeffects of field—aligned and ionosphericcurrents.

but rather on indirect measurements. Further, although a realistic model of the ionosphericcoriductivities must be given, there is at present no simple way the conductance over theentire polar region can be properly measured on an individual basis /8/. In view of thesomewhat high degree to which the electric field and Joule heat production rate depend onthe assumption of the ionospheric conductivity distribution /9/, crucial comparisons must beconducted between the results estimated from magnetogram—inversion techniques and thoseobtained by means of more direct techniques. This is why the application of the inversionmethods has been limited mostly to statistical data sets of magnetic variations /3/ or toempirical conductivity models /10/.

OUTLINE OF THE IMPROVED SCHEME

The recent availability of radar and satellite data at certain points tends to provide uswith a unique opportunity to make an optimized estimate of the electrodynamic features /11/.It is extremely useful to improve the numerical schemes in such a way that simultaneous,“more direct” measurements of electric fields, conductivities, and field—aligned currentscan be incorporated into the magnetogram—inversion algorithms. Our algorithm has now beenimproved in the following three ways: First, the auroral enhancement component of theionospheric conductance has been calculated on the basis of global images of auroral emis-sions observed from 20,000—km altitude with Dynamics Explorer (DE) 1 /12, 13/, instead ofemploying the statistical models that were used extensively in earlier studies. Althoughthe absolute values of the estimated conductivity need further cross—calibrations withelaborate calculations relating to the excitation of ionospheric constituents caused byprecipitating electrons /14/, the region of aurorally enhanced conductivities is fairlyaccurately determined.

Further, the use of simultaneous data of ion drifts from the sister satellite, DE 2, atlower altitudes (300 km) makes it possible to check the accuracy of our estimation bycomparing the calculated electric fields with ion drift measurements, although such acomparison can be properly made only along DE 2 orbits. The optimum conductivity distribu-tion has then been chosen on an iterative basis such that the resultant electric fieldsbecome consistent with DE 2 ion drifts /15/. For this purpose, the Rice conductivity modelhas been modified. For the maximum epoch of an intense substorm, Figure 2a shows thedistribution of the electric potential calculated from ground magnetometer data combinedwith the optimum conductivity. The distribution of the electrostatic potential for the Ricemodel without modifications is also shown on the left—hand side. The overall potentialdistributions for the two cases are represented by the familiar two—cell pattern. It isnoticed, however, that the total potential difference across the polar cap is increased by afactor of 2 by using the improved conductivity model. While both models are likely to havedifficulty in determining the electric potential accurately in the polar cap, where theconductance is very low, the improved model tends to yield less complicated and realisticpotential patterns.

Inferring Field-AlignedCurrents (9)335

ELECTRIC POTENTIAL

aics MODEL j~ IMPROVED MODEL is

at ee tn.i

Fig. 2a. Comparison of the electric potentials calculated for two different conductivitymodels for the maximum epoch of an intense substorm, during which nearly simultaneous DE—land DE—2 data were available. The potential at the north pole is normalized to zero. Notethat different contour intervals are used for (a) and (b): (a), 10 kV; (b), 20 kV,

Figure 2b compares the electric field estimated from measured ion drifts along the DE—2orbit approximately in the north—south direction with the electric field calculated usingthe two conductivity models (the Rice model and the improved model). The position of thesatellite orbit relative to the overall potential pattern is shown in Figure 2a It isevident that the locations of the reversals in the sign of the electric field, signallingthe polar cap boundary, do not change very much: both cases are in good agreement with thesatellite observations. However, the use of the statistical Rice model provides a smallelectric field at auroral latitudes, especially in the dawn sector. On the other hand, theimproved conductivity distribution reproduces the magnitude of the DE—2 electric fields(maximum 80—100 mV/rn along the orbit) reasonably well both at aurorat latitudes and in thepolar cap. Note that although the polar cap portion of the calculated electric field is notplotted in Figure 2b because of large fluctuations caused by low conductivity values (see/11/ for detailed discussions of this effect), the averages of the calculated electric fieldfor the improved conductivity agree with the DE—2 values. Both Figures 2a and 2b indicatethat for this case study the modifications to the Rice empirical model, together with theuse of ground—based magnetometer data, provide a significant improvement in the calculatedelectric field distribution along the satellite track. However, the quantitative evaluationof how well the electric field on a global scale can be reproduced by the use of the im-proved conductivity model must await further studies.

Among other numerous ionospheric parameters derived with the magnetogram—inversion scheme,

lit

vlsi I OAtH

1:: NortI,w~rd So,,tiiw~rA -

~J\Hn ti d

-100~

I I I I I I30 20 10 0 10 20 30

GI0005PIIIC COI.0TIT055 Ideg~~e~)

Fig. 2b. Observed Electric fields approximately in the north—south direction along the DE-2orbit together with calculated values using two conductivity models. See text for the twomodels.

(9)336 Y. Kamide

IONOSPHERIC CURRENTVECTORS

RICE MODEL 12 IMPROVED MODEL is(a) (b)

i ,~ 29..~.:~ti i2~ —S-’ ‘~

30A/m ~1uiY

SeHLT

Fig. 2c. Comparison of the calculated ionospheric current vectors for the two conductivitymodels.

Figure 2c shows the distribution of calculated ionospheric current vectors for the twoconductivity models. The current pattern is dominated by an intense westward electrojetflowing from late morning to evening hours. It is also important to notice that despite thesignificant changes in the adopted conductivity models, there is no major difference betweenthe two diagrams in terms of the direction and magnitude of the ionospheric current. Thisconfirms the earlier finding that the ionospheric current distribution is not very sensi-tive to the choice of the conductivity model, as long as the conductive belt is reasonablywell colocated in latitude with the enhanced auroral activity /3/. This means that as longas we deal only with the ionospheric currents, we do not need to pay too much attention tothe choice of an accurate conductivity model.

In the second form of improvement, many different types of simultaneous measurementscan beused /11/, such as electric fields and ionospheric conductivities from radars and polar—orbiting satellites, field—aligned currents from satellites and ionospheric currents fromradars, as well as ground—based magnetic perturbations. This updated technique also makesuse of available statistical information about the electrostatic potential /16/, in such away that in regions where any data are lacking the deduced pattern would tend toward thestatistical pattern. One of the advantages of the new algorithm is that it can quantify theerrors inherent in mapping the electric fields, thus demanding more specific quantitativeinput.

Figure 3a outlines the improvement /11/. The practical purpose of the approach is to deter-mine internally consistent patterns of the electrostatic potential, the ionospheric current,the field—aligned current, and magnetic perturbations at the ground and at satelliteheights, which fit well to the available observations and to any a priori information (suchas statistical properties) we have. In other words, even if point measurements by asatellite require us to modify not only local but also global structures of the ionosphericparameters, we must test the modifications quantitatively in terms of their feasibility.Towards this goal, each of the quantities shown in Figure 3a is expanded in a series ofbasis functions in latitude and longitude, and a statistical method nf optimization isfollowed to calculate expected values and variance of quantIties.

Figure 3b shows the results of the application to a case that has been previously analyzedby the simple KRM algorithm /10/. This example represents approximately the maximum epoch ofan intense substorm with the westward electrojet intruded deep into evening hours. It isseen that although the two techniques give generally similar results, there are somenoticeable differences, especially for the electric potentials in regions of low conduc-tance. The method after the improvement appears to yield less complex electric fields insuch regions.

Third, a realistic instantaneous conductivity distribution deduced from bremsstrahlung X—rayimage data from the DMSP—F6 spacecraft has been combined with the magnetogram—inversiontechnique /17/. The satellite X—ray imagery has a great advantage in that the scanningdetector can image a large portion of the auroral belt under both sunlit and non—sunlitconditions. In our upgrading of the numerical algorithm, the ionospheric conductancecalculated from the precipitating electron spectrum on the basis of the X—ray image datafollowing the so—called maximum—entropy method /18/ is utilized. Figure 4a, which is for

Inferring Field-Aligned Currents (9)337

IONOSPHERIC ELECTRODYNAMICS MAPPING

Statistical ________ Statistical

Modet I Model

Radar~ ~ IS. Radar

I “ Particle

Satellite H ‘“‘FluxesRadar I — a~ ‘ ~ —_~ ::-~~-----.....Magnetic

Variations

Satellite ~ 11 “\PhOtometricMagnetometer ~ Images

Ground,_—’ —

Magnetometer

~ ~ ~ L~_J

Data Fitted Fitted Basis Conduclances DataDistributions Coefficients Functions

Fig. 3a. Schematic diagram showing elements of the mapping procedure in the improved schemeof Richmond and Kamide /11/. There are potenmtially several types of data about the electricfields, currents, and magnetic variations that can be used to obtain fitted distributions(left side). Similarly, several types of data may be available to help determine theconductances (right side). The basis functions for the various electrodynamic parameters arephysically interrelated (see text), such that a single set of fitted coefficients is appli-cable simultaneously to the fitted distributions of all electrodynamic parameters.

shortly after the maximum phase of a substorm, consists of six polar plots: two of themrepresent input to the magnetogram—inversion technique and the other four are output. The“instantaneous’ Hall conductance is deduced from the X—ray image data, showing that, besidesthe overall enhancement along the auroral belt, there is a surge—like enhancement in themidnight sector.

Figure 4b shows an example of overlapping plots of the Hall conductance with the electro-static potential (upper plot) and with ionospheric current vectors. It is evident that the

EQUWALENT CURRENT FUNCTION ELECTRIC POTENTIAL1210 VT

w~l. Ira 121211 ‘II

101211 Contour 10120 Cn,L,,,,pt,,LntvtI

II 50000 A — 12 011(10 V

/ —- — / —— -

ao~~~~}ae leE~I~~~ lot

Ftp. 3b. Comparison between the mapping procedure of Kamide et al /3/ and that of Richmondand Kamide /11/ in terms of the equivalent current function and the electric potential.

(9)338 Y. Kamide

EQUIVALENT CURRENT SYSTEM HALL CONDUCTANCE

50,000£ 00 ItT 4.,Au 00 12*0.11ns

ELECTRICPOTENTIAL IONOSPHERICCURRENTVEcTORS

~ ~

FIELD-ALIGNED CURRENTS JOULEHEATING RATE

G ~00 Mu,. I ~ 00 500. 01 ,nW~n.

Fig. 4a. From top to bottom, the observed equivalent current, the Hall conductance estimatedfrom DMSP X—ray image data, the calculated electric potential, ionospheric current vectors,field—aligned currents and Joule heating rate distributions. The miii and max values listeditt the lower right corner of the field—aligned current diagrani stand for the maximum upwardand downward current densities, respectively. The four numerical values in the lower leftcoiner of the Joule heating rate distribution denote the globally integrated heating ratefroni the pole to 80 ° , 70°, 60°, arid 50°in latitude. The maximum Joule heating rate isalso shown in the bottom right corner.

equatorward portion of the westward electrojet in the morning sector is embedded in armenhanced conductance zone, while its poleward portion seems to be located in a strongelectric field region. However, a somewhat different situation is found in the midnightsector, where an enhanced conductance zone is colocated with the westward electrojet.Furthermore, there is an enhanced conductance region with no significant accompanyingionospheric current, equatorward of the westward electrojet in the postmidnight quadrant,suggesting that an enhancement of conductance even in the nightside auroral latitude doesnot necessarily accompany an enhanced ionospheric current. On the other hand, except for apatch—like enhancement in the dusk sector, most of the eastward electrojet is located in theregion of enhanced conductance of solar UV origin. This indicates that the eastward electro—jet seems to be generally dominatedby the electric field.

The field—aligned current distribution in Figure 4a also shows well—defined Region 1 andRegion 2 current systems both in the dawn and dusk hemispheres, except for the downwardRegion 2 current being confined within the postnoon quadrant. Only the upward Region 2current in the morning sector is reasonably well matched with the enhanced conductance zone,indicating that the electron spectrum is hard enough to produce a significant conductanceenhancementin the region.

Inferring Field-AlignedCurrents (9)339

ELECTRIC I’OTENTIAL AND HALL CONDUCTANCE

JULY 2~,I98~2S40 2355 UT ..—‘~

MIM~-4r kV

00 MAX. 54 kV

IONOSrI IERIC CURRENT VECTORS AND HALL CONI)UcTANCE

dLiJ ‘~n.. 24 sIlo 00

Fig. 4b. The spatial relationships between the electric potential distributions andenhanced Hall conductance regions (upper panel), and the relationships between the iono-spheric current vectors and enhaticed Hall conductanceregions (lower panel).

The isocontours of the Joule heating rate in Figure 4a show that the major heat productionregions roughly delineate the auroral electrojets. However, a closer look reveals that themajor heating region in the morning sector is located along the poleward portion of thewestward electrojet, thus indicating that the electric field is more important than thecommductance in the poleward portion of the westward electrojet and the opposite trendprevails in its equatorward portion. On the other hand, although the evidence is lesscertain, the tendency seems to be reversed in the eastward electrojet region. As expected,the local midnight sector, where the conductanceenhancement seems to be more important thanthe electric field, does not show any significant joule dissipation.

DISCUSSION

This paper has demonstrated that the magnetogram—inversiontechnique is a powerful tool ininferring the three—dimensional current system connecting electrically the earth’s magneto-sphere and the ionosphere, and other ionospheric quantities. It has also pointed out thatthe technique has recently been considerably improved in the sense that simultaneousmeasurements of electric fields, conductivities, and field—aligned currents by satellitesand radars can be incorporatedin a consistentmanner.

Relative Importanceof Electric Field and Conductivity

Through this series of improvements, a number of important characteristics, which were notexplicit in earlier studies, have become evident, even though the global patterns ininidividttal cases are quite variable depending upon solar wind conditions and geomagneticactivity. One of the characteristics seen repeatedly in the deduced diagrams of the globalelectrodynammc features is that a significant amount of ionospheric currents can flow inregions where auroral activity and the corresponding conductivity are quite low. That is,the region of the intense auroral electrojets is not completely the same as the region ofthe high conductivity and that of the large electric field, there being latitudinal shiftsamong these three quantities: see Figure 4a This effect is particularly significant overthe poleward half of the westward electrojet in the morning sector, where the electric fieldcombined with relatively low conductance is the main contributor to the ionospheric current.

(9)340 Y. Kamide

On the other hand, the equatorward half of the auroral electrojet is dominated by conductiv-ity enhancements,signalling high aurora! activity. Such a finding is hardly expected fromstudies in which statistically derived models of the ionospheric conductivity and of theelectric field are independentlygiven.

Figure 5a shows latitudinal profiles of the three quantities (the electric field, theconductance, and their product, the current) overlaid for 0400 MLT (magnetic local time).These quantities have been deduced from the best optimized result using nearly simultaneous —data of DE1 aurora! imagery and of DE2 ion drift, in addition to ground magnetometerrecords for the maximum epoch of an intense substorm /15/. It is clear that the electricfield peaks poleward of 69” latitude, whereas the highest conductivity occurs somewhatsouthward of it, extending to 64° latitude in this particular example, implying thatenhancements in the electric field and in aurora! activity control the strength of theelectrojet current separately. The peak of the westward electrojet is located between thetwo peaks.

Figure Sb is a sample of the latitudinal profiles of the three parameters /19/ for 0400 MUTfor active times, which are based on a statistical study of the convection electric fieldsfrom the Millstone Hill radar and of particle precipitation from the NOAA/TIROS satellites/16/. Although the exact locations of the three quantities and their magnitudes are differ-ent between the individual case shown in Figure 2a and the average case, the latitudinalseparation of the electric field and conductivity peaks by several degrees is consistentlynoticed. This offset is important because it has been a common practice to assume tacitlythat the aurora! electrojets, as the terminology implies, are flowing in the region of highconductancewhere the aurora! luminosity is highest.

It is noted that an earlier statistical study of the aurora! electrojets at different localtimes has indicated that the aurora! electrojets may have two different elements: theelectric field—dominant electrojet and the conductivity—dominant electrojet /20/. Combiningthis statistical indication and Figure 5, it is inferred that the aurora! electrojets do notgrow and decay as a whole, bttt only the portion in the midnight sector and the equatorwardhalf of the currents is enhanced at the time of aurora! breakup and the other portion iscontrolled by the electric field, which does not primarily reflect aurora! activity.Further, the implications of these two elements are interesting if they are viewed as twophysical processes for solar wind—magnetosphere energy coupling, i.e., the directly drivenand loading—unloading processes /21/. That is, the “electric field” electrojet may representdirectly the effects of the solar wind—magnetospheredynamo, whereas the uconductivity...rich~~electrojet may be a manifestation of a plasma instability process internal to the magneto-sphere, relating to intense and sporadic aurora! activity at substorm expansion onsets.

~Instantaneous” Conductivity Distribution

In view of the increasingly wide use of the magnetogram—inversion technique for mappingionospheric convection patterns in many joint projects, such as the GISMOS and MITHRASprograms, it is essential to have accurate, instantaneous conductivity distributions in theionosphere, which are one of the basic input parameters of the inversion techniques. There

(a) 1252 UT 04 MLT (0) LEVEL 7 04 ML’i’I ~I0 I

in DECEMBER 12, 1931 1’OS’I’Eit (1987)

— 30— E

:20

CORRECTED GEOMAGNETIC LATITUDE APEX LATITUDE

Fig. 5. (a) Individual latitude distribution of the electric field E, the Hall conducttv-~its’ ~ ,,, and the Hall current J for 0400 MLT, calculated through the magimetogram—inversiontechnique for 1252 UT, 12 December 1981. Vertical scale units: E, millivolts per meter;

,, mhos; J , 0.1 amps per meter. (bI Statistical profile of the three quantities, afterFoster /20/. Foster et al. /17/ obtained the distribution of ionospheric convection deter—mined from Millstone Hill radar data for different intemmsities of auroral particle precipi-tation, using a precipitation index based ott spacecraft observations. This diagram is forindex level 7 (see Fuller—Rowell and Evans /8/).

Inferring Field-Aligned Currents (9)341

is no doubt that in situ measurementsby satellites should provide a direct means of sensingthe state of the magnetosphere—ionospheresystem. Unfortunately, however, these satellitemeasurements provide useful information only along their orbits. By the same token,incoherent and coherent scatter radars can monitor the electrodynamic state of the E andF—region ionosphere only near the radar sites or along the meridian where the radars are

located. This is the reason why one has to average a large number of data sets from thoseudirect~~ measurements to obtain a global picture. It is important to combine high timeresolution records from satellites and radars with data from ground magnetometer arrays toinfer the ionospheric quantities on a global scale (instead of along satellite orbits).

This paper points out clearly that statistical conductivity models require modification foruse in the magnetogram—inversion schemes applied to individual substorms, during which theionospheric conductance structure is localized and highly variable. In particular, local

conductivity enhancements asociated with rapid aurora! motions cannot be properly represent-ed in the statistical models. Because of the high degree to which the electric field dependson the assumed ionospheric conductivity distribution, the inversion scheme must be combinedwith fairly accurate instantaneous distributions of the conductivity to study the variabil-ity of the high—latitude electrodynamics during substorms. The optimizing numericalprocedure of Kamide et a!. /15/ is very similar to that recently proposed by Marklund et a!./22/, who have made use of Viking measurements of aurora! images and electric fields toinfer the ionospheric conductance. The major difference between the two methods is thatMarklund et al. have not used ground—based magnetometer data but instead have relied on astatistical distribution of field—aligned currents that is modified using the UV—imager datawith the assumption that the upward field—aligned current should be colocated with activeauroras.

ACKNOWLEDGMENTS

The work presented in this paper was supported in part by the Ministry of Education, Scienceand Culture of Japan, under grant 62540310, and in part by the Japanese—american Fund, Inc.

REFERENCES

1. K—H. G1a~meier, Ground—based observations of field—aligned currents in the aurora!zone: Methods and results, Ann. Geophys. 5A, 115 (1987)

2. Y. Kamide, Electrodynamic Processes in the Earth’s Ionosphere and Magnetosphere,Kyoto Sangyo University Press, Kyoto (1988)

3. Y. Kamide, AD. Richmond, and S. Matsushita, Estimation of ionospheric electric fieldionospheric currents, and field—aligned currents from ground magnetic records, J. Geo

—

phys. Res. 86, 801 (1981)

4. J.L. Kisabeth, On calculating magnetic and vector potential fields due to large—scalemagnetospheric current systems and induced currents in an infinitely conducting earth,in: Quantitative Modeling of Magnetospheric Processes, ed W.P. Olson, American Geophy—sical Union, Washington, D.C., 1979, p. 473

5. P.S. Fayermark, Reconstruction of the three—dimensional current system of the high—latitude region from ground—based geomagnetic measurements, Geomagn. Aeron., Englishtranslation, 17, 114 (1977)

6. V.M. Mishin, GB. Shpynev, and A.D. Bazarzhapov, Large—scale electric field and currentsin the high—latitude ionosphere and magnetosphere as a function of solar wind para-meters, in: Dynamics of the Magnetosphere, ed. S—I. Akasofu, D. Reidel, Dordrecht,1980, p. 249

7. S.—!. Akasofu and Y. Kamide, Meridian chains of magnetometers as a powerful ~remote—sensing” too! in determining electromagnetic quantities in the ionosphere on a globalscale, EOS Trans. 66, 465 (1985)

8. T.J. Fuller—Rowe!! and D.S. Evans, Height—integrated Pedersen and Hall conductivity pat—terns inferred from the TIROSNOAA satellite data, j. Geophys. Res. 92, 7606 (1987)

9. Y. Kamide and AD. Richmond, Ionospheric conductivity dependence of electric fields andcurrents estimated from ground magnetic observations, 3. Geophys. Res. 87, 8331 (1982)

10. Y. Kamide, - 3.—H. Ahn, 5.-I. Akasofu, W. Baumjohann, & Friis—Christensen, H.W. Kroehl,H. Maurer, AD. Richmond, G. Rostoker, R.W. Spiro, 3K. Walker, and A.N. Zaitzev,Global distribution of ionospheric and field—aligned currents during substorm determined -:

(9)342 Y. Kamide

using magnetic data from six IMS meridian chains: Initial results, 3. Geophys. Res. 87,8228 (1982)

11. A.D. Richmond and Y. Kamide, Mapping electrodynamic features of the high—latitude iono-sphere from localized observation: Technique, 3. Geophys. Res. 93, 5741 (1988)

12. L.A. Frank, J.D. Craven, j.L. Burch, and 3D. Winningham, Polar views of the earth’saurora with Dynamics Explorer, Geophys. Res. Lett. 9, 1001 (1982); L.A. Frank, J.D.Craven, D.A. Gurnett, S.D. Shawhan, P.R. Weimer, J.L. Burch, 3D. Winningham, C.R. —

Chappell, J.H. Waite, R.A. Heelis, N.C. Maynard, M. Sugiura, W.K. Peterson, and E.G. —

Shelley, The theta aurora, J~Q~ophys.Res. 91, 3177 (1986) —

13. Y. Kamide, 3D. Craven, L.A. Frank, B.—H. Ahn, and S—I. Akasofu, Modeling substorm cur— —

rent systems using the conductivity distribution inferred from DE aurora! images, —

J.Geophys. Res. 91, 11235 (1986)

14. M.H. Rees, Auroral excitation and energy dissipation, in: Solar—Terrestrial Physics, ed.R.L. Carovillano and 3M. Forbes, D. Reidel, Dordrecht, 1983, p. 753

15. V. Kamide, Y. Ishihara, T.L. Killeen, 3D. Craven, L.A. Frank, and R.A. Heelis, Combin—ing electric field and aurora observation from DE 1 and 2 with ground magnetometerrecords to estimate ionmospheric electromagnetic quantities, submitted to 3. Geophys.Res. (1988)

16. J.C. Foster, 3M. Holt, R.G. Musgrove, and D.S. Evans, Ionospheric convection associatedwith discrete levels of particle precipitation, Geophys. Res. Lett. 13, 656 (1986)

17. B.—H. Ahn, H.W. Kroehl, V. Kamide, and P.3. Gorney, Estimate of ionospheric electro—dynamic parameters using ionospheric conductance deduced from bremsstrahlung X—ray image

data, submitted to J. Geophys. Res. (1988)

18. D.J. Gorney, P.F. Mizera, and J.F. Roeder, A maximum—entropy technique for deconvolutionof atmospheric bremsstrahlung spectra, Rep. No. SSL—86 (6940—06)—06, Aerospace Corp.,Los Angeles (1985)

19. J.C. Foster, Reply to Kamide and Richmond, Geophys. Res. Lett. 14, 160 (1987)

20. Y~ Kamide and J.F. Vickrey, Relative contribution of ionospheric conductivity and elec—trio fields to the aurora! electrojets, 3. Geophys. Res. 88, 7989 (1983).

21. S—I. Akasofu, Energy coupling between the solar wind and the magnetosphere,~ Sci.Rev. 28, 121 (1981)

22. G.T. Marklund, L.G. Blomberg, T.A. Potemra, 3.8. Murphree, F.J. Rich, and K. Stasiewicz,A new method to derive ‘instantaneous” high—latitude potential distributions from sate!—lite measurements including aurora! imager data, Geophys. Res. Lett. 14, 439 (1987)