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VOL. 78, NO. 7

JOURNAL

OF GEOPHYSICAL

RESEARCH

MARCH 1, 1973

Auroral

Oval I

Y. I. FELDSTEIN

IZMIRAN,

Academy o] Sciences,Moscow, USSR

Since the conceptof the auroral oval was put forward by Feldsteinand Khorosheva[cf. Feldstein et al., 1969; Akasofu, 1968; Khorosheva, 1967] there have been a large number of observations that confirmthe presence the of proposed oval configuration the distribution of
of auroral arcs and bands. Some of these recent

2. The projection of the inner boundary of the plasma sheet coincideswith the equatorward boundary of the oval [Vasyliunas, 1970; Feldstein, 1972].
3. The orientation of extended forms of au-

roras is parallel to the oval [Gustafsson, 1967; Feldsteinand Starkov, 1967; Gustafsson al., et
1969].

studies are listed below.

1. Occurrence frequency of auroras at six stationsover Greenlandand Spitzbergen[Lassen, 1967, 1970]. 2. Occurrencefrequency of auroras in the Alaska sector [Stringer and Belon, 1967]. 3. Occurrence frequencyof aurorasat Pyramida, Chelyuskin, Murmansk, Verkhoyansk, and others [Starkov and Feldstein, 1967, 1968; Feldstein and Starkov, 1967]. 4. Occurrence frequency of auroras over Antarctica [Jacka and Bond, 1968; Bond and Thomas,1971J.
5. Airborne observations in the northern

4. Field-aligned currents are present over the auroral oval [Zmuda et al., 1967, 1970]. 5. The distinct equatorwardboundaryof the

region eiectric fluctuations of field coincides with
the oval [Heppner, 1969; Maynard and Heppher, 1970]. 6. The electric field changes the polarity in the vicinity of the auroral oval [L. A. Frank, unpublished manuscript, 1972; Frank and Ackerson,1972; Cau#man and Gurnett, 1972]. 7. The projectionof the cuspcoincides with the midday part of the oval [Heikkila and Winningham,1971; Frank, 1971; Heikkila et al.,
1·7·].

polar region [Buchau et al., 1970, 1972]. 6. Auroral scanner observations (Isis 2), [Lui et al., 1972]. 7. 'Scanning' of the oval by the Alaska meridian chain of stations [Snyder and Akaso[u, There have alsobeen a large number of other types of observationsthat suggest that the auroral oval provides a 'natural' coordinatein which variouspolar upper-atmospheric phenomena may be ordered (to enhance understanding). 1. The projection of the outer boundary of the trapping region coincideswith the oval [Akasofu, 1968; Feldsteinand Starkov, 1970].

8. Precipitation of soft electrons occurs alongthe oval [HoffmanandBerko,1971; R. A. Hoffman, unpublished manuscript,1971; Frank and Ackerson,197i; J. D. Winninghamand W. J. Heikkila, unpublished manuscript,1972]. Recently, Mishin et al. [1970a, b] suggested
that the auroral distribution can be better

representedby two quasi-circular zones, the 'inner' one being along the dipolelatitude circle of 78Ü and the 'outer' one along the dipolelatitude circle of 67 Ü. On the basis of reexamination

of their resultsit is found that the presence of
their inner zone is based on observations from a

single station, Arctica 2. Their results imply that the inner zone was located preciselyat the this mustbe due XA review paper presented at the sympo- zenithof Arctica 2. Obviously, to the fact that the well-known aspect sensisium on the auroral oval and magnetospheric cusps,April 17-21, 1972. Complete publication in tivity bf auroras (pointed out by Elvey et al. Russian will appear in Aurora an.d Airglow, [1953]) has not been properly removed. FurMoscow, 1973. ther, they supported their suggestion examby Copyright (·) 1973 by the American GeophysicalUnion. ining all-sky recordsfrom a number of stations
1210


FELDSTEIN'

LETTER

1211

alongthe 200Ü dipolemeridianon February 11, earlier, this view is better than the conceptof 1958, during the great magnetic storm. The two circularzonesput forward by Mishin et al. recordsfrom the corresponding all-sky records [1970a, b]. from Arctica 2 were reexamined. It was found In particular,on very quiet days,auroral arcs that the lower boundaryof aurorasduringmid- and bands are more frequently seenin the daynight hours on that day was not clearly seen. side half than in the nightsidehalf [Lassen, Thus it is not proper to claim that suchauroras 1967, 1970]. On moderatelydisturbeddays the were distributedalong the inner zone,sincethe entire oval can be identifiedby the presence of distance(from Arcfica 2 to the auroras) cannot auroral arcs and bands. The two regions are be determined. Mishin et at. [1971] incorrectly connected a broad band of subvisualglow, by identified the twilight and moonlight as the even when the occurrence of visible auroras has outer zone in their reexamination of the aira discontinuityat the boundary of the regions borne study by Buchau et al. [1970]. Other [Buchau et al., 1972]. It shouldbe noted that criticismsof their proposedtwo circular dis- there is also another precipitation zone along tribution have been publishedelsewhere [Star- the auroral zonein the morningsector,which is kov et al., 1973]. produced by energetic electrons,particularly It shouldbe pointed out that the conceptof duringmagnetospheric substorms Hartz and [cf. the auroral oval is based on studies of the occurBrice, 1967; Starkov and Feldstein,1971]. rence of auroral arcs and bandsphotographed Figurei gives schematic a noon-midnight cross by all-sky cameras. The concept has never sectionof the magnetosphere, which indicates implied that characteristics the precipitation the oval location as inferred from aurora and of of auroral particles are uniform all along the plasmaobservations the magnetosphere. in oval [Feldstein, 1969]. In Figure 2 the portion of the auroral oval Recent progressin the observationof pre- is related to the intersection lines between the cipitatingparticles and the resulting luminosities polar ionosphere and the boundarysurfaces of has yielded someadditional evidencethat char- different plasma regionsin the magnetosphere. acteristicsof the oval in the daysidehalf and The auroral oval is divided into tw5 parts, the nightside half are considerablydifferent [cf. daysideand the nightside.Different characterHeikkila et al., 1972; Eather and Mende, 1972]. istics of luminescence there are caused parby Thus it may be proposed that the oval consists ticle precipitationfrom differentplasmaregions, of two parts,the daysidehalf and the nightside such as the magnetosheath the daysideand on half, althoughtogether they form the singIe the low-latitude plasmasheeton the nightside. oval band. On the basis of recent literature cited The equatorialoval boundaryis indicatedby
ú

SHOCK

úINNEllllOOEOF PLASMA

·A·NETOSHEATH

o· k
])i,$TANT MAGNETOTAIL

H·$H-LATJ, TUDE
SOLAll
PLASMASHEET

DW-LATiTUdE
PLASMASHEET

12 t'

·24 k
/MAGNETOPAUSE

·/·'AGNETOPAUSE ------ llF OVAL, SOUNDAlliES AUROIIAL

Fig. 1. Schematic cross sections the magnetosphere oval position creation of and at phase. (Left) Cross section the noon-midnight in meridianplane.Shaded regionshows plasma the sheetin the tail and the plasma fluxes flowing throughthe magnetospheric to the upper cusps atmosphere from the tail on the nightsideand from the magnetosheath the dayside. on (Right) Schematic sectionof the magnetosphere the equatorialplane at the end of the in
substormcreation phase.Shadedregion showsthe plasmasheet in the tail.


1212
12

FELDSTEIN.' LETTER

Buchau, J., G. J. Gassmann, C. P. Pike, R. A. Wagner, and J. A. Whalen, Precipitation patterns in the arctic ionosphere determined from airborne observations, Ann. Geophys., 28, 44306

18

454, 1972.

Cauffman, D. R., and D. A. Gurnett, Satellite measurements of high latitude convection elecCLOSED THROUGH

PLASMA 5HEE?

EQUATOR/,AL

trisc fields, Space Rev.,13, 369-410, Sci. 1972.
Eather, R. H., and S. B. Mende, Systematics in auroral energy spectra, J. Geophys. Res., 77, 660-673, 197oe. Elvey, C. T., H. Leinbach, and V. P. Hessler, Preliminary observations of the geographical distribution of auroras in Alaska, Science, 117,
466, 1953.

O0 AUgORAL OVAL ·0UNDARI( MAGNETJo FJELZ) TOPOLOGY

])iSTANT MAGNETO·POLAlt CUSP
'PAIL

Feldstein, Y. I., Polar auroras, polar substorms, and their relationships with the dynamics of the magnetosphere,Rev. Geophys. Space Phys.,

PLASM SHEET

.iG.LA'riT..· ·

O0

' LOW-LA1'iTUDE PLASMA 5HEl'

-OVAL

PLASMA I·EGiON DISTANT IN MAONETOSPXEItE

12

18

·.L··MAONE e?q.2.A c,% TI]5 H E TH
PI(ASMA

6

L0·/- LATiTU DE

PLASMA ELECTRON5 SHEET O0
PLASMAS AT LOrdALTITUDES

Fig. 2. Diagrams characterizing magnetic field topology and precipitating plasma fluxes in high latitudes at recovery phase of the substorm.

7, 179-218, 1969. Feldstein, Y. I., Auroras and associatedphenomena, in Solar-Terrestrial Physics/1970,edited by E. R. Dyer, pp. 111, 152-191, D. Reidel, Dordrecht, Netherlands, 1972. Feldstein, Y. I., and G. V. Starkov, Dynamics of auroral belt and polar geomagneticdisturbances, Planet. Space Sci., 15, 209-229, 1967. Feldstein, Y. I., and G. V. Starkov, The auroral oval and the boundary of closed field lines of geomagnetic field, Planet. Space Sci., 18, 501508, 1970. Feldstein, Y. I., S. I. Isaev, and A. L. Lebedinsky, Phenomenology and morphology of aurorae, Ann. Int. Quiet Sun Year, 4, 311-348, 1969. Frank, L. A., Plasma in the earth's polar magnetosphere, J. Geophys. Res., 76, 5202-5219, 1971. Frank, L. A., and K. L. Ackerson, Observations of charged particle precipitation in the auroral zone, J. Geophys. Res., 76, 3612-3643, 1971. Frank, L. A., and K. L. Ackerson, Local-time survey of plasma at low altitudes over the auroral zones, J. Geophys. Res., 77, 4116-4127,
1972.

a continuous curvebecause this boundaryis the projection (alonggeomagnetic field linesat ionosphereheights) of a continous surfacethat consistsof the inner boundaryof the plasmasheet in the magnetosphere tail on the nightsideof the earth and the magnetopause the dayside. on The two parts of the auroraloval are topologically connected the large-scale by magnetic field structure and plasma population in different regions the magnetosphere. of
t·EFERENCES

Akasofu, S.-I., Polar and Magnetospheric Substorms,D. Reidel, Dordrecht, Netherlands, 1968. Bond, F. R., and I. L. Thomas, The southern auroral oval, Aust. J. Phys., 24, 97-102, 1971. Buchau, J., J. A· Whalen, and S.-I. Akasofu, On the continuity of the auroral oval, J. Geophys. Res., 75, 7147-7160, 1970.

Gustafsson,G., On the orientation of auroral arcs, Planet. Space Sci., 15, 277-294, 1967. Gustafsson,G., Y. I. Feldstein, and N. F. Shevnina, The auroral orientation curves for the IQSY, Planet. Space Sci., 17, 1657-1667,1969. IIartz, T. R., and N.M. Brice, The general pattern of auroral particle precipitation, Planet. Space Sc{., 15, 301-329, 1967. Heikkila, W. J., and J. D. Winningham, Penetration of magnetosheath plasma to low altitudes through the dayside magnetosphericcusps, J. Geophys. Res., 76, 883-891, 1971. Heikkila, W. J., J. D. Winningham, R. II. Eather, and S.-I. Akasofu, Auroral emissionsand particle precipitation in the noon sector, J. Geophys. Res., 77, 4100-4115,1972.

IIeppner, J.P., Magnetosphericconvection patterns inferred from high latitude activity, in AtmosphericEmissions,edited by B. M. McCormac and A. Omholt, pp. 251-266, Van Nostrand Reinhold, New York, 1969.


FELDSTEIN: LETTER

1213

lioffman, R. A., and F. W. Berko, Primary electron influx to the dayside auroral oval, J. Geophys. Res., 76, 2967-2976, 1971. Jacka, F., and F. R. Bond, Optical auroral morphology, Ann. Geophys., 24, 547-554, 1968. Khorosheva, O. V., Spatial-temporal distribution

Snyder, A. L., and S.-I. Akasofu, Observationsof the auroral oval by the Alaskan meridian chain of stations, J. Geophys. Res., 77, 3419-3430,
1972.

Starkov, G. V., and Y. I. Feldstein, Variation of auroral oval boundaries, Geomagn. Aeron., 7,
62-71, 1967. Starkov, G. V., and Y. I. Feldstein, Auroral oval during magnetic disturbances,in Aurorae, no. 17, pp. 22-33, Academy of Sciences, Moscow,
1968.

of aurorae,in Aurorae (in Russian), no. 16, pp.
1-84, Academy of Sciences,Moscow, 1967. Lassen,K., Polar cap aurora, in Aurora and Air.

glow, edited by B. M. McCormac, pp. 453-464,
Reinhold, New York, 1967. Lassen, K., The position of the auroral oval over

Greenland and Spitzbergen,Phys. Norv., 4,
171-175, 1970.

Lui, A. T. Y., C'. Anger, and S.-I. Akasofu,
Observations of the auroral oval and a westward

Starkov, storm, Starkov, sheva, Invest.
1973.

G. V., and Y. I. Feldstein, Auroral subGeomagn. Aeron., 11, 560-562, 1971. G. V., Y. I. Feldstein, and O. V. KhoroEccentric oval or two quasi-circularzones, Geomagn. Aeron. Solo· Phys., in press,

traveling surge from Isis 2 satellite and Alaska meridian all sky cameras, submitted to J. Geophys. Res., 1972. Maynard, N. S., and J.P. lieppner, Variations

Stringer, W. J., and A. E. Belon, The morphology of the IQSY auroral oval, J. Geophys. Res., 72,
4415-4421, 1967.

in the electric fields from polar orbiting satel- Vasyliunas, V. M., Low energy particle fluxes in the geomagnetic tail, in The Polar Ionosphere lites, in Particles and Fields in the Magnetoand Magnetospheric Processes, edited by G. sphere, edited by B. M. McCormac, pp. 247Skovli, Gordon and Breach, New York, 1970. 253, D. Reidel, Dordrecht, Netherlands, 1970. Zmuda, A. J., F. T. lieuring, and J. li. Martin, Mishin, V. M., T. I. Saifudinova, and I. A. Dayside magnetic disturbances at 1100 kilomZhulin, Two zones of precipitating energetic eters in the auroral oval, J. Geophys.Res., 72, particles,J. Geophys.Res., 75, 797-806, 1970a. 1115-1117, 1967. Mishin, V. M., V. P. Samsonov, I. Saifudinova, T. and V. A. Kurilov, Main zones of corpuscular Zmuda, A. J., J. C. Armstrong,and F. T. lieuring, Characteristicsof transverse magnetic disturinvasions into ionosphere,Invest. Geomagm

Aeron. Solar Phys. (in Russian),no. 11, 3-23,
1970.b.

bances observed at 1100 kilometers in the au-

roral oval, J. Geophys. Res.,75, 4757-4762, 1970.
(Received April 12, 1972;
accepted October 27, 1972.) Communicatedby S.-I. Akasofu.

Mishin, V. M., V. P. Samsonov,G. V. PopOv,
and T. I. Saifudinova, New data on zones of

corpuscular invasions into the polar ionosphere,
Invest. Geomagn.Aeron. Solar Phys. (in Russian), no. 19, 38-44, 1971.