Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.izmiran.rssi.ru/magnetism/Feldstein_2012/PDF/385.pdf Äàòà èçìåíåíèÿ: Wed Mar 11 16:45:32 2009 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 21:12:47 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ultraviolet

GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO.16, PAGES 3083-3086, AUGUST 15, 1998

Conjugacy of geomagnetic disturbances and the substorm current wedge
Y. I. Feldstein, L. I. Groinova, and A. E. Levitin
Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troksk, Moscow Region, Russia

A.Grafe
Geo ForschungZen·rum Potsdam, Adolf Schmid· Observa·orium, Niemegk, Germany

Abstract. The conjugacy of geomagnetic phenomena at high latitudes in the northern and southern hemispheresis investigated using observationsof the geomagnetic field variations. Similar the magnetic distur-

latitudeshas been obtainedby [Meng, 1981;Makita et al., 1991]. Multisatelliteobservations auroralenergy of
plasma precipitation show that the transpolar band is located on closedmagnetic field lines.

bancesat the poleward edge of the auroral oval night
sector were observed in both hemispheres. These resuits show that magnetic field lines at the periphery of the plasma sheet are closed and that processes leading to the appearance of magnetic disturbancesare similar in conjugateregions. Modeling of geomagneticfield hne structure has shown that field hnes are closed up to a distance of several dozens of Earth radii during the existence of the tail current wedge. The region of closed field hnes maps to the nightside ionosphereup to · 80o geomagneticlatitude. Nttg _,
· ....

·

'·[

uz , ]I II,
II I ,, , ··
· ·!
·,

.·,1

'

· ·e L,I
', ·'

·,·

'

' ·-200

·L 200

·

............

.....
NflL
LYR

·:

· ·
,

I 11 , ,, · ,,·, Ii ;'·
·l · ,· ·
·,,

,

/ ·00 / , I· ' t- ·ÜÜ
/ · 200
/

.

· ....

,,

·l··

·w ....

,·

+ 200

-·oo

.......

·,,

·_·

.....

2o0

........

,·.

·

'·,,
, , I'·,·

· ....
.·_,

- 200
. - 200

Introduction

.·.·,1·

·

TRO

' ' ' ú ·F'
. ·· q, II

·,·
r, I

·, III

.....
.·.,.·

· -·oo
·u
. 200
qOr·

Akasofu[1968] has summarizedobservations auof
rorae and magnetic disturbances at auroral latitudes in geomagnetically conjugate regionsduring magnetosphericsubstormintervals. Conjugate discreteaurorae havesimilarforms and movements, brighteningand decaying simultaneously. The magnetic field variations are strikingly similar, too. These observationsindicate that energeticelectronprecipitate along magneticfield hnes into the upper atmosphereand auroral electrojets in geomagneticallyconjugate regionsare causedby the same.magnetosphericsource. Moreover, geomagnetic field lines mapping to the night sector of the auroral
oval are closed.

.....·W·,:,·..
.... ·,·

......
..

·

,I· ·

.... ··,,·

..

,, ··

200

KII k ·

. . .··,·.·., ..... r,''
._ .··,·· ....... ·'

- ,· l··
;'-r·
' · ·'·

III

I VI ·1 I

· ·0

,.·_·_· ·oo ·-·oo
.... ·

200

,l·,

Zoo -2oo

OUJ

........ ·'··.E
......... ,,''·
·

·

· r·

,·
t , II

...... ·oo
-·oo
-20O
, ,

....
NUR

;;'·: ':"- , ,·-·
iI, , i , ,i iJ ,

Simultaneousauroral observations the high latiin tudes of both hemisphereshave become possiblewith

the adventof globalfar ultraviolet(FUV} images from
the Viking and Dynamics Explorer-1 satellites. The first results of such a comparison,for the transpolar band observedon August 3, 1986, were presentedby
I-]ST
i

Cravenet al. [1991]. Vorobjev al. [1995]described et
this band's dynamics and showed that the band had a complicatedstructure consistingof three parallel arcs.
These arcs were connected with the main auroral oval

by continuous precipitation [Feldstein al., 1995].The et
interpretation of the polar arcs as the result of the ex-

Figure 1. Variations of the magnetic field X t component along the IMAGE chain during the storm main

phaseon February6-7, 1994 (at the top). Dotted vertical hnes correspond to UT's with latitudinal cross-

pansion plasmasheetprecipitationinto the very high of
Copyright 1998by theAmerican Geophysical Union.
Papernumber 98GL02323.
0094-8534/98/98GL-02323505.00

sections the X' and Z components of presentedfurther in the text. The Dst and the PC indicesof the magnetic field variations for the same storm are shown at

the bottom. The Antarctic station is marked by circle. The time of MLT midnight at each station is marked by a triangle.
3083


3084

FELDSTEtN

ET AL.'

CONJUGACY

OF GEOMAGNETIC

DISTURBANCES

There is also additional

data that shows a correlation

of the auroral luminosity in one hemisphereand precipitating auroral electrons in the other hemisphere. For

February 6-7, 1994. Vertical dotted hnes mark the latitudinal cross-sectionsfor which the quantitative com-

example,Mizera et al. [1987]and Obaraet al. [198]
found that polar arcs in the northern hemisphereare located in the same time sector and at the same geomagnetic latitude as auroral precipitation in the southern hemisphere. The aim of this investigation is to analyze the magnetic disturbances at the poleward edge of the auroral oval during a magnetic storm in the northern hemisphereand to comparetheir intensity with magnetic dis-

parisonsof the intensity of geomagneticfield variations were made. The hourly Dst index and the fifteenminute PC index variations are plotted in the bottom panel of Figure 1. From these magnetogramsone can seethat the geomagnetic variationsat Mirny are similar to the expected variations at the conjugatelatitudes of

thenorthern hemisphere between ·lesundandNord Ny
stations. One should also note that there is a time delay of the magnetic disturbance peak at the high latitudes with respect to the auroral zone.

turbances the conjugate in regionof the southern hemiFigure 2 showsthe latitudinal cross-sections X ' of sphere.We useddata from the IMAGE (International and Z (solidand dashed hnescorrespondingly) the at Monitor Auroral Geomagnetic Effects)meridianchain key times during the magnetic storm: -at the maximum of the storm at 1626 UT on Februof magnetometers (neargeomagnetic meridian110 in Ü) Scandinavia extending from Nurmijarvi (corrected geo- ary 6;

magnetic latitude ·- 57 to Ny 3Aesund · 76 (· Ü) ((I, Ü)
which is located on nearly the same geomagnetic meridian as the IMAGE chain.

-during the quiet interval betweensubstorms 2014 at
at substorm maximum at 2126 UT. on Febru-

and Nord station in Greenland((· -· 81Ü) and from UT; Mirny stationin the southernhemisphere · 77Ü) (·

Southern hemisphere station is marked by circle.
The cross-sections at 1700 UT and 2005 UT

Results

of the

observations

ary 7 characterizethe intensity distribution of the magnetic field disturbancesfor two different types of westward electrojet, namely, only at auroral zone latitudes

Figure I showsvariationsin the X' componentof the (1700UT) or at higherlatitudes(2005UT). The intengeomagnetic (the northwardcomponent the ge- sity of magnetic variations at Mirny is the same as at field in omagnetic meridiandirection)alongthe IMAGE chain the conjugatelatitudes in the northern hemisphere. Therefore,substormdevelopment practicallysimiis and for Mirny station during the magnetic storm of

8·

--

76

lar in both the northern and the southern hemispheres up to geomagneticlatitudes 780-82 Ü, the poleward hmit of the region to which disturbancesfrom auroral oval latitudes propagate. We can say that conjugacyof geomagneticphenomenais observedeven up to the poleward edgeof the auroral ovalsin both hemispheres.

· 7·
(· 7o

Results of magnetic field modeling
The similarity in the magnetic field variations and the good correlation of their intensity in both hemispheres at latitudes 770-820 suggest that the magneticfield hnes are closedeven at these high latitudes. Becausemagnetic field lines at auroral latitudes are definitely closed,the poleward expansionof disturbances is usually interpreted as a consequence reconnection of of initially open magnetic field hnes in the tail and the further dipolarisation of closed field lines, i.e., the sudden changefrom a stretched magnetospherictail configuration to a quasi-dipolar one. Thus the field hnes mapping to Mirny latitudes are probably closed. Figure 3 presentsresultsof modeling usingtwo exter-

ú

o

2'50 nT O

250 500 -7·

-SO0-2':20 0 nT
06.02. 2011 g· UT

27·. ·1500-1000-SO0 SO01000 0 nT
06.02.942126UT

06.02..g,· LIT 1626

'.: X: dZ I'·. clX, Nor-th

+:dXod· · X: Hc·th

+'.dX, dZ · X: Hc·th

· 7,.

nal magneticfield models: Tsyganenko's [1995]model (top panel) and the paraboloidal model of Alezeevet al. [1996](bottom panel). Input parameters Tsyof
ganenko'smodel are the solar wind dynamic pressure

(Pdyn),index Dst, the interplanetary magnetic field components and Bz, and the geodipole angle By tilt
- lSOO-1000-S00 n'r
07.02.9· +: dX, X:

0

SO0 1000 -500

-250
+: co(, x ú dZ Hocth He·

·p. For Alexeev's model, input parameters include the geocentric distancesto the subsolarpoint on the magne+: cO(, X: dI North H·

1·2 UT dZ Nor-th

(·.

dX, ·):

dZ South

topause (Rx) and to the inner edgeof the currentsheet in the magnetospheric (R2), the magnetic tail flux in the magnetospheric lobe ((·), and the geodipole tail

at Figure 2. The latitudinalcross-sectionX'(sohd hne) tilt angle ·p. For the latitudinal cross-section 2126 of andZ(dashed hne)at different instants the magnetic UT on February 6, 1994, the geomagneticlatitudes of of storms: 1626, 2014, and 2126 UT on February 6, 1994 the equatorward Ü, "1")and poleward(68Ü, "3") (61 (top panel),andthrough different types the westward boundaries of and the center(64Ü,"2" ) of the electrojet
electrojet: 1700 and 2005 UT on February 7, 1994.

were obtained. The magnetic field lines from these lat-


FELDSTEIN

ET AL.- CONJUGACY

OF GEOMAGNETIC

DISTURBANCES

3085

TSYGRNENKO'S
.

MODEL

06 Fob 1994

lILT : 00.4

z.· t

06

Fob

1994

MLT = 00.4

TSYGRNENKO"5 MODEL

..... ,-·.·'·,.·,, ' _ · ·.·_·.·.··.·_·.·
Z ..·<-....................... 2
-1

Figure 4. Magnetic field lines structure on February 6,
Z, Ri

1994,basedon Tsy#anenko's [1997]modelfor the same
RLEXEEV'S 06 Fob 1994 MLT = 00.4 MODEL

UT as Figure 3, but taking into accountthe emergence of the current wedgewith integral current magnitude of
106A.

.

.

5·

substorm development has been studied for the February 7, 1994, substorm in which the geocentric distance of the current wedge rs increasesfrom 6.2R· to 25R·.
·'·....;-'·';"r ....

' ' ' · ' ' ' "]:o" :-'r't;·':";'l'"·'·"·"; .....

Figure 5 showsthe results of modeling of the magnetic
field line structure. These two static models character-

ize the changein the structure of the nightside magnetosphere during the shift of westward electrojet center from auroral latitudes to (I, .-· 750 during the substorm [igure 3. Mappingof the equatorial(1) and poleward active phase. The sequence thesemodelswith changof ing input parameters may represent a considerably detailed descriptionof the geomagnetic field structure dyEooa] (top namics. Figure 5 shows that the geocentric distance of (bottom panel); the magneticfield line mappingfrom the electrojet equatorial boundary does not effectively ú - 770is markedas(4). The electrojet parameters are change. The center of the westward electrojet movesto defined from the 212· UT cross-section ·ebruary on the distant magnetospheric tail but it is still located on 1994. closedmagnetic field lines. This paper does not aim to demonstrate the possiitudes and the point conjugate to Mirny station in the bility of using geomagnetic variations for the determi-

··J theof westward its boundaries usingandcenter into magnetosphereof the electrojet the models

northernhemisphere , "4") were mappedinto the nation of A· (the outer boundaryof the regionwith (770 magnetosphere. closed but stretcheddowntailfield lines). Our purpose
The magnetic field line mapping from the poleward boundary of the westward electrojet is open according to both models, as is also the magnetic field line mapping from · - 770. Hence, neither model confirms magnetic field lines closing at such high latitudes during disturbances. has been to show the existenceof conjugacyup to very high latitudes and to show that field lines should be closedat suchhigh latitudes accordingto existing models. Determinations of A· with considerable accuracy may be obtained using satellite observations of auroral electron precipitation into the upper atmosphere.
TSYGRNENKO'S
ú

This result can be th· consequence either of the absenceof geomagneticconjugacyat · · 77Ü, or of the inadequacy of the models in representing real magnetospheric conditions during disturbances. In particular, the character of field lines in the nightside magnetosphere can change drastically as a result of the emergence of the current wedge. Figure 4 shows magnetic field structure on February 6, 1994, based on TsygaMODEL

1o I

07 Fob 1994

MLT = 22.6

2

:::::::::::::::::::::::::::::

...... .;":·0;·t·

R.

nenko's [1997]modelfor the sameUT as Figure3. Field
lines were modeled allowingfor the magneticfield of the current wedge with an integrated current magnitude of
-IC
Z.R,· T$¾GRNENKO"$ MODEL

a)

106 A, initial radiusof the currentloop r0 - 4.85Re,
and ratio between r0 and the radius of the current loop during the substorm rs equal to 0.2. It follows from Figure 4 that the whole electrojet maps to the tail in

07
10

Fob

1994

liLT

= 23.1

the closed magnetic fieldline region _<16Regeocenat

5

,-"' --·-' · ....... ú. · ,·- ..... --·-,-w-....-·=

tric distance. Even the field line with footprint at 770 ........ ,'0""";""·0"";";";;"·0""""""";"·0 .... '" ";'·;·'· is closed, although it maps into the tail out to 68R·. Thus, the emergenceof a current wedge during disturbances allows us to interpret the observed conjugacy -]o b) of geomagnetic disturbances up to very high latitudes in the framework of existing magnetosphericmagnetic Figure 5. Magneticfield line structureon February7,

',·" '·

_:.==.====.==.= ··

field

models.

The dynamics of the magnetic field line mapping of the westward electrojet boundaries and center during

1994,basedon Tsy#anenko's [1997]model,taking into account emergence the currentwedge (a) 1940 the of at UT, rs = 6.2R·; (b) 2005 UT, rs = 25Re


3086

FELDSTEIN

ET AL.: CONJUGACY

OF GEOMAGNETIC

DISTURBANCES

Suchprecipitation structuresand the method of identifying the boundariesof different plasma domainshave beenstudiedby Galperinand Feldstein [1991,1996]and Newell et al. [1996].

Feldstein, Ya. I., P. T. Newell, I. SandaM, J. Woch, S. V. Leontjev and V. G. Vorobjev, Structure of auroral precipitation during a theta-aurora from multi-satellite observations, J. Geophys. Res., 100, 17,429-17,442, 1995. Galperin, Yu. I. and Ya. I. Feldstein, Auroral luminosity and its relationship to magnetospheric plasma domains, Conclusions in Auroral Physics, edited by C.-I. Meng, M. J. Rycroft, and L. A. Frank, pp. 207-222, Cambridge Univ. Press, 1. The character and the intensity of geomagnetic New York, 1991. variationsat the poleward boundary of the auroral ovals Galperin, Yu. I. and Ya. I. Feldstein, Mapping of the prein the northern and southern hemispheresare similar. cipitation region to the plasma sheet, J. Geomagn. Geo2. This similarity suggeststhat magnetic field lines electr., ·8, N5-6, 857-875, 1996. are closedat these high latitudes. However, according Makita, K., C.-I. Meng and S.-I. Akasofu, Transpolar auro-

to the contemporarymodelsof magnetospheric magnet-

ras, their particle precipitation, and IMF By component,
J. Geophys. Res., 96, 14,085-14,095, 1991. Meng, C.-I., Polar cap arcs and the plasma sheet, Geophys.
Res. Left., 8, 273-276, 1981.

ic fieldsby Tsyganenko [1995] and Ale·eevet al. [1996],
the magneticfield lines mapping from these high latitudes are open.

3. Magneticfield linesin the nightsidemagnetosphere Mizera, P. F., D. J. Gorney, and D. S. Evans, On the conjugacy of the aurora: high and low latitudes, Geophys. Res. can become closed up to very high geomagneticlat-

itudes, if the emergence the current wedgeduring of
disturbancesis taken into account using the model of

Left., 1·, 190-193, 1987. Newell, P. T., Ya. I. Feldstein, Yu. I. Galperin, and C.-I.

Tsyganenko [1997].
Acknowledgments. This work has been supportedby grantsRFBR 96-05-65067and 96-05-66279, INTAS- RFBR95-0932. We are thankful to T. Lui for discussions of the

Meng,Morphology nightside of precipitation, Geophys. J.
Res., 101, 10,737-10,748; correction, 17,419-17,421, 1996. Obara, T., M. Kitayama, T. Mukai, N. IKaya, J. S. Murphree, and L. L. Cogger, Simultaneous observations of Sun-alignedpolar cap arcsin both hemispheres EXOSby C and Viking, Geophys. Res. Left., 15, 713-716, 1988. Tsyganenko, N. A., Modeling the Earth's magnetospheric ·nagnetic field confined within a realistic magnetopause, J. Geophys. Res., 100, 5599-5612, 1995. Tsyganenko, N. A., An empirical model of the substorm current wedge, J. Geophys. Res., 1012, 19,935-19,941, 1997. Vorobjev, V. G., S. V. Leontyev, and Ya. I. Feldstein, Extended period of polar cap auroral display: auroral dynamics and relation to the IMF and the ionospheric convection, Ann. Geophys., 13, 854-862, 1995. Y. I. Feldstein, L. I. Grinnova and A. E. Levitin,

problem of closedmagnetic field lines, N. Tsyganenkofor current wedge software, V. Papitashvili for sharing data
from the stations Komsomolskaya and Mirny, and DMI for Nord station data. We appreciate very much fruitful discussionswith H. Luehr. We are grateful to the IMAGE

magnetometer chain teams. We are very thankful to the
volunteer copyeditor Dr. J. Rodriguez.

References

Akasofu,S.-I., Polar and magnetospheric substorms, ReiD.
del Publ. Comp., Dordrecht, 1968. Alexeev, I. I., E. S. Belenkaya, V. V. K alegaev, Ya. I. Feld-

IZMIRAN, 142092Troitsk, Moscow region,Russia. (e-mMl: lgromova@iz an.troit sk.ru) mir
A. Grafe, GeoResearch Center, D-14482 Potsdam,

stein, and A. Grafe, Magnetic storms and magnetotail
currents, J. Geophys. Res., 101, 7737-7747, 1996.

Germany.(c-mail: grafe@gfz-potsdam.de)

Craven, J. D., J. S. Murphree, L. A. Frank, and L. L. (Jogger, Simultaneous optical observations transpolar arcsin the (Received March 22, 1998: revised June 01, 1998; of two polar caps, Geophys. Res. Left., 18, 2297-2300, 1991. acceptedJune 05, 1998.)