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Global convection electric field and current : Comparisons between model’s predictions and data from STARE, SAINT-SANTIN and magnetometers C. Mazaudier, C. Senior, E. Nielsen To cite this version: C. Mazaudier, C. Senior, E. Nielsen. Global convection electric field and current : Comparisons between model’s predictions and data from STARE, SAINT-SANTIN and magnetometers. Journal of Geophysical Research, American Geophysical Union, 1987, 92 (A6), pp.5991-5999. HAL Id: hal-00976880 http://hal.upmc.fr/hal-00976880 Submitted on 10 Apr 2014 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. JOURNAL OF GEOPHYSICAL Global RESEARCH, Convection VOL. 92, NO. A6, PAGES 5991-5999, JUNE Electric Field 1, 1987 and Current: Comparisons Between Model's Predictions and Data From STARE, Saint-Santin, and Magnetometers C. MAZAUDIER AND C. SENIOR Centre de Recherchesen Physique de l'Environnement,St.-Maur des Fosses,France E. NIELSEN Max-Planck lnstitut fiir Aeronomie,Katlenburg-Lindau, Federal Republic of Germany Ionospheric electric field and ground magnetic field measurementsat high, middle and low latitudes are used to study the global pattern of the convectionelectricfield on March 26, 1979. The IMF B: component was southward and relatively steady over a prolonged period of time. The data set is thus representativeof a steady magnetosphericconvection. A semi-analytical time-dependent convection model is used to interpret the observations.During the daytime the model steady state results roughly reproduces the mean observed convection pattern. Fluctuations of the observed electric field from the model predictionsare interpretedas resultingfrom (1) the transientresponsesof the ionosphereto small time variations of the IMF, (2) substorm effects,(3) neutral wind disturbances.Only the first type of fluctuationscan be reproducedby the initial stateprediction of the convectionmodel. 1. made by both coherentand incoherentradars [Brekke et al., INTRODUCTION Axford and Hines [1961] and Dungey [1961] first suggested that solar wind/magnetosphereviscousinteraction and magnetic reconnection transfer solar wind energy and momentum to the magnetosphereand ionosphere.This coupling createsa large-scalecirculation of the magnetosphericplasma (current convection cells). Since then, it has gradually been recognized that the ionospherealso plays an important role in determining this plasma flow. Different methods have been developed to study the ionosphericelectriccurrent and field generatedby the solar wind-magnetosphereinteractions. First, the observations of the ground magnetic variations 1974; Zi and Nielsen, 1981, 1982; Mazaudier et al., 1984]. Third, theseobservationswere interpretedby usingtheoretical models which considered the effects on the electric field distribution of ionosphericconductivities,ring current and interplanetary magneticfield (IMF). The influenceof the magnetosphericring current on the ionosphericelectric field was investigated in analytical studies [Vasyliunas, 1970; 1972; Pellat and Laval, 1972; Southwood and Wolf, 1977] semianalytical studies [Senior and Blanc, 1984], and numerical methods [Jaggi and Wolf, 1973; Hard et al., 1981a, b; Spiro et al., 1981; Wolf et al., 1982; Chen et al., 1982; Spiro and Wolf, ledto theestablishment of theSqpandDPe equivalent current 1984]. systems[Na•lata and Kokubun, 1962; Nishida, 1968]. Both current systemsare composedof two cells.They differ only in their latitudinalextension:the Sq• currentsystemremains To progressfurther in the experimentaldeterminationof the global convection patterns, multi-instrument studies are essential. We have made observations of convection electric confined at high latitudes, while the DP e one extendsto low fieldsby meansof coherentand incoherentradars (Scandinalatitudes. Nishida was the first to interpret these current sys- vian twin auroral radar experiment(STARE) and Saint-Santin tems as having their origin in the interaction betweenthe solar radars), and equivalent current systems(Troms/5 magnetometer), and comparedtheseobservationswith model predictions wind and the magnetosphere. in order to understand the solar wind, magnetosphere,and Second,observationsof the ionosphericelectric fields led to ionosphere interactions. the recognitionthat the convectionelectricfieldsgeneratedby In a companionpaper, Mazaudier et al. [1984] carried out the solar wind/magnetospheredynamo penetrate to middle and low latitudes. This is contrary to an earlier belief that the an analysisof this kind, using magnetic and radar observaonly ionosphericregion fed by the energy available at the tions together with convectionmodel predictions.This first solar wind/magnetosphereinterfaceis the auroral zone. Inco- study investigatedthe transient responseof ionosphericelecherent scatter radars have played an essentialrole in the ob- tric fields to an increaseof magnetosphericconvectiondue to servations of these fields at the equator [Fejer et al., 1979; a sudden southward turning of the IMF B: component.The Gonzales et al., 1979; Kelley et al., 1979], at midlatitudes present paper is concernedwith steady state convection,i.e., [Wand and Evans, 1981; Blanc, 1983a, b] and at both lo- with the global convection pattern observed during a procations simultaneously[Gonzaleset al., 1983]. At high lati- longed period of southwarddirectedIMF B•. We presentobtudes, in the auroral oval, important contributions have been servations made during an 18-hour period during which the Copyright 1987 by the American GeophysicalUnion. Paper number 6A8600. 0148-0227/87/006A-8600505.00 IMF was southward and showedsmall magnitude fluctuations in time. In the following section, we present the geomagnetic conditions characterizing this time interval. We then relate electricfield and magneticobservationsat high, middle, and low latitudes to the Senior and Blanc [1984] model predic5991 5992 MAZAUDIER ET AL,' GLOBAL CONVECTION ELECTRIC FIELD AND CURRENT 0 6 12 18 2t, UT TIME 0 The total crosspolar cap potential drop •o and the local time of the maximum potential at the polar cap boundary are taken, respectively,as 70 kV and 0400 LT for the simulation. These values are chosento fit the best the high latitude data Bz (IMF) from the STARE DST -S0 (b) formularelatingthe IMF B• componentto •o givenby Re/ff +500 AU o (c) AL -500 330 et al. [1985]. 3.1. High Latitudes H Component (d) (Y) ! Tromsi• (69øN) 0 6 12 18 radar. The value of 70 kV is smaller than the estimation of ~ 110 kV that is calculated from the empirical 2t• UT TIME Fig. 1. The four panels outline the magnetic activity on March 26, 1979. (a) Bz componentof the IMF measuredby the IMP 8 satellite; (b) equatorial magnetic Dst index; (c) AU and AL auroral magnetic indices; (d) H component of the ground magnetic field at Troms6. Figure 2 showsa polar plot of the E x B drift as measured by the STARE coherent radar system,[Nielsen and Whitehead, 1983; Nielsen and Schlegel,1983, 1985]. It illustratesthe typicalconvectionpattern at high latitude,with westwardion drift in the afternoon sector and eastward in the morning sector. Two reversals of the drift occur around tions. This linear time-dependentmodel estimateselectricfield due to the sole physicalprocessof direct penetrationof magnetosphericconvection. 2. GEOMAGNETICCONDITIONSON MARCH 26, 1979 March 26, 1979,is a magneticallydisturbedday (ZKp - 31, ZKn- 27). The amplitude of the IMF as measured by the IMP-8 satellite (located near the magnetopausein the solar wind) is quasi steadyduring the entire day (around 20 nT); the 2100 and 2200 MLT (1930 and 2030 UT). Around 1200 MLT (1030 UT), the amplitudeof the auroral electricfield was probably smaller than 15 mV/m, the thresholdat which the STARE radar can measure electric fields. The convection pattern observedon March 26, 1979, correspondsto the average convectionpattern obtainedby Zi and Nielsen[1982]. In Figure 3 we have superimposedthe STARE southward electric field measured at the latitude of 69øN extracted from the Figure 2 and the B• componentof the interplanetarymagnetic field. There is some correlation between the maxima of Bycomponent remainspositive(around18 nT). The Bz com- the electricfield and the southward intensificationof the B• ponent, shown in the first panel of Figure 1, is negative centered around the mean value of -3 nT from 0000 to 1800 UT. After 1800 UT, its magnitude decreasesand Bz turns northward at about 2230 UT. The Dst index (Figure lb) shows two major negative excursions at 1200 and nT. The 1800 A U and AL UT. auroral This index indices remains are shown below -25 in the third panel. These curvesreveal sustainedactivity during the entire day with two clear substorm onsetsshown with arrows. The most intense substorm begins around 1700 UT with a maximum AL of about 1200 y at 1800 UT. At 2230 UT, when the IMF turns northward, the auroral activity stops.In the European sector, the Troms6 H component (Figure ld) remains undisturbed from 0500 to 1100 UT, while the Dst is quasi steady.From 0000 to 0500 UT, the Troms6 station is under the westward electrojet, and from 1200 to 1700 UT under the component.This suggeststhat variationsof the B• component of the IMF is an important parameter governing the ionosphericelectricfields. On Figure 4 we superimposedthe diurnal variation of the H componentof the ground-magneticperturbationfor March 26, 1979, at Troms/5(samedata as Figure ld) and the averaged Sd variation of H over Troms/5 obtained by Mayaud [1965]. The averaged Sd variation is the mean value of the five most disturbeddays (following the Kp index) of each month. This Sd curve givesthe magneticvariation that would be observed by a station if it were rotating under a systemof two convection current cells of fixed intensity and location. Hence the 65 eastward one. At the time of the 1700 UT substorm, the Troms6 H trace shows westward directed currents for a short period, before being again dominated by the eastward electrojet. From 2030 to 2230 UT Troms6 moves back into the westward electrojet. At 2200 UT, the auroral activity at Troms6 ends. 3. OBSERVATIONS AND RESULTS In this section, we present separately the IMF measurements in the solar wind, and the electric field at high, middle and low latitudes and we compare some of these data to the outputs of the convection model of Senior and Blanc [1984]. The logic and main assumptionsof this model are describedin the appendix. Briefly, it calculates the time-dependent responseof the ionosphere to a step function of the convection source,i.e., the crosspolar cap potential •o. The electricfield pattern has been shown to reach a steady state after 30-60 min. Thus for steady interplanetary conditionssuch as those prevailing on March 26, 1979, we compare the data to the model outputs at steadystate. 18I[ 6 ß •;'_'- "-< 5: 0 (MLT) 22.30 (UT) Fig. 2. Polar plot of the ion drift observed at high latitudes by the STARE radar, in an MLT-invariant latitude coordinate system. MAZAUDIER ET AL.' GLOBAL CONVECTION ELECTRIC FIELD AND CURRENT 5993 uT Fig. 3. Southwardcomponentof the STARE electricfield and B: componentof the IMF. The southward/northward electricfieldintensifications in theauroralzonearegenerallyassociated with southward increases of differencebetweenthe two curveson Figure 4 can be interpreted as due to variations in intensity and/or location of the current cells. The best agreement between the two curves is obtained on the dayside between 0500 and 1800 UT. It shows that during that time interval, the European sector moves under a steady convection pattern. Before 0700 UT and after 1700 UT the H component at Troms/3 fluctuates and reaches maxima which correspondin generalto the averagedSd value except during the main substormaround 1800 UT. According to Chapman and Bartels [1940] the variation of the ground magnetic field is related to the height-integrated ionosphericcurrent densityby IABI = f. JI 12" (la) for an infinite current sheetabove a plane earth. In expression(la), B is in 7, J is in amperesper kilometer, andf is equal to 0.6 [Kamide and Brekke, 1975]. An horizontal ionosphericeastwardJy currentinducesa variationin the horizontal component of the magnetic field AH _• Jy (lb) Following Ohm's law, and assuminghomogeneousconductivity [see Wilkinsonet al., 1986] the eastwardcurrent density is related to the ionosphericelectricfield by J• -• Z.E x (2) where Z n is the height-integratedHall conductivity,E•, is the northward electricfield in the plane perpendicularto the magnetic field. From expressions(lb) and (2) we can derive AH -• Zn,, (3) Figure 5 illustrates the relation between the ground magnetic perturbation and the southward electric field. In this figure the STARE southward electric field measured in the region over Troms/3 is superimposedon the H component at 106 I I I _h,• . i I% I I •/ I II I 0 1 2 3/ Ir•A 5/ 6.'' 7 8 9 10 11 12 13 16 '5 16 17 t',8 q',19' 20 •1 22 • f :..... (-..., • I I I II uT.Time , Fig. 4. The H componentof the ground magnetic field obserwd at Troms6 on March 26, 1979 (solid li•), is superimposed on the mean Savalue of the H componentestimatedby Mayaud [1965] (dashedline).This Sd variationis the mea• valueowr a solarcycleof the fiw most magneticallydisturbeddaysof eachmonth. 5994 MAZAUDIER ET AL.: GLOBAL CONVECTION ELECTRIC FIELD AND CURRENT Fig. 5. The southwardSTARE electricfield and ground magneticH componentat Troms• are superimposed. A good correlation is found between the southward/northward intensificationsof the electric field and the northward/southward increasesof the magnetic field, exceptduring the 1800-2000 UT substormevent. Troms/5.A very good agreementbetweenthe variations of AH ponent. Its amplitude has been chosen as 70 kV, with a maxiand E,, is found except from 1700 to 2000 UT, during the mum at 0400 LT. substorm event. The ratio between the H component and the The auroral conductivityhas beenselectedby comparing southward electric field gives an estimate for the height- the Troms/5H componentand the northward STARE electric integrated Hall ionospheric conductivity in the auroral zone. field.In Figure6a the modelsouthwardelectricfield is superFor this data set the Hall conductivity varies between 5 and imposedon our STARE data. The modelreproducesthe mean 12 mhos. These two extremas have been selected for simula- tions. diurnal variation observedexceptduring the 1800 UT substorm event. The model obviously does not reproduce the The convection model of Senior and Blanc [1984], which fluctuations of the electricfieldrelatedto the Bz fluctuations. considersthe direct penetration of convection to midlatitudes This is because we consider the convection electric field to be (seethe appendix), has been used to determine the steady state inducedby a steadypotential drop over the polar cap. The ionospheric electric field. The two simulations developed in agreement between model predictions and data for the eastthis study are describedin Table 1. Some of the input parame- ward componentof the electricfieldis ratherpoor (Figure6b). ters have been derived from our observations. The electric This is in fact not very surprisingsincethis componentis potential •0 along the polar cap/auroralzone boundaryhas knownto be veryweakand to showlittle systematic magnetic been adjusted to fit the STARE northward electric field com- activity dependenceI-Seniorand Blanc, 1984; Mazaudier et al., TABLE 1. Inputs of the ConvectionModel for the Two Simulations S 1 and S2 S1 Latitudinal Range S2 CrossPolar Cap Potential j. = 72 ø •o = 70 kV* •o = 70 kV* Conductivities Auroral zone 67 ø _< J. _< 72 ø Subauroral zone 64 ø _< 2 _< 67 ø Midlatitudes 10 o _</• _< 64 ø Z n = 12 mhos Zn/Ze = 2 Ea = 5 mhos ZH/Z P '-' 2 mhos 1.6 Z n - 5 mhos Y•n/Y•v= 1.6 daytimeZn = Z•ø(Bo/B)cosX nighttime•n = (•nø/(30)(Bo/B) •n/•v = 1.7 Equatorial region 2 _< 10 o equatorialnoontimeconductance SO So=3.83 x 108f•m same local time dependence as midlatitude *Maximum at 0400 LT. conductivities same as S 1 same as S 1 MAZAUDIER ET AL.' GLOBAL CONVECTION ELECTRIC FIELD AND CURRENT 60 1• •o: 70kV Hmax =0400LT Stare (X =68 ø) Simulation E 5995 / I I-"•-Stare data ---- , , - 20- , 1 Simulation 2 , , .. . , • model. • 40 • -60 - Fig. 6a. The southwardcomponentof the STARE electricfield on March 26, 1979 (solid line), is superimposedon the southward convection electric field obtained from two distincts numerical simulations of the Senior and Blanc [1984] model. The model predictionscorrespondto the steady state of magnetosphericconvection. 1984]. It is interesting to note that the model steady state convectionelectric field (Figure 6a) is fairly well related to the Sd variation of the H componentat Tromsb (Figure 4, dashed line). The Sd variations,like the electricfield model one, are nisms by case studies. Mazaudier et al. [1985] developed an analysis of dynamo region neutral wind disturbancesat SaintSantin generated by storm Joule heating. These papers smoothed. tion is frequently observed on the dayside at midlatitudes. By contrast the ionospheric disturbance dynamo processesdevelop less frequently on the dayside in the midlatitude dynamo region. On March 26, 1979, the neutral wind analysis was performed at Saint-Santin in the F region during the night, and in the E region during the day, when the incoherent scatter signal was strong enough. The data reveal strong neutral wind disturbances at F region altitudes on the morningside from 0000 to 0700 UT. Remembering these points we can comment on Figures 7a and 7b. On these figures we superimpose the southward (Figure 7a) and eastward (Figure 7b) electric field model and Saint-Santin data. The data represent the disturbed electric field obtained by subtracting from the observations the magneticallyquiet-time electric field model as defined by Blanc and Amayenc [1979]. On the dayside from 0700 UT to 1700 UT (local time and universal time are the same at Saint- showedthat the direct penetrationof magnetosphericconvec- The steadystate model reproducesthe $d amplitude of the H componentat Tromsb if we assumean enhancedHall conductivity auroral ring of 10-12 mhos, uniform in longitude within the auroral zone. This indicates that simulation 2 is closer to the actual data than simulation 1 (seeTable 1). 3.2. Middle Latitudes At middle latitudes, electric field disturbancesare produced by various physical mechanisms.Two of thesemechanismsare particularly important: (1) the penetration of convection electric fields to subauroral latitudes during periods of slow change in the solar wind dynamo (our interest in this paper); (2) changesin global thermosphericcirculation produced by storm-time Joule heating affecting the ionospheric wind dynamo [Blanc and Richmond,1980]. Mazaudier [1985] has recently illustrated this two mechaq'o= 70kV Stare {X =68• ) Hmox: 0400LT ----- Simulation 1 S•mulation 2 E 20 ___•_Steady states ofthe convection model • o • • •i I i I I I II I • I •:20 • _ Fig. 6b. Similar to Figure 3b for the eastwardcomponentof the auroral electricfield. 5996 MAZAUDIER ET AL.' GLOBAL CONVECTION ELECTRIC FIELD AND CURRENT % = 70 kV Hmax= 0400 LT Saint-Santin( X =/,/.,*) Simulation 1 -----Simulation 2 . Santin data / I i •9 / •• I , I I [ i • , , , • I J [ J • / LT. hours ........ --, Ls ready st •o= 70kV Saint- Santin ( X = 44* ) Hmax=0400LT ----• Simulation 1 Simulation 2 2 Fig. 7. Our two convectionsteadystatemodelpredictionsare superimposed on the (a) southwardand (b) eastward components of the disturbedelectricfield at Saint-Santin.The disturbedfield is obtainedby subtractingthe quiet time variation definedby Blancand Arnayenc[1979] from the observations. Santin), the steady state convection model give a rough estimate of the southward electric field variation observed on sentsthe usual equatorial electrojet of the quiet ionospheric dynamo.Following Akasofuand Chapman[1961] the ground magneticvariation can be expressedby March 26, 1979. The same agreement is obtained for the eastward component (Figure 7b) on the dayside.It should be noAH = DR + DP + DCF + D T (4a) ticed however that, for midlatitudes, the convection model predicts similar convectionpatterns on the dayside at the ini- in this expressionDR, DP, DCF, and D T correspondto ring, tial and steady states. On the nightside strong discrepancies ionospheric,magnetopause and tail currents,respectively. are observed between model and data for both components. On both March 21 and 26, due to the fact that there is no Those occurring on the morningside (from 0000 to 0700 UT) magnetic storm, the equatorial variation reduced to [Fukucan be attributed to neutral wind disturbances. Those ocshimaand Kamide, 1973] curring on the eveningside(after 1700 UT) can be explained AH = DR + DP (4b) by, the substorm that affects the Troms6 area from 1800 to 2000 UT, and by the northward turning of Bz around 2230 The symmetricpart of the DR field is approximatedby Dst UT, both effects that are not taken into account in the model. cos 2, where Dst is the magnetic equatorial index and 2 the latitude 3.3. Equatorial Latitudes of the station. To emphasize the DP disturbance on March 26, 1979, it is Figure 8a is composed of two panels, the upper one for Addis-Ababa (geographic latitude 9.03øN, geographic lon- necessaryto have a quiet referencefor the ionosphericDP current system.This referenceis representedby the circled gitude 38ø77E, LT -• UT + 3) and the bottom one for Huan- crosseson Figure 8a. It is obtainedby subtractingthe DR field cayo (12.05øS,284ø67E, LT • UT- 5). On these two panels (DR -- Dst cos 2) from the H componentof the ground magwe have superimposed the H component of the terrestrial netic variations of the quiet referenceday (March 21). Theremagnetic field on March 26, 1979 (dashed line), and the same fore, the differencebetweenthe H componentof ground magcomponent observed on March 21, 1979; March 21 was a netic field on March magneticallyquiet day, that we use as a reference.It repre- the ionosphericDP disturbanceon that day. 26 and the circled crosses is a measure of MAZAUDIER ET AL..' GLOBAL CONVECTION ELECTRIC FIELD AND CURRENT 90J;[ 3 6 FHorch, 21 1979 quiet reference doy 9 12 5o• [ 0 ] 5997 15 ADDIS- 18 ABABA .- 21 ......... CQ•_ ._•D_. ?_-•, 2•, UT.Time • 3 LT.Time HUANCAYO ,,-";• ,,'• 6 9 LT "ø UT 5 •. .............. 12 ./J',; • '• © x('5•xxrch 21,1979 lB _!,._A •© •)._ . )1-•.• V. UT. Time 12 - 1/+ ",," '•"•.....1•. LTTime North 26, 1979-1 Fig. 8a. Ground magnetic H component on March 26, 1979 (dashed lines), and March 21, 1979 (solid line) at Addis-Ababa (upper panel) and Huancayo (lower panel). March 21, 1979, is a magnetically quiet day used as a reference level. On the two panelsthe crossesrepresentthe quiet day observationscorrectedfor the Dst variations on March 21 and 26, 1979. At Addis-Ababa, the equatorial DP disturbance on the dayside observed on March 26, 1979, is southward, and corresponds to a westward equivalent current. It occurs from 1100 to 1500 LT (0800 to 1200 UT). At Huancayo the equatorial DP disturbancefluctuates and showsstrong eastward intensifications of the electrojet from 0700 to 1300 LT (1200 to 1800 UT). In Figure 8b the northward component of the Stare electric of neutral wind disturbanceson the nightside until 0700 UT. It is thus possible that these disturbances propagate southeastward toward It is clear that the northward intensifications of the auroral southwardincreasesof Bz and are the signatureof the DP2 equivalent current system. The convection model of Senior and Blanc [1984] which includesa rough description of the electrojet region through its low-latitude boundary condition (see appendix and Table 1), predicts the total equatorial currents at initial state and steady state (see Figure 9). On the dayside, at the initial state, the total electrojet increaseis eastward. This variation is similar to the H component fluctuations observed at Huancayo. The total current in the equatorial electrojet was estimated from the Huancayo data by assumingthe jet to be 10ø latitude wide in the northern hemisphereas in the model, and to have uniform electric current density of 100 A/km (100 nT from Figure 8b). The total current in the equatorial electrojet is then 100 kA; this order of magnitude correspondsto the initial state model predictions. At Addis-Ababa (Figure 8a upper panel), the daytime electrojet disturbance is westward with an intensity of about 100 kA. This is not in good agreementwith the predictions of the convectionmodel. It is thereforeprobablethat another mechanism operateslocally at Addis-Ababa. In fact, Blanc and Richmond [1980] have shown that the ionospheric disturbance dynamo has a negativeeffect on the equatorial electrojet,ie a westward increaseof the current during the daytime. Study of the F region neutral winds at Saint-Santin reveal the presence with a time constant of several hours, characteristicof the ionosphericdynamo process.The result would be westward electrojet disturbanceas observedat Addis-Ababa. Huancayo which is located west of Saint-Santin, would not seetheseperturbations. 4. field and the DP disturbanceat Huancayo are superimposed. zone electric field correspondto the eastward equatorial electrojet intensifications.These fluctuationsare also associatedto Addis-Ababa DISCUSSION AND CONCLUSION In this paper we have combined magnetic data with coherent and incoherentradar data, and comparethesedata to the predictions of a convection model. This enables us to analyze quantitatively the large-scaleconvection electric field pattern on March 26, 1979. On this particular day, (1) the IMF Bz component was southward and rel.atively steady over a prolonged period of time from 0000 to 1900 UT, (2) there was no neutral wind disturbance at midlatitudes in the dynamo region from 0700 to 1800 UT. This made it possible to study the prolonged action of the magnetosphericconvectionprocessfrom 0700 to 1800 UT. The convection model of Senior and Blanc [1984] was used to calculate the ionosphericelectric field. The steady state model prediction was used to establishthe mean diurnal variation of the electric field due to the mechanism of direct penetration of magnetosphericconvection. 12 15 , electrojet d•s • v 18 UT " IJ •electric •/-•---northword store field mc•rch26,1979 Fig. 8b. Comparisonbetweenthe DP intensificationof the equatorial electrojet and the northward STARE electric field. 5998 MAZAUDIERET AL.' GLOBALCONVECTIONELECTRICFIELD AND CURRENT EqUQfOrIQI perfurbQfion APPENDIX' DESCRIPTION OF THE SENIORAND BLANC [1984] MODEL 100 / • - SfeQdy sfQfe -• • so i/I \\\ This linear time-dependentand self-consistentmodel calcu- lates the responseof the magnetosphere ionospherecircuit to a stepfunctionof the source,i.e., the crosspolar cap potential. It takesinto accountthe latitudinal and longitudinalgradients of the midlatitudeionosphericconductivitiescreatedby solar radiations. O0 Or, 08 12 16 Locol Time_ hours 20 Fig. 9. Localtime response of the total equatorialelectrojetcurrent predictedby the convectionmodelfor the initial (dashedline) and steady state (solid line) of magnetosphericconvectionevent [Seniorand Blanc, 1984,Figure 17]. This model keeps the simplicity (and also indeed the limitations) of its linearity and has freely adjustablevaluesof the high latitude conductivities.The conductivityin the auroral zone is simulatedwith two uniform conductivityrings' the auroral zone from colatitudes0o to 02 and a subauroralzone from 02 to 0•. For 0 greaterthan 0• (middleand low latitudes) the integratedPedersenconductivityvariesduring the daytime as This paper showsthat on the daysidethe steadystateof the Senior and Blanc convectionmodel givesa rough estimateof the ionosphericconvectionpattern in the latitude range from the auroral zone to midlatitude. Bo Zv= Zvøcos Z-•where Z is the solar zenith angle, B is the local value of the magnetic field,B0 and•,o arethe valuesof theequatorial At auroral latitudes, the main diurnal variation of the magnetic field and conductivity at local noon. During the southwardSTARE electricfield is roughly reproducedby the night the midlatitude conductivities are small and uniform in steadystatemodelas well as the Sd variationof the H compo- local time' nent observedat Tromsb [Mayaud, 1965]. E•øB0 E•-30 B The southward/northward observed electric field intensi- fications,usuallyassociated with southwardBz increases, are not reproducedby the steadystatemodel.They wereinterpreted as due to transient responsesof the ionosphereto the southward Bz fluctuationsand reproducedby initial state of The subsolar Pedersen conductance has been taken as 20 northward time variations as the midlatitude Mhos and a smoothtransition betweenthe day and night values,modeledas a parabolicfunctionof Z, is imposedon the the convection model. dawn and dusksectorsover 20ø of the parameter.Finally, the At middle latitudes,the daytime variations of the two elec- midlatitude Hall to Pedersenconductivityratio is 1.7 and the tric field componentsare well reproducedby the convection magnetic field is dipolaf with an equatorial value of 0.28 x 10 -'• T. model, both the initial and steady statesof the model (which The equatorial electrojetregion is included in the model as are closeto each other on the dayside). At Huancayo, closeto the equator, the H componentof the a boundarycondition.It is a small conductingring though ground magneticfield showedstrongeastwardintensifications which the meridional currentsclose.The equatorial conducof the equatorial electrojet associatedwith increasesof the tance is 3.83 x 108 mho m at noon and has the same local STARE auroral electric field. These observations conductivities. The inner boundary of the equatorial ring current is as- were not reproducedby the steadystate model, which predicts a small westward electrojet intensification associated with northward electric field penetration as due to the transient sentsthe equatorial boundary of the auroral zone. The model response of the ionosphere (initial statemodel)to the IMF B• yields self-consistent variationsof the inner boundaryin the sumedto map dawnon the circleof colatitude0• whichrepre- fluctuations(•o crosspolar cap potential). The discrepancies magnetosphericequatorial plane and of the LT distribution of Birkelandcurrentsgeneratedalongthis boundary.The colatibetween convection model and data at Addis-Ababa has been tudes 0o and 02 and conductivitiesin each zone are free painterpreted as a local effectdue to the ionosphericdisturbance rametersof the model and can be adjustedto fit the observadynamo process. A previouscompanionpaper [Mazaudier et al., 1984] illustrated the initial state of convectionelectricfield inducedby rapid changein the solar wind magnetosphere dynamo (southward turningsof B0. This paper showedthat even during a tions. Acknowledgments. The STARE radar systemis operatedby the Max-Planck-Institut ffir Aeronomiein cooperationwith ELAB, the Universityof Trondhum,Norway,and the FinnishMeteorological time of prolongedsouthwardIMF B•, as on March 26, 1979, Institute in Helsinki, Finland. The extensionof the CNET (Centre incoherentscatterfacility it is difficultto find a perfectsteadystateof ionosphericcon- Nationald'EtudesdesT616communications) vection electricfield in the whole ionosphere.Rather, the data can be analyzed in terms of a mean diurnal variation correspondingto the steadystate model, and of short-termfluctu- ationsproducedby transientchangesof the sourcepotential due to IMF variations. It seems therefore that a linear model to a quadristatic configuration was supported by the Institut d'Astronomieet de G6ophysiqueand by the Direction desRecherches et Moyens d'Essais.The facility is operatedwith financial support fromtheCentreNationaldela Recherche Scientifique. The Editor thanks M. Harel and J. M. Holt for their assistancein evaluating this paper. of the convectionprocessis sufficientto interpret quantitatively the electric field observationswhen there is no substorm or neutral wind disturbanceoperating simultaneouslyto the convection process. REFERENCES Akasofu,S.-I.,andS.Chapman,A neutrallinedischarge theoryof the aurora Polaris,Philos.Trans.R. Soc.London,Set. A, 253, 359-406, 1961. MAZAUDIER ET AL.: GLOBAL CONVECTION ELECTRIC FIELD AND CURRENT Axford, W. I., and C. O. Hines, A unifying theory of high latitudes geophysicalphenomenaand geomagneticstorms, Can. J. Phys., 39, 1433, 1961. Blanc, M., Magnetospheric convection effects at midlatitudes, 1, Saint-Santin observations,J. Geophys.Res.,88, 211, 1983a. Blanc, M., Magnetospheric convection effectsat midlatitudes, 3, Theoretical deviation of the disturbance convection in the plasmasphere,J. Geophys.Res.,88, 235, 1983b. Blanc, M., and P. Amayenc, Seasonal variations of the ionospheric E x B drifts, J. Geophys.Res.,84, 2691, 1979. Blanc, M., and A. Richmond, The ionosphericdisturbance dynamo, J. Geophys.Res.,85, 1669, 1980. Brekke, A., J. R. Doupnik, and P.M. Banks, Incoherent scatter measurementsof E region conductivities and currents in the auroral zone, J. Geophys.Res., 79, 3773, 1974. Chapman, S., and J. Bartels, Geomagnetism, Oxford University Press, New York, 1940. Chen, C. K., R. A. Wolf, M. Harel, and J. L. Karty, Theoretical magnetogramsbased on quantitative simulation of magnetic substorm, J. Geophys.Res.,87, 6137, 1982. Dungey, T. W., Interplanetary magnetic field and the auroral zones, Phys. Rev. Lett., 6, 47, 1961. Fejer, B. G., C. A. Gonzales, D. T. Farley, M. C. Kelley, and R. F. Woodman, Equatorial electric field during magnetically disturbed conditions, 1, The effect of the interplanetary magnetic fields, J. Geophys.Res., 84, 5797, 1979. Fukushima, N., and Y. Kamide, Partial ring current models for worldwide geomagnetic disturbances, Rev. Geophys., 11, 4, 795, 1973. Gonzales, G. A., M. C. Kelley, G. C. Fejer, J. F. Vickrey, and R. F. Woodman, Equatorial electric fields during magnetically disturbed conditions,2, Implications of simultaneousauroral and the equatorial measurements,J. Geophys.Res.,84, 5803-5812, 1979. Gonzales, C. A., M. C. Kelley, R. A. Behnke, J. F. Vickrey, R. Wand, and J. Holt, On the latitudinal variations of the ionosphericelectric field during magnetospheredisturbances,J. Geophys.Res.,88, 9135, 1983. Harel, M., R. A. Wolf, P. H. Reiff, R. W. Spiro, W. J. Burks, F. J. Rich, and M. Smiddy, Quantitative simulation of a magnetospheric substorm, 1. Model logic and overview, J. Geophys.Res., 86, 2217, 1981a. Harel, M., R. A. Wolf, R. W. Spiro, P. H. Reiff, C. K. Chen, W. J. Burke, F. J. Rich, and M. Smiddy, Quantitative simulation of a magnetospheric substorm, 2. Comparison with observations, J. Geophys.Res.,86, 2242, 1981b. Jaggi, R. K., and R. A. Wolf, Self-consistentcalculation of the motion of a sheet of ions in the magnetosphere,J. Geophys.Res., 78, 2852, 1973. Kamide, Y., and A. Brekke, Auroral electrojet current density deduced from Chatanika radar and from the Alaska meridian chain of magneticobservatories,J. Geophys.Res.,80, 587, 1975. Kelley, M. C., B. G. Fejer, and C. A. Gonzales, An explanation for anomalous equatorial ionospheric electric fields associatedwith a northward turning of the interplanetary magnetic field, Geophys. Res. Lett., 6, 301, 1979. Mayaud, P.M., A propos de la variation journalibre Sq du champ magnbtique terrestre par la variation journalibre SD et d'un type special de perturbations contribuant au SD d'•t•, Ann. Geophys., 21, 219, 1965. Mazaudier, C., Electric currents above Saint-Santin, 3. A preliminary study of disturbance, June 6, 1978; March 22, 1979; March 23, 1979, J. Geophys.Res.,90, 1355, 1985. Mazaudier, C., M. Blanc, E. Nielsen,and M.-Y. Zi, Latitudinal profile of the magnetosphericconvectionelectric field at ionosphericaltitudes from a chain of magneticand radar data, J. Geophys.Res.,89, 375, 1984. Mazaudier, C., R. Bernard, and S. V. Venkateswaran, Saint-Santin radar observationsof lower thermosphericstorms,J. Geophys.Res., 90, 2885, 1985. $999 Nagata, T., and S. Kokubun, An additional geomagneticdaily vari- ationfield(s•v field)in the polarregionon geomagnetically quiet days, Rep. Ionos. Space. Res. Jpn., 16, 256, 1962. Nielsen, E., and K. Schlegel, A first comparison of STARE and EISCAT electrondrift velocitymeasurements,J. Geophys.Res.,88, 5745, 1983. Nielsen, E., and K. Schlegel, Coherent radar doppler measurements and their relationship to the ionospheric electron drift velocity, J. Geophys.Res., 90, 3498, 1985. Nielsen, E., and J. D. Whitehead, Radar auroral observations and ionosphericelectricfields,Adv. SpaceRes.,2(7), 131-144, 1983. Nishida,A., A coherenceof geomagnetic DP 2 fluctuationswith interplanetary magneticfield variations,J. Geophys.Res., 73, 5549, 1968. Pellat, R., and G. Laval, Remarks on the steady and time mathematical convection models, in Critical Problems of Magnetospheric Physics,edited by E. R. Dyer, Inter-Union Commission on Solar Terrestrial Physics,Washington, D.C., 1972. Reiff, P. H., R. W. Spiro, R. A. Wolf, Y. Kamide, and J. H. King, Comparison of polar cap potential drops estimated from solar wind and ground magnetometerdata: CDAW 6, J. Geophys.Res., 90, 1318, 1985. Senior, C., and M. Blanc, On the control of magnetosphericconvection by the spatial distribution of ionospheric conductivities, J. Geophys.Res.,89, 261, 1984. Southwood, D. J., and R. A. Wolf, The role of hot plasma in magnetosphereconvection,J. Geophys.Res.,82, 5512, 1977. Spiro, R. W., and R. A. Wolf, Electrodynamicsof convection in the inner magnetosphere, in Magnetospheric currents, Geophys. Monogr. Ser., vol. 28, edited by T. A. Potemra, p. 247, AGU, Washington, D.C., 1984. Spiro, R. W., M. Harel, R. A. Wolf, and P. H. Reiff, Quantitative simulation of a magnetosphericsubstorm, 3, Plasmasphericelectric fields and evolution of the plasmapause,J. Geophys.Res., 86, 2261, 1981. Vasyliunas,V. M., Mathematical models of magnetosphericconvection and its coupling to the ionosphere,in Particles and Fields in the Magnetosphere,edited by B. M. McCormac, p. 60, D. Reidel, Hingham, Mass., 1970. Vasyliunas, V. M., The interrelationship of magnetosphericprocess,in Earth's Magnetospheric Processes,edited by B. M. M½Corma½, p. 29, D. Reidel, Hingham, Mass., 1972. Wand, R. H., and J. V. Evans, The penetration of convection electric fields to the latitude of Millstone Hill (2 = 56ø), J. Geophys.Res., 86, 5809, 1981. Wilkinson, P. J., E. Nielsen, and H. Lurh, Ionospheric conductances: Associations between ionospheric E region electric fields and ground magnetometervariations, J. Geophys.Res.,91, 5839, 1986. Wolf, R. A., M. Harel, R. W. Spiro, G. H. Voigt, P. H. Reiff, and C.-K. Chen, Computer simulation of inner magnetosphericdynamics for the magnetic storm of July 29, 1977, J. Geophys.Res., 87, 5949, 1982. Zi, M.-Y., and E. Nielsen, Spatial variations of ionospheric electric fields at high latitudes on magnetic quiet days, in Exploration of the Polar Upper Atmosphere,edited by C. S. Deehr and J. A. Holtet, p. 293, Hingham, Mass., 1981. Zi, M.-Y., and E. Nielsen, Spatial variation of electric fields in the high-latitude ionosphere,J. Geophys.Res.,87, 5202, 1982. C. Mazaudier and C. Senior, Centre de Recherchesen Physique de l'Environnement, 4 Avenue de Neptune, 94107 St.-Maur des Fosses Cedex, France. E. Nielsen, Max-Planck-Institut f/Jr Aeronomie, Postfach 2D, D-3411 Katlenburg-Lindau, Federal Republic of Germany. (ReceivedJune 16, 1986; revised February 9, 1987; acceptedFebruary 25, 1987.)