The ring current in the magnetosphere and the polar magnetic substorms

The ring current in the magnetosphere and the polar magnetic substorms

Journal of Atmospheric and Terrestrial Physics, 1972, Vol. 34, pp. 846-858. Pergamon Press. Printed in Northern Ireland The ring current in the magne...

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Journal of Atmospheric and Terrestrial Physics, 1972, Vol. 34, pp. 846-858. Pergamon Press. Printed in Northern Ireland

The ring current in the magnetosphere and the polar magnetic substorms 0. A. TROSHICHEV Physical Institute, Leningrad State University, U.S.S.R. YA. I. FELDSTEIN Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, Academy of Sciences, Moscow, U.S.S.R. (Received

16 AUgplst1971)

Ab&8&--Measurements of charged particles made in the ATS-1, OGO-3, and Explorer-34 satellites and simultaneous measurements of the magnetic field at the ground are used to investigate the temporal-spatial characteristics of some magnetic storms. The following conclusions are reached: (1) The low energy protons (5 < E 5. 60 keV) observed by Frank in space cannot be the initial cause of the development of magnetic disturbances at the Earth’s surface. (2) To separate spatial and temporal variations of particle intensitiesit is necessaryto use both ground-based and satellite data. It is then possible to define the parameters of the ring current responsible for the decrease of the geomagnetic field. (3) The low-latitude bays that occur during polar disturbancesmay be explained by a partial ring current flowing outside the region of stable trapping. (4) The diamagnetic effect of ring current particles is responsible for the decrease of the magnetic field at satellite orbits. The simultaneity of the magnetic disturbance development at the satellite and at the Earth’s surface is explained by the variation of the incoming particle density. (5) The changes in the current system responsiblefor a highlatitude magnetic disturbance are traced. It is shown that an almost single-vortex current

structure (the westward electrojet) occurs during the maximum of the substorm, and a twinvortex structure is observed during the onset of the disturbance development and during the recovery phase. IN THIS paper, observational results obtained during magnetic satellites ATS-1 (FREEMAN and ~MAQUIRE, 1968; CUMMINGS (FRANK, 1970a; FRANK and OWENS, 1970) and Explorer-34 compared with simultaneous magnetic observations made on

disturbances by the et al., 1968), OGO-3 (FRANK, 1970b) are the Earth’s surface.

RINGI CURRENT AND LOW-LATITUDE MAGNETIC BAYS

When comparing the data from the geosynchronous satellite ATS-1 (particle flux and magnetic field measurements) with those from the magnetic ground-based observatories at the same meridian (College and Honolulu) a remarkable agreement has been found between the variations of particle flux intensities at the satellite orbit and those of the magnetic field, both on the Earth’s surface and on the satellite (FREEMAN and MAQUIRE, 1968; CUMMINGS et al., 1968). An increase in the particle flux (positive ions of all energies and electrons with E, > 3 keV) was accompanied by a simultaneous depression of the magnetic field at the satellite orbit and at Honolulu (at pre-midnight hours of local time) ; the recovery of the magnetic field was observed, while the flux was decreasing (Fig. 1). It is demonstrated (FRANK, 1971) that the particle fluxes which have been measured by ATS-1 in the evening sector may be both the ring current protons with energy 4 I E I 50 keV during moderate magnetic activity and the electrons with E, > 3 keV during a strong 846

846

0. A. TEOSHICIXEV and Y. I. FELDSTFXN

UT

Fig. 1. Variations in density of particles at the orbit of the satellite ATS-1 and the corresponding variations in the magnetic field at the satellite and at the observatories Honolulu (# = 21*3’N) and College (4 = 64.9’N) occurred on 24 December 1966. A scalefor the transitionfrom the counting rate in relativeunits to that in absolute units is given in FREEMANand MACQUIRE(1968).

disturbance. The character of the magnetic field variations at the satellite and at the Earth’s surface supports the belief that the main contribution to the measured results on that day comes from energetic protons. The magnetic field variations have been considered by TROSHICHEV and FELDSTEIN (1969) at other low-latitude stations for one such period (24 December 1966) (Fig. 2). It has been found that the above regularity is characteristic of all the stations in the night and evening longitude sectors : The magnetic disturbance which commences with a positive impulse at 0435 UT (according to the data from all lowlatitude stations) reaches maximum negative values at 0700-0800 UT and at about 1000 UT, that is, in the periods of maximum intensities of plasma fluxes at the satellite orbit (6.6 RE). In the morning and day hours, a decrease of the field is also observed. However, the magnitude of this depression is negligible and has an indistinct, ‘diffuse’ character. These regularities suggest that the magnetic disturbances observed at the lowlatitude observatories are due to the same extra-ionospheric source that causes the disturbances at the ATS-1 orbit in the evening and night magnetosphere. Consequently, the main change of the field, the so called low-latitude bay, should not be attributed to the return currents from the aurora1 electrojet. It will be noted that the results of ground observations (AKASOFU and MEENG, 1968) and measurements obtained by 000-2 also show (LANGEL and CAIN, 1968) that the source of DSvariations at low-latitudes is external with respect to the satellite heights (h = 4001500 km). Thus it may be assumed that the development of low-latitude magnetic bays is connected with the formation of the ring current in the evening and premidnight sectors of the magnetosphere.

The ring current in the magnetosphere

and the polar magnetic substorms

w

San Juon(X=66

647

I”W)

TucsonC X= 110.8’W) HonoluluC

X= 158.1 “WI

Tashkent

( X=69.2”E )

e

Bangui( X = 18.6” E 1

v

M’BoudX

= 17” W)

Fig. 2. Bay-like disturbances of the magnetic field on 24 December istered at observatories located at different longitudes.

1966, reg-

As has been mentioned above, the magnitude of the depression is not the same at different hours of local time: It is a maximum at stations in the evening longitude sectors. Moreover, the further to the west from the midnight meridian is the station, the later is the depression maximum observed at it. To illustrate this, consider the magnitude and the time delay of a characteristic depression peak which was observed at the midnight meridian at 0715 UT (see Fig. 2). This peak was very clearly visible at stations in the afternoon longitude sector (Kanoja) and one could trace it even to forenoon hours (Tashkent). At all stations the magnitude of the depression was estimated from the size of the positive impulse, which was observed at 0435 UT ; it is assumed that the depression was developing at this time, being superposed on the background of the enhanced geomagnetic field. The value of the negative deviation AH thus obtained is shown in Fig. 3 as a function of local time. The data given in Fig. 3 indicate that the peak of the geomagnetic field depression shifts westward at a velocity of 2-4 deg min- l. This effect seems to be caused by a drift of quasi-trapped protons with energy E, of order 50-100 keV. LT 6

/

9

I

12

I5

I

Kanojo

I

0750

UT

18

I

21

I

Memambetsy0750

24

3

1

I

6

I

0

I

UT

Fig. 3. Dependence of the maximum depression of the magnetic field on local time. The universal time of the peak occurrence at the corresponding observatory is given in brackets.

848

0.

A. TROSHICHEV and Y. I. FELDSTEIN

RING CURRENT AND POLAR MAGNETIC DISTURBANCES The development of polar magnetic disturbances during the same period (24 December 1966) has been analysed in TROSHICHEV and FELDSTEIN (1970). The data from 19 high-latitude stations (4 > 60“) located in the northern hemisphere were used. At high latitudes the disturbance under consideration consists of two successive substorms with maximum intensities near 0800 and 1000 UT, respectively. The spatial distribution of the horizontal (AZ’ = dAH2 + A02) and vertical (AZ) components of the disturbance vector has been mapped for 15 different epochs. These maps are given in full by TROSHICHEV (1969), some of them being shown in Fig. 4. The magnitude of a disturbance vector was calculated at each station as the difference between the magnetic field at a given universal time and the field during a magnetically quiet period preceding the disturbance. From the distributions of AH and AZ some equivalent systems of currents have been plotted by using an approximate method described elsewhere (CHAPMAN and BARTELS, 1940) ; these are shown in the same figures. It should be noted that the instantaneous current systems, that give a generalized representation of the disturbance-field distribution, are diflicult to draw because of the obvious lack of data. Nevertheless, the current systems seem to be the most convenient tool for describing the processes which characterize the substorm development at high latitudes. The basic results of the analysis are as follows: 1. The field remains relatively quiet (Fig. 4(a)) in high latitudes for about 1 hr after the start of the disturbance (0435 UT-the moment of a positive impulse at low-latitude stations). The current system consists of a weak current vortex with counterclockwise current and is analogous to DPC-the current system described elsewhere (FELDSTEIN and ZAITZEV, 1967 ; IVANOV and MIKERINA, 1967). 2. The transition from a quiescent state to a disturbed one is characterized by intensification of the westward currents (Fig. 4(b)) which gives rise to a second current vortex with a clock-wise direction (Fig. 4(c)). This is accompanied by intensification of the magnetic field depression at low latitudes, both on the Earth’s surface and at the satellite ATS-1. By 0630 UT a current system is formed at high latitudes which remains roughly unchanged till the end of the disturbance ; there are then twin current vortices, the vortex with a westward electrojet being predominant. 3. Currents responsible for negative bays undergo strong changes during both substorms (Fig. 4(d-f)) and the westward electrojet reaches its maximum intensity (about 3-4 x lo5 A) in the periods of the maximum depression of the magnetic field at low-latitude stations and at the satellite (which is in accord with the result of MAISURADZE (1967). At this time the currents which flow clockwise encompass the whole polar cap, confining the effect of the opposing currents to a narrow zone of latitudes in the evening sector of the aurora1 zone. After the westward electrojet has reached its maximum intensity, is suffers an abrupt decrease to about 1.5 2 x lo5 A (see Fig. 4(f)). On the contrary, the intensity of the eastward electrojet, which is responsible for positive bays, remains relatively stable (about 1 x lo5 A) during each substorm, and this leads, during the recovery phase of the substorm, to the formation of a characteristic twin current vortex system (Fig. 4(f)).

The ring current in the magnetosphere and the polar magnetic substorms

0530

UT

(b)

0930

UT

\ ,

(d)

(e)

(f)

Fig. 4. Distribution of the horizontal and vertical components of the magnetic disturbance vector for different universal times on 24 December 1966. The direction and value of the horizontal component are indicated by arrows. The light circle at the base of the arrow indicates a negative value of the vertical component (direction to zenith), the shaded circle shows a positive deviation. The midnight meridian is marked by a triangle. Coordinates corrected geomagnetic latitude and time of the eccentric dipole. There are 80,000 A between the current lines.

849

850

0. A. TROSHICHEV and Y. I. FELDSTEIN

Thus, the distribution of currents in the polar cap is very variable and cannot be clearly identified as a ‘known’ current system. In fact, a structure close to the onevortex system will be observed when the westward currents are intensified (which corresponds to the maximum depression at low latitudes), while the twin-vortex system will be observed as the westward current decreases rapidly. One may consider the eastward and westward electrojets to be of different natures and to develop independently of each other during the substorm. 4. Near the midnight meridian the development of substorms is characterized at first by an increase in the westward electrojet intensity at higher latitudes, about 70’ (intensification of disturbances at Churchill and Barrow) and then by an expansion (or displacement) of the current to the lower latitudes, about 60-62” (Meanook, Sitka). Such a change in the position of the westward electrojet agrees with the observations of the equatorial drift of aurorae during a substorm (FELDSTEIN and STARKOV, 1967; BELJYKOVA et al., 1968; STARKOVet al., 1972). 5. A certain concentration of jet currents is observed in the aurora1 zone not only at night but at late morning hours, as well as at forenoon hours. This effect is particularly noticeable when the western current vortex intensity is not large enough to have an influence on the zonal stations of the forenoon longitude sector (Fig. 4(c)). This fact may be considered as a confirmation of earlier conclusions (TROSHICHEV, 1969; &SHIN and TROSHICHEV, 1966) that the intensification of magnetic disturbances accompanies an enhancement of the planetary activity not only along the oval but also along the circular zone, in our case along its morning sector. Negative disturbances that arise there are connected with the closing currents of the westward electrojet returning at midlatitudes (FELDSTEIN and ZAITZEV, 1965). 6. A gradual westward displacement of the maximum of positive bays is characteristic of the evening longitude sector. As the station is further from the midnight meridian the positive bay development registered at it is later. The direction of displacement (westward) allows one to relate this fact to the proton precipitation that drifts in longitude. Then estimating the drift velocity (l-5-3 deg min-l) we obtain the proton energy E, = 40-80 keV. A similar drift of the positive bay maximum has been noted in PUDOVRIN and SMIRNOV (1966). The results reported in TROSHICHEVand FELDSTEIN (1969, 1970) enable one to come to a general conclusion that the development of the disturbance under study is associated with the penetration of intense fluxes of charged particles (protons and electrons) deep into the magnetosphere. Particles with sufficiently large pitch angles are involved in the longitudinal drift around the Earth, which corresponds to the formation of a partial or closed ring current responsible for the magnetic field depression at the Earth’s surface (at low latitudes) and at a satellite. This is accompanied by a precipitation of particles with sufficiently small pitch angles into the aurora1 ionosphere, which causes polar substorms. DETERMINATION OP RING CURRENT PARAMETERS The parameters of the ring current that is responsible for the field depression at the Earth’s surface can be determined from the ground-based and satellite data. During the event of 24 December 1966 the maximum depression of the magnetic field at low latitudes was observed in the longitude interval from 1000 LT to 2409

The ring current in the magnetosphereand the polar magnetic substorms

851

LT (Fig. 3). If this interval is assumed to determine the longitudinal extension of the main portion of ring currents, then the observed depression of the magnetic field is caused by the partial ring current with a longitude extent (Al) of about 210°. The radial extension of the region in which these currents are localized can be determined from the following considerations. During the period from 0700 UT to 0830 UT magnetic disturbances at high latitudes encompassed the latitude zone from about 70” to about 62-60°, which corresponds to geocentric distances from L, % 8.6 to L, k 4. One may believe that during the disturbance period this whole region in the magnetosphere is filled with unstable radiation (aurora1 and quasitrapped particles) (TROSHICHEV, 1969). The precipitating particles cause the magnetic disturbances at high latitudes and the quasi-trapped particles, constitute the ring current. These estimates are also consistent with the observations of the polar oval dynamics (FELDSTEIN and STARKOV, 1967). Thus the volume occupied by the newly arrived particles that form the ring current lies between two magnetic shells (L1 = 8.6, L, = 4) and within a longitude interval Al = 210’ and equals (AKASOFU and CHAPMAN, 1961): v = $5

n(L13 -

L,3)RE3 $$ ‘U 1.65 x 10zg cm3.

The particle (proton) density in this volume can be estimated from simultaneous measurements of the magnetic field on the satellite ATS-1. The difference between the magnetic field at 0716 UT and the field (about 1307) which preceded the development of the depression was about 60~. Making use of an approximate expression for the diamagnetic effect produced by the particles (see BROWN and CAYHILL, 1968) and taking account of the constancy of the total pressure of plasma and the magnetic field (VASYLIUNAS, 1969; TAYLOR and PERKINS, 1971), obtain AB % CmE/B.

(2)

For the protons with energy E + 50-100 keV the density 12 + O&O+ cm-3 and the energy density nE + 6.4 x 1O-s erg cm-3. Then the total kinetic energy of the ring current particles will be

K, = nEV + I.05 x 10z2 ergs.

(3)

The magnitude of the depression set up at the Earth’s surface by such a current can be estimated (considering the currents induced inside the Earth) according to the relation (DESSLER and PARKER, 1959; SCOPKE, 1966)

AB/B = -K,/Ks

(4)

where B is the magnitude of the Earth’s main magnetic field at the Equator, AB is the field variation at the Equator and K, is the energy of the undisturbed magnetic field of the Earth. Substituting the known values: B = 3.2 x 104y, K, = 0.8 x 1O26ergs; K, = I.05 x 1O22ergs into (4), we find the depression magnitude of the depression at the Earth’s surface, AB = -442~. The maximum depressions observed at the Earth’s surface during this period lie in the interval from -40~ to -60~ (Fig. 3). Considering that equation (2) is rather approximate it may be assumed that the calculated and observed values of the depression fit well. This confirms the earlier conclusion that the low-latitude

862

0. A. TROSHICHEV and Y. I. FELDSTEIN

magnetic bays are caused by the extra-ionospheric partial ring current and, thus, are one of the forms of the Dat variation. The longitude extent of the partial ring current can be determined from the data of ground-based observations. The development of a typical DBt variation can be well exemplified by the magnetic storm of 9 July 1966. The intense proton fluxes (30 < E, < 50 keV) responsible for the development of this storm were observed by the OGO-3 satellite at L = 3-5 (Fig. 5) (FRANK, 1968, 1970a). The proton energy density reached the value nE = 3 x lo--’ erg/cm 3. The character of the magnetic field variations at the Earth’s surface was investigated using the data from 10 low-latitude observatories in the northern hemisphere (Tucson, Honolulu, Memambetsy, Kanoja, Tashkent, Tbilisi, Bangui, M’Bour, San Juan, Ulan-Bator). The results of the ground-based observations are summarised in Fig. 6 by plots representing the magnetic field deviation from the quiet level as a function of local time for different universal times (UT). A negative deviation of the field from a quiet level appears near the evening meridian (16-1800 LT) and then, growing in magnitude with time, expands westward. At the maximum of the .DRtvariation (0700 UT) an abrupt azimuthal asymmetry is observed in the distribution of the disturbance field AH. AH + -100~ at the evening meridian, and AH + -10~ at the morning meridian. By 1000 UT the value of the D,, variation is almost the same at all longitudes (AH & -50~). For a model of the ring current appropriate to that time (A?, = 360°, L, = 3, L, = 5; E YJ 3 x lo-‘erg om-3) we obtain ‘v = 5 x lo28 om3, K, N 1.5 x 1022 ergs, AB N 45~ which is in good agreement with the observed depression.

9

8

Jul.

1966

-

Sep.1966

Fig. 6. Intensityof proton fluxes(31 5 E 5 49 keV) as a function of L for two moderate geomagnetic storms on 8 September 1966 and 9 July 1966 according to the data of FRANE (1968, 1970a). The solid line representsthe inbound pass, the dashed line, the outbound pass.

The ring current in the magnetosphere

and the polar magnetic substorms

863

2100

8 Jul. 1966 (SC)

2300

UT

0300

UT

0700UT

9 Jul. 1966

maximum

0900 UT onset of recovery

Ds,

phase

1200 UT

0

4

8

12

16

20

24

LT

Fig. 0. Development of the asymmetric ring current for the storm on 8-9 July 1966, 2100 UT-the sudden commencement, 0700 UT-a maximum of the Dgt variation, 0900 UT-the onset of the recovery phase.

SEPARATION OF TEMPORAL AND SPATIAL VARIATIONS IN THE PARTICLE DISTRIBUTION OF DR CURRENTS During the passes of the satellite OGO-3 in the evening sector of the magnetosphere at distances corresponding to L = 3-8, proton fluxes (E, < 50 keV) have been detected, with their intensities varying in harmony with the D,, variation (FUNK and OWENS, 1970). A systematic difference has been found between the values of the fluxes observed on the inbound and outbound passes (FRANK, 1970a). This difference was found to be especially large for the initial phase of the substorm of 8 September 1966 (Fig. 5): The proton flux on the inbound pass (near 2000 LT) was about five times that on the outbound pass (near 1300 LT). In FRANK’S (1970a) paper this effect is treated as an indication of the longitudinal asymmetry in the However, such a conclusion is not unambiguous spatial distribution of particles. since the measurements on the inbound and outbound passes are separated by an interval of 3 hr so that the difference may result from the time-variations of the proton intensities. The satellite data alone do not allow one to separate the spatial and temporal variations of the proton flux. Such a separation is however possible if the results of the ground-based magnetic observations are available. Figure 7 shows the magnetic field deviation from a quiet level at the low-latitude stations and Fig. 8 shows the corresponding maps of the disturbance vector at fixed universal times on 8 September 1966 for high latitude. On 8 September 1966 from 0300 UT to 0400 UT a depression of the magnet,ic field reaching 40-50~ was observed at all low-latitude stations located both in the evening and daytime sectors. At the same time the whole polar cap experienced from the quiet intense magnetic disturbances : The deviation of the H-component level was as high as 500~ in the aurora1 zone. Therefore, in the period from 0300 to 0400 on 8 September, a substorm occurred, which was accompanied by world-wide

0. A. TROSHICHEVand Y. I. FELDSTEIN

854

r’

^’

k .:

LX-LX i

1

.-A

1 - 0200UT -

8 Sep. 1966

0330 UT 0350 IIT

IIIllllllllII,,II,,,I,,,I 0

4

8

12

16

20

0500

UT

0650

UT

24

LT

Fig. 7. Development of the asymmetric ring current for the storm on 8 September 1966 at consecutive moments of UT according to the data of 10 low-latitude stations.

?

12LT

16LT

6Ll

Fig. 8. Development

of polar magnetic disturbances for the storm on 8 September 1966 in the northern polar cap.

variations of the magnetic field. At 0400 UT the substorm ceased and the field started to recover. However, after 0600 UT a new disturbance gradually developed (first at high latitudes, then at low latitudes), which lasted over 12 hr and which had a well-defined D,, variation. Thus, the results of the ground-based observations show that on 8 September 1966 two successive disturbances were observed which were separated from one another by a relatively quiet period. On the basis of these data one may conclude that, at the moment of detection of particles on the inbound pass (0350 UT), increased proton fluxes occurred both in the evening and noon sectors whereas by 0500 UT the protons disappeared not only in the noon but also in the evening sector. Consequently, the measurements made on the satellite OGO-3 on 8 September 1966 reflect primarily the temporal variations of the proton intensities in the magnetosphere. At 0350 UT the ring current model will hsve the following parameters (according to the experimental data): Ail + 210° (from 0800

The ring current in the magnetosphere

LT to 2200 LT);

and the polar magnetic substorms

855

_L, = 4; j + 5 x 10’ proton cm-2 ster-l see--l (30 < cm-3). Making use of the formulae (l), (3) and (4), we obtain the value of the magnetic field depression on the Earth’s surface, AB k 4Oy, which is equal to the value of AB observed at 0350. At 0650 the satellite detected a proton flux of about 1 x 10’ cm-2 ster-l se& (see Fig. 5), the magnetic field depression AB at the Earth’s surface being at this time about 10-15~ (A,? k 210°, for the evening and noon longitudinal sectors). Thus, during 3 hr the depression of the field decreased by a factor of approximately 3, while the proton flux (according to the satellite data) decreased by a factor of 5. This discrepancy is eliminated if one takes into account that on the inbound passes the satellite OGO-3 systematically observed greater particle fluxes than on the outbound passes (approximately by a factor of 2). This fact appears to be connected with the orbit peculiarities, e.g. the satellite latitude was 0’ on the inbound pass, whereas on the outbound pass it was above 23”.

E, < 50 keV);

L, = 65;

nE + 2.1 x lo-‘erg

INTERPLANETARY PROTONS AND GEOMAGNETICDISTURBANCES Low-energy protons (5 < E < 50 keV) were registered for the first time in interplanetary space by the satellite Explorer-34 (FRANK, 1970b) during the period from 26 July to 13 August 1967. Proton fluxes with a density up to 10m2protons cm-3 and lasting for about 24 hr were observed twice during this period (29 July and 11 August) (Fig. 9). Comparing the variations of the interplanetary proton intensities with the D,, variation during the same period (SUGIURA and CAIN, 1969),

m Magnetosphere

26

28

30

I

3

July

5

7

9

II

13

August 1967

Fig. 9. Proton fluxes (11 I E 5 18 keV) in interplanetary space in the antisolar (sector II) and solar (sector I) directions according to FRANK (1970b).

866

0. A. TBOSHICFXEV and Y. I. FELDSTEIN

Frank came to the conclusion that each increase in the proton intensity is accompanied by the occurrence of a small magnetic storm and, consequently, that the presence of interplanetary protons is possibly a necessary condition for the development of the main phase of a geomagnetic storm (that is, for the DR current formation). This result is based upon preliminary estimates of the D,, variation derived from measurements made at two low-latitude observatories. In the following, this problem is discussed in more detail. During each interval of 15 min the values of the magnetic field negative deviations from the quiet level were calculated at six lowlatitude stations: Muntinlupa, San Juan, M’Bour, Tbilisi, Kakioka, Honolulu. The maximum of these values is taken as a characteristic of the intensity of the magnetic field depression at low latitudes--ED (equatorial depression). This characteristic reflects not only variations in intensity of the symmetric ring DR current (the Dst variation) but also the process of the formation of the partial or asymmetric DR currents (during the low-latitude magnetic bays or the development phase of planetary magnetic storms). Thus, the ED index characterizes the maximum depression of the low latitude magnetic field as distinct from the average D,, variation which eliminates all longitudinal differences. The ED index variations during the period from 1 August through 11 August 1967 are shown in Fig. 10 where variations of the AE and AU indices of magnetic activity are also given, which characterize the magnetic disturbance in the aurora1 zone. The AE and AU indices were calculated for every hour using the data acquired at the stations of the northern hemisphere : Murmansk, Burrow, Churchill, Meanook, Tromso, Kiruna, Reykjavik, Dixon, College and Great Whale River, located at

-40

,

,

,

(

,

,

,

,

,

,

I2345’67891011 Augus!

1967

Fig. 10. Changes in the hourly AE and AU indicesfor the period l-11 August 1967 according to the data of 10 stations located in the aurora1zone and changesin the 15-min index ED according to the data of six low-latitude stations.

The ring current in the magnetosphere and the polar magnetic substorms

L

1 I

1 2

1 3

1 4

’ 5

1 6

August



’ 7

8

1 9

857

1 IO

I,

1967

Fig. 11. Changes in the hourly DC indices, which characterize disturbance in the polar cap.

the magnetic

6670’ latitudes. A fairly good agreement between the variations of the AE, AU and ED indices is observed; for each peak of magnetic activity in the aurora1 zone there is a corresponding peak of the low-latitude depression (with a delay of about 2 hr). The most important feature of these variations-the magnetic disturbance remains relatively low on 1,2 and 3 August, but increases drastically on 4 August, whereas no increase in the interplanetary proton intensities is observed. The magnetic field is perturbed over the whole period from 4 to 11 August, the disturbance (according to the data of the AE and ED indices) being a maximum on 10 August, that is, 24 hr before the sudden increase of the interplanetary proton intensity. A similar regularity is observed for the variations of the disturbance field in the polar cap (according to the data from Alert, Thule, Resolute Bay, Godhavn stations) (Fig. 11). The data from ground-based observatories enable one to infer that the ring currents (responsible for the low-latitude depression of the magnetic field) and polar magnetic disturbances developed almost independently of the presence (or absence) of protons with an energy of tens of keV in the interplanetary medium. The occurrence of intensive fluxes of the interplanetary protons cannot be the initial cause of the magnetic disturbance development on the Earth’s surface. REFERENCES AKASOFU

S.-I. and &fENa C. J.

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1968 1968

J. Atmo8ph. Tew. Phys. 30, 227. Geomag. & Aeronomy 8, 712.

1968 1940 1968

J. geophy8. Rea. 73, 153. GeomugnetGm. Oxford. J. geophy8. Res. 73, 6687.

1959 1967 1965 1967

J. geophy8. Rec. 64, 2239. Planet. Space Sci. 15,209.

Geomq. BEAeronomy 5,1123. Geonuq. & Aeronomy 7, 204.

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A.

TROSHICHEV and Y.

I.

FELDSTEIN

FRANX L. A.

1968

Earth’s Particles and Field8 (Edited by

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197oa 197Ob 1971 1970 1968 1967 1968 1967 1966 1966 1966 1972

J. J. J. J.

1971 1969 1970

J. geophys. Res. ‘76, 272. Kosm. Issled. 7, 309. Geomag. 8z Aeronomy 10,1114.

B. M. MCCORMAC), p. 67. gwphys. Res. 15, 1263.

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Reference is also made to the following unpublished material: AKAsopv S.-I. and CEAPXAN S. SUQIURA M. and CAIN S. I.

1961 1969

TR~~HICEEV 0. A. VASYLIUNAS V. M.

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Rep. N7, NSF Grand N 4 (22, 6) Provisional hourly values of equatorial .Z& for 1964-1967 Goddard Space Flight Center, N X-612-69-20. D. P. Thes, Irkutsk. “Low energy particle fluKes in the geomagnetic tail”, preprint CSR-P-69, p. 17.