There are three main processes by which energy is transferred from the magnetosphere to the thermosphere: (1) charge exchange of the ring current particles; (2) precipitation of charged particles; and (3) joule dissipation by the magnetosphere-ionosphere current systems. The importance of this last process has been recognized and the rate of joule heating has been estimated by many workers. Observations of the electric (E) and magnetic (B) fields from Dynamics Explorer Satellite 2 are providing a new set of data on field-aligned currents. One of the remarkable features found in these observations is the high correlation between an orthogonal pair of the E and B field components. In recent years, observational data have accrued concerning the relationship between the interplanetary magnetic field and the size of the polar cap and also about the evolution of a substorm or a magnetic storm. It is suggested that these findings be incorporated in future model calculations

Sugiura, M.

English

NASA Technical Reports Server

JOULE HEATING AND FIELD-ALIGNED CURRENTS:
PRELIMINARY RESULTS FROM DE-2
M. Sugiura
Laboratory for Extraterrestrial Physics
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
There are three main processes by which energy is transferred from the magnetosphere to the
thermosphere. These are, not necessarily in the order of importance: (a) charge exchange of the
ring current particles; (b) precipitation of charged particles; and (c) joule dissipation by the
magnetosphere-ionosphere current systems. The importance of this last process has been recog-
nized and the rate of joule heating has been estimated by many workers (references given in Table
1).
Observations of the electric (_E)and magnetic (_B)fields from DE-2 are providing a new set of
data on field-aligned currents. One of the remarkable features found in these observations is the
high correlation between an orthogonal pair of the E and B field components (Siguira et al., 1982,
1984; Sugiura, 1984; general references on field-aligned currents are given in these papers). Figure
1 shows an example, where AB_is the perturbation magnetic field obtained by substracting a model
internal field from the observed field. The north-south component of the electric field is well cor-
related with the east-west component of the magnetic field. The correlation is 0.94, using ½ sec-
ond averages. Figure 2, which gives high-pass filtered data of the same set as Figure 1, shows that
the correlation between the orthogonal E and B components is equally good for the fluctuating
components; the correlation coefficient is 0.93.
Figure 3 demonstrates this reasoning. Figure 3 shows the spacecraft X, Y, and Z components of
AB and the spacecraft X component of E during a northern polar pass. The interplanetary
magnetic field was northward (Bz> 0), and hence the size of the polar cap was small. Figure 4
shows how the angle, o_, between the orbit plane and the dipole meridian plane changes along the
pass; the definition of the angle o_is illustrated in Figure 5. The interval between 1417 and 1423
UT was further divided into 1-minute intervals and the correlation coefficient between/XB z and Ex
was calculated for each of these 1-minute intervals. The results are shown in Table 2. We conclude
that the proportionality between the orthogonal B and I3 components is invariant with respect to
rotation of the coordinate system. Hence the missing Ez must be proportional to/XB x to the same
extent that Ex is correlated to/XB z.
Comparing ABz with Ex for the evening auroral oval pass in Figure 3, ABz changes are very
small, but are correlated with E× as seen in the correlation coefficient, r, for intervals D and E.
The ABz amplitudes are small in these intervals because the ionosphere was not illuminated and
hence the conductivity was low. The precipitating electrons did not have energies large enough to
produce appreciable ionization in the E region of the ionosphere (according to the LAPI plasma
observations); hence field-aligned currents could now flow, and the electric field was large, being
not short-circuited. The solar elevation angle along the pass is indicated in Figure 3.
451
https://ntrs.nasa.gov/search.jsp?R=19860019864 2020-03-20T14:36:40+00:00Z
Figure 6 shows a pass on the following day when IMF Bz became southward. Now the size of
the polar cap has expanded, and there are appreciable field-aligned currents in the auroral oval in
darkness (near midnight) because of enough ionization from auroral electrons. Note the good cor-
relation in interval C where o_changed rapidly.
From the DE-2 observations of E_and AB, we conclude that the electric field and the perturba-
tion magnetic field are orthogonal and that their magnitudes are proportional. Their directional
relation is such that E x AB is downward. This relation between E and AB is frequently observed,
especially on the dayside.
It can be shown that when the above relation between the electric and magnetic fields holds, the
following equations constitute a particular solution of the current continuity equation.
Ep - k/_o = 0 (1)
V.J H = 0 (2)
where Ep is the ionospheric Pedersen conductance, k the constant of proportionality between the
orthogonal perturbation magnetic field and electric field components, i% the permeability of free
space, and _JHthe height-integrated Hall current. If (1) holds, then with the proportionality be-
tween the electric and perturbation magnetic fields, we obtain a relation that the vertical compo-
nent of Poynting's vector equals joule dissipation, namely that the vertically downward energy
flow equals joule dissipation; that is, the divergence of the horizontal energy flux is zero. The
energy flux from below the ionosphere is expected to be negligible because the perturbation
magnetic vector is parallel to the electric field; this is because the magnetic field below the
ionisphere is mainly from the Hall current. It seems reasonable that the divergence of the Hall cur-
rent is zero to the same extent as the plasma convection flow is horizontally divergence free. If this
is true, then the field-aligned current sheets are parallel to the convective flow pattern or the
equipotential surfaces.
If we accept the above solution, then the Polynting vector E x AB_//_o provides the energy flux
from the magnetosphere that is expended in the ionosphere by joule dissipation. During the
magnetic storm of September 6, 1982 the peak energy flux reached 200 mW/m 2 in the cusp
region. In an auroral oval pass the peak energy flux is typically a few tens of mW/m 2 under
moderately dislturbed conditions.
In recent years, observational data have accrued concerning the relationship between the in-
terplanetary magnetic field and the size of the polar cap and also about the evolution of a
substorm or a magnetic storm. It is suggested that these findings be incorporated in future model
calculations.
452
REFERENCES
Maynard, N. C., J. P. Heppner, and A. Egeland, Intense, variable electric fields at ionospheric
altitudes in the high latitude regions as observed by DE-2, Geophys. Res. Lett., 9, 981-984,
1982.
Sugiura, M., A fundamental magnetosphere-ionosphere coupling mode involving field-aligned
currents ad deduced from DE-2 observations, Geophys. Res. Lett., 11, 877-880, 1984.
Sugiura, M., N. C. Maynard, W. H. Farthing, J. P. Heppner, B. G. Ledley, and L. J. Cahill,
Jr., Initial results on the correlation between the magnetic and electric fields observed from the
DE-2 satellite in the field-aligned current regions, Geophys. Res. Lett., 9, 985-988, 1982.
Sugiura, M., T. Iyemori, R. A. Hoffman, N. C. Maynard, J. L. Burch, and J. D. Winningham,
Relationships between field-aligned currents, electric fields, and particle precipitation as
observed by Dynamics Explorer-2, in Magnetospheric Currents, T. A. Potemra, ed., Geophys.
Monograph 28, Am. Gephys. Union, pp. 96-103, 1984.
453
JOULE DISSIPATION BY ELECTRIC CURRENTS
COLE 1962 Austr. J. Phys., 15, 223
1971 Planet. Space Sci., 19, 59
1975 J. Atmos. Terr. Phys., 37, 939
KATO 1962 Planet. Space Sci., 9, 939
REES and WALKER 1968 Annls. Geophys., 24, 193
MAYRand VOLLAND 1972 Planet. Space Sci., 20, 379
1974 J. Atmos. Terr. Phys., 36, 2025
BATES 1973 Planet. Space Sci., 21, 2073
HAYS et al. 1973 Planet. Space Sci., 21, 559
CHANGet al. 1974 J. Atmos. Terr. Phys., 36, 889
BANKSand SIREN 1974 EOS, 56, 1157
WICKWARet al. 1975 J. Geophys. Res., 81, 4364
RICHMONDand MATSUSHITA 1975 J. Geophys. Res., 80, 2839
TAEUSCHand HINTON 1975 J. Geophys. Res., 80, 4346
STRAUSSand SCHULTS 1976 J. Geophys. Res., 81, 5822
BANKS 1977 J. Atmos. Terr. Phys., 39, 179
BANKS et al. 1981 J. Geophys. Res., 86, 6869
THIELE et al. 1981 Planet Space Sci., 29, 455
VICKREY et al. 1982 J. Geophys. Res., 87, 5184
NISBET 1982 J. Atmos. Terr. Phys., 44, 797I
KAMIDE et al. 1982 J. Geophys. Res., 87, 8228I
BAUMJOHANNand KAMIDE 1984 J. Geophys. Res., 89, 383
Table 1
454
DAY 81 251 8 SEPTEMBER 1981
INTERVAL ANGLE _ MLT CORR. _p
UT DEGREES HRS COEFF. M HOS
1417-1 41 8 151-1 37 13.4-14.4 0.99 11 34_
1418-1419 137-109 14.4-16.5 0.98 7.4
141 9-1 420 109-68 1 6.5-1 9.3 0.99 6 0
1420'1 421 68-40 1 9.3-21.0 0.90 2 8
1421-1 422 40-27 21.0-21.8 0.97 4.1
1422-1 423 27-20 21.8-22.2 0.97 2 7
Table 2
DE - 2 II OCT 1981
(MV/M) 0 ..........................
-I00 -_,,,,' 750
Z&88 (nT) ....................................................................................................0
750 -,----,-_,-,-_-,-4-,-,_......_-,-,+_-,-,_-_-_-,-,+,-,-,-_-,+,.,,:' ..... I,_.,., -750
1"
ABqs(nT) 0 .............................................................................
-750 .,-+-_-,+,+-,-+-,-_........., i.........J........_.......++-,-,-,_..... _.... ,-4..........
UT 02:51 02:52 02:55 02:54 02:55 02:56
ALT(KM) 358 347 338 331 324 319
MLT (HR) 8.5 8.8 9.0 9.1 9.2 9.2
ILAT (DEG) 81.2 78.4 75.1 71.5 67.6 63.7
Figure 1. The north-south component of E, the north-south and east-west components (in dipole
coordinates) of the peturbation B field.
" 456
DE-2 FILTERED II OCT 1981
Ex(MV/M) 0
AB 0 (nT) ..... -_____-__ .......... 0
UT 02:51 02:52 02:55 02:54 02:55 02:56
Figure 2. Data in Figure 1 were passed through a high-pass filter to extract fluctuating
components. The orthogonal components of E and B are still well correlated.
457
DE-2 8 SEPTEMBER1981
ABx(nT) 0 ........................................................................................... i
-IO00 _-_-,. ...... f...... +_ ..... , ..... _..... _,,,-,_ .... ._..... _1000
A By (nT) ................ _Z__--_-__/ ...................... _ 0
1 082 1
r I 0.98 _ 099 1 078 '097 092 1I I I i
_P " I 12,4 I 7,3 I 3.5 12.7 I 0.9 i 0 9 I
1000 ..... _..... ! ..... _..... : ...... _...........,- :..... : ..... _....... 1000
i A II B IRI_ i i .l I [:)l Fi
I _ _ I I
V-'- i
A8 Z (nT) 0 +_ J I ' ' ............ l .................. _ .................................................. I I I I I *
I i i I I
I I I I a _.I I
t I i I _ i
i _ I I I
I ] I i I I
I I _ i i I
I _ I I I I.d I
EX (mV/M) .......... i_ 0
, ' ' ',SOLAR 40 I 30 1210 Ill0 I i 0 IELEV.(DEG) ,,,,,,, ..........' ':' ......... " "I';':""L':"'" ,'::",_' .... -150
UT 1410 1414 1418 1422 1426 1430
ALT(KM) 563 319 299 305 336 391
MLT (HR) 12.0 12.4 14.4 21.8 22.8 25.1
[LAT(DE6) 48.5 64.2 79.2 81.7 67.2 51.2
MLAT(DEG) 51.1 67.0 81.9 78.3 62.8 46.9
Figure 3. A northern polar pass of DE-2 on 8 September 1981 during IMF Bz > O. The
correlation between the orthogonal pair of B and E components (i.e., AB z vs. F,x) is high
even when the angle o_(Fig. 4) changes rapidly as in intervals A and B.
458
18o 1 I 1 I 1 I 1
8 SEPTEMBER 1981
160 I
I
140 I
I
I A
120 I
09
iii
LU 100
rr"
(.9
LU
a
80
60 B I
I
I
40 I [ --
CJ
2oJ--- l"',,J D -I -
I _ _ ,
o I 1 1 1 I 1 I I I 1
1414 i416 1418 1420 1422 1424 1426 1428 1430 UT
Figure 4. Angle c_along the pass in Fig. 3.
459
N m
SATELLITE VELOCITY
N I GEOGRAPHICNORTH POLE
'G EOMAGNETIC
N rn DIPOLE NORTH
.POLE
S
/
/ N
$
/'NmS
/
S
Figure 5. Angle, o_, between the orbit plane and the dipole meridian plane; a is
measured from the dipole south direction to the direction of the spacecraft velocity.
460
DE-2 9 SEPTEMBER1981
I000 ..... q...... _......
ABx(nT) 0 .............................................................................................
-I000 ..... +..... ', ..... ', ..... t ..... , ..... _ ..... _ .... I000
ABy(nT) .......... I ...... f .......... :llIII "_ 0
I I n I I
+ I I
r =1 0.98 i 0911 093 079 I 0.97I I I
_P :1 71 158 [ 24 I 19 I 3.8
I000 .... -,-H--,--_-,,,..... _........... ,,..... _..... +..... I000
I I I I i I
, A IBL C i D _ E i
A BZ (nT) 0 .....]..._ --_.-----_--.................L.....................' .... _..: ............
I ' _ I I i
I I L I
i I I I I
I o I ] I
-I000 ..... +..... I ..... '........... : ..... _''": ',.... 150I , I I I I
I ] n i n
I L I _ t
EX (mY/M) I---L-' I , _!-':._ 0
SOLAR
ELEV.(DEG)] i_ , , l_20 l 10 0 1 -IO I t1 ..... I...... ,.... , ..... , , , -150
UT 0140 0144 0148 O152 0156
ALT(KM) 302 301 326 375 443
MLT (HR) 10.8 9.9 4.7 0.8 0.2
ILAT (DEG) 62.5 78.2 81.6 68.0 5:5.2
MLAT(DEG) 58.9 74.:5 8:.5.1 71.0 55.9
Figure 6. A northern pass when IMF Bz < on September 1981. The angle o_changed
rapidly from intervals B to C. The field-aligned current was appreciable on the nightside
because of auroral electrons.
461


Joule heating and field-aligned currents: Preliminary results from DE-2

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server