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Magnetic field configuration of the heliosphere in interstellar space
Planet. Space Sci. Vol. 29, pp. 313-316 OiPergamon Press Ltd., 1981. Printed in Northern Ireland
MAGNETIC
0032-0633/81/030313-04.$02.00/0
FIELD CONFIGURATION IN INTERSTELLAR S.-I. AKASOFU
OF THE HELIOSPHERE SPACE
and D. N. COVEY
Geophysical Institute, University of Alaska, Fairbanks, AK 99701, U.S.A. (Received 12 September 1980)
AlMmct-A model of the heliospheric magnetic field configuration is constructed by including a uniform interstellar magnetic field to the model proposed by Akasofu et al. (1980).
1. INTRODUCTION
In a recent paper, Akasofu et al. (1980) constructed a model of the heliospheric magnetic field configuration by assuming that the heliospheric magnetic field consists of (i) the solar dipole field, (ii) the magnetic arcade field, (iii) the field of the poloidal current system generated by the solar unipolar induction and (iv) -the field of an extensive current disk around the sun lying in the ecliptic plane. The heliosphere was assumed to have a spherical boundary of radius of 20 a.u. and all the field components are assumed to be confined in it. In this short paper, an improved model of the heliospheric magnetic field configuration is presented by including a uniform interstellar magnetic field and by adopting different values for a few magnetic field parameters. All the basic expressions for the magnetic field components remain the same. The changes are made in the following features. (a) In (ii), the magnetic field of the spherical dipoles (constituting the arcade field) is changed from 500 to 50 G. (b) In (iv), the solar current disk extends from a distance of 1.5Ro, instead of 10RO; the current density in the disk between r = 1.5Ro and r = 10Ro is assumed to be constant and has the same value at r = lOR,. (c) A uniform and southward directed interstellar magnetic field of 0.22~ (Spitzer, 1978, p. 66) is included. It is assumed that the heliosphere tends to exclude the interstellar magnetic field by the action of the solar wind (cf. Davis, 195.5), so that it is assumed that a uniform field of 0.01-y (namely, 5% of 0.22~) is allowed to penetrate inside the spherical heliosphere. This is accomplished by adding a spherical dipole of radius of 20 a.u. and the polar field of 0.21~ to the heliosphere. (d) The total magnetic field configuration is constructed for the northward and southward orienta313
tions of the solar dipole field. Note that by changing the orientation of the solar dipole field (i), the direction of the magnetic field components (ii), (iii) and (iv) is also reversed. 2. RESULls
Figure 1 shows the meridian and equatorial projections of magnetic field lines which “originate” at the polar angle 0 = 10 and 20” on the photosphere for the case in which the solar dipole moment is directed northward. Figure 2 is similar to Fig. 1 except that the field lines originate at 8 = 30 and 40” on the photosphere. When the solar dipole moment is oriented northward, none of the heliospheric magnetic field lines are connected to the interstellar field lines except for the singular line from 8 = 0” (though not shown). This situation corresponds to a closed magnetosphere in a northward directed interplanetary magnetic field. Figure 3 shows the meridian and equatorial projections of magnetic field lines which “originate” at the polar angle 13= 10 and 20” on the photosphere for the case in which the solar dipole moment is directed southward. Figure 4 shows field lines which originate at 8 = 30 and 40”. In this situation, all field lines which originate at 0 < - 43” are connected to the interstellar field lines. On the other hand, all field lines which originate at 0 > - 43” are “closed”, having a stretched dipolar configuration. This situation corresponds to the open magnetosphere in which the polar cap field lines are connected to the interplanetary magnetic field lines. The magnetic field configuration at distances r< 50Ro is shown in Fig. 5 for the sum of the fields (i), (ii) and (iv). Such a closed configuration may be required to explain an interesting space probe observation of Forbush decreases by Van Allen (1979). It is expected that the large differences of the magnetic field configuration of the heliosphere have
4000~~ 3000 2000.~ 1000, Y
0,
-1000 -2000~ -3000 - 4000 I -5000’
FIG.
- 4000
1.
THE
ORIGINATE
-2000
MERIDIAN
2000
!
(x, z)
AND
AT THE POLAR ANGLE
4000
EQUATORIAL
@ = 10”
J & -4000 R@
(x, y)
(LEFT) AND @ =
PROJECTIONS
uniform
interstellar field (directed southward)
2000
!
OF MAGNETIC
RELD
4000
LINES WHICH
20”
DIPOLE M0MTSN-I IS DIRECTED A
-2000
(RIGHT) FOR THE CASE IN WHIcH NORTHWARD.
THE SOLAR
is allowed to partially penetrate into the heliosphere.
5000 4000 z
3000 2000 1000 0
4000 3000 2000 ” 1000 ”
Y
0
-1000
I
-2000 -3000 -4000 -5000
’
I
-4000
-2000
0
2000
4000
R@
- 4000
- 2000
X
FIG. 2. sAh4E As
FIG.
1, EXCEPT FOR ti =
314
30 AND 40”.
0 X
2000
4000
4000. 3000.. 2000~. 1000,. Y
0.
-1000. -2000 -3000, -4000,
FIG. 3. THE MERDL4N(X,2) ANTJEQUATORIAL ORIGINATE
AT THE POL.AR ANGLE
(X, y)
0 = 10” (LEJFT) AND
DIPOLE
MOMENT
PROJEXTIONS
20” (RIGHT)
6 =
IS DIRECR!D
OF MAGNETIC
FIELD
LINES
FOR THE CASE LN WHICH
WHICH
THE SOLAR
SOUTHWARD.
A uniform interstellar field (directed southward) is allowed to partially penetrate into the heliosphere.
-siloo~
-4000
I -2000
2000 FIG.
4000
Re
I
-4000
4. !%MEAs FIG. 3, EXCEPT FOR 315
8 =
-2000
30 AND40”.
2000
4000
FIG.
5. THE
vALuEs
-IAN
OF THE POLAR
PROJECITON ANGLE
OF MAGNETIC
f3 (EXCLUDING
FIELD
THE AzumrmL
profound effects on motions of cosmic ray particles which penetrate into the heliosphere from interstellar space, as suggested by Ahluwalia (1979) and Nagashima and Morishita (1980a,b). Acknowledgements-This work was supported in part by a grant from the National Aeronautics and Space Administration, NSG-7447 and in part by a grant from the National Science Foundation, ATM77-26522. REFERENCES
Ahluwalia, H. S. (1979). Solar polar field reversals and secular variation of cosmic ray intensity, presented at the I.A.U. Symp 91 on rhe Solar and the Interplanetary Dynamics, held at Harvard University on 27-31 August.
LINES Up TO A DISTANCE COMPONENT
OF 50Ro
FOR VARIOUS
AND THE INTERSTELLAR
FIELD).
Akasofu, S.-I., Gray, P. C. and Lee, L. C. (1980). A model of the heliospheric magnetic field configuration. Planet. Space Sci. 28, 609. Davis, L., Jr. (1955). Interplanetary magnetic fields and cosmic rays. Phys. Rev. 100,1440. Nagashiia, K. and Morishita, I. (1980a). Long term modulation of cosmic rays and inferable electromagnetic state in solar modulating region. Planet. Space Sci. 28, 177. Nagashima, K. and Morishita, I. (198Ob). Twenty-two year modulation of cosmic rays associated with polarity reverse and of polar magnetic field of the sun. Planet. Space Sci. 28, 19.5. Spitzer, L. Jr. (1978). Physical Processes in the Interstellar Medium, John Wiley & Sons, New York. Van Allen, J. A. (1979). Propagation of a Forbush decrease in cosmic ray intensity to 15.9 a.u. Geophys. Res. Len. 6, 566.
MAGNETIC
0032-0633/81/030313-04.$02.00/0
FIELD CONFIGURATION IN INTERSTELLAR S.-I. AKASOFU
OF THE HELIOSPHERE SPACE
and D. N. COVEY
Geophysical Institute, University of Alaska, Fairbanks, AK 99701, U.S.A. (Received 12 September 1980)
AlMmct-A model of the heliospheric magnetic field configuration is constructed by including a uniform interstellar magnetic field to the model proposed by Akasofu et al. (1980).
1. INTRODUCTION
In a recent paper, Akasofu et al. (1980) constructed a model of the heliospheric magnetic field configuration by assuming that the heliospheric magnetic field consists of (i) the solar dipole field, (ii) the magnetic arcade field, (iii) the field of the poloidal current system generated by the solar unipolar induction and (iv) -the field of an extensive current disk around the sun lying in the ecliptic plane. The heliosphere was assumed to have a spherical boundary of radius of 20 a.u. and all the field components are assumed to be confined in it. In this short paper, an improved model of the heliospheric magnetic field configuration is presented by including a uniform interstellar magnetic field and by adopting different values for a few magnetic field parameters. All the basic expressions for the magnetic field components remain the same. The changes are made in the following features. (a) In (ii), the magnetic field of the spherical dipoles (constituting the arcade field) is changed from 500 to 50 G. (b) In (iv), the solar current disk extends from a distance of 1.5Ro, instead of 10RO; the current density in the disk between r = 1.5Ro and r = 10Ro is assumed to be constant and has the same value at r = lOR,. (c) A uniform and southward directed interstellar magnetic field of 0.22~ (Spitzer, 1978, p. 66) is included. It is assumed that the heliosphere tends to exclude the interstellar magnetic field by the action of the solar wind (cf. Davis, 195.5), so that it is assumed that a uniform field of 0.01-y (namely, 5% of 0.22~) is allowed to penetrate inside the spherical heliosphere. This is accomplished by adding a spherical dipole of radius of 20 a.u. and the polar field of 0.21~ to the heliosphere. (d) The total magnetic field configuration is constructed for the northward and southward orienta313
tions of the solar dipole field. Note that by changing the orientation of the solar dipole field (i), the direction of the magnetic field components (ii), (iii) and (iv) is also reversed. 2. RESULls
Figure 1 shows the meridian and equatorial projections of magnetic field lines which “originate” at the polar angle 0 = 10 and 20” on the photosphere for the case in which the solar dipole moment is directed northward. Figure 2 is similar to Fig. 1 except that the field lines originate at 8 = 30 and 40” on the photosphere. When the solar dipole moment is oriented northward, none of the heliospheric magnetic field lines are connected to the interstellar field lines except for the singular line from 8 = 0” (though not shown). This situation corresponds to a closed magnetosphere in a northward directed interplanetary magnetic field. Figure 3 shows the meridian and equatorial projections of magnetic field lines which “originate” at the polar angle 13= 10 and 20” on the photosphere for the case in which the solar dipole moment is directed southward. Figure 4 shows field lines which originate at 8 = 30 and 40”. In this situation, all field lines which originate at 0 < - 43” are connected to the interstellar field lines. On the other hand, all field lines which originate at 0 > - 43” are “closed”, having a stretched dipolar configuration. This situation corresponds to the open magnetosphere in which the polar cap field lines are connected to the interplanetary magnetic field lines. The magnetic field configuration at distances r< 50Ro is shown in Fig. 5 for the sum of the fields (i), (ii) and (iv). Such a closed configuration may be required to explain an interesting space probe observation of Forbush decreases by Van Allen (1979). It is expected that the large differences of the magnetic field configuration of the heliosphere have
4000~~ 3000 2000.~ 1000, Y
0,
-1000 -2000~ -3000 - 4000 I -5000’
FIG.
- 4000
1.
THE
ORIGINATE
-2000
MERIDIAN
2000
!
(x, z)
AND
AT THE POLAR ANGLE
4000
EQUATORIAL
@ = 10”
J & -4000 R@
(x, y)
(LEFT) AND @ =
PROJECTIONS
uniform
interstellar field (directed southward)
2000
!
OF MAGNETIC
RELD
4000
LINES WHICH
20”
DIPOLE M0MTSN-I IS DIRECTED A
-2000
(RIGHT) FOR THE CASE IN WHIcH NORTHWARD.
THE SOLAR
is allowed to partially penetrate into the heliosphere.
5000 4000 z
3000 2000 1000 0
4000 3000 2000 ” 1000 ”
Y
0
-1000
I
-2000 -3000 -4000 -5000
’
I
-4000
-2000
0
2000
4000
R@
- 4000
- 2000
X
FIG. 2. sAh4E As
FIG.
1, EXCEPT FOR ti =
314
30 AND 40”.
0 X
2000
4000
4000. 3000.. 2000~. 1000,. Y
0.
-1000. -2000 -3000, -4000,
FIG. 3. THE MERDL4N(X,2) ANTJEQUATORIAL ORIGINATE
AT THE POL.AR ANGLE
(X, y)
0 = 10” (LEJFT) AND
DIPOLE
MOMENT
PROJEXTIONS
20” (RIGHT)
6 =
IS DIRECR!D
OF MAGNETIC
FIELD
LINES
FOR THE CASE LN WHICH
WHICH
THE SOLAR
SOUTHWARD.
A uniform interstellar field (directed southward) is allowed to partially penetrate into the heliosphere.
-siloo~
-4000
I -2000
2000 FIG.
4000
Re
I
-4000
4. !%MEAs FIG. 3, EXCEPT FOR 315
8 =
-2000
30 AND40”.
2000
4000
FIG.
5. THE
vALuEs
-IAN
OF THE POLAR
PROJECITON ANGLE
OF MAGNETIC
f3 (EXCLUDING
FIELD
THE AzumrmL
profound effects on motions of cosmic ray particles which penetrate into the heliosphere from interstellar space, as suggested by Ahluwalia (1979) and Nagashima and Morishita (1980a,b). Acknowledgements-This work was supported in part by a grant from the National Aeronautics and Space Administration, NSG-7447 and in part by a grant from the National Science Foundation, ATM77-26522. REFERENCES
Ahluwalia, H. S. (1979). Solar polar field reversals and secular variation of cosmic ray intensity, presented at the I.A.U. Symp 91 on rhe Solar and the Interplanetary Dynamics, held at Harvard University on 27-31 August.
LINES Up TO A DISTANCE COMPONENT
OF 50Ro
FOR VARIOUS
AND THE INTERSTELLAR
FIELD).
Akasofu, S.-I., Gray, P. C. and Lee, L. C. (1980). A model of the heliospheric magnetic field configuration. Planet. Space Sci. 28, 609. Davis, L., Jr. (1955). Interplanetary magnetic fields and cosmic rays. Phys. Rev. 100,1440. Nagashiia, K. and Morishita, I. (1980a). Long term modulation of cosmic rays and inferable electromagnetic state in solar modulating region. Planet. Space Sci. 28, 177. Nagashima, K. and Morishita, I. (198Ob). Twenty-two year modulation of cosmic rays associated with polarity reverse and of polar magnetic field of the sun. Planet. Space Sci. 28, 19.5. Spitzer, L. Jr. (1978). Physical Processes in the Interstellar Medium, John Wiley & Sons, New York. Van Allen, J. A. (1979). Propagation of a Forbush decrease in cosmic ray intensity to 15.9 a.u. Geophys. Res. Len. 6, 566.