The warped heliospheric current sheet in early 1976 was calculated from the observed photospheric magnetic field using a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity in early 1976 obtained at several locations in the heliosphere at Helios 1, Helios 2, Pioneer 11 and Earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field, and that "ballerina skirt" effects may add small scale ripples

Hoeksema, J. T.

Scherrer, P. H.

Wilcox, J. M.

English

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-^ - !'HE ORIGIN OF THE WARPED
4. I-IP.1,10SPHERIC CURRENT SHEE
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3b491
J.",& Wilcox, P.H. Scherrer
and
J.T. Hoeksema
Office of Naval Research
Contract N(10h14-76-(:-0207
National Aeronautics and Space Administration
Grant NCR 05-020-559
Contract NASS-24420
National Science Foundation
Grant ATM77-20560
StJIPR Report No. 803
%larch 19M)
G4
INSTITUTE FOR PLASMA RESEARCH
STANFORD UNIVERSITY, STANFORD, CALIFORNIA
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REPORT NU !. GOVT ACCESSION NO R III N S CATALOG 
SUIPR Report No. 803
TITLE (And Subtitle) S. TYPE OR REPORT a 1 10 111,1100 COVERED
The Origin of the Warped Heliospheric Scientific; Technical
Current Sheet {. PERFORMING ORB. R4PORT NUM99R
7. AUTMOR(e) 11. CONTRACTORN	 NUM
J. M. Wilcox, P. H. Scherrer, and N00014-76-C-0207
J. T. Hoeksema
6. PERFORMING ORGANIZAT I ON NAME AND ADDRESS to. P"RAM ELEMENT. PROJECT. TASKIA & WORKAR 	 UNIT NUMBERS
Institute for Plasma Research
Stanford University
Stanford, California 94305
11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT CATS
Office of Naval Research March 1980
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IS. SUPPLEMENTARY NOTES
Tech; Other
1S. KEY WORDS (Centime* an forms side it necessary and ldntffy by Meek mwthsr)
Interplanetary Magnetic Field
Solar Magnetic Field
Interplanetary Sector Structure
20. ABSTRACT (Centfmne an revolve side ft mecoseary SW fd mtfb' h Meek MMAW)
The warped heliospheric current sheet in Parly 1976 is calculated
from the observed photospheric magnetic field using a potential field
method.	 Comparisons with measurements of the interplanetary magnetic
field polarity in early 1976 obtained at several locations in the
heliosphere at Helios I, Helios II, Pioneer XI and Earth show a rather
detailed agreement between the computed current sheet and the observa-
tions.	 It appears that the large-scale structure of the warped (cont.)
DD FORM	 EDITION OF 1 NOV SS IS OBSOLETEW 1 JAM TS ^L73	 UNCLASSIFIEDS/N 0102.014•{{01 SECURITY CLASSIFICATION OF THIS PAGE	 a
UNCLASSIFIED
..L1.1191TY GLAiililGATlC'N OF THIS rA99"M40 DMa
20.
heliospheric current sheet is determined by the structure
of the photospheric magnetic f±Pid, and that "ballerina
skirt" effects may add small-scale ripples.
1t
t
3
i
UNCLASSIFIED
![CUNITY CLAWFICATION OF TNII PAG9MhM Data &WOO
THE ORIGIN OF THE WARPED
HELIOSPHERIC CURRENT SHEET
by
J. M. Wilcox, P. H. Scherrer
and
J. T. Hoeksema
Office of Naval Research
Contract A00014-76-C-0207
National Aeronautics and Space Administration
Grant NGR 05-020-559
Contract NAS5-24420
National Science Foundation
Grant ATM77-20580
SUIPR Report No. 803
March 1980
Institute for Plasma Research
Stanford University
Stanford, California
Submitted to: SCIENCE
This manuscript is not yet refereed. It is mailed out when the
paper is submitted for publication. The published version is often
improved by the refereeing process. This SUIPR report should not
be cited after the published version has appeared. We would appre-
ciate receiving any comments that might improve the published version.
Abstract
The warped heliospheric current sheet in early 1976 is calculated
from the observed photospheric magnetic field using a potential field
method. Comparisons with measurements of the interplanetary magnetic
field polarity in early 1976 obtained at several locations in the
heliosphere at Helios I, Helios II, Pioneer XI and Earth show a rather
detailed agreement between the computed current sheet and the observa-
tions. Ir_ appears thist L..,! large-scale structure of the warped
heliospheric current sheet is determined by the structure of the
photospheric magnetic field, and that "ballerina skLrt" effects may
add small-scale ripples.
i
a
M
The existence of a warped current sheet in the non-polar regions of the
heliosphere is now generally accepted (1-4). An artist's impression of an
average shape of the current sheet at a time near sunspot minimum (2) is
shown in Figure 1. As the current sheet rotates with the sun the sector struc-
ture of the interplanetary magnetic field (5) is produced. At the phase of
the sunspot cycle discussed in this paper, the large-scale interplanetary
ma-netic field is directed away from the sun northward of the current sheet,
and is directed toward the sun southward of the sheet. It should be noted
that the term "interplanetary sector structure" coined by Wilcox and Ness (5)
describes the structure in the plane of the ecliptic and does not refer to
to three-dimensional structures such as the sectors of an orange.
There are two pcints of view regarding the origin of the warped heliospheric
current sheet. Svalgaard and Wilcox (6) review the computations of the magnetic
field at a "source surface" using as a boundary condition the photospheric magnetic
field observed using the Zeeman effect. Outside of the source surface the warped
current sheet is assumed tc be carried radially outward by the solar wind. In this
model the structure of the current sheet (i.e. the location in solar longitude and
the extent in solar latitude of the maxima and minima) is a direct consequence
of the observed photospheric magnetic field.
Alfven (4; see also 7) has proposed an alternative viewpoint in which the solar
origin of the current sheet is a plane similar to the plane (i.e. her waist) in which
1	 L
the skirt of the ballerina originates. In this model the current sheet waves
up and down like the skirt of a spinning ballerina.
It is the purpose of this note to show that the observations of the inter-
planetary magnetic field (IMF) during the first months of 1976 (i.e. near sun-
spot minimum) at Earth, by Pioneer XI near a heliospheric latitude of 16 0N (8),
and by Helios I and II between 0.28 and 1 A.U. within a latitudinal excursion
+/- 7.230 from the solar equatorial plane (9) are in good agreement with a warped
current sheet computed from the observed photospheric magnetic field by the
methods reviewed ill (6). It thus appears that the large-scale structure of the
heliospheric current sheet is controlled by the photospheric magnetic field,
although small-scale ripples may be added by dynamic solar wind processes (the
ballerina effect).
The curved line in Figure 2 represents the average warped current sheet
that separates regions with magnetic field away from the sun (above the line)
and toward the sun (below the line), as computed on a source surface at 2.6
solar radii during the interval 20 January through 26 May 1976. The solar wind
is assumed to carry the magnetic structure on the source surface radially out-
ward into the heliosphere. In fact, the curved line in Figure 2 is rather
similar to the bottom panel of Figure 4 in Svalgaard and Wilcox (6) which was
computed as the average of eighteen 27-day solar rotations starting S May 1976
and ending 7 August )977, i.e. just after the interval discussed in the present
note. This similarity is evidence of the long-term stability of the large-
scale photospheric and heliospheric magnetic fields.
Such long-term stability would not be expected from the dynamic effects
of the ballerina skirt model. This stability would also not be expected if the
predominant warps in the current sheet were caused by coronal holes (9) since
the lifetime of a coronal hole is typically only several rotations. Since coronal
holes appear in the central portion of sectors (6) it would be expected that
s
2
	 L
3the longitudes of coronal holes would correspond to the longitudes of maximum
warp of the heliospheric current sheet.
(
	
	
The dashed horizontal line in Figure 2 represents the heliographic latitude
of 16°N near which Pioneer XI observed the interplanetary magnetic field to be
predominantly away from the sun during the interval discussed in this note (8).
The plus (away) and minus (toward) signs in Figure 2 represent the interplanetary
ragnetic field polarity as observed by Helios I and II (9) projected onto the
solar corona. The computed current sheet in Figure 2 is similar to the inferred
current sheet shown in Figure 4b of reference 9.
Figure 2 shows that the Helios spacecraft observations of the polarity of
the interplanetary magnetic field are in good agreement with the computed location
of the current sheet. Of particular interest is the detailed agreement in that
when the Helios spacecraft were at southern heliographic latitudes they observed
• two-sector pattern whereas when they were at northern latitudes they observed
• four-sector pattern, just as is computed in Figure 2.
The curved line in Figure 2 representing the warped heliospheric current
sheet is repeated in Figure
IMF polarity at Earth (10).
in mapping this back to the
two-sector pattern when the
of the four-sector structure
3, where the plus and minus signs show the inferred
A 4^ day travel time from sun to Earth (11) is used
corona. The IMF structure at Earth also shows a
Earth is near 7°S heliographic latitude, but hints
e are seen as Earth moves northward.
We note that if a 5^ day travel time had been used, the data in Figure 3
would be moved to the right by about 130 longitude, which would significantly
improve the agreement. The same situation exists with regard to the spacecraft
data in Figuia 2. This suggests that the simple mapping techniques used in
preparing Figures 2 and 3 may be only an approximation.
Vim_
r I	
While the large-scale structure of the current sheet persists for many
solar rotations, on any particular rotation changes in the current sheet may
occur due to the effects of solar activity and coronal holes (12). Nevertheless,
the overall agreement in Figures 2 and 3 between the observed IMF polarities and
the structure of the heliospheric current sheet as computed from the observed
photospheric magnetic field is impressive.
Two predictions may be made from the considerations discussed in this
note. First. If Pioneer XI had been at 16 0S heliospheric latitude in the first
part of 1976 rather than at 16 0N it would have observed a well-defined two-
sector structure. Second. Although Pioneer XI did observe an interplanetary
field polarity that was predominantly away from the sun, we would predict that
for intervals of a few days corresponding to Carrington sol-.r longitudes near
350 and	 1600 Pioneer XI may have observed toward polarities. We note in
Figure 2 of Smith et al. (8) that during the interval of interest Pioneer XI
observed that the ratio of the number of away polarity observations to the total
number of observations was about 0.8. the computed current sheet in Figure 2
would correspond to a ratio of about 0.7.
We suggest that the observations of the interplanetary magnetic field
polarity by Pioneer XI and by Helios I and II support the viewpoint that the
large-scale structure of the warped heliospheric current sheet can be computed
from the observed photospheric magnetic field, with the ballerina effect perhaps
adding small-scale ripples. Since coronal holes are effects of conditions
pertaining to the large-scale photospheric magnetic configuration (6) 	 the
influence of coronal holes on the warped current sheet is to a considerable
extent already included in the present calculations.
The observations by Pioneer XI at 16 0 North heliospheric latitude 0)
have been widely misinterpreted to mean that the heliospheric current sheet is
almost parallel to the solar equatorial plane (see for example 13). Figure 2 shows
that even near the minimum of the eleven year sunspot cycle the current sheet probably
4
reached appreciable south heliospheric latitudes, and the considerations dis-
cussed by Svalgaard and Wilcox (2) indicate that near the maximum of the sun-
s	 spot cycle the current sheet reaches heliographic lctituden of 50 0 or more (3).
Acknowledgements
We thank Dr. Robert Howard for observations of the photospheric magnetic
field obtained at Mt. Wilson Observatory. This work ;+as supported in part by
the Office of Naval Research under Contract N00014-76-C-0207, by the National
Aeronautics and Space Administration under Grant NGR 05-020-559 and Contract
NAS5-24420 and by the Atmospheric Sciences Section of the National Science
Foundation under Grant ATM77-20580.
J. M. Wilcox, P. H. Scherrer, ind J. T. Hoeksema: Institute for Plasma Research,
Stanford University, Via Crespi, Stanford, California 94305
5
References
(1) K. H. Schatten, in C. P. Sonett, P. J. Colman, Jr. and J. K. Wilcox,
Eds., Solar Wind (National Aeronautics and Space Administration,
Washington, A. C., 1912), p. 88;
M. Schulz, Astrophys. Space Sci. 24, 371 (1973);
E. H. Levy, Nature 261, 394 (1976);
M. Schulz, E. N. Frazier and D. F. Boucher, Jr., Solar Phys. 60, 83
(1978).
2, 766 (1976).
5, Geophys. 23. 37 (1975).
271 (1977).
Res. 70, 5793 (1965).
Astron. Astrophys. 16, 429
(2) L. Svalgaard and J. M. Wilcox, Nature 26
(3) T. Saito, Sci. Repts. T6hoku Univ., Ser.
(4) H. Alfven, Rev. Geophys. Space Phys. 15,
(..) J. M. Wilcox and N. F. Ness, J. Geophys.
(6) L. Svalgaard and J. M. Wilcox, Ann. Rev.
(1978).
(7) E. J. Smith and J. H. Wolfe, mace Sci. Rev. 23, 217 (1979).
(8) E. J. Smith, B. T. Tsurutani, and R. Rosenberg, J. Geophys. Res. 83,
717 (1978).
(9) U. Villante, R. Bruno, F. Marini, L. F. BurlaRa, and N. F. Ness,
J. Geophys. Res. 84, 6641 (1979).
(10) L. Svalgaard, J. Geophys. Res. 77, 4027 (1972).
(11) J. M. Wilcox, Space Sci. Rev. 8, 258 (1968).
(12) R. H. Levine, Astrophys.s. J. 218, 291 (1977); in J. Zirker, Ed.,
Coronal Holes and High Speed Wind Streams (Colorado Associated
University Press, Boulder, 1977), pp. 103-143.
(13) M. A. Livshits, T. E. Valchuk, and Y. I. Feldstein, Nature 278, 241
(1979).
6
Figure Cap•ions
Figure 1	 An artist's impression of this warped heliospheric current
sheet. Presently the region above the current sheet has
interplanetary magnetic field (IMF) directed away from the
sun and the region below has field directed toward the sun.
(Artist: Werner Heil)
Figure 2 The curved line represents the calculated average heliospheric
current sheet foi the S rotations including January 20 through
May 23, 1976. The dashed line at 160N latitude represents the
approximate heliographic latitude of the Pioneer XI spacecraft
which was about 4 A.U. from the sun. The plus (away from the
sun) and minus (toward) signs indicate the IMF polarity
measured at Helios I and II projected back onto the sol&_
corona. The observed IMF polarities agree well with the
computed current sheet.
Figure 3	 The same as Figure 2, except that the pluses and minuses
represent the inferred IMF polarity at Earth mapped back to
the solar corona. The observed pclarity changes occur near
crossings of the computed current sheet
7
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SOLAR LONGITUDE
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10


The origin of the warped heliospheric current sheet

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