A suggestion by McDiarmid and Budzinski that an annual variation of geomagnetic activity can explain a sector polarity asymmetry is shown not to be necessary. The correct explanation is that the Kp-index exhibits systematic errors that enhance the UT variation during Toward polarity and decrease the UT variation during Away polarity

Svalgaard, L.

English

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AD-A024 603
COMMENT ON 'KP DEPENDENCE ON SECTORS' BY I. B.
McDIARMID AND E. E, BUDZINSKI
STANFORD UNIVERSITY
PREPARED FOR
OFFICE OF NAVAL RESEARCH
MARCH 1976
iI
45112
Comr wt on `Kp
by
Leif Svalgaard 1 r Lr,_IV!	 1 ;,
Sectors' by I. B. McDiarmid arid
^J
	 E. E. 8uclainski
March 1976
Reprodnetiea in whole or is part
is permitted for any purpose of
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vl^
SUIPR Report No. 655
Office of Naval  Research
Contract NOGJI4-76-r-0207,t^
National Aeronautics and
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National Science Foundation
Gram ATM 74-19007, and
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Comment on 'Kp Dependence on Sectors' Scientific, Technical
by I.B. McDiarmid and E.E. Budzinski
G. PERFORMING ORG. REPORT NLMBER
1. AUTHORISI
8. CONTRACT OR GRANT NUMBERIst
Leif Svalgaard N00014-76-C-0207
PERt(IRMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PRO.II,:
Institute for Plasma Research AREA & WORK UNIT NUMHF •'
Stanford University
Stanford, California
12. REPORT DATE 13	 N::	 OF Pr3 I`.•
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1976 1
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1R SUPP: I MPNTARY NOTES
TECH; OTHER
i	 ,W FIDS
	
Commmur on revmse side It necessary and identify by block number)
Geomagnetic activity
Interplanetary field
UT variation
I	 ..nl7 HACT I Cnotmur on rr y
r 
rsr side	 f necessary and mam,fy by block
A suggestion by MCDiarmid and Budzinski
number)
that an annual variation of geo-
magnetic activity can explain a sector polarity asymmetry is shown not to be
necessary.	 The correct explanation is that the Kp-index exhibits systematic
errors that enhance the UT variation during Toward polarity and decreases the
UT variation during Away polarity.
FORM
DD
/qy 7_/+gp
F DITION OF 1 NOV 65 IS OBSOLETE
U\CLASS IF'IL'D
SECURITY CLASS 4 1CATION OF THIS PAGE (When Data Entered)
i
v
Comment on 'Kp Dependence on Sectors'
by I.B. McDiarmid and E.E. Budzinski
by
Leif Svalgaard
Office of Naval Research
Contract N00014-76-C-0207
National Aeronautics and Space Administration -
Grant NGR 05-020-559
National Science Foundation
Grant ATA174-19007
and
The Max C. Fleischmann Foundation
r
^i"v 	-	 6hYr .,"silnn ^I
SUIPR Report No. 655	 s S:caa i_)
March. 1976
EY.	 _	 ...	 .._..
L; A 4J7 - r!RY.IV uP ifY PO:CS
Institute for Plasma Research 	 "'•^^!" .=`='"'
Stanford University
Stanford, California	 y
i
Submitted to: JourAal of Geophysical Research
11
i
Comment on 'Kp Dependence on Sectors'
by I.B. McDiarmid and E.E. Budzinski
by
Leif Svalgaard
Institute for Plasma Research
Stanford University
Stanford, California 94305
;t
r
	
	 McDiarmid and Budzinski (1975) examined the Kp-index as a function
of the average geocentric solar magnetospheric (GSM) latitude of the inter-
planetary magnetic field. Their results seem to indicate that the Kp-index
depends on cos b, where d is the angle between the average interplanetary
magnetic field direction and the Z axis of the GSM coordinate system. Such
r
a dependence is predicated by the merging theory of geomagnetic activity
(Russell and McPherron, 1973; Svalgaard, 1976a). A striking feature of
McDiarmid and Budzinski'sanalysis was that the correlation between Kp and
cos b was present only when the polarity of the interplanetary magnetic
field was directed towards the sun. During away polarity there was little
or no correlation between .
 Kp and cos b. This difference between away and
toward polarity was explained by McDiarmid and Budzinski in terms of an
additional annual variation of geomagnetic activity. It is the purpose
of the present note to point out that such an assumption is not necessary
to explain the difference between the Kp dependence of cos b for the two
sector polarities. The correct explanation is simply that Kp is not suited
for the kind of analysis attempted by McDiarmid and Budzinski.
The angle d depends both on time of year and on Universal Time, In
constructing the Kp index it was,realized that the Kp observatories were
so unevenly distributed in longitude (most of them are in Europe) that
true Universal Time variations would be masked by local time effects, As
a consequence standardization tables are used to eliminate local time (and
UT) variations„ Ideally Kp should have no UT variation at all, As Michel 	
i
(1964) points out, this goal was not quite achieved and a small residual
1
a
(and entirely artificial) UT-variation is still present. Except for
the lowest values, the Kp-index in the beginning of the UT-day is,
systematically too high, while it is too low in the middle of the UT day.
Becnuse cos 6 changes sign when the sector polarity changes, the UT-
vnriations of geomagnetic activity according to the merging theory should
be opposite for the two polarities. During away polarity the activity
should have a maximum of 10,10 LIT and during toward polarity maximum
activity should occur at 2290 UT. Using a geomagnetic index devised by
Mayaud (1967), the so-called am-index, it is possible to verify that such
UT-variations exist. The am-index is derived from stations having a nearly
uniform distribution in longitude and is therefore capable of showing the
proper UT-variations. Figure 1 shows the result of an nnalysis by Svalgnard
(1976x). Note that the observed variations are just as expected from the
merging theory.
The magnitude Of these UT variations is comparable to the systematic
errors in the Kp index and the observed Kp dependence .onUT is a result of
superposing the real UT variations and the systematic errors. The net re-
sult is that the systematic errora enhance 	 the UT-variation during to-
ward polarity and decreases the UT-variation during away polarity. Figure 2
shows the result of this superposition. It is apparent that the UT-variation
during away polarity indeed 	 is completely masked by the residual systematic
errors in Kp. One could then conclude as did 61cDiarmid and Budzinski that
Kp has different cos d dependence in different interplanetary sectors. Such
a conclusion is formally correct but does not mean that geomagnetic activity
has different cos h dependence for opposite polarities.
The present author ( Svalgaard, 1976b) has recently proposed that
the Kp index be replaced by 1layaud's Km-index (Km being derived from am,
as Kp is related to the np-index). The investigation by McDiarmid and
Budzinski, which is commented upon in this note, is a good' , ndication that
such replacement is strongly needed,.
2
r
3Acknowledgements
This work was 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 by the Atmospheric Scier_.ps
Section of the National Science Foundation under Grant ATIM74-19007 and
Grant DES75-15664, and the Max C. Fleischman Foundation.
..f
i3y
i
3
IReferences
1layaud, P.N., Calcul proliminaire d'indices Km. Kn et Ks ou am, an et as,
mesures de 1'activitemagnetique a 1 1 echelle mondiale et dans les
hemisphe^es Nord et Sud s Ann. Geophys., 23, 585, 1967.
McDiarmid, I.B. and E.E. Budz,inski, Kp dependence on sectors, J. Geophys.
Res., 80, 4755, 1975.
Michel, F,C., Kp as a planetary index, J. Geophys.. Res., 69, 4182, 1961.
Russell, C.T. and R,L. McPherron, Semiannual variation of geomagnetic
activity, J. Geophys. Res., 78, 92, 197:3.
S.•.aigaard, L., On the causes of geomagnetic activity, StauJ:'ord University
Institute for 	 Research Report No. 616, submitted to J. Geophys.
Res., 1976x.
Svalgaard, L., Recalibration of Bartels' . geomagnetic activity indices Kp
and ap to include Universal Time variations, J. Geophys. Res.,
(in press), 1976b.
n
LL
Figure Captions
Figure S	 Universal time variations of geomagnetic indices an,am,
and as. The interplanetary magnetic field polarity (measured
by spacecraft during 1.962-1970) was used to divide the data
into two groups: Away polarity (open circles) and Toward
polarity (filled circles). In the righthnnd panel the dif-
ference between the universal time variations (away-toward)
is shown. (After Svalgnard, 1976x.)
Figure 2	 Universal time variations of Kp for different sector polarity:
Away (open circles) and Toward (filled circles). The bottom
panel shows the nverage UT variation of Kp with no regard of
the polnrity, The average variation is consistent with the
result of Michel (1964) using data before 1962 cnly.
am
I 
)
3
o—o A, *—o T
	 A-T
21
i
19
an	
18
i
17 i
16
0 6 12 18 24h
4
0 a 12	 1
I
I
as
I
I
I
8
7-11
s ik
5
4- ^^
3
0 6 12 18 24h
Figurc 1
6
Kp
r
UNIVERSAL TIME VARIATION OF K. INDEX
2.2k TOWARD
Kp
1.8k AWAY
2.2^ ALL DAYS
,x'—x•
	Kp 2.0	 `x\ 	 ,-x	
'x`	 , X.'"
^x	 ^`	 ^x
x. 
'x' 
.x°	 x.
max' 
.x.
	1.8	 -
0	 6	 12	 IS 24 6	 12 18 24 h UT
DATA INCLUDES 2500 THREE-HOUR INTERVALS
DURING 1962-1970
Figure 2


Comment on 'Kp dependence on sectors, by I. B. McDiarmid and E. E. Budzinski

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