4. Significance of Non-coherent Variations of DP-2 and Auroral Electrojet Indices

In the previous Section, we showed numerous examples of close correlations between DP-2-like
changes and the occurrence of polar magnetic substorms. Further, in these examples, it can clearly
be seen that whenever the electrojet indices indicate that polar magnetic substorms are occurring
the polar cap records tend to be DP-2-like. However, the converse is not always true. That is,
DP-2-like polar cap changes are not always accompanied by enhancements of the auroral electrojet
indices. Furthermore, often there does not exist a one-to-one correspondence between polar cap
changes and the variations in the electrojet indices (although the duration of the activity can be
identical). Thus, one might be led to believe that (because of the lack of coherency with substorm
fields or the occurrence of polar cap DP-2 type variations in the apparent absence of substorms)
some polar cap variations are distinct from substorm fields. That is, that there could indeed be a
"pure" DP-2 mode. But, in fact, such a conclusion is based on the misconception that a single sta-
tion or the auroral electrojet indices, for that matter, can accurately monitor the growth and decay
of polar magnetic substorm fields.

It is well known that the auroral electrojet is a rather dynamic phenomenon as evidenced by the
accompanying auroral displays. Not only does the intensity of the currents in the electrojet and
its associated circuit vary in time, but also their configurations and locations with respect to the
observing stations. It is impossible from the ground observations of the auroral zone stations alone
to separate the spatial from the temporal development of the auroral electrojet

It is clear from this that the time development of the substorm current does not necessarily
closely follow the development of the field observed at an auroral zone station

In this connection, it should be noted that the AE (or AL) index is too crude to define the
growth and expansive phases of substorms. Akasofu [1960] showed that an intensification or a decay
of the H-component records at a single station may only be an apparent one due solely to rapid north-
south motions of the electrojet toward or away from the station. Further, even if there were no
longitudinal and latitudinal motions of the electrojet with respect to the sun, because of the rota-
tion of an observing station underneath the time-developing electrojet, the time-development of the
field observed at the station can differ significantly from the actual one.

It should also be noted that the variations identified as DP-2 occur during periods of weak to
toderate magnetic activity and near local noon for the polar cap stations. For the polar cap sta-
tions used in the present and previous investigations, local noon occurs when the midnight portion
of the auroral oval is located in the Siberian sector. Unfortunately, during weak to moderate ac-
tivity, it is likely that the midnight portion of the oval is located north of the Siberian coast-
line in the Arctic Ocean where little or no data are available. Consequently, it is not surprising
that the auroral electrojet indices sometimes show little or no correlation with DP-2 variations.

Thus, it is not valid to conclude on the basis of a comparison of the variations of the pres-
ently available electrojet indices and the polar cap magnetic records alone that the polar cap
variations are unrelated to polar magnetic substorms.

5. Relationships with Auroral Substorms

For further evidence to support the conclusions in the last two sections we have examined
auroral displays during DP-2 variations.

Here we show an example of auroral activity during the DP-2 variations on October 2, 1965,
which was examined in Section 3 (see Fig. 18). Figure 22 shows selected all-sky camera photographs
taken from College during the DP-2 variations. It is quite clear in this example that all the major
features of auroral substorms, such as westward traveling surges (1130-1147 UT), the subsequent pole-
ward motion (1150-1240 UT) and the eastward drifting inverted @ bands (1405-1416 UT) are present
Thus, the magnetic disturbances between 1000 and 1420 UT should not be identified as a new type of
magnetic disturbance, but rather as the effect of polar magnetic substorms in the polar cap. This
example is enough to indicate that it is difficult to define different types of magnetic variations
on the basis of magnetic records alone; for many other such examples, see Akasofu and Snyder [1972].

6. Relationship of Interplanetary Magnetic Field Changes to Z-component Polar Cap Magnetic Variations

Svalgaard [1968], Mansurov [1969] and Friis-Christensen et al. [1971] have shown that there is
a clear relationship between variations of the sector structure of the solar wind and the Z-component
variations at polar cap stations. Friis-Christensen et al. [1972] showed from hourly values that
the correlation is actually better for the Y-component (the component perpendicular to the sun-earth
line) of the interplanetary field rather than the sector structure.

We wish to show in this section that the variations described by Nishida and Svalgaard are re-
lated. Figure 23 gives the interplanetary magnetic field components Yse and Zse (bold traces), the

16



previous investigations. However, the fact that the onset of the polar cap variations coincides
with the growth of the electrojet strongly suggests that there is a close relationship between the
two types of variations. Indeed, the shaded Alert and AL variations are quite similar. Moreover,
the interval starting at about 1200 UT, November 30 and ending at 0300 UT, December 1, 1965 (see
Figure 16) during which DP-2-like variations were observed in the polar cap coincides precisely
with a period of occurrence of numerous substorms.

Thus, it is concluded from the comparison of auroral electrojet indices and polar cap magnetic
changes given in this section that many of the polar cap variations identified as DP-2 are actually
manifestations of polar magnetic substorms and hence cannot be ascribed to a current system distinct
from that of substorms.

Era maf Naren Ko
ane aa
“ it A
Ln A NM A
posers Lar eT llr iny
ne err
_. HN. PO eaten ek AA dca
oo te A Td Cpe
ota y Lay tn
Gotan H ae emeneal nr
eaten 0 L ef at Larrea |
v * oa uly (965 *

Fig. 13. Polar cap magnetic records, auroral electrojet
indices and interplanetary magnetic field angle 6
on duly 24, 1965.

Note the shift in time of the interplanetary
record to obtain the best correlation with ground
data.

|
|
|



(viii)

(ix)

In brief, care is required in examining relationships between certain polar cap phenom-
ena and auroral zone magnetic records. The presently available AE index is also too
crude to define the growth phase and the expansive phase of substorms [Akasofu and Snyder,
1972].

The study of Onwumechilli, Kawasaki and Akasofu [1972] indicates that it is not a simple
matter to define the baselines of the DP-2 variations along the magnetic dip equator.

It has been found by Heikkila and Winningham [1971] and Frank [1971] that there is a
continuous flux of magnetosheath electrons into the midday part of the oval. In addition
there is a permanent E layer along the midday part of the oval [Buchau et al., 1972].
Thus, the conductivity distribution for the dynamo theory even on extremely quiet days
should be modified to take into account the existence of a conductive strip along the
auroral oval.

8. Acknowledgement

We woul
The work rep

d like to thank Dr. C. A. Onwumechilli for discussions during the preparation of the paper.

jorted here was supported by the National Science Foundation Grant GA 28101.

REFERENCES

AKASOFU, S.-I. 1960 Large Scale Auroral Motions and Polar Magnetic Disturb-
ances - I; a Polar Disturbance at about 1100 hours on
23 September 1957, J. Atmos. Terr. Phys., 19, 10-25.

AKASOFU, S.-I. and 1972 Comments on the Growth Phase of Magnetospheric Substorms,

A, L. SNYDER Submitted to J. Geophys. Res.

AKASOFU, S.-I.5 1971 Results from a Meridian Chain of Observatories in the

C. R. WILSON, Alaskan Sector (I), Planet. Space Sci., 19, 477-482.

A. L. SNYDER and

P. D. PERREAULT

ARNOLDY, R. L. 1971 Signature in the Interplanetary Medium for Substorms,
J. Geophys. Res., 76, 5189-5201.

AXFORD, W. I. 1969 Magnetospheric Convection, Rev. Geophys., 7, 421-459.

BUCHAU, J., 1972 Precipitation Patterns in the Arctic Ionosphere Determined

G. J. GASSMANN, from Airborne Observations, Ann. de Geophys., (in press).

C. P. PIKE,

R. A. WAGNER and

J. A. WHALEN

DAVIS, T. N. and 1966 Auroral Electrojet Activity Index AE and its Universal

M. SUGIURA Time Variation, J. Geophys. Res., 71, 785-801.

FELDSTEIN, Y. I. 1969 Polar Auroras, Polar Substorms and Their Relationships
with the Dynamics of the Magnetosphere, Rev. Geophys. ,
7, 179-218.

FELDSTEIN, Y. I. and 1967 Magnetic Field Variations at High Latitudes on Quiet

A. N. ZAITZEV Days in Summer During the IGY, Geomag. and Aeron., 7,
160-162.

FRANK, L. A. 1971 Plasma in the Earth's Polar Magnetosphere, J. Geophys.
Res., 76, 5202-5219.

FRIIS-CHRISTENSEN, E., 1971 Interplanetary Magnetic Sector Polarity from Polar

K. LASSEN, Geomagnetic Field Observations, Nature, Phys. Sci.,

J. M. WILCOX, 233, 48-50.

W. GONZALEZ and
D. S. COLBURN

20

|

|



"A Study of Polar Cap and Auroral Zone Magnetic Variations"

by

K. Kawasaki
S.-I. Akasofu
Geophysical Institute
University of Alaska
Fairbanks, Alaska 99701

ABSTRACT

It is shown that the daily:magnetic variation in the polar cap on moderately disturbed
days is essentially identical to that of extremely quiet days, but significantly enhanced.
On the basis of an extensive analysis of magnetic and auroral records, it is inferred that
the particular type of magnetic variation identified as the DP-2 mode is not a new and dis-
tinct variation, but is one of the manifestations of magnetospheric substorms.

1, Introduction

It was found by Hasegawa [1939] and Nagata and Kokubun [1962] that there exists a particular
type of daily magnetic variation in the polar cap, which differs from what one would expect from the
dynamo theory of daily magnetic variations. The latter authors denoted this daily variation SB and
demonstrated that its equivalent current system resembles the SD current system, consisting of two
current vortices.

Later, this daily variation was examined in great detail by Kawasaki and Akasofu [1967] and
Feldstein and Zaitzev [1967]. Although their methods of analyses were different, their results |
(the polar plot of the distribution of magnetic vectors associated with the daily variations) were
quite similar. They showed that the polar cap daily variation is essentially a daytime phenomenon
and thus their results differ considerably from what was obtained by Nagata and Kokubun [1962].
They concluded also that Nagata and Kokubun's results were representative of a somewhat disturbed
“yather than an extremely quiet period. [For more details, see a review paper by Feldstein, 1969].

Feldstein and Zaitzev [1967} showed further that the equivalent current system for the quiet day
daily variation is a single vortex located in the dayside of the polar cap. This single vortex
representation appears to be somewhat oversimplified. However, the salient characteristic of See name-
ly, its confinement to the dayside polar cap was demonstrated in both analyses. Hereafter, by the
SR variation, we refer to the daily variation elucidated by Kawasaki and Akasofu [1967] or Feldstein
and Zaitzev [19671], rather than that by Nagata and Kokubun [1962}. The SP variation has been found
to occur even during two extremely quiet days of the IQSY (zKp=1+, 0+) and is important in studying
disturbance variations, since disturbance variations are, in general, defined as deviations from the
quiet day level.

It has been proposed by Nishida et al. [1966] that there exists a distinctive type of world-wide
magnetic variations which is not directly associated with enhancements of the auroral electrojet.
This variation, subsequently called the DP-2 variation [Nishida, 1968a], has been found to be cor-
related with changes of the north-south component of the interplanetary magnetic field [Nishida,
1968b]. Nishida also showed that the equivalent current system of the DP-2 variation consists of
two "vortices", one in the early afternoon sector and the other in the early morning sector. The
former is more intense and covers a larger area than the latter

It has been suggested by Axford [1969], Nishida and Kokubun [1971] and others that such a
magnetic variation might be related to the convection of the magnetospheric plasma. Further, it
has recently been suggested by Kokubun [1971], Nishida and Kokubun {1971] and lijima and Nagata
[1971] that the DP-2 or DP-2-like magnetic variations appear before the explosive phase of magneto-
spheric substorms.

Recently, it has been noted by Svalgaard [1968], Mansurov [1969] and Friis-Christensen et al.
{1971] that there is a close correlation between the Z-component variations of polar cap stations
and the sector structure of the interplanetary field. From these observations, it has been sug-
gested by Mansurov [1969] and Wilhjelm and Friis-Christensen [1972] that merging can occur between
an ecliptic component of the interplanetary magnetic field and the earth's field.

The purpose of this paper is to examine some of these geomagnetic disturbances in the polar
cap. [See also Kawasaki and Akasofu, 1972a]. Our study is mainly based on magnetic records on
the days selected by Dr. A. Nishida for the Working Group IV, Commission IV of IAGA, and also on
those days examined by Nishida [1971] for his studies of the DP-2 variations. These days are
called DP-2 days in this paper and are listed in Table 1.



2 October 1965
6 a to 2 “4 6 a
-90°

490°

ALERT (1)

2507 an
AL

COLLEGE ALL-SKY PHOTOGRAPHS

Fig. 22. College all-sky camera photographs during DP-2
variations at Alert on October 2, 1965. The

AL index and the interplanetary magnetic field
angle 8 are also shown.

p
i
'

7 |


magnitude Vise? + Zse* of the field component in the Yse - Zse plane, and the Z-component of Thule
and the Y-component of Alert (dashed traces) on August 14, 1965. As in previous figures, the inter-
planetary components have been shifted in time. It is quite clear that variations of the Z-component
of Thule (plotted positive downward) and the interplanetary field component Yse are well-correlated
between 1000 to 1800 UT; further, the variations of the component Zse are well-correlated with those
of the Alert Y-component (plotted positive downward) also during the same interval. However, as was
indicated in Section 3 (see Fig. 15), the variations of the southward component of interplanetary
magnetic field were correlated fairly well with the auroral electrojet indices during this interval.
Thus, as might be expected, the Z-variations over the polar cap also appear to be substorm-associated.
A more detailed study of the polar cap Z-component variations and its relationship to the interplane-
tary field may be found in Kawasaki and Akasofu [1972b].

Actually, one should not discuss variations of the various components of the interplanetary and
ground magnetic fields separately as can be seen in Figure 23. The magnitude AYse” + Zse remained
relatively constant, but the components Yse and Zse varied up to +5 gammas during the interval 1000
to 1800 UT. Thus, in this example the variation of the vector in the Yse~Zse plane can be represented
by an oscillation of the vector which changed little in magnitude. It should be emphasized that the
variation appears to be an oscillation to and fro through some preferred direction rather than a full
rotation.

7. Discussions and Conclusions

The following conclusions may be drawn from our present, earlier and some other related studies:

(i) The SP variation exists even during extremely quiet days [Kawasaki and Akasofu, 1967;
Feldstein and Zaitzev, 1967].

(ii) The Sh variation is significantly enhanced on days when substorms occur frequently.

(iii) Fluctuations of lifetime of order 1 hour are superposed on the enhanced sP variation.
Some of these fluctuations were identified as the DP-2 variation by Nishida [1968a].
Our magnetic studies indicate that it is not necessary to invoke this new type of magnetic
variation, the DP-2 disturbance field, which is distinct from the substorm field. The
proposed DP-2 field is fairly coherent with the substorm field.

(iv) Typical features of auroral substorms are observed during the DP-2 variations, defined by
Nishida. Thus, his DP-2 variations are associated with magnetospheric substorms and are
not distinct from them.

(v) The DP-2 variations of Nishida and the variations described by Svalgaard are related.
A single current system or mechanism is responsible for both types of variations. It
may thus be inferred from the examples studied in this report, that the variations ob-
served in the polar cap are associated with substorms. [For further details see Kawasaki
and Akasofu, 1972b].

(vi) It should not be assumed that the substorm fields are well known. We are still quite un-
certain about the geometry of the substorm current system and its variations during the
life time of substorms. With the presently existing network of polar magnetic observa-
tories, it is difficult to distinguish one type of disturbance from another. In partic~
ular, the auroral oval is not a fixed pattern. For example, the auroral oval tends to
contract poleward during quiet periods. The initial indications of "isolated" substorms
may occur far poleward of the usual oval location [Akasofu et al., 1971], causing only
minor magnetic disturbances along the auroral oval.

Thus, small AE indices during an early phase of a substorm or during an isolated substorm
(which occurs during otherwise quiet periods) could be due to the fact that an auroral
substorm is in progress along the contracted oval, well poleward of the auroal zone
[Akasofu and Snyder, 1972].

(vii) It is thus difficult to monitor accurately the growth and decay of the auroral electrojet
activity by only several auroral zone stations as is presently done; one would need a
large number of closely-spaced meridian chains of stations for this purpose. Akasofu
[1960] showed also that the H-component variation as a function of time should not be
taken to be proportional to the variation of the intensity of the auroral electrojet;
an apparent intensification of negative bays could be partly due to a rapid approach of.
this jet to the observing station, and an apparent decay of negative bays could be partly
due to a rapid recession of the jet from the station. It is also not difficult to show
that the observed "time variation" of negative bays at auroral zone stations (which move
under the jet as the earth rotates) can be very different from the true time variation
of the jet intensity as a function of time.

19



-90)

(i)
Interofanetory phon ida Ma ely
moo ‘ a a AL
80 : 1 A
w
NEE: eae AN owl

AL

Alert X

Alert ¥

Resolite Boy X

Resolute Boy ¥

Mould Bay X

Mould Boy Y

Boker Loke X

Boker Lote ¥

Godhaun HTT

Godrovn Dom

OT

Fig. 20.

04 OF 7%

// December 1965

Polar cap magnetic records, auroral electrojet
indices and interplanetary magnetic field angle 6

on December 11, 1965,

14



Mould Bay (X comp)
T r

ie PN ed
~

:

ie

8 May 1964

\
$
>

12 May (964

00UuT 04 08 2 16

/}-—4
8
=

[2] 6 Uy 1965, 24 uly 1965, 2 August 1965,
/4 August 1965, 4 September 1965

Fig. 7. Superposed records of Mould Bay X-component on summer DP-2 days and
quiet days: May 8 and May 12, 1964.

Mould Bay (¥ comp)
7 T

T T

ae

250y

n 1 1 ‘

12 May 1964

S

oouT 04 08 we

16 July 1965, 24 July 1965, 2 August 1965,
CA) 14 ‘august 965, 4 September 1965

Fig. 8. Superposed records of Mould Bay Y-component on summer DP-2 days and
quiet days: May 8 and May 12, 1964.

6



Zz,

*T alge ul parseL
‘skep Z-d0 4aqUiM 40 SeoLpUL yafouzo91a [e4ouny *Z “BLA

. | |

L2.

9961 290 11

S961 290 J

SESH S96) AON OF

296 190

skep 2-dd sauuins 40 seoppul yafouzoa1@ Leuouny

of

*T age, ul payzsly
“T “Bld

IS 5961 boy 2

9961 MP v2

9961 Ainp 9



TABLE 1

DP-2 Days
duly 16, 1965
duly 24, 1965

August 2, 1965
August 14, 1965
September 4, 1965
October 2, 1965
November 30, 1965
December 1, 1965
December 11, 1965

Figures 1 and 2 show the combined H-component records from the standard auroral zone stations
for the DP-2 days (College, Cape Wellen, Tixie Bay, Dixon Island, Kiruna, Leirvogur, Fort Churchill,
Meanook and, when available, Great Whale River). The upper and lower envelopes give, respectively,
the AU and AL indices; the distance between the two envelopes gives the AE index [Davis and Sugiura,
1966].

2. The Quiet Day Daily Magnetic Variation in the Polar Cap

As the first step of our study, we combine each vector component of the magnetic records for
each polar cap station for summer days listed in Table 1. Figures 3 through 12 are the results of
this analysis. In the upper part of each figure, the upper and lower envelopes of the combined
records of the DP-2 days are shown. It seems clear that the envelopes delineate a "daily" variation,
together with short-period "fluctuations". The records of Thule are not shown here but also exhibit
a "daily" variation of the same type. Added to the envelopes is the record of May 8, 1964, one of
the quietest days (EKp=1+) during the IQSY, which was studied by Kawasaki and Akasofu [1967]. It can
be seen that the quiet day variation and the envelopes have a very similar variation, although the
magnitude on the DP-2 days is a few times greater than that on May 8, 1964. In order to see more
clearly the daily variation on May 8, 1964, the lower parts of Figures 3 through 12 show the same
records reproduced at a greater sensitivity scale (x5). These also show the records on May 12, 1964,
another quiet day (ZKp=5-); the daily variation is somewhat greater during the period 1200-2400 UT
on May 12 than on the corresponding period of May 8 although the sum of the three-hourly Kp indices
of the period 1200-2400 UT on May 12 was less than that of May 8, 1964. (The data on May 8, 1964,
were digitized at 3 minute intervals whereas those of May 12, 1964, are essentially analog data;
this accounts for the retention of high frequency components on the latter day). The tendency for
similar variations is seen in both the “x- and Y-components (or H and D) from all the polar cap stations.

One important point to be clarified in this connection is the question of whether the enhance-
ment of the daily variation is only an apparent one resulting from the frequent occurrence of dis-
turbances which have a life-time of the order of a few hours (such as substorm variations). We note
in this connection that the SB variation exists even on extremely quiet days and that it is unlikely
to be due to the superposition of substorm variations, since on such quiet days the interplanetary
magnetic field, is in general, fairly steady and has a northward component. On moderately disturbed
days, however, it is not possible to exclude the possibility that the enhanced 24-hour component is
simply an apparent one. To be more specific, it is possible that the substorm field may contain a
long period variation (say 6 to 12 hours) upon which are superposed the intense fluctuations more
usually identified as substorms. Thus this long period variation of the substorm field may contrib-
ute to the daily variation in one direction for a period of time at a polar cap station and, as the
earth rotates, it may contribute in the opposite direction during a later period. However, it is
‘important to note that both the upper and lower envelopes clearly delineate a 24-hour component in
spite of the fact that polar magnetic substorms of differing intensities and durations occurred fre-
quently (see Figure 1) on the superposed days.

We may infer the vector distribution of the 24-hour variation on the basis of our analysis of
the SB variation on May 8, 1964 [Kawasaki and Akasofu, 1967]. Note that both Kawasaki and Akasofu
[1967] and Feldstein and Zaitzev [1967] showed that the SE variation is very different from the SD
type variation; for details of the harmonic analysis of See see Kawasaki and Akasofu [1967].

|
|
|
|
|
|
|



a)
Interplanetary ws

ake 3 Fad

ny)
+90!

aw

| vlimess oma
250y

AL

Alert x fd

Alert ¥ RR

ny
Resolute Boy X Pen A | pens

—
Resolute Bay ¥ wee

perenne rye |
Mould Boy 2 [nares

Would Bay ¥en nen earner]

Goahovn D nd

we

won

Coston H Raney porny Nyt iy | [Nene
Vaan

our 04 08 @
3O November I965

Fig. 21. Polar cap magnetic records, auroral electrojet
indices and interplanetary magnetic field angle 6
on November 30, 1965.

“5

a
ty
BY

|



8 May 1964 Aen pain’

| 2 May 1964 me

Ts

L

oouT 04 08 2 6 20
16 July 1965, 24 July 1965,
C7 2 ‘august 1965, 4 September 1965

Fig. 5. Superposed records of Resolute Bay X-component on summer DP-2 days
and quiet days: May 8 and May 12, 1964.

Resolute Bay (Y comp)

8 May 1964 | and

Std Pata

rN Yaw at “et

|=

OOUT 04 08 ae 6 20

16 July 1965, 24 July 1965,
CD 2 figust B65, 4 September 1965

Fig. 6. Superposed records of Resolute Bay Y-component on summer DP-2 days
and quiet days: May 8 and May 12, 1964.

5

|
|



FRIIS-CHRISTENSEN, E.,
K. LASSEN,

J. WILHJELM,

J. M. WILCOX,

W. GONZALEZ and

D. S. COLBURN

HASEGAWA, M.

HEIKKILA, W. J. and
J. D. WINNINGHAM

IIJIMA, T. and
T. NAGATA

KAWASAKI, K. and
S.-I. AKASOFU

KAWASAKI, K. and
S.-1. AKASOFU

KAWASAKI, K. and
-I. AKASOFU

KOKUBUN, S.
MANSUROV, S. M.

NAGATA, T. and
S. _KOKUBUN

NISHIDA, A.

NISHIDA, A.

NISHIDA, A.

NISHIDA, A.,
N. IWASAKI and
T. NAGATA

NISHIDA, A. and
S. KOKUBUN

ONWUMECHILLI, A.,
K. KAWASAKI and
-I. AKASOFU

SVALGAARD, L

WILHJELM, J. and
E, FRIIS-CHRISTENSEN

1972

1940

1971

1971

1967

1972a

1972b

1971

1969

1962

1968a

1968b

1971
1966

1971

1972

1968

1972

Critical Component of the Interplanetary Magnetic Field
Responsible for Large Geomagnetic Effects in the Polar

Cap, J. Geophys. Rss., (in press).

Provisional Report of the Statistical Study on Diurna
Variations of Terrestrial Magnetism in the North Polar

Regions, Trans. of Washington Meeting, Sept. 4-15, 1939,
I.U.G.G. A.T.M.E., Bull. No. 115 311-318, A. H. R.
Goldie, ed., Edinburg.

Penetration of Magnetosheath Plasma to Low Altitudes
Through the Dayside Magnetospheric Cusps, J. Geophys.
Res., 76, 883-889.

Signatures of the Development of the Growth Phase and
Expansion Phase, Preprint, Geophys. Res. Lab., Univ. of
Tokyo, Report UT-GRL-71-03.

Polar Solar Daily Geomagnetic Variations on Exception-
ally Quiet Days, J. Geophys. Res., 72, 5363-5671.

Geomagnetic Disturbances in the Polar Cap: sh and DP-2,
Planet. Space Sci., (in press).

In preparation

Polar Substorm and Interplanetary Magnetic Field, Planet.
Space Sci., 19, 697-714.

New Evidence of a Relationship Between Magnetic Fields
in Space and ‘on Earth, Geomag. and Aeron., 9, 622-623

An Additional Geomagnetic Daily Variation in Field (sb-
Field) in the Polar Region on Geomagnetically Quiet Days»
Rept. Ionos. Space Res. Japan, 16, 256-274.

Geomagnetic. DP-2 Fluctuations and Associated Magneto-
spheric Phenomena, J. Geophys. Res., 73, 1795-1803

Coherence of Geomagnetic DP-2 Fluctuations with Inter-

planetary Magnetic Variation, J. Geophys. Res., 73,
5549-5559.

DP-2 and Polar Substorm, Planets Space Sci., 19, 205-221.

The Origin of Fluctuations in the Equatorial Electrojet;
a New Type of Geomagnetic Variation, Ann. Geophys., 22,
478-484,

New Polar Magnetic Disturbances: SP, SP, DPC and DP-2,
Rev., Geophys. and Space Phys., 9, 417-425.

Relationships between the Equatorial Electrojet and Polar
Magnetic Variations, Planet. Space Sci., (submitted).

Sector Structure of the Interplanetary Magnetic Field and
Daily Variation of the Geomagnetic Field at High Latitudes,
Danish Meteor, Inst. Geophys. Papers, R-6.

Electric Fields and High-Latitude Zonal Currents induced
by Merging of Field Lines, Danish Meteor. Institute’
Geophys. Papers, R-31.

ar



WORLD DATA CENTER A

for
Solar-Terrestrial Physics

A STUDY OF POLAR CAP
AND AURORAL ZONE
MAGNETIC VARIATIONS

sy |
c.

REPORT UAG-18

June 1972



Godhavn (Hcomp)

8 May 1964

SMe
cual

2 May [964 a

Te

oour 04 08 72 16 20
[CT 6h 965, 24 duly 1965, 2 August 1965,
14 August 1965, 4 September 1965
Fig. ll. Superposed records of Godhavn H-component on summer DP-2 days and
quiet days: May 8 and May 12, 1964.
Godhavn_(D comp)

anne ;
|~

8 May 1964

L 2May 1964 LA wry

[-

our 4 08 a 16 20

[aay 6 ey 1965, 24 uly 1965, 2 August 1965,
/4 August 1965, 4 September 1965

Fig. 12. Superposed records of Godhavn D-component on summer DP-2 days and
quiet days: May 8 and May 12, 1964.

8



Baker Lake (X comp)

mies

| l= |
8 May 1964 ri

Pm ey

(2 May 1964 I

oour OF 08 2 3 ra 3,

[I 5 de 965, 24 sly 1968, 2 August 1965,

1 August (965, 4 September 1965

Fig. 9. Superposed records of Baker Lake X-component on summer DP-2 days and
quiet days: May 8 and May 12, 1964

Baker Lake (Y comp)
T r

12 May 1964

I ; |

oour 04 08 2 "6 xo 2

16 uy (968,24 duly 1965, 2 August 1965,
co (a August B65 9 September

Fig. 10. Superposed records of Baker Lake Y-component on summer DP-2 d;
quiet days: May 8 and May 12, 1964. ays and

7


Alert (X comp) |

|=

T

8 May 1964

1 \Rancane)

~\

22 May (964

our 04 08 2 16 20 a4

16 July 965, 24 July (965, 2 August 1965,
CD ia aiqust 865, 4 ‘September

Fig. 3. Superposed records | of Alert X-component on summer DP-2 days and quiet
days: May 8 and May 12, 1964.

Alert (Y comp) I

8 May 1964

— : i
/
s

NA A fA

hw

| 2 May 1964 :
le :
n n in i
our 04 08 2 6 20 24 i

[5 ay 965,24 duly 1965, 2 August 1965,
14 August 1965, 4 September

Fig. 4. Superposed records of Alert Y-component on summer DP-2 days and quiet
days: May 8 and May 12, 1964.

4

«


IMP -/

|
if
|
|
|
i
F

1
oourT 04 OB 12 1 20 24
ALERT
14 AUG 65

Fig. 23. Magnitude of interplanetary magnetic field component in Yse-Zse
plane in solar-ecliptic coordinates and a comparison of Yse and
Zse (solid lines) with the Thule Z-component, and Alert Y-compon-
ent (dotted lines), respectively, on August 14, 1965.

18






“S961 ‘ty daquezdaes uo
aquL pue sadipuL

Aaezaue ld
spuooaa 2
SIE 42GHIO 2
[Ay ee er
eee Vd
A eee WoW | i _
al Dany WLLL 4307 2088
Se Cee ores
PD AR Spm “em
Hen te “we
ra [Sg aor
i OA | NY 9 ary
C\ hd Ne _f” | 1 mvi
Ni ia qi Vi-
Pn ol PAP] 7 «=|
fs bn te Taw Ege



WORLD DATA CENTER A

for
Solar-Terrestrial Physics

REPORT UAG-18

A STUDY OF POLAR CAP AND AURORAL ZONE
MAGNETIC VARIATIONS

by |

K. Kawasaki |
S.-I. Akasofu

Geophysical Institute

University of Alaska |
Fairbanks, Alaska 99701 SS :

Prepared by World Data Center A for =|
Solar-Terrestrial Physics, NOAA, Boulder, Colorado nec

and published by

U.S. DEPARTMENT OF COMMERCE
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

ENVIRONMENTAL DATA SERVICE
Asheville, North Carolina, USA 28801

{
|
|
|
i
I

June 1972 i

SUBSCRIPTION PRICE: $9.00 a year; $2.50 additional for foreign mailing; single Hy
copy price varies.* Checks and money orders should be made payable to the
Superintendent of Documents, and orders should specify the Catalog order number.
Orders, remittances, and correspondence regarding subscriptions should be sent

fo the Superintendent of Documents, Government Printing Office, Washington, D. C.

0402.

*Price this issue $.20 (Catalog Order Number C55.220:18)


Publication Notice

WORLD DATA CENTER A for SOLAR-TERRESTRIAL PHYSICS REPORT UAG
(Prepared by World Data Center A for Solar-Terrestrial Physics, NOAA, Boulder, Colorado)

These reports are for sale through the Superintendent of Documents, Government Printing Office, Washington, D. C. 20402.
Subscription price: $9.00 a year; $2.50 additional for foreign mailing; single copy price varies. These reports aré issued on
an irregular basis with 6 to 12 reports being issued each year. Therefore, in some years the single copy rate will be less
than the subscription price, and in some years the single copy rate will be more than the subscription price. Checks and money
orders should be made payable to the Superintendent of Documents.

Upper Atmosphere Geophysics Report UAG-1, "IQSY Night Airglow Data" by L. L. Smith, F. E. Roach and J. M. McKennan
of Aeronomy Laboratory, ESSA Research Laboratories, July 1968, single copy price $1.75. [Catalog No. C52.16/2:1]

Upper Atmosphere Geophysics Report UAG-2, "A Reevaluation of Solar Flares, 1964-1966" by Helen W. Dodson and E. Ruth
Hedeman of McMath-Hulbert Observatory, The University of Michigan, August 1968, single copy price 30 cents. [Catalog
No. €52,16/2:2]

Upper Atmosphere Geophysics Report UAG-3, "Observations of Jupiter's Sporadic Radio Emission in the Range 7.6-41 Miz,
6 July 1966 through 8 September 1968" by James W. Warwick and George A. Dulk, Department of Astro-Geophysics, University
of Colorado, October 1968, single copy price 30 cents [Catalog No. C52.16/2:3]

Upper Atmosphere Geophysics Report UAG-4, "Abbreviated Calendar Record 1966-1967" by J. Virginia Lincoln, Hope I. Leighton
and Dorothy K. Kropp, Aeronomy and Space Data Center, Space Disturbances Laboratory, ESSA Research Laboratories, January
1969, single copy price $1.25. [Catalog No. C52.16/2:4]

|

Upper Atmosphere Geophysics Report UAG-5, "Data on Solar Event of May 23, 1967 and its Geophysical Effects" compiled
by J. Virginia Lincoln, World Data Center A, Upper Atmosphere Geophysics, ESSA, February 1969, single copy price 65
cents. [Catalog No. (52.16/2:5]

Upper Atmosphere Geophysics, Report UAG-6, “International Geophysical Calendars 1957-1969" by A. H. Shapley and J.
Virginia Lincoln, ESSA Research Laboratories, March 1969, single copy price 30 cents. [Catalog No. C52.16/2:6)

Upper Atmosphere Geophysics Report UAG-7, "Observations of the Solar Electron Corona: February 1964-January 1968"
by Richard T. Hansen, High Altitude Observatory, Boulder, Colorado and Kamuela, Hawaii, October 1969, single copy
price 15 cents. [Catalog No. C52.16/2:7]

Upper Atmosphere Geophysics Report UAG-8, "Data on Solar Geophysical Activity October 24-November 6, 1968", Parts
1 and 2, compiled by J. Virginia Lincoln, World Data Center A, Upper Atmosphere Geophysics, ESSA, March 1970, single
copy price (includes Parts 1 and 2) $1.75. Part 1 [Catalog No. €52.16/2:8/1], Part 2 [Catalog No. C52.16/2:8/2]

Upper Atmosphere Geophysics Report UAG-9, "Data on Cosmic Ray Event of November 18, 1968 and Associated Phenomena"
compiled by J. Virginia Lincoln, World Data Center A, Upper Atmosphere Geophysics, ESSA, April 1970, single copy
price 55 cents. [Catalog No. (52.16/2:9]

Upper Atmosphere Geophysics Report UAG-10, "Atlas of Ionograms" edited by A, H. Shapley, ESSA Research Laboratories,
May 1970, singl¢ copy price $1.50 [Catalog No. ¢52.16/2:10]

Upper Atmosphere Geophysics Report UAG-11, "Catalogue of Data on Solar-Terrestrial Physics”,
compiled by J. Virginia Lincoln and H. Patricia Smith, World Data Center A, Upper Atmosphere Geophysics; ESSA,
June 1970, single copy price $1.50. [Catalog No. C52.16/2:11]

Upper Atmosphere Geophysics Report UAG-12, "Solar-Geophysical Activity Associated with the Major Geomagnetic storm
of March 8, 1970", Parts 1, 2 and 3, compiled by J. Virginia Lincoln and Dale B. Bucknam, World Data Center A, Upper
Atmosphere Geophysics, NOAA, April 1971, single copy price (includes Parts 1-3) $3.00. [Catalog NO. 055.220:12/

Pt 1, Pt 2, Pt 3]

Upper Atmosphere Geophysics Report UAG-13, "Data on the Solar Proton Event of November 2, 1969 through the Geomagnetic
Storm of November 8-10, 1969", compiled by Dale B. Bucknam and J. Virginia Lincoln, World Data Center A, Upper Atmos-
phere Geophysics, NOAA, May 1971, single copy price 50 cents. [Catalog No. C55.220:13]

Upper Atmosphere Geophysics Report UAG-14, "An Experimental Comprehensive Flare Index and its Derivation for ‘Major’
Flares 1955-1969", by Helen W. Dodson and E. Ruth Hedeman, McMath-Hulbert Observatory, University of Michigan, July
1971, single copy price 30 cents. [Catalog No. C55.220:14]

|
|
Upper Atmosphere Geophysics Report UAG-15, "Catalogue of Data on Solar-Terrestrial Piysics", prepared by Research |
Laboratories, NOAA, Boulder, Colorado, July 1971, single copy price $1.50. (Supersedes Report UAG-11, June 1970.) 1
[Catalog No. C55.220:15] |

|

|

Upper Atmosphere Geophysics Report UAG-16, "Temporal Development of the Geographical Distribution of Auroral Absorp-
tion for 30 Substorm Events in each of IQSY (1964-65) and LASY (1969)" by F. T. Berkey, V. M. Driatskiy; K. Henriksen,
D, H, Jelly, T, I, Shchuka, A, Theander and J, Yliniemi, September 1971, single copy price 70 cents. [Catalog No.
C55.220:16]

Upper Atmosphere Geophysics :Report UAG-17, "Ionospheric Drift Velocity Measurements at Jicamarca, Peru (July 1967 - |
March 1970)", by Ben By Balsley, Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, |
Colorado, and Ronald F. Woodman, Jicamarca Radar Observatory, Instituto 'Geofisico del Peri, Lima, Peru, October 1971,
single copy price 35 cents. [Catalog No. C55.220:17]

USCOI-NOAA-ASHRVILLE,NC~6-23-72--1200



WORLD DATA CENTER A

National Academy of Sciences
2101 Constitution Avenue, N, W. Washington, D, C, U.S.A., 20418

World Data Center A consists of the Coordination Office

and nine subcenters:

World Data Center A
Coordination Office

National Academy of Sciences
2101 Constitution Avenue, N.W.
Washington, D. C., U.S.A. 20418
Telephone (202) 961-1478

Solar and Interplanetary Phenomena,
Tonospheric Phenomena, Flare-Associated
Events, Aurora, Cosmic Rays, Airglow:

World Data Center A:

Upper Atmosphere Geophysics
National Oceanic and Atmospheric
Administration

Boulder, Colorado, U.S.A. 60302
Telephone (303) 447-1000 Ext. 3381

Geomagnetism, Seismology ana Gravity:
World Data Center A:

Geomagnetism, Seismology and Gravity
Environmental Data Service, NOAA
Boulder, Colorado, U.S.A. 80302
Telephone (303) 47-1000

Glaciology:
World Data Center A:
Glaciology
U. S. Geological Survey
1305 Tacoma Avenue South
Tacoma, Washington, U.S.A, 98402
Telephone (206) 363-2861 ext. 318

Longitude and Latitude:
World Data Center A:
Longitude and Latitude
U. 8. Naval Observatory
Washington, D. C., U.S.A. 20390
Telephone (202) 698-8422

Meteorology (and Nuclear Radiation):
World Data Center A:
Meteorology
National Climatic Center
Federal Building
Asheville, North Carolina, U.S.A. 28801
Telephone (704) 254-0961

Oceanography:
World Data Center A:
Oceanography
National Oceanic and
Atmospheric Administration
Rockville, Maryland, U.S.A. 20852
Telephone (202) 698-3753

Rockets and Satellites:
World Data Center A:
Rockets and Satellites
Goddard Space Flight Center
Code 601
Greenbelt, Maryland, U.S.A, 20771
Telephone (301) 982-6695

Tsunami:
World Data Center A:
‘Tsunami
National Oceanic and Atmospheric
Administration
P. 0. Box 3887
Honolulu, Hawaii, U.S.A. 96812
Telephone (808) 546-5698

Upper Mantle Project:
World Data Center A:
Upper Mantle Project
Lamont-Doherty Geological Observatory
Palisades, New York, U.S.A. 10964
Telephone (914) 359-2900 Ext.’ 209

Notes:

(1) World Data Centers conduct international exchange of geophysical observations in accordance
with the principles set forth by the International Council of Scientific Unions. WDC-A is established
in the United States under the auspices of the National Academy of Sciences.

(2) Communications regarding data interchange matters in general and World Data Center A asa
whole should be addressed to: World Data Center A, Coordination Office (see address above).

(3) Inquiries and communications concerning data in specific disciplines should be addressed to
the appropriate subcenter Hsted above.



3. Relationships between the Field of the DP-2 Variations and Polar Magnetic Substorm Field

It has been proposed by Nishida [1968a, b, 1971] that many short-period geomagnetic fluctuations
on moderately disturbed days are distinct from polar substorm fields. We have made an extensive re-
examination of this particular point by analyzing both auroral zone and polar cap magnetic records.
Figures 13 through 21 summarize the results of this analysis. In each of the figures, the inter-
planetary magnetic field angle 6 observed by IMP 3, the AU and AL indices and both the X-and Y-(or
H and D) component records of several polar cap stations are plotted. Following Nishida, the inter-
planetary records have been shifted approximately 20 minutes later in time with respect to the ground
records to obtain the best correlation with the polar cap data. Arnoldy [1971] has shown that the
auroral electrojet index (AE) is best correlated with the southward-directed field B, in the solar
magnetospheric coordinate system integrated over the hour preceding the hourly average of AE; we
have used the interplanetary magnetic field angle 6 in solar ecliptic coordinates in the analysis of
this section, since in most of the cases studied here the variations in 6 are clearly related to
those in Bg.

According to Nishida [1968a, b, 1971], the major characteristics of the DP-2 variations which
distinguish them from magnetic substorm variations are that (a) they are not coherent with polar
magnetic substorms, (b) they can occur in the absence of polar magnetic substorms, (c) they have a
lifetime of about one hour and (d) they are observed world-wide. In Figures 13 through 21, some of
the variations shaded are the same as those identified as DP-2 variations by Nishida [1971].

In this section we wish to show that many of the variations which have DP-2 like characteristics
or have been previously identified as DP-2 are, in fact, associated with polar magnetic substorms,
that is, they are coherent with changes in the auroral electrojet. Figures 13 through 16 are par-
ticularly good examples of such coherency. Most of the shaded variations on August 2, 1965 (Fig.
14), August 14, 1965 (Fig. 15) and December 1, 1965 (Fig. 16) in the Alert Y-records have been pre~
viously identified as DP-2 [Nishida, 1971]. It is clear the polar cap variations that have been
shaded occur in association with the shaded variations in the electrojet indices. Thus, in these
examples the variations described as DP-2 are actually coherent with the occurrence of polar magnetic
substorms as inferred from the electrojet indices.

Although changes in the interplanetary magnetic field angle 6 are often best-correlated with the
Alert Y-component records from about 1000 UT to 1700 UT, it is readily apparent in Figures 13 through
21 that such changes are sometimes better correlated with the Alert X-component or with the components
of other polar cap stations at other UT hours. Figures 15, 17, 18, 19 and 20 show examples of these
correlations between 0000 UT to 1000 UT. These examples suggest that the current system which is
responsible for the variations observed in the polar cap is fixed with respect to the sun.

In Figure 15, there is a prolonged period of August 14, 1965 during which the interplanetary
field remained southward; the AL index indicates there also existed a prolonged period of polar mag-
netic substorms. During this interval, the angle 6 of the interplanetary field remained fairly con-
stant, yet the Alert-X record exhibited considerable variation. However, it can be seen from an
examination of the solar ecliptic magnetic field component Zse (see Figure 23) that the southward-
directed field did indeed follow closely the Alert X-component. On the other hand, the Alert X-com-
ponent exhibits time-variations of the DP-2 type which are not precisely correlated with those of
the electrojet indices. The significance of such non-coherent cases will be discussed in Section 4.

Figure 17 shows an example on July 16, 1965 during which the Alert X-component correlates with
the interplanetary record but there is little or no correlation with the electrojet indices from
0000 UT to 0800 UT. This period is, however, a period of enhanced electrojet activity. From about
1200 UT to 1800 UT, although the interplanetary magnetic field remained southward there is an apparent
absence of polar magnetic substorms. It is seen that there are variations of the DP-2 type most
easily seen in the Resolute Bay and Mould Bay records during this interval. Thus, the absence of
activity in the electrojet indices coupled with the correlation between the polar cap and interplan-
etary changes between 1200 and 1800 UT on July 16, 1965 might indicate this is a case of the occur-
rence of a "pure" DP-2 mode. However, an examination of the Point Barrow magnetogram during this
interval shows there occurred a period of negative bays with a maximum deviation of about 180 gammas.
Thus, these changes also appear to be substorm-associated.

Figures 18 through 20 are further examples of the correlation between polar cap changes, the AL
index and the interplanetary magnetic field angle 6. Most of the variations shaded have obvious
counterparts in the auroral records. The changes shaded between 0000 and 0300 UT on December 11,
1965 (Figure 20) are seen in all the records; however, an examination of the magnetograms of several
world-wide stations indicate these variations are actually si's and thus not necessarily substorm-
related. There can be no doubt, however, that the polar cap and interplanetary field variations
between 0300 and 0700 UT are related to the substorm changes which occurred simultaneous to them.

Finally, Figure 21 shows a case in which the onset of DP-2-like variations in the polar cap
coincides with the growth of the auroral electrojet. The shaded portions of the Alert and inter-
planetary records exhibit coherence and thus may be identified as DP-2 variations in the sense of

9

|
|
i



Lv