Observation of polar geomagnetic disturbances in connection with polar cap absorptions of slow onset typ

Hakura, Y.

Nagai, M.

English

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ABSTRACT 
A new type of polar geomagnetic disturbance was ob- 
served in connection with PCA's of slow onset type. A 
synoptic analysis of the February 10, 1958 event shows that 
the distrubance is an intensified SgP-field due to an en- 
hanced ionization produced in the ionosphere dynamo 
region. Protons with energies 0.1 - 1 Mev in the solar 
cosmic rays may be the cause of the disturbance. 
ii 
https://ntrs.nasa.gov/search.jsp?R=19680011029 2020-03-24T00:18:15+00:00Z
. 
CONTENTS 
Abstract . .  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii 
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . .  1 
SLOW-ONSET TYPE PCA ASSOCIATED WITH A 
GEOMAGNETIC POLAR DISTURBANCE . . . . . . . . 1 
SYNOPTIC PATTERNS O F  THE PCA AND 
EQUIVALENT CURRENT SYSTEM O F  THE 
GEOMAGNETIC DP- FIELD. . . . . . . . . . . . . . . . . 4 
DISCUSSIONS.. . . . . . . . . . .  . . . . . . . . . . . . . . . . 4 
CONCLUSIONS.. . . . . . . . . . . . . . . . . . . . . . . . . . 7 
ACKNOWLEDGMENTS.. . . .  . . . . . . . . . . . . . . . . 8 
References . . . .  . .  . . . .  . . .  . . .  . . .  . . .  . . .  . .  . . 8 
iii 
SLOW ONSET TYPE PCA EVENTS AND ASSOCIATED PRE-SSC 
POLAR GEOMAGNETIC DISTURBANCES 
by 
Yukio Hakura* 
Goddard Space Flight Center 
and 
Masao Naga i  
Magnetic Observatory 
INTRODUCTION 
Polar Cap Absorptions (PCA) are classified into two fundamental types according to the delay- 
t ime of a PCA onset from an associated flare, i.e. F-type and S-type. The F-type represents a 
fast-onset in increase of absorption, with its maximum absorption well before the onset of a sub- 
sequent geomagnetic storm. 
after the associated flare, and its development is also very gradual. 
The S-type has a slow onset, being delayed several hours o r  more 
The main ionizing radiation responsible for PCA is protons with energies 1 to a few hundreds 
MeV. When they enter the earth's upper atmosphere, they precipitate in the lower ionosphere, in 
a height region, 30 km - 90 km. Since the region lies below the dynamo layer, PCA is originally 
an event which occurs without accompanying any geomagnetic disturbance. However, an existence 
of a polar geomagnetic disturbance has been analytically shown in connection with some of PCA 
events during the IGY (Hakura, Nagai, and Sano, 1961; Hakura and Nagai, 1964). The present paper 
shows an affinity between the geomagnetic polar disturbance and the slow-onset type PCA's. Pro- 
tons with energies 0.1 - 1 Mev precipitate in the dynamo region and may be the cause of the polar 
disturbance. Production of the low energy protons will be discussed. 
SLOW-ONSET TYPE PCA ASSOCIATED WITH A GEOMAGNETIC 
POLAR DISTURBANCE 
An outstanding geomagnetic disturbance was observed on February 1958 with its sudden com- 
mencement at 01:26 UT on February 11. The disturbance stemmed from a major solar flare ob- 
served around the center of the solar disk at 21:08 UT on February 9. A typical slow-onset type 
'Senior research associate of the National Academy of Sciences, on leave of absence from the Radio Research Laboratories, Tokyo, Japan. 
1 
PCA was observed in association with the flare which accompanied outstanding solar radio out- 
bursts of type IV. Time variation in the PCA both in the polar region (top) and in the auroral  zone 
(middle) on February 9th through 13th a r e  shown in Figure 1, where variation in geomagnetic K, 
index (bottom) is also given. Onset times of the flare and the geomagnetic s sc  are indicated at the 
top of the figure. Two different kinds of onsets were noted in time historyof the PCA. In the polar 
region, the first PCA was observed at 07 UT on February 10, when auroral zone stations did not 
detect any appreciable PCA yet. The second and intenser PCA started at  1 2  UT in the auroral 
zone, and a few hours later in the pole region. Detailed discussions of the two-stepped onset of 
the PCA were given elsewhere (Hakura and Nagai, 1964). The main interest in the present paper 
will be concentrated in the second PCA and its association with a peculiar polar geomagnetic 
storm. 
b 
Figure 2 shows storm-time variations of (a) geomagnetic storm-time variation, Dst at 32.5" 
in geomagnetic latitude, (b) DS-component of geomagnetic disturbance field at Churchill (70.3" in 
FLARE sc 
B - 4.0 
3.0 PCA IN THE POLAR REGION 
G 
I .E 2 . 0  v 
v 
4 
1 .o 
0 
PCA IN THE AURORAL ZONE 
- B  5 4.0 
5 - 3.0 
1- 
1; 2.0 PRE - EXISTING 
1 .o 
0 
( 3 1  
O18 0 12 
9th 10th 
11: 0 1  0 12 
1 1  th 
FEBRUARY 1958 
12th 
0 12 
13th 
Figure 1-Time variations in PCA both in the polar region (top) and auroral zone (middle), and variation in 
geomagnetic KP index (bottom), on 9th through 13th of February, 1958. PCA i s  expressed by Dst (Afrnin) which 
i s  a mean of Afmin values in several stations. Thule, Alert, Fletcher5 Ice, Resolute Bay, and Godhavn were se- 
lected for Dst (Afrnin) in the pole, while Narsarssaak, Tikhaya Bay, Reykjavik, Churchill, Point Barrow, Arctica 
I, and Trornso were picked for computing Dst (Afrnin) i n  the auroral zone. 
2 
corrected geomagnetic latitude), and (c) cosmic 
noise absorption at Churchill. As indicated by 
the arrows in the figure, the pre-sc polar dis- 
turbance, DP(PreSC), started at -13 hours in 
storm- time, showing rather surprisingly good 
time coincidence with the onset of (PCA)A. The 
(PCA)A observed at Churchill can never be 
identified as an auroral zone absorption which 
usuallyappears in a zig-zag shape after the on- 
set of an ssc, because of its long duration and 
smooth variations. Corresponding to the pre- sc 
disturbances, the Dst field also shows a slight 
depression. However, it must be noted that the 
ratio IDS/Dst/ at the pre-sc stage is about 3 
t imes higher than that at the post-sc stage. The 
polar disturbance, DP(PreSC), must be a special 
disturbance whose origin is connected with the 
invasion of solar cosmic rays. 
I 
Solar flare 
I I I 
During the IGY, 1957-58, when sunspot ac- 
tivity was maximum, five other well defined 
slow onset type PCA were observed (Hakura, 
1968). Table 1 shows some information of all 
the S-type events, such as year, month, date, 
and time in UT of the PCA-producing flare, the 
delay-time Atb of the PCA from the flare, and 
the delay-time At,  of the ssc from the flare. 
Figure 3 shows mean variations in PCA in the 
pole region, geomagnetic K-index at a pole sta- 
tion (Thule which is located at 86.0" in cor- 
rected geomagnetic latitude), geomagnetic K, 
index, and equatorial Dst, for the six disturb- 
ances shown in the table. The Dst (Afmin) pole 
is an average value of Afmin values observed at 
several pole stations located in roughly equal 
longitudinal intervals. The equatorial Dst is 
quoted from Sugiura (1964). The zero hour in 
the figure is the time of sudden commencements 
of the corresponding geomagnetic storms. A 
gradual increase in Dst (Afmin) pole in the 
preSC stage shows an average behaviour of 
slow-onset type PCA events. Corresponding to 
the PCA, an enhancement of K-index at Thule 
PCA 
STORM TIME 
4 -12 0 12 24 36 48 
August 
September 
October 
February 
March 
August 
I I I 
28 09:13 
11 02:43 
20 16:37 
09 21:08 
23 09:50 
20 00:43 
CHURCHILL 
GEOMAGNETIC 
FIELD (AXm) 
1 
CHURCH1 LL 
RIOMETER 
(30  Mc/s)  
13 01 13 
1 1  12 
FEBRUARY, 1358 
Figure 2-Storm-time variations of Dst (32.5"), Ax,,, 
(Churchill), and cosmic noise absorption at Churchill 
(D. H. Jelly, 1961). 
Table 1 
Slow Onset Type PCA Events During the IGY. 
- 
Year 
1957 
1958 
Month Date h m Position . 1 1 1 l*A;:s. 
30s35E 
llN03' 
25'45' 
13'14' 
14S77E 
16N23E 
12 
29 
12.5 
10 
46 
38 
~1 
50 
3 
is clearly seen at -12h through Oh, showing the 
existence of DP(preSC). It must be noted that 
K(Thule)/Kp ratios at the preSC and postSC 
stages are 1.8 and 1.0 respectively and that no 
appreciable disturbance is seen in Dst-variation 
till the onset of the SSC. 
2 
SYNOPTIC PATTERNS OF THE PCA AND 
EQUIVALENT CURRENT SYSTEM OF THE 1- 2 .0  
GEOMAGNETIC DP- FIELD 
A synoptic analysis will help us in having a 
further insight into the nature of the polar dis- 
turbances. Figure 4 shows a se r i e s  of onset 
patterns of the polar absorptions (expressed by 
contours of Afmin: hatched region in the upper 0 -150 
rank) and equivalent current systems of the 
geomagnetic DP-field (expressed by arrowed 
lines in the lower rank). 
STORM TIME (HOUR) 5 .  C. 
The first coup1e ( l )  Of the charts 
shows the slight PCA in the polar region, i.e. 
(PCA)p, and the corresponding current system 
of geomagnetic variations. The latter consists 
of two oppositely circulating vortices centered in the polar region and set along the morning mer- 
idian. This is essentially identical with the S," current system proposed by Nagata and Kokubun 
(1 962) for explaining an additional geomagnetic daily variation in geomagnetically quiet days. At 
12:30 (2), the region of abnormal ionization suddenly began to expand along the auroral zone, 
(PCA)A. A transition from the S," field to a peculiar polar disturbance field DP(PreSC) was found 
at this very stage. In the next two couples (3) and (4), are seen more intensified twin current vor- 
tices, corresponding to further developed (PCA)* event. 
Figure 3-Mean variations in Est (Afmin)pole , K index 
at Thule,KP index,ond equatorial Dst 6 slow onset type 
events during the IGY* 
DISCUSSIONS 
Nagata and Kokubun (1962) have explained the S: system as a Hall-current set  up by electric 
charges in the polar ionosphere. The charges are produced in the magnetosphere through a 
viscous-like interaction between the solar wind and the geomagnetic field, and conveyed to the 
ionosphere-dynamo-region through geomagnetic field lines. The S:- system could be intensified 
by either an increase in the solar wind velocity or  by an enhanced ionization produced in the dy- 
namo region. 
4 
4 -
4 
Y 
B 
- 
t 
Y VI
Z 
0 - 
N - 
L 
4 U 
n 
z 
re 
0 
5 
The propagation of sub-cosmic rays through the interplanetary medium is a process of dif- 
fusion. The t ime delay of solar cosmic rays reaching maximum intensity at the earth is inversely 
proportional to their velocities. In a typical F-type event of July 7, 1966, for example, 100 Mev 
proton flux reached its maximum a few hours after a corresponding flare, while 1 Mev proton flux 
increased gradually and reached its maximum one and a half days after the flare (Heristchi et al., 
1967; Armstrong et al., 1967. 
similar to a slow onset type PCA. A speculation goes that a particle acceleration in some solar 
cosmic r a y  flares is very ineffective and produces only protons with lower energies. This gives 
a possible explanation for the S-type PCA. 
The PCA due to 1 Mev protons would have shown a time history 
It is well known that most of solar cosmic rays during solar active period are connected with 
a solar flare accompanied with radio outbursts of type 1V (Hakura and Goh, 1959). A further sta- 
tistics of PCA's and type IV outbursts have shown that the F-type PCA follows solar radio out- 
bursts with predominating micro and decimeter parts, while the S-type PCA is related to radio 
outbursts with a rather weak micro part  and a outstanding meter wave part (Hakura, 1961). Fig- 
ure  5 shows a pair of typical type IV outbursts which produced F-type and S-type PCA events, 
respectively. Dynamic spectral features in both the outbursts are evidently different from each 
other. Solar cosmic rays responsible for the S-type PCA might be produced in a higher coronal 
region where meter wave radio wave is emitted. Solar magnetic field is too weak to keep protons 
trapped until they were accelerated to 10 Mev or higher. 
Besides the diffusion process, propagation of solar cosmic rays is greatly influenced by the 
interplanetary magnetic field configuration. The spiral  shaped interplanetary fields give a shorter 
path to solar cosmic rays propagating from the west side of the solar disk than to those from the 
east side. A linear relation exists between the delay-time of F-type PCA's and the heliographic 
longitudes of the PCA-producing flares (Obayashi and Hakura, 1960). A magnetized plasma cloud 
responsible for a geomagnetic storm, when supperposed with the stationary interplanetary field, 
also modulates the propagation of solar cosmic rays. Another speculation is that sub-cosmic rays 
could be trapped in the magnetized cloud, carried out into the interplanetary space, and then es- 
cape from it after the magnetic field is weakened by i ts  expansion, causing a PCA event of slow 
onset type (Sinno, 1961). Figure 6 shows a relation between atb and at, in cases of slow-onset 
type events shown in Table 1. The linearity actually shows the importance of the ssc-producing 
cloud for the propagation of the sub-cosmic rays producing the PCA. 
Energy spectrum of solar cosmic rays may change while they a r e  trapped in the cloud for  
several hours. Thus, the ampleness of low energy protons may be expected. 
As shown in the preceeding sections, the DP(PreSC) is a S: -augumentation which is possibly 
connected with sub-cosmic rays of solar origin. Protons with energies 0.1 - 1 MeV, when they 
come down in a standard atmosphere, precipitate in a height region of 110 - 90 km, and thus could 
be an origin of the S; -augumentation. Thus the discussion in the present paper is directed to a 
possible ampleness of the low energy protons in a solar cosmic ray event producing a slow-onset 
type PCA. 
1001 
101 
. 
loo( 
Io( 
1 oo( 
lo( 
loo( 
lo( 
200 Mc - 
(HIRAISO) 
(TOYOKAWA) 
3750 Mc 
(TOYOKAWA) 
FLARE 
N25, W07 IMP. 3 +(HAWAII)  
loo( 
2oc 
loo( 
2oc 
i U T  
DYNAMIC SPECTRUM 
100-580 Mc 
TYPE Ip ( TEXAS) 
u ( HOLLANDIA) 
1420 Mc 
FLARE 
513, W14 IMP. 2 (HAWAII) 
I I  I l l  I 1 1  I I  
01:oo 01 : 30 02 : 00 02: 
JUL 7, 1958 
Figure 5-Dynamic spectra of solar radio outbursts and solar flares associated with 
(a) Fast onset type PCA (b) Slow onset type PCA 
Atb = 1 hour Atb = 10 hours 
Atm = 31 hours Atm = 28 hours 
CONCLUSIONS 
1 I I 1 I I I 
23:00 UT 21:w 22: 00 
FEB 9, 1958 
Development patterns of a slow onset type PCA, the February 10, 1958 event were reviewed 
in comparison with equivalent current systems of geomagnetic polar disturbance field, DP. A 
peculiar geomagnetic disturbance started simultaneously with a sudden development of the PCA, 
some 12 hours before the associated ssc. A remarkable feature of the geomagnetic disturbance 
7 
SLOW TYPE PCA EVENTS 
50 sified Sq" field due to an enhanced ionization 
produced in the geomagnetic dynamo region. 2 
is the absence of the ordinary Dst-part. A sta- 
tistic of slow onset type PCA's assured the re- 
sult. The disturbance is regarded as an inten- 
ACKNOWLEDGMENTS 
I- 
40- 
Low energy protons with energies 0.1 - 1 Mev 
in the solar cosmic rays may be the cause of 
4 the disturbance. 0 
I 2 30- 
2 U
W es
4 
Y 20- 
U 
L 
I- 
The present work was  carried out while one 
of the authors (YH) held a senior post doctral 
resident research associate of the NAS-NAE at 
the NASA- Goddard Space Flight Center, on leave 
of absence from the Radio Research Labora- 21 I I I I 
tories, Tokyo, Japan. He is grateful t o  Dr. T. G. 
0 2 l o  
n 
- 
w 
9 
O10 20 30 40 50 61 
At, DELAY FROM THE FLARE TO THE SCC 
a2 
1 
Northrop for his hospitality. 
.,, 
Figure 6-Relaticn between Atb and At,, for six slow 
onset type PCA events. 
Atb: delay time of PCA from a corresponding flare. 
Atm: delay time of ssc from a corresponding flare. 
REFERENCES 
Armstrong, T. P., S. M. Krimigis, and J. A Van Allen, Observations of solar particles events of 
7 July 1966 with University of Iowa detectors, presented at the Joint IQSY/COSPAR symposium, 
in London, England, 1967. 
Hakura, Y., Some statistics on the solar cosmic rays produced by solar eruptions associated with 
type IV outbursts, Proceedings of 12th Alaskan Science Conference, September 1961. 
Hakura, Y., Polar cap absorptions and associated solar-terrestrial  events throughout the 19th 
solar cycle, NASA TND-4473, 1968. 
Hakura, Y., and T. Goh, Pre-sc polar cap ionospheric blackout and type IV solar radio outburst, 
Journal of Radio Research Laboratories, - 6, 635-650, 1959. 
Hakura, Y., M. Nagai, and K. Sano, Development of ionospheric and geomagnetic storms caused by 
solar corpuscular emissions 11. polar blackout, storm Es, and geomagnetic storms, Report of 
Ionosphere and Space Research in Japan, - 15, 1-30, 1961. 
Hakura, Y. and M. Nagai, Synthetic study of severe solar terrestrial disturbances of February 
9-12, 1958, Journal of Radio Research Laboratories, - 11, 197-249, 1964. 
8 
. 
Heristchi, Pj, J. Kangas, G. Kremser, J. P. Legrand, P. Masse, M. Palous, G. Pfotzer, W. Riedler, 
K, Wilhelm, Balloon measurements of solar protons in northern Scandinavia on h l y  ?, 1966, 
presented at the Joint IQSY/COSPAR symposium in London, England, 1967. 
Nagata, T. and S. Kokubun, An additional geomagnetic daily variation field @:-field) in the polar 
region on geomagnetically quiet days, Report of Ionosphere and Space Research in Japan, 16 
256, 1962. 
-9 
Obayashi, T. and Y. Hakura, Propagation of solar cosmic rays through interplanetary magnetic 
field, Journal of Geophysical Research, - 65, 3143- 3148, 1960. 
Sinno, K., Characteristics of solar energetic particles which excite polar- cap blackouts, Journal 
of the Radio Research Laboratories, - 8, 1-10, 1961. 
Sugiura, M., Hourly values of equatorial Dst for the IGY, Annals of the International Geophysical 
Year, - 35, 9-45, 1964. 
9 
Figure 1. Time variations in PCA both in the polar region (top) and auroral 
zone (middle), and variation in geomagnetic K index (bottom), on 
9th through 13th of February, 1958. PCA is egpressed by Dst 
(A fmin) which is a mean of A fmin values in several stations. Thule, 
Alert, Fletchers Ice, Resolute Bay, and Godhavn were selected for 
Dst (Afmin) in the pole, while Narsarssaak, Tikhaya Bay, Reykjavik, 
Churchill, Point Barrow, Arctica I, and Tromso were picked for 
computing Dst (Afmin) in the'auroral zone. 
Figure 2. Storm-time variations of Dst (32.5"), Axm (Churchill), and cosmic 
noise absorption at Churchill (D. H. Jelly, 1961). 
Figure 3. Mean variations in Dst (Afmin)po e ,  K index at Thule, KP index, 
and equatorial Dst 6 slow onset type PCA events during the IGY. 
Figure 4. Four pairs of synoptic patterns of PCA (upper rank) and equivalent 
current systems of geomagnetic disturbance (lower rank) in the 
initial phase of February 10, 1958 events. 
Figure 5. Dynamic spectra of solar radio outbursts and solar f lares associated 
with (a) Fast onset type PCA 
Atb = 1 hour 
Atm = 31 hours 
(b) Slow onset type PCA 
A tb = 10 hours 
A tm = 28 hours 
Figure 6. Relation between tb and tm, for six slow onset type PCA events. 
Atb : delay time of PCA from a corresponding flare. 
A t m  : delay time of ssc  from a corresponding flare. 


Slow onset type PCA events and associated pre-SSC polar geomagnetic disturbances

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