- Email: [email protected]
Analysis of geomagnetic effect of previous 5 solar eclipses occurring in China during past 50 years
oo32-o633/62/o605pl-oaWM.OO/O PelEZt"IOn Press Ltd.
Plonel. Space Sci., Vol. 30. No. 6, pp. 587-594, 1982 Printed in Great Britain.
ANALYSIS OF GEOMAGNETIC EFFECT OF PREVIOUS 5 SOLAR ECLIPSES OCCURRING IN CHINA DURING PAST 50 YEARS TSCIIU KANG-KUN,ZIIANG JING-EIU and LIU CIIANG-FA Institute of Geophysics, Academia Sinica, P.O. Box 928, Beijing, China (Received 4 January 1982) Abstract-In this paper results and analysis of geomagnetic observations during previous 5 solar eclioses occurred in China are summarized. Thev are solar eclipses: No. 1, on 19 June 1936 in Heiiongjiang of NE China; No. 2, on 21 September 1941 in Fujian; No. 3, on 19 April 1958 in Hainandao; No. 4, on 22 September 1968 in Xinjiang; and No. 5, on 16 February 1980 in Yunnan of SW China. The authors took part in the last 2 expeditions and joint programmes in the track of totality. The methods of evaluation for eclipse effects on the geomagnetic field are briefly described both for the quiet and disturbed days. The discussion of these data is made with reference to Chapman’s theoretical consideration on optical eclipse effect, together with the quiet-day overhead current systems in the upper atmosphere. We conclude that optical eclipse effects are easily observable under favourable conditions, and further observations are essential to establish the yet unknown effects due to corpuscular eclipses. 1. INTRODUCTION:EARLIER STUDIES
Since the beginning of the twentieth century, many attempts have been made to discover geomagnetic-field changes produced by a solar optical eclipse. One of those most active in this field was the late Dr. L. A. Bauer, the first director of the Department of Terrestrial Magnetism, the Carnegie Institution of Washington. Bauer (1900, 1902, 1920) sent many expeditions to places where there were solar eclipses, and he thought he had found eclipse effects. But other people (e.g. Chree, 1915) were skeptical of the existence of eclipse effects, in view of rather vague changes during eclipses and frequent overlapping of disturbances. In contrast to the solar flare effects, eclipse effects on the geomagnetic field are much more difficult to detect because of their infrequent occurrences with lesser effects in narrower zones. In this respect conjunctions of theoretical guidance and observed results are helpful. The famous and simplified model of an optical eclipse was presented first by Chapman (1933); and is reproduced in Fig. 9, Chapter 23, in Geomagnetism by Chapman and Bartels (1940). A revised model was presented by Nagata et al. (1955), and later, Ashour and Chapman (1965) reported more detailed results of calculated currents. Solar eclipses cause a decrease of ionization; hence, a reduction of the quite-day overhead current system occurs. Also, we have surveyed some good examples relating to the geomagnetic variations caused by the eclipses,
respectively on 20 June 1956, 12 October 1958, and on 11-12 November 1966. The former two are due to Japanese workers led by Kato (1956, 1960), the third is made by Bomke (1967). But all these eclipses occurred in low latitudes during magnetically quite periods; this results in more promising observations of optical eclipse effect. 2. GEOMAGNETIC OBSERVATIONS OF 5 ECLIPSES IN CHINA In this paper results and analysis of geomagnetic observations during previous 5 solar eclipses occurring in China for half century are sum-
marized. They are solar eclipses (see Fig. 1 and Table 1): No. 1, on 19 June 1936 in Heilongjiang of NE China; No. 2, on 21 September 1941 in Fujian; No. 3, on 19 April 1958 in Hainandao; No. 4, on 22 September 1968 in Xinjiang; and No. 5, on 16 February 1980 in Yunnan of SW China. The authors took part in the last two expeditions and joint programmes of our Academy in the track of totality. Figure 1 is a map showing sites of geomagnetic observations in relation to the track of totality of previous 5 eclipses. Table 1 shows details of geomagnetic stations used in this study for each solar eclipse. Briefly stated, the treatment of observations is as follows: In general, geomagnetic variation is composed of the quiet variation, the disturbed variation of the eclipse effect concerned. Or in 587
K.-K.
TSCHU et al.
Staton
HUMA QIQIHAER CHANGCHUN QINGDAO
DGNGYINDAO CHONGAN SHESHAN
GUANGZHOU SHESHAN BEIJING CHANGCHUN
ZHAOSU WULUMUQI KASHI LANZHOU LASA
RUILI KUNMING LIJIANG
Date
19 June 1936
21 September 1941
19 April 1958
22 September 1968
16 February 1980
24 25 26
43 43 39 36 29
23 31 40 43
26 27 31
51” 47 43 36
01 01 55
12 47 32 05 38
06 06 02 50
23 44 06
44’N 19 52 04
Latitude
97 102 100
81 87 76 103 91
113 121 116 125
120 117 121
126” 123 125 120
35 41 18
06 37 06 50 02
21 11 11 18
30 60 11
39’E 56 20 19
Longitude
00
10
17 17
18 18 18
27 31
46 48 50
09 11 09 43 0959 10 21
07
36 36 43 49
10
12 12 12 12
Beginning h min
38 30 30
53.5 57.0 3.6 7.0
18 18
19 19 19
32 34
56 50 56
10 52 11 28 1129 11 52
11 11 11
13 13 14 14
37 51 48 31
Total eclipse h min set
19 19
12 13 13 13
13
13
31 30
48 20 05 23
04
05
15 05 15 10 15 17 15 18
Ending h min
103 102.9
100 99 96
90 82 57 56
101.8 101.8 92
100 89 81 56
Degree of totality %
TABLE 1. DETAILS OF GEOMAGNETIC STATIONSUSEDFOR EACHSOLARECLIPSEIN CHINA
20 00
53
19 19 19
21 08 54
20 20 20
Sunset h min
K.-K.
590
TSCHU
et al.
symbol,
&q$!s HUMA
SH=6H,,+SH,+EGSq+6H,+E.
(1)
2
,I 2’
In quiet day, we may put S Hd = 0; hence, we have
;:
m
I
0’ [
SH - S, = E. But in disturbed
(2)
2' 0'[ 2' 0'[
day, it is evident that SH-S,=6H,+E.
P
m t
=
- K(6H - S,) eclipsed station
QINGDAU SHESHAN
(3) HUMA
In this case we may try to use the following approximated relation in order to evaluate the eclipse effect. Thus, E = (6H - S,)
CHANGCHLJN
CHANGCHUN
.
QINCDAU
non-eclipsed station
SHESHAN
(4)
HUMA
here K + 1. In the following all results and analyses according to this scheme are depicted in figures.q Some brief comments may appropriately be added. 2(a). Solar eclipse of 19 June 1936 The track of totality runs from USSR to the Hokkaido of Japan, via Heilongjiang Province of NE China. Japanese and Russian workers were very active for this occasion both in geomagnetic and ionospheric observations, as testified by bibliography appended in the book Solar Eclipses and the Ionosphere (Beynon and Brown, 1956). Data of five stations are used, of which only Huma is situated in the zone of total eclipse (see Table 1, and also Hayami et al., 1937). Three components H, D, Z, of the geomagnetic field on the eclipse day of 19 June 1936 are shown in Fig. 2. That day is a very disturbed day, being K = 7; the overlapping of disturbances are so great, being not able to discover the eclipse effects easily, especially for the Hcomponent. But it is interesting to note from difference-curves between different stations (not shown in this text) for D and 2 that such effects seem to be present. 2(b). Solar eclipse of 21 September 1941 Path of total eclipse starts in the NW part of Xinjiang, via Provinces Qinghai, Gansu, Shanxi, Hubei, Jiangxi and Fujian, right across the central part of our country, and ends in the Eastern *There are too many figures in the original text; this edited version keeps the minimum necessary.
CHANGCHUN
QINGDAU SHESHAN
FIG 2.
THREECOMPONENTSOFGEOMAGNETIC JUNE 1936.
FIELDON
19
Ocean. This was an excellent chance, being along a distance of 3500 km, for making geophysical observations in search of eclipse effects, the maximum duration of solar obscuration was of three minutes. Due to the unfortunate Sino-Japanese war at that time, Japanese workers made extensive observations of ionsophere and earth’s magnetism at the total solar eclipse at Hankow and Eastern Islands (e.g. Senda et al., 1942). Nevertheless, Chinese scientists Parker Chen and his associates did make geomagnetic observations during an expediation to Chongan in Fujian and published their preliminary results (1941). Figures 3(a) and 3(b) are examples, depicting the variations of H on 21 and 22 September 1941. From these figures it seems that the horizontal component shows a definite change corresponding to the eclipse, though the magnitude of depletion is of uncertain character.
Geomagnetic eciipse effects in China
591
(b) 7
8
9
10
11
12
13
BEIJING
14
15
UANGZHOU -CHANGCHUN
TIME
FIG.~. (a) H~OMPONENTOF~EOMAGNETICF~ELDONZ~AND 22 SEPT 1941. (b) ~I~ERENCE-CURVE OF H-COMPONENT BETWEENECLIPSEDAYANDTHENEXTDAY. In
10 0
,&_?
_
2(c). Solar eclipse uj 19 April 1958
During the annular eclipse of 19 April 1958 in Hainandao of South China, all four geomea~etic observatories (Table I), established for IGY and situated in our mainland, have registered the variations of three components of geomagnetic field. From the geomagnetograms of 5 quiet days around the date 19 April, we take readings every 5 min, and upon an average get typical curves for S,. Then the resulting disturbed curves for 3 components according to formula (3) were made; examples for H are shown in Figs. 4(a) and 4(b). From these figures the following conclusions may be stated. (i) The eclipse conditions are good because of higher altitude of the sun, near 60” above the horizon. Hence the eclipse effects are evident; the time lag is of about 10min. (ii) The effects are to decrease the horizontal component, to increase the vertical intensity, and to make the declination eastwards. All recover gradually to the normal trends fotlowing the sequence of this annular eclipse. (iii) As indicated in Table 1 degree of totality varies from 90% for Guangzhou to 56% for Changchum. The magnitude of eclipse effects depends on the degree of totality, other things being equal. Therefore, it may be estimated in the case of H, Guangzhou minus Changchung is of - 35 y in ma~itude, Sheshan minus Changchun of -20-y, while Beijing and Changchun are of same order. 2(d). Solar eclipse of 22 September 1968 This total eclipse occurred after sunset time for most parts of our country, other than a small part
-
__ ---5
--.&
IO
0
3
6
9
12
I:,
BEIJING-CHANCCHUN 18
2,
BEIJINGTIME
FIG. 4. (a) H-S,(H) CURVES ON 19 APRIL 1958. (b) DIFFERENCE-CURVES FOR H-S,(H) BETWEEN DlFFERENT STATIONSON 19 APRIL 1958.
in Xingjiang. Our Academy organized joint programmes of scientific observations for the study of this total eclipse; Zhang, Liu and other associates went to set up 3 temporary geomagnetic stations, as listed in Table 1. In analyses, geomagnetic data of all relevant stations are compiled and listed. Fig. 5(a) shows H - S,(H) curves for 6 stations. It is seen after 19 h 12 min Beijing time the Hcomponent decreases similarly for all 6 stations; the geomagnetic condition is rather disturbed. With reference to equation (4) above, differencecurves for H -S,(H) between Beijing and other stations are shown in Fig. 5(b). Perhaps minor decrease ( < 5y) may be seen for Wulumuqi and Kashi, but not for Lanzhou. Similar analyses and variation curves were made and drawn for other 2 components, D and 2, but not included here. All in all, the eclipse effects for this case are very small, due to various unfavourable reasons. 2(e). Solar eclipse of 16 February 1980 This is the last solar total eclipse occuring in our country before the end of this century. An extensive expedition both for solar, ionspheric and geomagnetic observations have been well organized by our Academy. As shown in Table 1, Ruili and Kunming are situated in the zone of
K.-K.TSCHU
592
et al.
LANZHOU
2
-10
t
IOr
17 18 19 20 21 22 23 0
Suns:tKASHI
01
17
18
19
20
21
22
-BEIJING
23
01
(h)
(a)
CURVESON 22 SEPTEMBER~~~~.(~)DIFFERENCE-CURVESFOR H-S,(H) DIFFERENTSTATIONS ON 22 SEPTEMBER 1968.
totality. Geomagnetic data for a temporary station at Ruili and several neighboring stations were collected and analysed; detailed results were published in the July issue of Acta Geophysics Sinica, 1981. Here are shown difference-curves between different stations Fig. 6(a) for H - S,(H), Fig. 6(b) I
0
BEIJINGTIME
BEIJINGTIME
Fm.5. (a) H-S,(H)
- BELING
0
=i
BETWEEN
for D-S,(D); the treatments are just the same as described above. It may be added many unfavorable factors result in very small eclipse effects; declination D towards east (-OX’), Z component increasing, and horizontal component H decreasing (-2.9~) as estimated in the paper cited.
RUILI -CHENGDU
RUILI -CHENGDU
-0.’
KUNMING
5L
-CHENGDU
0.’ 5 0: 0 L
LIJANG
I
-CHENGDU
RUILI
-LIJIANG
KUNMING
-LIJIANC
m
-0.’
5
- 0:
5-
1 KUNMING -LIJIANG
5.0 0.0
- 0: 5I
L
16
17
18
19
20
21
16
17
18
BEIJING TIME (a) Frc.6.
19
20
21
BEIJING TIME (b)
(a) DIFFERENCE-CURVESFOR H- S,(H) BETWEENDIFFERENTSTATIONSONI~FEBRUARY 1980.(b) DIFFERENCE-CURVESFOR D- S,(D) BETWEENDIFFERENTSTATIONSON16 FEBRUARY 1980.
Geomagnetic
eclipse effects in China
3. SOME DISCUSSIONS
After a brief survey of solar eclipses and the geomagnetism occurring in China during past 50 years, we are going to make further discussions of these data, with reference to Chapman’s theoretical consideration on optical eclipse effect, together with the quiet-day overhead current systems in the upper atmosphere. 3(a). Comparison with ionospheric observations Because solar eclipses cause a decrease of ionization, especially in the E layer, it is profitable to make comparison of eclipse effects of geomagnetism and ionosphere, when relevant data are available. Three cases of such a comparison were made, respectively for the station Guangzhou (19 April 1958), Kashi (22 September 1968) and Ruili (16 February 1980); here is shown Fig. 7 for Kashi. On the whole departures of critical frequency of E layer from their quiet days seem to accord with the geomagnetic companions. 3(b). Corresponding overhead &,-current systems According to Chapman’s theory, the reduction in electron and ion content of the atmosphere during a solar eclipse must reduce the conductivity of the upper atmosphere, and therefore must affect the overhead current systems which produce S, magnetic variations. If i0 is the current intensity over the whole sheet before the eclipse, the current when the conductivity K is reduced to K’ becomes i’ = i,,2K’/(K + K’). If K’ = l/2 K, then i’ = (2/3)&. If K/K’ is l/4, then we get i’li,, = 2/5. With very few geomagnetic data at hand, it was impossible to draw the overhead ¤t systems for the above-mentioned 5 solar eclipses. Instead, making use of Matsushita and Maeda’s studies (1965) on the external S, current systems averaged world wide for D, E and .I months, we have redrawn by interpolation four patterns of S-current systems approximately corresponding to
FIG. 7. COMPARISON
OF ECLIPSE
EFFECTS
593
the eclipse period of 19 June, 19 April, 22 September and 16 February as depicted in Figs. 8(a)_ (d). In conjuction with eclipse conditions listed in Table 1, it is quiet easy to interpret by these figures the geomagnetic-field changes produced by a solar optical eclipse, e.g. the larger eclipse effect in the case of 19 April 1958, while much smaller effects for last 2 eclipses. 3(c). Favourable conditions to discover the optical eclipse-effects These are: the degree of totality, geographical position of geomagnetic station in relation to the $-current system, the local time of eclipse occurrence, the seasons and the epoch of solar activity, together with geomagnetically quiet condition and high altitude of the sun. The resulting magnitudechange in intensity and direction due to solar eclipse depends on the combined effect of all these factors; this may explain why the observed results are vaguely changeable. Nevertheless, we are rather convinced, through the present study, of having unmistakable effects easily observable under favourable conditions. 3(d). Towards the night value In his theoretical discussion Chapman (1933) concluded that “at points near the center of a total eclipse, the H- and D-curves given by the magnetographs would be deflected during the eclipse, by about one third of the way towards the night value”. Using our results it may be similarly identified, though the ratio varies from one occasion to another. 3(e). On the corpuscular eclipse There are a few reports of geomagnetic pulsations caused by eclipses and of the due to corpuscular eclipses, e.g. Astbury Kato (1965a, b). In connection with the last total eclipses listed in Table 1, we did make
OF GEOMAGNETISM
AND
IONOSPHERE
ON
22 SEPTEMBER
1968.
microeffects (1952); 2 solar quick-
K.-K. TSCXU et al.
594
LOCAL TIME
LOCAL TIME
LOCAL TIME
LOCAL TIME
&3.8. ~VRRH~A~S~~U~E~SYSTEMCO~ESPO~RI~GTOTHE EC~PS~FERIO~OF:~a)l9sU~E 22 SEPTEMBER 1968, (c) 19 APRIL 19.58 AND (d) 16 FEBRUARY 1980.
run registrations of geomagnetic field at temporary stations, but we failed to confirm these effects. Undoubtedly, further observations are very essential to establish the yet unknown effects due to corpuscular
eclipsees.
Acknowledgement-The authors wish to thank Professor S. -1. Akasofu for valuable remarks and suggestions for this edited version of our paper. REFERENCES
Ashour, A. A. and Chapman, S. (1965). Geophys. J. R. As& Sot. 10,31. Astbury, N. F. (1952). Nature, Land. 170,68. Bauer, L. A. (1900). Tew. Magn. atmos. Elect. 5, 143. Bauer, L. A. (1902). Tew. b4agn. atmos. Elect. 7, 155. Bauer, L. A. (1920). Terr. Magn. atmos. Elect. 25, 81. Beynon, W. J. G. and Brown, G. M. (Eds.) (1956). Solar Eclipses and the Ionosphere. pp. 310-313, Pergamon Press, London.
1936,(b)
Bomke, S. A. (1967). I; geophys. Res. T&,5913.
Chapman, S. (1933). Terr. Mugn. otmos. Elect. 38, 175. Chapman, S. and Barteles, J. (1940). Geomagnetism Vol. II, p. 796, Oxford University Press, Oxford. Chen, Parker et al. (1941) Reports on solar eclipse of 21 Sept. (1941). p. 50. (in Chinese). Chree, C. (19l$. Te& Magn. &t&s. Elect. 20,71. Hayami, S. et al. (1937). JQ~. J. As&o. Geophys. 14, 181. Kato, Y. (1956). Scienr. Rep. Tohaku Univ. Fifth Ser. 7, Suppl. 1. Kato, Y. (1960). Scient. Rep. Tohaku Univ. Fifth Ser. 12, 1. Kate, Y. (1965a). Scient. Rep. To~ok~ Univ. Fifth Ser. l&49. Kato, Y. (l%Sb). Scient. Rep. Tohoku Univ. Fifth Ser. l&63. Liu C. F., et al. (198i) Acfa Geophysics Sinicn 24,269. (in Chinese). Matsushita, S. and Maeda, H. (1965). J. geophys. Res. 70, 2535. Nagata, T. et al. (19551. Rep. ~onosp~. Res. Japan 9, 121. Senda, K. and Li, S. (1942). Radio 34,232.
Plonel. Space Sci., Vol. 30. No. 6, pp. 587-594, 1982 Printed in Great Britain.
ANALYSIS OF GEOMAGNETIC EFFECT OF PREVIOUS 5 SOLAR ECLIPSES OCCURRING IN CHINA DURING PAST 50 YEARS TSCIIU KANG-KUN,ZIIANG JING-EIU and LIU CIIANG-FA Institute of Geophysics, Academia Sinica, P.O. Box 928, Beijing, China (Received 4 January 1982) Abstract-In this paper results and analysis of geomagnetic observations during previous 5 solar eclioses occurred in China are summarized. Thev are solar eclipses: No. 1, on 19 June 1936 in Heiiongjiang of NE China; No. 2, on 21 September 1941 in Fujian; No. 3, on 19 April 1958 in Hainandao; No. 4, on 22 September 1968 in Xinjiang; and No. 5, on 16 February 1980 in Yunnan of SW China. The authors took part in the last 2 expeditions and joint programmes in the track of totality. The methods of evaluation for eclipse effects on the geomagnetic field are briefly described both for the quiet and disturbed days. The discussion of these data is made with reference to Chapman’s theoretical consideration on optical eclipse effect, together with the quiet-day overhead current systems in the upper atmosphere. We conclude that optical eclipse effects are easily observable under favourable conditions, and further observations are essential to establish the yet unknown effects due to corpuscular eclipses. 1. INTRODUCTION:EARLIER STUDIES
Since the beginning of the twentieth century, many attempts have been made to discover geomagnetic-field changes produced by a solar optical eclipse. One of those most active in this field was the late Dr. L. A. Bauer, the first director of the Department of Terrestrial Magnetism, the Carnegie Institution of Washington. Bauer (1900, 1902, 1920) sent many expeditions to places where there were solar eclipses, and he thought he had found eclipse effects. But other people (e.g. Chree, 1915) were skeptical of the existence of eclipse effects, in view of rather vague changes during eclipses and frequent overlapping of disturbances. In contrast to the solar flare effects, eclipse effects on the geomagnetic field are much more difficult to detect because of their infrequent occurrences with lesser effects in narrower zones. In this respect conjunctions of theoretical guidance and observed results are helpful. The famous and simplified model of an optical eclipse was presented first by Chapman (1933); and is reproduced in Fig. 9, Chapter 23, in Geomagnetism by Chapman and Bartels (1940). A revised model was presented by Nagata et al. (1955), and later, Ashour and Chapman (1965) reported more detailed results of calculated currents. Solar eclipses cause a decrease of ionization; hence, a reduction of the quite-day overhead current system occurs. Also, we have surveyed some good examples relating to the geomagnetic variations caused by the eclipses,
respectively on 20 June 1956, 12 October 1958, and on 11-12 November 1966. The former two are due to Japanese workers led by Kato (1956, 1960), the third is made by Bomke (1967). But all these eclipses occurred in low latitudes during magnetically quite periods; this results in more promising observations of optical eclipse effect. 2. GEOMAGNETIC OBSERVATIONS OF 5 ECLIPSES IN CHINA In this paper results and analysis of geomagnetic observations during previous 5 solar eclipses occurring in China for half century are sum-
marized. They are solar eclipses (see Fig. 1 and Table 1): No. 1, on 19 June 1936 in Heilongjiang of NE China; No. 2, on 21 September 1941 in Fujian; No. 3, on 19 April 1958 in Hainandao; No. 4, on 22 September 1968 in Xinjiang; and No. 5, on 16 February 1980 in Yunnan of SW China. The authors took part in the last two expeditions and joint programmes of our Academy in the track of totality. Figure 1 is a map showing sites of geomagnetic observations in relation to the track of totality of previous 5 eclipses. Table 1 shows details of geomagnetic stations used in this study for each solar eclipse. Briefly stated, the treatment of observations is as follows: In general, geomagnetic variation is composed of the quiet variation, the disturbed variation of the eclipse effect concerned. Or in 587
K.-K.
TSCHU et al.
Staton
HUMA QIQIHAER CHANGCHUN QINGDAO
DGNGYINDAO CHONGAN SHESHAN
GUANGZHOU SHESHAN BEIJING CHANGCHUN
ZHAOSU WULUMUQI KASHI LANZHOU LASA
RUILI KUNMING LIJIANG
Date
19 June 1936
21 September 1941
19 April 1958
22 September 1968
16 February 1980
24 25 26
43 43 39 36 29
23 31 40 43
26 27 31
51” 47 43 36
01 01 55
12 47 32 05 38
06 06 02 50
23 44 06
44’N 19 52 04
Latitude
97 102 100
81 87 76 103 91
113 121 116 125
120 117 121
126” 123 125 120
35 41 18
06 37 06 50 02
21 11 11 18
30 60 11
39’E 56 20 19
Longitude
00
10
17 17
18 18 18
27 31
46 48 50
09 11 09 43 0959 10 21
07
36 36 43 49
10
12 12 12 12
Beginning h min
38 30 30
53.5 57.0 3.6 7.0
18 18
19 19 19
32 34
56 50 56
10 52 11 28 1129 11 52
11 11 11
13 13 14 14
37 51 48 31
Total eclipse h min set
19 19
12 13 13 13
13
13
31 30
48 20 05 23
04
05
15 05 15 10 15 17 15 18
Ending h min
103 102.9
100 99 96
90 82 57 56
101.8 101.8 92
100 89 81 56
Degree of totality %
TABLE 1. DETAILS OF GEOMAGNETIC STATIONSUSEDFOR EACHSOLARECLIPSEIN CHINA
20 00
53
19 19 19
21 08 54
20 20 20
Sunset h min
K.-K.
590
TSCHU
et al.
symbol,
&q$!s HUMA
SH=6H,,+SH,+EGSq+6H,+E.
(1)
2
,I 2’
In quiet day, we may put S Hd = 0; hence, we have
;:
m
I
0’ [
SH - S, = E. But in disturbed
(2)
2' 0'[ 2' 0'[
day, it is evident that SH-S,=6H,+E.
P
m t
=
- K(6H - S,) eclipsed station
QINGDAU SHESHAN
(3) HUMA
In this case we may try to use the following approximated relation in order to evaluate the eclipse effect. Thus, E = (6H - S,)
CHANGCHLJN
CHANGCHUN
.
QINCDAU
non-eclipsed station
SHESHAN
(4)
HUMA
here K + 1. In the following all results and analyses according to this scheme are depicted in figures.q Some brief comments may appropriately be added. 2(a). Solar eclipse of 19 June 1936 The track of totality runs from USSR to the Hokkaido of Japan, via Heilongjiang Province of NE China. Japanese and Russian workers were very active for this occasion both in geomagnetic and ionospheric observations, as testified by bibliography appended in the book Solar Eclipses and the Ionosphere (Beynon and Brown, 1956). Data of five stations are used, of which only Huma is situated in the zone of total eclipse (see Table 1, and also Hayami et al., 1937). Three components H, D, Z, of the geomagnetic field on the eclipse day of 19 June 1936 are shown in Fig. 2. That day is a very disturbed day, being K = 7; the overlapping of disturbances are so great, being not able to discover the eclipse effects easily, especially for the Hcomponent. But it is interesting to note from difference-curves between different stations (not shown in this text) for D and 2 that such effects seem to be present. 2(b). Solar eclipse of 21 September 1941 Path of total eclipse starts in the NW part of Xinjiang, via Provinces Qinghai, Gansu, Shanxi, Hubei, Jiangxi and Fujian, right across the central part of our country, and ends in the Eastern *There are too many figures in the original text; this edited version keeps the minimum necessary.
CHANGCHUN
QINGDAU SHESHAN
FIG 2.
THREECOMPONENTSOFGEOMAGNETIC JUNE 1936.
FIELDON
19
Ocean. This was an excellent chance, being along a distance of 3500 km, for making geophysical observations in search of eclipse effects, the maximum duration of solar obscuration was of three minutes. Due to the unfortunate Sino-Japanese war at that time, Japanese workers made extensive observations of ionsophere and earth’s magnetism at the total solar eclipse at Hankow and Eastern Islands (e.g. Senda et al., 1942). Nevertheless, Chinese scientists Parker Chen and his associates did make geomagnetic observations during an expediation to Chongan in Fujian and published their preliminary results (1941). Figures 3(a) and 3(b) are examples, depicting the variations of H on 21 and 22 September 1941. From these figures it seems that the horizontal component shows a definite change corresponding to the eclipse, though the magnitude of depletion is of uncertain character.
Geomagnetic eciipse effects in China
591
(b) 7
8
9
10
11
12
13
BEIJING
14
15
UANGZHOU -CHANGCHUN
TIME
FIG.~. (a) H~OMPONENTOF~EOMAGNETICF~ELDONZ~AND 22 SEPT 1941. (b) ~I~ERENCE-CURVE OF H-COMPONENT BETWEENECLIPSEDAYANDTHENEXTDAY. In
10 0
,&_?
_
2(c). Solar eclipse uj 19 April 1958
During the annular eclipse of 19 April 1958 in Hainandao of South China, all four geomea~etic observatories (Table I), established for IGY and situated in our mainland, have registered the variations of three components of geomagnetic field. From the geomagnetograms of 5 quiet days around the date 19 April, we take readings every 5 min, and upon an average get typical curves for S,. Then the resulting disturbed curves for 3 components according to formula (3) were made; examples for H are shown in Figs. 4(a) and 4(b). From these figures the following conclusions may be stated. (i) The eclipse conditions are good because of higher altitude of the sun, near 60” above the horizon. Hence the eclipse effects are evident; the time lag is of about 10min. (ii) The effects are to decrease the horizontal component, to increase the vertical intensity, and to make the declination eastwards. All recover gradually to the normal trends fotlowing the sequence of this annular eclipse. (iii) As indicated in Table 1 degree of totality varies from 90% for Guangzhou to 56% for Changchum. The magnitude of eclipse effects depends on the degree of totality, other things being equal. Therefore, it may be estimated in the case of H, Guangzhou minus Changchung is of - 35 y in ma~itude, Sheshan minus Changchun of -20-y, while Beijing and Changchun are of same order. 2(d). Solar eclipse of 22 September 1968 This total eclipse occurred after sunset time for most parts of our country, other than a small part
-
__ ---5
--.&
IO
0
3
6
9
12
I:,
BEIJING-CHANCCHUN 18
2,
BEIJINGTIME
FIG. 4. (a) H-S,(H) CURVES ON 19 APRIL 1958. (b) DIFFERENCE-CURVES FOR H-S,(H) BETWEEN DlFFERENT STATIONSON 19 APRIL 1958.
in Xingjiang. Our Academy organized joint programmes of scientific observations for the study of this total eclipse; Zhang, Liu and other associates went to set up 3 temporary geomagnetic stations, as listed in Table 1. In analyses, geomagnetic data of all relevant stations are compiled and listed. Fig. 5(a) shows H - S,(H) curves for 6 stations. It is seen after 19 h 12 min Beijing time the Hcomponent decreases similarly for all 6 stations; the geomagnetic condition is rather disturbed. With reference to equation (4) above, differencecurves for H -S,(H) between Beijing and other stations are shown in Fig. 5(b). Perhaps minor decrease ( < 5y) may be seen for Wulumuqi and Kashi, but not for Lanzhou. Similar analyses and variation curves were made and drawn for other 2 components, D and 2, but not included here. All in all, the eclipse effects for this case are very small, due to various unfavourable reasons. 2(e). Solar eclipse of 16 February 1980 This is the last solar total eclipse occuring in our country before the end of this century. An extensive expedition both for solar, ionspheric and geomagnetic observations have been well organized by our Academy. As shown in Table 1, Ruili and Kunming are situated in the zone of
K.-K.TSCHU
592
et al.
LANZHOU
2
-10
t
IOr
17 18 19 20 21 22 23 0
Suns:tKASHI
01
17
18
19
20
21
22
-BEIJING
23
01
(h)
(a)
CURVESON 22 SEPTEMBER~~~~.(~)DIFFERENCE-CURVESFOR H-S,(H) DIFFERENTSTATIONS ON 22 SEPTEMBER 1968.
totality. Geomagnetic data for a temporary station at Ruili and several neighboring stations were collected and analysed; detailed results were published in the July issue of Acta Geophysics Sinica, 1981. Here are shown difference-curves between different stations Fig. 6(a) for H - S,(H), Fig. 6(b) I
0
BEIJINGTIME
BEIJINGTIME
Fm.5. (a) H-S,(H)
- BELING
0
=i
BETWEEN
for D-S,(D); the treatments are just the same as described above. It may be added many unfavorable factors result in very small eclipse effects; declination D towards east (-OX’), Z component increasing, and horizontal component H decreasing (-2.9~) as estimated in the paper cited.
RUILI -CHENGDU
RUILI -CHENGDU
-0.’
KUNMING
5L
-CHENGDU
0.’ 5 0: 0 L
LIJANG
I
-CHENGDU
RUILI
-LIJIANG
KUNMING
-LIJIANC
m
-0.’
5
- 0:
5-
1 KUNMING -LIJIANG
5.0 0.0
- 0: 5I
L
16
17
18
19
20
21
16
17
18
BEIJING TIME (a) Frc.6.
19
20
21
BEIJING TIME (b)
(a) DIFFERENCE-CURVESFOR H- S,(H) BETWEENDIFFERENTSTATIONSONI~FEBRUARY 1980.(b) DIFFERENCE-CURVESFOR D- S,(D) BETWEENDIFFERENTSTATIONSON16 FEBRUARY 1980.
Geomagnetic
eclipse effects in China
3. SOME DISCUSSIONS
After a brief survey of solar eclipses and the geomagnetism occurring in China during past 50 years, we are going to make further discussions of these data, with reference to Chapman’s theoretical consideration on optical eclipse effect, together with the quiet-day overhead current systems in the upper atmosphere. 3(a). Comparison with ionospheric observations Because solar eclipses cause a decrease of ionization, especially in the E layer, it is profitable to make comparison of eclipse effects of geomagnetism and ionosphere, when relevant data are available. Three cases of such a comparison were made, respectively for the station Guangzhou (19 April 1958), Kashi (22 September 1968) and Ruili (16 February 1980); here is shown Fig. 7 for Kashi. On the whole departures of critical frequency of E layer from their quiet days seem to accord with the geomagnetic companions. 3(b). Corresponding overhead &,-current systems According to Chapman’s theory, the reduction in electron and ion content of the atmosphere during a solar eclipse must reduce the conductivity of the upper atmosphere, and therefore must affect the overhead current systems which produce S, magnetic variations. If i0 is the current intensity over the whole sheet before the eclipse, the current when the conductivity K is reduced to K’ becomes i’ = i,,2K’/(K + K’). If K’ = l/2 K, then i’ = (2/3)&. If K/K’ is l/4, then we get i’li,, = 2/5. With very few geomagnetic data at hand, it was impossible to draw the overhead ¤t systems for the above-mentioned 5 solar eclipses. Instead, making use of Matsushita and Maeda’s studies (1965) on the external S, current systems averaged world wide for D, E and .I months, we have redrawn by interpolation four patterns of S-current systems approximately corresponding to
FIG. 7. COMPARISON
OF ECLIPSE
EFFECTS
593
the eclipse period of 19 June, 19 April, 22 September and 16 February as depicted in Figs. 8(a)_ (d). In conjuction with eclipse conditions listed in Table 1, it is quiet easy to interpret by these figures the geomagnetic-field changes produced by a solar optical eclipse, e.g. the larger eclipse effect in the case of 19 April 1958, while much smaller effects for last 2 eclipses. 3(c). Favourable conditions to discover the optical eclipse-effects These are: the degree of totality, geographical position of geomagnetic station in relation to the $-current system, the local time of eclipse occurrence, the seasons and the epoch of solar activity, together with geomagnetically quiet condition and high altitude of the sun. The resulting magnitudechange in intensity and direction due to solar eclipse depends on the combined effect of all these factors; this may explain why the observed results are vaguely changeable. Nevertheless, we are rather convinced, through the present study, of having unmistakable effects easily observable under favourable conditions. 3(d). Towards the night value In his theoretical discussion Chapman (1933) concluded that “at points near the center of a total eclipse, the H- and D-curves given by the magnetographs would be deflected during the eclipse, by about one third of the way towards the night value”. Using our results it may be similarly identified, though the ratio varies from one occasion to another. 3(e). On the corpuscular eclipse There are a few reports of geomagnetic pulsations caused by eclipses and of the due to corpuscular eclipses, e.g. Astbury Kato (1965a, b). In connection with the last total eclipses listed in Table 1, we did make
OF GEOMAGNETISM
AND
IONOSPHERE
ON
22 SEPTEMBER
1968.
microeffects (1952); 2 solar quick-
K.-K. TSCXU et al.
594
LOCAL TIME
LOCAL TIME
LOCAL TIME
LOCAL TIME
&3.8. ~VRRH~A~S~~U~E~SYSTEMCO~ESPO~RI~GTOTHE EC~PS~FERIO~OF:~a)l9sU~E 22 SEPTEMBER 1968, (c) 19 APRIL 19.58 AND (d) 16 FEBRUARY 1980.
run registrations of geomagnetic field at temporary stations, but we failed to confirm these effects. Undoubtedly, further observations are very essential to establish the yet unknown effects due to corpuscular
eclipsees.
Acknowledgement-The authors wish to thank Professor S. -1. Akasofu for valuable remarks and suggestions for this edited version of our paper. REFERENCES
Ashour, A. A. and Chapman, S. (1965). Geophys. J. R. As& Sot. 10,31. Astbury, N. F. (1952). Nature, Land. 170,68. Bauer, L. A. (1900). Tew. Magn. atmos. Elect. 5, 143. Bauer, L. A. (1902). Tew. b4agn. atmos. Elect. 7, 155. Bauer, L. A. (1920). Terr. Magn. atmos. Elect. 25, 81. Beynon, W. J. G. and Brown, G. M. (Eds.) (1956). Solar Eclipses and the Ionosphere. pp. 310-313, Pergamon Press, London.
1936,(b)
Bomke, S. A. (1967). I; geophys. Res. T&,5913.
Chapman, S. (1933). Terr. Mugn. otmos. Elect. 38, 175. Chapman, S. and Barteles, J. (1940). Geomagnetism Vol. II, p. 796, Oxford University Press, Oxford. Chen, Parker et al. (1941) Reports on solar eclipse of 21 Sept. (1941). p. 50. (in Chinese). Chree, C. (19l$. Te& Magn. &t&s. Elect. 20,71. Hayami, S. et al. (1937). JQ~. J. As&o. Geophys. 14, 181. Kato, Y. (1956). Scienr. Rep. Tohaku Univ. Fifth Ser. 7, Suppl. 1. Kato, Y. (1960). Scient. Rep. Tohaku Univ. Fifth Ser. 12, 1. Kate, Y. (1965a). Scient. Rep. To~ok~ Univ. Fifth Ser. l&49. Kato, Y. (l%Sb). Scient. Rep. Tohoku Univ. Fifth Ser. l&63. Liu C. F., et al. (198i) Acfa Geophysics Sinicn 24,269. (in Chinese). Matsushita, S. and Maeda, H. (1965). J. geophys. Res. 70, 2535. Nagata, T. et al. (19551. Rep. ~onosp~. Res. Japan 9, 121. Senda, K. and Li, S. (1942). Radio 34,232.