- Email: [email protected]
Lunar effects on the equatorial Es
RESEARCH NOTES
L,mar effects on the equatorial Es (Received 3 November
1956)
I s the equatorial region, Es reflection is abnormally intense in the daytime (M_ATSUSHITA, 1951 and 1953; SMITH, 1955). This equatorial Es occasionally disappears suddenly around noon or the early afternoon, although it usually continues till evening (M-cTSVSmTA, 1955). Fig. 1 is an example of the effect in ionograms obtained with a vertical incidence ionosonde (N.B.S., Model C-3) made at Huaneayo every 15 min. In Fig. la, the equatorial Es disappeared suddenly at 1345 75 ° WMT, although it had the usual appearance at 1315 and 1330. The time at which the Es disappeared, in this example, was taken to be 1345 for the present study. I n Fig. lb, the Es almost disappeared at 1430, and completely disappeared at 1445. As the time at which the Es disappeared in this example, 1430 was used, instead of 1445. After once disappearing, the equatorial Es sometimes reappears a half-hour to a few hours after the time of disappearance, and also occasionally disappears again. For the following study, the time at which the Es first disappeared during the period from 1000 to 2000 on each day at Huancayo was obtained from ionograms. The equatorial Es, however, usually disappeared between 1700 and 2000. Sometimes it lasted even after 2000, when it changed its type of reflection. In my study, this effect was ignored, because it only occurred on a few days during the month. The geomagnetic storm effect and the power change of the ionosonde were also ignored in finding the Es disappearance-time. The approximate lunar age of each day was calculated, and the local time at which the Es disappeared was plotted as a function of the lunar age. The variation of the averaged values is shown in Fig. 2. As can be seen in Fig. 2a, the equatorial Es often disappeared earlier than usual in the vicinity of the full and the new moons. This relation is more conspicuous during the December-solstice months than during the June-solstice months. Fig. 2b is the variation during the December-solstice months from 1952 to 1955. The solar time of the disappearance plotted as a function of corresponding lunar hour shows a much clearer relation, as shown in Fig. 3. The total number of disappearances occurring before 1700 solar time was computed for each lunar hour. (The Es usually disappears after 1700 solar time.) This is shown in the upper part of the figure. I conclude from this result that the equatorial Es often disappears around noon or the early afternoon (solar local time) if these times lie between 0000 and 0300 or between 1200 and 1500 lunar time. In other words, the equatorial Es often disappears during the first haft of the periods of the westward lunar electric current flow in the equatorial region. This current is responsible for the lunar daily magnetic variation (CHAPMANand BARTELS, 1940). The lunar tidal variation of foEs at Huancayo has minima at 0000-0300 and 1200-1500 lunar time (MATSUSHITA, 1953), which also agrees with the present result. The equatorial Es m a y be caused by the vertical upward drift force due to the eastward electric current jet, as the author has already suggested. Accordingly, the disappearance of the equatorial Es m a y be explained by the assumption that the vertical upward drift force due to the eastward electric current of the solar magnetic variation is weakened by the
163
Research notes
g') a')
/i
t,
-
,
i
:
I',
.." 4-
it
.i-,'::.
t
I
k'J " I
I [
",
o
.: ~ L:
I::1~
V
,'
"
0 >., 0 0 0 3 "I"
I
0
~
I
0
~
Q. Q.
I
0
I
o
eBo Joun"l
.~_ III U')
c-
/
r"
/',
.....
./ i
,.- ',..~.,', t,,/ • "~,,
........./kl~1 " !-..
E
.'-
.."".-
[:::1
... ';.-- ..~~'1 ~ :.... ~ f ~ \ :"' l ',I'/
6h-
7
/^ /~Lp
'"
V)'
'
o
.~
o
J
o
e S o aoun'l
164
TT
0
¢i
lxl,~
Z
I
42
I
I
o
don25, 1955 (o)
July30, 1954. (b)
Fig. 1. Ionograms from Huaneayo showing sudden disappearance of equatorial Es.
p. 164
Research notes
d o w n w a r d drift force due to the westward electric c u r r e n t of the lunar m a g n e t i c variation• The l u n a r stratification of the F2 a t H u a n c a y o , reported b y GAUTIER, KNECHT, a n d McNIsH (1951), occurs d u r i n g the period of 0600-0900 a n d 1800-2100 l u n a r time. I t is interesting t h a t there is a 6-hours time-lag between the l u n a r effect on the Es a n d the l u n a r stratification of the F2. This suggests t h a t the l u n a r stratification is caused b y the eastward l u n a r c u r r e n t effect, in contrast with the disappearance of the Es, caused b y the westward l u n a r current. nar-solar time of disappearance orE s at Huancayo • solstice, 1952-55) and numbers of occurrence
10-,
12
14
-- . . . . --
°
,~ .
°,
.
:, . . ' . . "
.
..
.
. v . - . . , - . .. . . "'"
16 -
(~ 18
.
•-"~ .••° ,
"°%
• °°.
,
.
.
.
.
". • ".. ": ," ." " . . ." " .. : . : / i , ° °* " " •., o. , o * • .o • ""
.:•...::..,
, . . . . . . .
,," . °., . . ~ • to ° , . :~%.• .~
.
•
. . . . . •...
• ; • : ; .. .
"~ •
20~
--
":•- °
°
~,"
0
,~,•:
" "
I l l l l J J l l l l J l l J , l t l l l i l l l l l l l
20
0
4
8
12
LunoP
16
20
24
houP
Fig. 3. Sudden disappearances of equatorial Es that take place before 1700 solar time occur more frequently between O000 and 0300 or between 1200 and 1500 lunar time. Dots of lower graph indicate solar and lunar times of sudden disappearances orEs; upper histogram indicates total number of such disappearance by lunar hours. Data: December-solstice months, 1952-55.
Acknowledgements--The a u t h o r wishes to express his t h a n k s for support of the present s t u d y by the Geophysical Research Directorate, Air Force Cambridge Research Center, u n d e r contract AF19(604)-969. He wishes also to express his sincere gratitude to Dr. L. V. BERKNER, Dr. W. O. ROBERTS, Mr. A. H. SHAPLEY, Mr. T. N. GAUTIER, Mr. A. G. McNIsH, l)r. E. H. VESTINE, a n d Mr. S. FORBUSH for their kind help a n d advice, a n d to the Central Radio P r o p a g a t i o n Laboratories, N a t i o n a l Bureau of Standards, for use of ionograms involved in this s t u d y a n d for e x t e n d i n g to him the facilities of the Boulder Laboratories. ttigh Altitude Observatory, Boulder, Colorado
S. ~¢[ATSUSHITA~"
REFERENCES CHAPMAN S. and BARTELS J. C~AUTIERT. N., KNECHT R . W . , and McNIs~ A . G . •IATSUSI-[ITA S.
1940 1951
1951 1953 1953 1955 ~MITH E . K . 1955 * On leave from Kyoto University, Japan.
Geomagnetism Oxford Press. Mixed Commission on Ionosphere, Prec. of Second Meeting, page 100. J. Geomag. Geoelect. 3, 44. J. Geomag. Geoelect. 5, 109. Rep. Ionos. Res. Japan. 7, 45. J. Geomag. Geoelect. 7, 91. NBS Report No. 3575.
165
L,mar effects on the equatorial Es (Received 3 November
1956)
I s the equatorial region, Es reflection is abnormally intense in the daytime (M_ATSUSHITA, 1951 and 1953; SMITH, 1955). This equatorial Es occasionally disappears suddenly around noon or the early afternoon, although it usually continues till evening (M-cTSVSmTA, 1955). Fig. 1 is an example of the effect in ionograms obtained with a vertical incidence ionosonde (N.B.S., Model C-3) made at Huaneayo every 15 min. In Fig. la, the equatorial Es disappeared suddenly at 1345 75 ° WMT, although it had the usual appearance at 1315 and 1330. The time at which the Es disappeared, in this example, was taken to be 1345 for the present study. I n Fig. lb, the Es almost disappeared at 1430, and completely disappeared at 1445. As the time at which the Es disappeared in this example, 1430 was used, instead of 1445. After once disappearing, the equatorial Es sometimes reappears a half-hour to a few hours after the time of disappearance, and also occasionally disappears again. For the following study, the time at which the Es first disappeared during the period from 1000 to 2000 on each day at Huancayo was obtained from ionograms. The equatorial Es, however, usually disappeared between 1700 and 2000. Sometimes it lasted even after 2000, when it changed its type of reflection. In my study, this effect was ignored, because it only occurred on a few days during the month. The geomagnetic storm effect and the power change of the ionosonde were also ignored in finding the Es disappearance-time. The approximate lunar age of each day was calculated, and the local time at which the Es disappeared was plotted as a function of the lunar age. The variation of the averaged values is shown in Fig. 2. As can be seen in Fig. 2a, the equatorial Es often disappeared earlier than usual in the vicinity of the full and the new moons. This relation is more conspicuous during the December-solstice months than during the June-solstice months. Fig. 2b is the variation during the December-solstice months from 1952 to 1955. The solar time of the disappearance plotted as a function of corresponding lunar hour shows a much clearer relation, as shown in Fig. 3. The total number of disappearances occurring before 1700 solar time was computed for each lunar hour. (The Es usually disappears after 1700 solar time.) This is shown in the upper part of the figure. I conclude from this result that the equatorial Es often disappears around noon or the early afternoon (solar local time) if these times lie between 0000 and 0300 or between 1200 and 1500 lunar time. In other words, the equatorial Es often disappears during the first haft of the periods of the westward lunar electric current flow in the equatorial region. This current is responsible for the lunar daily magnetic variation (CHAPMANand BARTELS, 1940). The lunar tidal variation of foEs at Huancayo has minima at 0000-0300 and 1200-1500 lunar time (MATSUSHITA, 1953), which also agrees with the present result. The equatorial Es m a y be caused by the vertical upward drift force due to the eastward electric current jet, as the author has already suggested. Accordingly, the disappearance of the equatorial Es m a y be explained by the assumption that the vertical upward drift force due to the eastward electric current of the solar magnetic variation is weakened by the
163
Research notes
g') a')
/i
t,
-
,
i
:
I',
.." 4-
it
.i-,'::.
t
I
k'J " I
I [
",
o
.: ~ L:
I::1~
V
,'
"
0 >., 0 0 0 3 "I"
I
0
~
I
0
~
Q. Q.
I
0
I
o
eBo Joun"l
.~_ III U')
c-
/
r"
/',
.....
./ i
,.- ',..~.,', t,,/ • "~,,
........./kl~1 " !-..
E
.'-
.."".-
[:::1
... ';.-- ..~~'1 ~ :.... ~ f ~ \ :"' l ',I'/
6h-
7
/^ /~Lp
'"
V)'
'
o
.~
o
J
o
e S o aoun'l
164
TT
0
¢i
lxl,~
Z
I
42
I
I
o
don25, 1955 (o)
July30, 1954. (b)
Fig. 1. Ionograms from Huaneayo showing sudden disappearance of equatorial Es.
p. 164
Research notes
d o w n w a r d drift force due to the westward electric c u r r e n t of the lunar m a g n e t i c variation• The l u n a r stratification of the F2 a t H u a n c a y o , reported b y GAUTIER, KNECHT, a n d McNIsH (1951), occurs d u r i n g the period of 0600-0900 a n d 1800-2100 l u n a r time. I t is interesting t h a t there is a 6-hours time-lag between the l u n a r effect on the Es a n d the l u n a r stratification of the F2. This suggests t h a t the l u n a r stratification is caused b y the eastward l u n a r c u r r e n t effect, in contrast with the disappearance of the Es, caused b y the westward l u n a r current. nar-solar time of disappearance orE s at Huancayo • solstice, 1952-55) and numbers of occurrence
10-,
12
14
-- . . . . --
°
,~ .
°,
.
:, . . ' . . "
.
..
.
. v . - . . , - . .. . . "'"
16 -
(~ 18
.
•-"~ .••° ,
"°%
• °°.
,
.
.
.
.
". • ".. ": ," ." " . . ." " .. : . : / i , ° °* " " •., o. , o * • .o • ""
.:•...::..,
, . . . . . . .
,," . °., . . ~ • to ° , . :~%.• .~
.
•
. . . . . •...
• ; • : ; .. .
"~ •
20~
--
":•- °
°
~,"
0
,~,•:
" "
I l l l l J J l l l l J l l J , l t l l l i l l l l l l l
20
0
4
8
12
LunoP
16
20
24
houP
Fig. 3. Sudden disappearances of equatorial Es that take place before 1700 solar time occur more frequently between O000 and 0300 or between 1200 and 1500 lunar time. Dots of lower graph indicate solar and lunar times of sudden disappearances orEs; upper histogram indicates total number of such disappearance by lunar hours. Data: December-solstice months, 1952-55.
Acknowledgements--The a u t h o r wishes to express his t h a n k s for support of the present s t u d y by the Geophysical Research Directorate, Air Force Cambridge Research Center, u n d e r contract AF19(604)-969. He wishes also to express his sincere gratitude to Dr. L. V. BERKNER, Dr. W. O. ROBERTS, Mr. A. H. SHAPLEY, Mr. T. N. GAUTIER, Mr. A. G. McNIsH, l)r. E. H. VESTINE, a n d Mr. S. FORBUSH for their kind help a n d advice, a n d to the Central Radio P r o p a g a t i o n Laboratories, N a t i o n a l Bureau of Standards, for use of ionograms involved in this s t u d y a n d for e x t e n d i n g to him the facilities of the Boulder Laboratories. ttigh Altitude Observatory, Boulder, Colorado
S. ~¢[ATSUSHITA~"
REFERENCES CHAPMAN S. and BARTELS J. C~AUTIERT. N., KNECHT R . W . , and McNIs~ A . G . •IATSUSI-[ITA S.
1940 1951
1951 1953 1953 1955 ~MITH E . K . 1955 * On leave from Kyoto University, Japan.
Geomagnetism Oxford Press. Mixed Commission on Ionosphere, Prec. of Second Meeting, page 100. J. Geomag. Geoelect. 3, 44. J. Geomag. Geoelect. 5, 109. Rep. Ionos. Res. Japan. 7, 45. J. Geomag. Geoelect. 7, 91. NBS Report No. 3575.
165