Occurrence Frequency of Aurora Derived from ASCAPLOT. J unji NAKAMURA* 1tU:.tJ:v' : 0):r''-5'v=:0v,-cv:t K"Etf"A

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1 o ] (1361) Occurrence Frequency of Aurora Derived fro ASCAPLOT J unji AKAMURA* 1959 : 1cf 196 : ) Ascaplot r::5rt L r tj:*1ett2: t -C BiffP t-fur::t3vt t :Yt;O) Fsi Fsil J t:1:1:ej}j;jt)jt 2: *cy) t.:.. t :Yt;U:ttv:: ffi:jjv=: J:: < tf:l:ejll. l it.:. 11Z91tJ1c&v=:t1:l vij\ lv*m 1tU:.tJ:v : ):r-5v=:v-cv:t K"Etf"A :t ly:t O);j: 2:Dal«K:t U : Y tirs"!ij!jtij\.rl:: f7tlt-.::. t stt:-cfv=: K:t O)* ""d i?i. t :Yt i:t.{ *it:1jt1jl1jr::ij.::. t 1)\1if7] cy) Gnt.:.. Abstract This paper reports on the occurrence frequency of aurora derived fro ascaplots observed at Syoa Station in 1959 and 196. Aurora as frequently in the south and :after idnight. The correlation beteen K index at Syoa Station (K s ) and auroral :activity as also discussed. 1. Statistical Results: Fig. 1 shos the percentage of onthly occurrence in three s r---. LLJ r-- : \... UJ 5 t \ \ "\ -- \ \; ::: ::: 5 - i \ r---i----r r-.-- F M A M J J A S O F M A M J J A S Fig. 1. Percentage of onthly occurrence in three regions of Z and S. a) in 1959 b) in 196. * * ** $ * XXEi. 1 t7z.&.-cf 2 tlzffit t-fu laillu - 3 tlzffit t-fu WillU - College of General Education and Tokyo Astronoical Observatory the University of Tokyo. Meber of the Japanese Antarctic Research Expeditions and Meber of the Wintering Party the Japanese Antarctic Research Expedition

2 24 Junji AKAMURA regions of Zand S in 1959 and 196. Data in February ere deficient and the tie of observation as liited to around idnight hence the results are unreliable. Aurora appears ore frequently in the south. n 1959 aurora as liable to appear in autun and in spring but in 196 it appeared in inter also. The sall frequency for inter ay be due to the fact that observation in inter as carried out during the long evening tie hen aurora appeared only scarcely (Fig. 4). Fro this point of vie it ay be concluded that aurora shos no distinct seasonal variation. Fig. 2 shos the ratio of occurrence frequency of enith intensity : :. The ratio sees to be alost constant throughout the year. n 1959 slight axia are found in April and in inter and in 196 axia occur in April and August. Fro Figs. 1 and 2 it can be said that the larger the occurrence frequency the stronger the auroral activity. - () <t :c 5. E 5-1::::1 }- <t H ll. o... F M A M J J A S O F M A M J J A S O Fig. 2. Monthly ean ratio of enith activity. Densely hatched area corresponds to activity hatched area to and hite area to. a) 1959 b) 196. Fig. 3 shos the daily variations of occurrence frequency in three regions Z and S. Most of aurora occurred after local idnight (about 21: U. T.) and ere alays ore frequent in the south region than in the north region. n 1959 a axiu occurrence is seen beteen 21 : and : U. T. hile in 196 it is seen at about 3: U.T. Fig. 4 shos the three-hourly ratios of enith activity : :. The values of ratios are alost constant as in the case of seasonal variation. Slight axiu of activity ay fall beteen 21: and : U.T. Auroral activity of 1959 is generally higher than that of Correlation ith K index at Syoa Station: We reduced three-hourly values fro ascaplots and copared the ith agnetic activity K s that is the K-index at Syoa Station in D

3 o ] (1363) Occurrence frequency of aurora 25 - t- - - :c.. t- :c t=f S 5 J::t.. u...o... LL. H t- C i== : U. T. U.T Fig. 3. Percentage of 3-hourly occurrence in three regions of Z and S. a) 1959 b) 196. ][ 12 :: o 5 u s... "" 5 :: r --...: U.T L.T 1959 <..) _... 1r U. T. 196 Fig hourly ean ratio of enith activity : :. a) 1959 b) 196. Fig. 5 shos the correlation beteen auroral activity and Ks. The relation is alost linear and coparing it ith Table 1 in the previous paper it is knon that the absolute intensity of [OJ 5577.A is proportional to the geoagnetic change. Fig. 6 shos the percentage of spatial occurrence in the case of K s :?::5 and K s 4. As ay be expected the larger the K s value the greater the occurrence frequency.

4 26 Junji AKAMURA (1364) (j;fi_ff;pj. - l o...j er ::: e e Ks DEX 7 8 Fig. 5. Correlation beteen enith activity of aurora and K s CK-index at Syoa Station) in J 9 r- 2 () :: a.. t) :: :::: t) t) 5 Fig. 6. Percentage of spatial occurrence in the case of Ks 5 and K s ::;:; 4 in s When the K s value is large aurora sees to appear at loer latitudes hereas aurorae are liited to higher latitudes hen K s is sall. Fig. 7 shos the seasonal variation of percentage of occurrence. The variation is larger in the north region. n inter season even hen K s?::.5 the percentage is reduced ith longer observation tie. L&J ::: : :: " r - K5 :5.Ks< 4 : LJ r r-----"t " "" Fig. 7. o---r--r r-- --r F M A M J J A S Percentage of onthly occurrence in three regions of Z and S in the case of K s 5 and Ks ::;:; 4.

5 o ] (1365) Occurrence frequency of aurora 27 Fig. 8 shos th ean onthly enith activity in the case of K s -:?:5 and K s 4. Activity sees to be proportional to occurrence. -. :;E n \. \ \ \ \ " K}5 K( 4 F M A M J J A S Fig. 8. Monthly ean value of enith activity in the case of K s ;;::: 5 and Ks 4. UJ Z LfJ : ::: L&J Q ; r o r # U. T Fig. 9. Percentage of 3-hourly occurrence in three regions of Z and S in the case of K s ;;::: 5 and K s :5: 4. 2 s

6 28 J unji AKAMURA (1366) [ffitai fl n Fig. 9 daily variation of occurrence percentage 1s shon. n this exaple aurora also appears after idnight and hen K s 5 aurora is inclined to appear in the hole sky but hen K s 4 aurora is apt to be restricted to the south region. Fig. 1 shos the ean enith activities that are high hen K s 5 and lo in the evening hen K s 4. )... Ks 5 < < l.&j ---- Ks U.T. Fig hourly ean value of enith activity in the case of Ks 5 and Ks :::;;; o:scussions: As as reported previously 2) the auroral one near Syoa Station sees to occur in the southern region and in the tie of agnetic stors it ill spread out toard loer latitudes. Generally the higher the occurrence frequency the stronger the auroral intensity. Coparing auroral activity and K-index the absolute intensity of [OJ 5577 A sees to be proportional to the absolute value of geoagnetic disturbance. But its proportional coefficient does not coincide ith OGUTs value 3) our value being considerably loer than his. The relation in hich auroral luinosity is proportional to the square of geoagnetic change hen Kss are sall ill have to be checked also. n Fig. 9 hen K s 5 the percentage of occurrence shos nearly constant value but hen K s 4 the value becoes uch saller in the evening especially in the north. This tendency agrees ith our consideration pertaining to tie correlation beteen the incidented proton and the ain auroral activity 4). Fig. 1 also confirs it. The author expresses his sincere gratitude to Prof. M. HURUHATA of Tokyo Astronoical Observatory for his kind guidance and valuable discussions. References 1) T. Oguti: Antarctic Record o (1961). 2) J. akaur Antarctic Record o (1961). 3) T. Oguti: Rep. onos. Space Res. Japan (196). 41 J. akaur Proc. CCRES in Kyoto (1961). (Received Feb )