Indian Journal of Radio & Space Physics Vo\. 11, December 1982, pp. 229-231 Solar Activity with respect to Ca-Plages P P KURIYAN, V MURALlDHARAN & S SAMPATH Atmospheric Sciences Division, Centre for Earth Science Studies, Trivandrum 695010 Received 15 March 1982 Analysis of Ca-plage areas obtained from Kodaikanal K232 spectroheliograms has been extended to 1977 for two solar cycles 19and 20).The correlation of Ca-plage areas with other solar parameters, viz. relative sunspot numbers, sunspot areas, prominence areas and faculae areas has been obtained. Indices similar to Baur index which is based on faculae areas have been prepared separately with Ca-plage areas and prominence areas; and they have been compared with Baur index. These indices are interrelated and an index based on one parameter may be used in the absence of any other index. 1 Introduction numbers from 1955 to 1977. Data from 1905 to 1954 Butlerl, Babcock and Babcock2, Leighton3 and are available in Kodaikanal bulletin4• Kuriyan4 have shown that the areas of Ca-plages can be used as a measure of solar activity. The Ca-plages 3 Results and Discussion which are chromospheric features are essentially Ca-plage areas have been correlated with relative chromospheric faculae. They are associated with sunspot numbers, sunspot areas, prominence and sunspots and disturbed regions. Since the solar flares faculae areas. The linear regression equation obtained originate from these active centres, the study of Ca• in each case is given below: plage activity has become important. C a-plage area A few observatories, viz. Mount Wilson (USA) y= 150x+ 1042, where x=relative sunspot number Tokyo (Japan) Kodaikanal (India) and World Data ... (1) Center A for Solar-Terrestrial Physics are publishing y = 8.2x + 2310, where x = sunspot area (2) details of Ca-plage activity regularly 5 . y=6.8x-727, where x=area of faculae (3) In this paper we have consolidated Ca-plage areas for a period of 73 years from 1905 to 1977. y=2770x-1715, where x = area of prominence in sq. Correlations of Ca-plage areas with relative sunspot degrees ... (4) numbers, sunspot areas, prominence areas and faculae The correlation coefficients (r) of-Ca-plage areas areas have been worked out. An index in the form of with respect to relative sunspot number, sunspot area, Baur index6 has been prepared with Ca-plage data and faculae area and prominence area are 0.93, 0.90, 0.83 it is seen that there is good agreement between the two and 0.61, respectively. indices. A similar index prepared with prominence The above analysis supports the fact that sunspots, data also shows high correlation with Baur index. prominences, photospheric faculae and Ca-plages are interrelated. The prominences are seen at the limb of 2 Data Analysis the solar disc, whereas facu1ae are seen near the limb, The relative sunspot numbers and sunspot areas and the Ca-plages are seen across the disc. The close have been extracted from Greenwich Observatory association between spots and faculae has been publication 7 and Zurich publication8•9. The areas of summarized lion the basis of intensive observations Ca-plage coverage of solar hemisphere obtained by over a number of years. The transition from projecting K232 spectroheliograms on appropriate photospheric to chromospheric faculae (Ca-plages) is a Stonyhurst disc have been taken from Kodaikanal continuous oneil. However, the important difference bulletin4 and Ca-plage areas from 1955 to 1977 and that Ca-plages are visible, both at the limb and at the areas of prominences have been obtained from the centre of the disc, makes Ca-plages longer-lived than Indian Institute of Astrophysics, Bangalore10. the photospheric faculae and easier to observe. Since Fig. 1 gives solar activity for the entire period of 73 their relationship is in good agree~ent, any index yr from 1905 to 1977 with respect to relative sunspot obtained on the basis of area of faculae will also agree numbers, prominences and Ca-plages. Table 1 gives well with the index evolved on the basis of area of Ca• the daily mean areas of Ca-plages and relative sunspot plages. 229 INDIAN J RADIO & SPACE PHYS, VOL. 11, DECEMBER 1982 The sunspot numbers which indicate only the sunspots, respectively. An index with areas of areas of cooler regions on the sun, when taken alone, prominences has also been prepared in the similar cannot give a very good index of variation of solar manner. It is seen that they are in good agreement with output. Baur6,12 formulated the index which measures Baur index. The correlation coefficients obtained with the total area of faculae (bright sun) minus the total Baur index in the case of two parameters, namely Ca• area of spots (dimmed sun). Mironovitch13 used this plage and prominences are 0.69 and 0.86, respectively. index for the study of zonal westerly type of earth's wind circulation and various other indices of Table I-Relative Sunspot Number and Mean Daily Area atmospheric circulation vigour and found that there of Ca-Plages was high degree of correlation. Recent study made by Cycle Year Relative Ca-plage area Chowdhury et al.14 indicates that the Baur solar index number sunspot number (in millionths) bears significant correlation with north-west Indian 19 1955 38.0 7224 rainfall and peninsular rainfall particularly in the 1956 141.7 25250 middle of waxing phase of a solar cycle. 1957 190.2 25487 An index similar to Baur index has been prepared 1958 184.8 27037 1959 159.0 25138 based on Ca-plage areas. The continuous transition of 1960 112.3 19024 photospheric faculae to the chromospheric faculae 1961 53.9 7141 shows that, as suggested by Baur6, the hot area 1962 37.5 5376 covered by Ca-plages minus the cool area of the spots 1963 27.9 3/81 willgive the net output from the sun with respect to the 20 1964 12.3 1851 Ca-pJage phenomena. The advantage in computing the 1965 16.3 3169 index based on Ca-plage areas is that they are seen for 1966 49.7 8960 a longer duration across the solar disc, unlike 1967 89.7 19712 1968 photospheric faculae which are seen only in the limb 106.6 22235 1969 106.4 22733 and are short-lived. The index obtained by Ca-plages 1970 100.4 19327 according to the principle applied as in Baur index is as 1971 69.7 10296 follows. 1972 66.8 10098 1973 39.0 8963 1974 32.2 7800 1975 17.4 3497 S.1. (based on Ca-plage area) = 1001~-~ 1976 13.4 4140 21 1977 27.5 5932 where K and D are areas ofCa-plages and spots, and K and jj are long-term means of areas of Ca-plages and 200 32lXDi .~ I 90'150 •..~ ~ C> SUN SPOTS 11007° ~F.lJ°5l <0( Z~ IE~ 75 013°nO,0 ~ ~ Co -PlAGE o----.G 175S°3° 1!.0 15025 PROMINENCE '2~ ~ e u; o~ 20000 ji 18000 -'5000 ~ ~ 14000 /", 1(/\ ", " \ \\ / \. \_- / \.~ 6000 -\ "_ 4000 2000 o 70 75 1905 10 15 40 45 50 55 YEAR Fig. 1~ Plots showing the solar activity in respect of sunspot numbers, prominences and Ca-plages for the years 1905-77 230 I"'~' ',I 1I11" I I' KURIYAN et al.:SOLAR ACTIVITY WITH RESPECT TO Ca-PLAGES 200 30 ft 4' 10 15 10 YEAR Fig.2-Plots showing the Baur index and Ca-plage index for the years 1905-65 100 Ca-Pl •••GE INDt'X -• agreement in respect of all the other six cycles eo I'ACUlAE INDEX •.••••••.•• ~N£NCEIHDEX----- regarding the three indices. 4 Conclusion The analysis made in this paper indicates that the solar indices are interrelated and the index based on one parameter may be applied with advantage in the absence of any other index. Ack.nowledgement The authors are grateful to the Director, Centre for Earth Sciences Studies, Trivandrum, for the constant -10 encouragement throughout this work. The authors are also thankful to late Dr M K Vainu Bappu, Director, and Dr K R Sivaraman of the Indian Institute of -140: 14 l' 1S 17 ,. 19 20 Astrophysics, Bangalore, for kindly giving data CYCLE needed for this work. Fig. 3-Plots showing the solar indices for solar cycles 14 to 20 References The solar index based on prominence data shows a I Butler C p, Mon-Not R Astron Soc (GR), 84 (1924) 134. closer relationship with Baur index, as faculae and 2 Babcock H D & Babcock H W, Astrophys J(USA), 121 (19S5) prominences are seen in the limb, whereas Ca-plages 349. are seen across the disc. 3 Leighton R B, Astrophys J (USA), 140 (1964) 1547. Fig. 2 shows the plot of the solar index prepared with 4 Kuriyan P p, Kodaikanal Obs Bull Ser A (India), 172 (1967) 10. Ca-plage areas and sunspot areas along with Baur 5 World Data Center Afor Solar-Terrestrial Physics, Rep UAG, 81 (1981) 4. index of yearly values for the period 1905-65. Fig. 3 6 Baur F, Beziehungen des Grossowel/ers zu kosmischen Vorgangen gives the values obtained for each cycle from 14 to 20 in Hannsuring Lehrbuch der Meteorologie, 1949,970. with respect to the three solar phenomena and shows 7 Royal Greenwich Observatory, Sunspot and geomagnetic storm good agreement except for cycle 16. The indices with data for years 1874-1954, 1955. 8 Waldmeier M, Sunsporactivity datafor years 1610-1960(Zurich), area of faculae and prominences show positive values 1961. whereas Ca-plage index gives negative value in this 9 Waldmeier .M, Solar activity data for years 1964-76 (Zurich), particular cycle.