We examine four long-term databases of monthly means of the whole disc green coronal brightness which cover the period of the last five and a half solar cycles to verify them, and compare their usefulness, as indices characterize the solar activity. We use the data from (1) the Norikura Observatory, (2) the Kislovodsk Observatory, (3) intensities detected by several coronographs and converted to the common photometric scale of Pic du Midi, (4) coronal indices obtained from detections of several observatories and converted to the photometric scale of Lomnicky Stit. We compare them by means of correlative analysis with the time series of sunspot numbers. The data (2) demonstrate the best agreement with sunspot number as the reference (r = 0.88)

Ajabshirizadeh, A.

Baranska, A.

Kobylinski, Z.

Kinematika i fizika nebesnyh tel (Online)

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ON THE LONG-TERM VARIABILITY OF THE GREEN CORONAACCORDINGLY TO FOUR EXISTING DATABASESZ. Kobylinski1, A. Baranska2, A. Ajabshirizadeh31Dept. of Renewable Energies, University of Podlasie, Siedlce, Polande-mail: zbigniewkobylinski@yahoo.com2Faculty of Mining Surveying and Environmental EngineeringUniversity of Mining and Metallurgy, Krakow, Polande-mail: abaran@agh.edu.pl3Dept. of Theoretical Physics and Astrophysics, Tabriz University, Irane-mail: ali-ajabshir@yahoo.comWe examine four long-term databases of monthly means of the whole disc green coronal bright-ness which cover the period of the last ﬁve and a half solar cycles to verify them, and comparetheir usefulness, as indices characterize the solar activity. We use the data from (1) the NorikuraObservatory, (2) the Kislovodsk Observatory, (3) intensities detected by several coronographs andconverted to the common photometric scale of Pic du Midi, (4) coronal indices obtained from detec-tions of several observatories and converted to the photometric scale of Lomnicky Stit. We comparethem by means of correlative analysis with the time series of sunspot numbers. The data (2)demonstrate the best agreement with sunspot number as the reference (r = 0.88).INTRODUCTIONThe solar corona is the source of solar wind. Therefore, it is responsible for various processes and disturbances inthe interplanetary space, geomagnetic ﬁeld, and Earth’s atmosphere. The green coronal line (Fe XIV, 530.3 nmline) (GCL) observed during the last ﬁve and a half solar cycles would be a good indicator of coronal and solaractivity. However, there are considerable discrepancies between the observational long-term databases of thiscoronal line detected at diﬀerent observatories. Unfortunately, there are only a few coronal stations that provideresults of systematic patrol registrations of the green and red coronal brightness. The systematic observationsof the green and red coronal lines have been performed since 1947 (sporadically since 1939) at a number ofcoronal stations. During the 1960s and 1970s several registrations have been closed. At present, only fourcoronal stations observe the green corona regularly: Norikura (NO), Kislovodsk (KI), Lomnicky Stit (LS), andSacramento Peak (SP), as it is seen from Table 1 where the stations and their abbreviations used in this paperare enumerated. Two last stations do not observe corona regularly. Data of these observatories were publishedin 1947–1976 in the Quarterly Bulletin on Solar Activity printed at Zurich (QBSA) edited by M. Waldmeier,later transferred to Japan [3]. The Sacramento Peak Observatory after the break from 1966 to 1973 begunregistration again, and the data were published in graphical form in QBSA, Solar Geophysical Data, and theycan be obtained on-line on the Web site of this Observatory [5].The time series of GCL contain the daily intensities of GCL measured around the Sun in steps of 5◦ ofthe position latitudinal angle, beginning at the north solar pole (0 degrees) and proceeding through east,270 degrees and west, following the program introduced by d’Azambuja [1]. Thus, one set of these data consistsof 72 values. After the observation the collected data are averaged for each day at the central meridian.Subsequently, these data are averaged monthly or by Bartels rotations.The time coverage of GCL brightness at single observatory is poor, mainly owing to weather conditions(on the average only 50 to 100 days per year, sometimes more). The number of missing whole months insets of observations could be treated as index of quality of the station’s work. The list is shown in Table 2.The equipment in diﬀerent coronal observatories and method of measurements of coronal intensities have notbeen identical. Photographic and photoelectric methods used were diﬀerent in details. As pointed out byStorini and Sykora [15], heights above solar limb where coronal intensities were recorded, have diﬀered from 40to 60 seconds of arc (40′ corresponds to 0.04 solar radii). At SP since 1973 the height is about 140 seconds ofarc (0.15 solar radii) and the GCL intensities are scanned at every 3 degrees of latitude. Rybansky et al. [13]remarked: both the method of observations and photometry have never been the same at all stations. We canc© Z. Kobylinski, A. Baranska, A. Ajabshirizadeh, 2004129Table 1. The list of coronal observatoriesObservatory Abbrev. Country Altitude Geog. Geog. Aperture Const- Operatingm Long. Lat. cm ruction periodPic du Midi PM France 2860 0◦ 09′ E 42◦56′ N 20, 15 1930 1947–1974Arosa AR Switzerland 2050 9◦ 40′ E 46◦47′ N 20, 12 1938 1947–1975Wendelstein WE Germany 1837 12◦ 01′ E 47◦42′ N 20 1941 1947–1979Kanzelhohe KH Austria 1526 13◦ 54′ E 46◦40′ N 11 1943 1948–1964Climax CL USA 3394 106◦ 12′ W 39◦23′ N 40, 13 1940 1947–1957Norikura NO Japan 2876 137◦ 33′ E 36◦07′ N 25, 10×2 1949 1951–presentSacramento Peak SP USA 2840 105◦ 49′ W 32◦47′ N 40, 20 1951 1953–1966Kislovodsk KI Russia 2050 42◦ 31′ E 43◦44′ N 53, 20 1957 1957–presentAlma Ata AT Kazakhstan 3001 76◦ 57′ E 43◦11′ N 53, 20 1958 1957–19621973–1991Lomnicky Stit LS Slovakia 2632 20◦ 13′ E 49◦12′ N 20, ×2 1964 1966–presentUlan Bator UB Mongolia 1600 107◦ 03′ E 47◦50′ N 20 1970 1971–1973Mauna Loa ML USA 3400 155◦ 36′ W 19◦28′ N 24 1965 1966–presentHaleakala HA USA 3050 156◦ 26′ W 20◦71′ N 25, 10 1967 1967–presentTable 2. Percentage of missing whole observational months at observatories during operating periodObservatory Abbrev. Percent Observatory Abbrev. PercentPic du Midi PM 3 Norikura NO 3.3Arosa AR 34.8 Sacramento Peak SP 0.6Wendelstein WE 8.9 Kislovodsk KI 0.7Kanzelhohe KH 8.5 Alma Ata AT 21.2Climax CL 0 Lomnicky Stit LS 4.5Ulan Bator UB 25add that during years, methods were changed at the same stations as well. At Pik du Midi (PM) it happenedtwo times between 1943–1975 [8], at LS a new method of measurements was introduced in 1971 [17]. At NOthe photometry acquirement was changed two times, in 1981 and in 1997 [14]. Another question is referredto the staﬀ of the station. Accordingly to [9], the most stable staﬀ who had been working with registrationof GCL had appeared to be at the KI Observatory. At the NO Station during 48 years more than 40 personshad contributed to the observations, since foundation of the Station. They had been using the direct-visionspectroscope [14].Diﬀerences and discrepancies between registrations of GCL at diﬀerent stations were raised for more detaileddiscussion at Venus 2000 Tranzit Conference at Tabriz [6].THE SEARCH FOR THE MOST HOMOGENEOUS DATA OF GCL INTENSITIESThere are some methods to complete data in order to construct a long-term set of GCL intensities. The data fromselected station should be re-scaled and completed by the results of registration of other stations. They are basedon the assumption that the time series from diﬀerent observatories are linearly dependent. There is no place herefor the detailed description and discussion, therefore we refer the reader to the bibliography [2, 11, 16, 19, 20].As a result of such sewing up, the diﬀerent data and compilations four data sets were obtained (here we do notconsider the complete data set from Sacramento Peak). There is no completely independent long-time series ofdata between them. They were artiﬁcially, a posteriori improved by their own authors. Here we consider:(1) NO re-scaled data obtained from preliminary registration by using (3) series as a reference [14]. Duringthe periods 1950–1954 and 1963.5–1997 whole time series was simply multiplied by a factor of 2, betweenthem more complicated formula for re-scaling factor was used.(2) KI data in which intensities from other stations had been taken to ﬁll gaps [9].(3) intensities detected with several coronographs and converted to the common photometric scale of PMby [7, 18, 19], signed here as IN.(4) intensities from several observatories converted to the photometric scale of LS and published as coronalindex CI ([12] and references therein).130In (3), database measurements at the PM Observatory have been used to cover the period 1943–1973,when the registration was closed, later intensities from the KI Observatory and other stations were chosen andconverted to the photometrical scale of PM. In (4), data from several coronal stations has been taken andconverted to LS scale, but this Station was opened only in 1966. So, the results of procedure used in (3) after1974 and in (4) before 1966 would give not the best quality of the data. The amplitudes of the cycles maximaof (4) show a steady increase since 1940. This is unlike the behaviour of other solar indices. Therefore, thisgroup [10] decided to rescale their set before 1965, using a linear correlation formula with sunspot number.In the present paper we use an earlier set of CI. In (1), (2), and (3) GCL intensities are expressed in absolutecoronal units, i.e., millionths of energy radiated from the centre of the Sun’s disc in 0.1 nm strip of the spectrumnear the corona emission line. Data (4) are in the form of CI, which was derived from coronal intensities andexpressed in the units of 1016 W/sr. Every set of data used here is the monthly means.DATA ANALYSIS AND CONCLUSIONAn important question arises as to which set could be recommended for further use for investigators whostudy the eﬀects caused by coronal activity in the time scale of years. Assuming that the coronal and solaractivity in such time scale is caused by the same reason, we use Zurich sunspot number (SN) from [4] asa reference data and compare them to time series of the monthly means of the full disc coronal brightness detectedat Norikura (rescaled data) [3]: Jan. 1951 – Jan. 1997, Kislovodsk [9]: Jan. 1951 – Jan. 1997, IN [7, 18, 19]:Jan. 1943 – Nov. 1993, CI [12]: Jan. 1943 –Dec. 1998. These data sets are presented in Figs. 1 and 2. In Fig. 3the time variations of smoothed by 13-month moving average coronal intensities in a.c.u. and coronal index in1016 W/sr are shown during the whole studies period. In these pictures the amplitudes of 11-years variation ofthe brightness of the green corona (I/I, where I is the intensity) not proportional to the amplitude of sunspotnumber from cycle to cycle could be seen. Therefore, a rescaling of data set by means of the sunspot number setseems to give inaccurate result. The linear rising trend of CI is visible. The reason of it is unknown. Generally,the times of minimum are the same for every time series, with the exception during minimum between the 19thand 20th cycles when they diﬀer. At this period the IN data are overestimated and demonstrate one year totwo years delay relatively to other indices. During the 22nd cycle data of NO are underestimated. There arediscrepancies between coronal data during maximum phases of the 21st and 22nd cycles, 21st cycle maximum:CI delayed more than two years relatively to KI and IN data, maximum phase of the 22nd cycle: the eﬀect isopposite.Figure 1. Monthly means of coronal data sets NO and KI versus 11 months moving average of sunspot number. The rightscale is graduated, thereby the SN data would ﬁt well the coronal sets in the 20th solar cycle131Figure 2. Monthly means of coronal data sets IN and CI versus 11 months moving average of sunspot number. The rightscale is graduated, thereby the SN data would ﬁt well the coronal sets in the 20th solar cycleFigure 3. 13 months moving averages of coronal data sets NO, KI, IN, CIa) Norikura b) Kislovodsk c) IN by Sykora et al. [19] d) coronal indexFigure 4. Scatter plots of the monthly mean sunspot numbers and the monthly mean green corona intensities in a.c.u.(NO, KI, IN), and the coronal index CI in the units of 1016 W/sr for whole time periods under investigation. Parametersof linear least-squares ﬁt (constant and slope) of performed regression analysis are also shown for every case132Table 3. Pearson correlation coeﬃcients (r) between monthly means of sunspot numbers and coronal data setsData set NO KI IN CISN 0.742± 0.021 0.881± 0.009 0.804± 0.015 0.763± 0.014The variability of the data can be compared by correlative and regression analysis. The Pearson correlationcoeﬃcients between monthly coronal data sets and sunspot numbers are presented in Table 3. All coeﬃcientshave the signiﬁcance level p < 0.01. As it is seen from the Table 3 and from the scatter plots in Fig. 4, the bestcorrelation for the full periods of data availability was obtained for the KI data sets. Other data give worseresults. NO data are characterized by larger variability than other. The KI changes are in the best agreementwith sunspot number SN (coeﬃcient equals 0.88). In conclusion we should say that a comparison with othersolar indices is needed and will be considered in the further paper.Acknowledgements. We acknowledge the Main Astronomical Observatory, Kyiv, Ukraine, for the ﬁnancialsupport in participation in the MAO-2004 Conference and we thank Dr. V. Rusin and Dr. T. Sakurai for sendingthe GCL data sets.[1] d’Azambuja L. // Quarterly Bull. on Solar Activity.–1947.–77.[2] Gnevyshev M. N. // Astron. Zh.–1963.–40.–P. 401.[3] [http://solar.nro.nao.ac.jp].[4] [http://www.ngdc.noaa.gov].[5] [http://www.nso.edu].[6] Kobylinski Z., Ajabshirizadeh A. The long term green coronal line data: a critical review // Proc. of VENUS 2004TRANSIT Conf., Tabriz University, Iran.–2004.[7] Kulcar L., Sykora J., Letfus V. Monthly data on the green corona brightness in the period 1947–1976 // Contr.Astron. Obs. Skalnate Pleso.–1991.–11.–P. 65–98.[8] Leroy J. L., Trellis M. Trois cycles d’activite dans la basse courone // Astron. and Astrophys.–1974.–35.–P. 283.[9] Makarov V. I., Tlatov A. G., Callebaud D. K. 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On the long-term variability of the green corona accordingly to four existing databases

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On the long-term variability of the green corona accordingly to four existing databases

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