Coronal Index Of Solar Activity Research Articles

Spatial and Temporal Distribution of Solar Green-Line Corona for Solar Cycles 18 – 24

The homogeneous coronal data set (HCDS) of the green corona (Fe xiv) and the coronal index of solar activity (CI) have been used to study the time–latitudinal distribution in Solar Cycles 18 – 24 and compared with similar distribution of sunspots, the magnetic fields, and the solar 10.7 cm radio flux. The most important results are: i) the distribution of coronal intensities related to the cycle maximum are different for individual cycles, ii) the poleward migration of the HCDS from mid-latitudes in each cycle exists, even in the extremely weak Cycle 24, and the same is valid for the equatorward migration, iii) the overall values of HCDS are slightly stronger for the northern hemisphere than for the southern one, iv) the distribution of the HDCS is in coincidence with the strongest photospheric magnetic fields (B>50 Gauss) and histograms of the sunspot groups, v) the Gnevyshev gap was confirmed with at least 95% confidence in the CI, however with different behavior for odd and even cycles. Principal component analysis (PCA) showed that the first and second components account for 87.7% and 7.3% of the total variation of the CI. Furthermore, the second PCA component of the green corona was quite different for Cycle 21, compared with other cycles.

Predictive ARIMA Model for coronal index solar cyclic data

Many solar activities, e.g. sunspots, Mg II indices, coronal index of solar activity, etc., are produced by solar magnetic fields that affect both, the solar atmosphere and heliosphere, including the terrestrial environment. The atmosphere of the sun is recognized by photosphere, as a visible solar disk and layers above it: chromosphere, transition zone and corona. The nature of solar activity can be, in the emission solar corona, recognized by the coronal index of solar activity (CI). Its dataset in the period 1944–2009 will be used to test the ARIMA model. Based on the minimum AIC and BIC values, ARIMA(1,0,1) model is selected for each CI cycle and total dataset. The quality of the selected model is endorsed by (RMSE, MAPE, & FPE). The behaviour of the observed (original) CI cycle with predictive CI cycle shows a strong correlation, of more than 0.8 between actual and predictive CI cycles, which is a predictive power of ARIMA(1,0,1) model. Further model persistency estimated by Hurst exponent (smoothness) with the help of fractal dimension (complexity). All predictive CI cycles show persistence and positively correlated, the total dataset equation is given as X(t) – 0.977(t-1) = Z(t) - 0.546(t-1). • The purpose of the paper to understand the search of model for coronal index solar data. • By using of model predict the CI cycles. • Check the appropriateness of predicted cycle with original cycle by selected model. • After all persistency of the original and predictive data obtained by Hurst & fractal dimension.

Search for periodicities in galactic cosmic rays, sunspots and coronal index before arrival of relativistic protons from the sun

Using different approaches and techniques of wavelet analysis we analyze variations (oscillations) of galactic cosmic rays, solar spot number, and coronal index of solar activity before ground level enhancements of solar cosmic rays. Obtained results are discussed in frames of recent ideas about periodicity phenomena in the photosphere, and corona of the Sun, interplanetary medium, and cosmic rays.

Total Solar Irradiance and the Fe XIV Corona

Analyzing daily values of the total solar irradiance (TSI), the coronal index of solar activity (CI), and the Mg II 280-nm core-to-wing ratio (Mg II index), we have found that the temporal variations of these indices are very similar to each other during the period from 1978 to 2005. The correlation between CI and TSI, with the PSI correction lying within the interval under study, has been found to be 0.699, which is very close to the value of 0.703 of the correlation between Mg II and TSI for 27-day averages (the CI – Mg correlation is 0.824). The regression equation between CI and TSI is almost linear, except for TSI depletions when a large number of sunspots are present on the visible disk. By employing CI, an extrapolation of TSI back to 1947 is presented.

Reexamination of the coronal index of solar activity

The coronal index (CI) of solar activity is the irradiance of the Sun as a star in the coronal green line (Fe XIV, 530.3 nm or 5303 Å). It is derived from ground‐based observations of the green corona made by the network of coronal stations (currently Kislovodsk, Lomnický Štít, Norikura, and Sacramento Peak). The CI was introduced by Rybanský (1975) to facilitate comparison of ground‐based green line measurements with satellite‐based extreme ultraviolet and soft X‐ray observations. The CI since 1965 is based on the Lomnický Štít photometric scale; the CI was extended to earlier years by Rybanský et al. (1994) based on cross‐calibrations of Lomnický Štít data with measurements made at Pic du Midi and Arosa. The resultant 1939–1992 CI had the interesting property that its value at the peak of the 11‐year cycle increased more or less monotonically from cycle 18 through cycle 22 even though the peak sunspot number of cycle 20 exhibited a significant local minimum between that of cycles 19 and 21. Rušin and Rybanský (2002) recently showed that the green line intensity and photospheric magnetic field strength were highly correlated from 1976 to 1999. Since the photospheric magnetic field strength is highly correlated with sunspot number, the lack of close correspondence between the sunspot number and the CI from 1939 to 2002 is puzzling. Here we show that the CI and sunspot number are highly correlated only after 1965, calling the previously‐computed coronal index for earlier years (1939–1965) into question. We can use the correlation between the CI and sunspot number (also the 2800 MHz radio flux and the cosmic ray intensity) to recompute daily values of the CI for years before 1966. In fact, this method can be used to obtain CI values as far back as we have reliable sunspot observations (∼1850). The net result of this exercise is a CI that closely tracks the sunspot number at all times. We can use the sunspot‐CI relationship (for 1966–2002) to identify which coronal stations can be used as a basis for the homogeneous coronal data set (HDS) before 1966. Thus we adopt the photometric scale of the following observatories for the indicated times: Norikura (1951–1954; the Norikura photometric scale was also used from 1939 to 1954); Pic du Midi (1955–1959); Kislovodsk (1960–1965). Finally, we revised the post‐1965 HDS and made several small corrections and now include data from Kislovodsk, Norikura, and Sacramento Peak to fill gaps at Lomnický Štít.

Coronal index as a solar activity index applied to space weather

All possible changes of the solar activity can be expressed by the coronal index of solar activity that represents the averaged daily power of the green corona emitted from the Sun’s visible hemisphere. The representative character of this index allows us to study long-term, intermediate and short-term variations of the Sun as a star. This index can be expressed well as a function of other solar indices. As green line reflects the distribution of the photospheric magnetic fields in the solar corona, the dependence of this index on the solar magnetic field is confirmed by means of statistical analysis of these two parameters. Daily values of the coronal index, as well as of the magnetic field data obtained from the Wilcox Solar Observatory, has been analysed by Fast Fourier analysis and Wavelet Transform analysis for the time period 1966–1998 covering more than three solar cycles. Periodicities of 11.4, 3.2, 2.3, 1.7, 1, 0.29, 0.07 and 0.04 years have been found in both parameters that means once again that the coronal index is probably related to the underlying photospheric magnetic fields and can be used as a global index of solar activity useful for Space Weather studies.

The 530.3 nm corona irradiance from 1939 to 2001

We introduce the coronal index of solar activity (CI) for the period 1939–2001. The CI represents the total irradiance for the Sun as a star in the 530.3 nm coronal emission line as observed with ground-based coronagraphs over the world. There have been found long-term variations in the values of CI (monotonously increasing from 1947 to 1996), cycle variations (11 years), intermediate variability (from 3 months to 5 years), and rotational rate of 27.3 days (with some subsidiary peaks ranging from 25 to 30 days). Comparison between the CI and total magnetic flux showed a good relationship in 1976–1999. This relation was used to derive the magnetic flux before 1976 back to 1939 when the green corona (530.3 nm, the Fe XIV) began to be observed. Similar comparisons have been made between the CI and total solar irradiance, enabling us to extrapolate the values of total solar irradiance from 1986 back to 1939. It follows that density, temperature, magnetic flux and total solar irradiance increased in the observational period from 1946 to 1996 of cycle maxima. The last solar cycle 23 exhibited a drop-off in irradiance about a third in comparison with the solar cycle 22.

An empirical model of the daily evolution of the coronal index

Global changes of the solar activity can be expressed by the coronal index that is based upon the total irradiance of the coronal 530.3 nm green line from observations at five stations. Daily mean values of the coronal index of solar activity and other well-correlated solar indices are analyzed for the period 1966–1998 covering over three solar cycles. The significant correlation of this index with the sunspot number and the solar flare index have led to an analytical expression which can reproduce the coronal index of solar activity as a function of these parameters. This expression explains well the existence of the two maxima during the solar cycles taking into account the evolution of the magnetic field that can be expressed by some sinusoidal terms during solar maxima and minima. The accuracy between observed and calculated values of the coronal index on a daily basis reaches the value of 71%. It is concluded that the representative character of the coronal index is preserved even when using daily data and can therefore allow us to study long-term, intermediate and short-term variations for the Sun as a star, in association with different periodical solar–terrestrial phenomena useful for space weather studies.

Evolution of the Green Corona in 1996–2002

We analysed the green-line coronal intensities (530.3 nm, Fexiv), both their time- latitudinal distribution as well as the coronal index of solar activity (CI) over the period 1996–2002. Maximum values of the CI (smoothed) were observed in mid-August 2001, even though the `first' peak was observed in the period January–April 2000. The maximum of the Wolf number occurred in 2000, April – July, and the `second peak' occurred in December 2001–March 2002. Both indices have a similar course in the cycle, but their maxima are shifted by 1.5 year. There was high correlation between CI and Wolf number, the 2800 MHz radio flux, the X-ray 0.1–0.8 nm flux and cosmic-ray flux. The CI values in present cycle 23 are lower than those of the two former solar cycles 21 and 22 by about 1/3. Polar branches, which separated from the principal equatorward branch at mid-latitudes in the cycle minimum, 1996, reached the poles around 2000. The new principal branch for cycle 24 split in 2001, turned over around ±60° in 2002.5 and moves to the equator, where it will end in 2019. Minimum between cycles 23 and 24 will occur around 2007.5, cycle maximum 24 around 2012.5. Poleward branches in cycle 24 will reach the solar poles in 2011.

Long-term modulation of the coronal index of solar activity

Monthly mean values of the coronal index of solar activity and other solar indices are analyzed for the period 1965–1997 covering three solar cycles. The coronal index is based upon the total irradiance of the coronal 530.3 nm green line from observations at five stations. The significant correlation of this index with the sunspot number and the number of the grouped solar flares have led to an analytical expression which can reproduce the coronal index of solar activity as a function of these parameters. This expression well explains the existence of the two maxima during the solar cycles taking into account the evolution of the magnetic field that can be expressed by a sinusoidal term with a 6-year period. The agreement between observed and calculated values of the coronal index on a monthly basis is high enough and reaches the value of 92%. It is concluded that the coronal index can be used as a representative index of solar activity in order to be correlated with different periodic solar–terrestrial phenomena useful for space weather studies.

Coronal index of solar activity - Solar-terrestrial research

The purpose of this paper is to introduce a coronal index of solar activity (CI) as computed from ground-based observations of the green coronal line intensities (Fe xiv; 530.3 nm). This index, expressed in W s−1, is derived for the period 1939–1998 and belongs to the class of ground-based indices used to study solar activity and its influence on the heliosphere. The smoothed peak solar cycle intensity of the CI increased monotonically during the period of research. On the other hand, comparative studies have shown relatively good agreement with similar solar indices. CI can be used to study, among other things, the rotation of the Sun as a star, and long-term, intermediate- and short-term periodicities. The CI is inferred from a homogeneous coronal data set that can be used to study such topics as the 2D distribution of the green corona and photospheric/chromospheric activity, the differential rotation of the emission green corona, and the relationship between the green corona and cosmic rays.

Determination of the solar minimum period between cycles 22 and 23 from the coronal index of solar activity

We present the coronal index of solar activity (CI) for 1997 and use the 1996 and 1997 data to examine the properties of the solar minimum between cycles 22 and 23. To compute CI, we used only the intensities of the green corona from Lomnický Stit and Sacramento Peak coronal stations. Values of CI were low in the first half of 1997 with an increase from September toward the end of 1997. We determined the minimum in the green corona to be May 1996, which is in coincidence with the results from 2800 MHz radio flux, the Mg II index and the Wolf number.

Coronal index of solar activity VIII, years 1992–1994

The coronal index of solar activity over the period 1992–1994 is given. The data are a good tool to study solar activity, for the Sun as a star, in the solar corona over a solar cycle and its influence in the heliosphere.

Coronal index of solar activity VII, years 1988–1991

A brief description is given of the coronal index of solar activity (CI) derived from ground-based observations of the green coronal line 530.3 nm (FeXIV) and its computation. The final data of CI are presented in graphical form over the period 1988–1991. The maximum of CI coincided with the Wolf number in cycle 22, and no second maximum, sometimes seen two years after the first one, was observed in this cycle.