Greenwich Photoheliographic Results Research Articles

Prediction of the amplitude of solar cycle 25 from the ratio of sunspot number to sunspot-group area, low latitude activity, and 130-year solar cycle

Prediction of the amplitude of solar cycle is important for understanding the mechanism of solar cycle and solar activity influence on space-weather. We analysed the combined data of sunspot groups from Greenwich Photoheliographic Results (GPR) during the period 1874–1976 and Debrecen Photoheliographic Data (DPD) during 1977–2017 and determined the monthly mean, annual mean, and 13-month smoothed monthly mean whole sphere sunspot-group area (WSGA). We also analysed the monthly mean, annual mean, and 13-month smoothed monthly mean version 2 of international sunspot number (SNT) during the period 1874–2017. We fitted the annual mean WSGA and SNT data during each of Solar Cycles 12–24 separately to the linear and nonlinear (parabola) forms. In the cases of Solar Cycles 14, 17, and 24 the nonlinear fits are found better than the linear fits. We find that there exists a secular decreasing trend in the slope of the WSGA–SNT linear relation during Solar Cycles 12–24. A secular decreasing trend is also seen in the coefficient of the first order term of the nonlinear relation. The existence of ≈77-year variation is clearly seen in the ratio of the amplitude to WSGA at the maximum epoch of solar cycle. From the pattern of this long-term variation of the ratio we inferred that Solar Cycle 25 will be larger than both Solar Cycles 24 and 26. Using an our earlier method (now slightly revised), i.e. using high correlations of the amplitude of a solar cycle with the sums of the areas of sunspot groups in 0–10° latitude intervals of the northern hemisphere during 3.75-year interval around the minimum–and the southern hemisphere during 0.4-year interval near the maximum–of the corresponding preceding solar cycle, we predicted 127±26 and 141±19 for the amplitude of Solar Cycle 25, respectively. Based on ≈130-year periodicity found in the cycle-to-cycle variation of the amplitudes of Solar Cycles 12–24 we find the shape of Solar Cycle 25 would be similar to that of Solar Cycle 13 and predicted for Solar Cycle 25 the amplitude 135±8, maximum epoch 2024.21 (March 2024)±6-month, and the following minimum epoch 2032.21 (March 2032)±6-month with SNT≈4.

Long-Term Variations in Solar Activity: Predictions for Amplitude and North–South Asymmetry of Solar Cycle 25

We analysed the sunspot group data from Greenwich Photoheliographic Results (GPR) during 1874-1976 and Debrecen Photoheliographic Data (DPD) during 1977-2017 and studied the cycle-to-cycle variations in the values of 13-month smoothed monthly mean sunspot-group area in whole sphere (WSGA), northern hemisphere (NSGA), and southern hemisphere (SSGA) at the epochs of maxima of Sunspot Cycles 12-24, and at the epochs of maxima of WSGA, NSGA, and SSGA Cycles 12-24. The cosine fits to the values of WSGA, NSGA, and SSGA at the maxima of the sunspot number, WSGA, NSGA, and SSGA Cycles 12-24, and to the values of the corresponding north-south asymmetry, suggest the existence of a ~132-year periodicity in the activity of northern hemisphere, a 54-66-year periodicity in the activity of southern hemisphere, and a 50-66 year periodicity in the north-south asymmetry in activity at all the aforementioned epochs. By extrapolating the best-fit cosine curves we predicted the amplitudes and the corresponding north-south asymmetry of the 25th WSGA, NSGA, and SSGA cycles. We find that on average Solar Cycle 25 in sunspot-group area would be to some extent smaller than Solar Cycle 24 in sunspot-group area. However, by inputting the predicted amplitudes of the 25th WSGA, NSGA, and SSGA cycles in the linear relationship between sunspot-group area and sunspot number we find that the amplitude (130 +or- 12) of Sunspot Cycle 25 would be slightly larger than that of reasonably small Sunspot Cycle 24. Still it confirms that the beginning of the upcoming Gleissberg cycle would take place around Solar Cycle 25. We also find that except at the maximum of NSGA Cycle 25 where the strength of activity in northern hemisphere would be dominant, the strength of activity in the southern hemisphere would be dominant at the maximum epochs of the 25th sunspot, WSGA, and SSGA cycles.

On the Decay of Sunspot Groups and Their Internal Parts in Detail

Abstract The decay of sunspot groups is a relatively unknown field since most studies have focused mainly on the decay of sunspots or sunspot groups, but only on small samples. As an extension of the recent work of Muraközy (2020), which is based on a large verified sample, this study investigates not only the long-term behavior of the decay of sunspot groups but also the dynamics of their parts. The aim of the present work is to search for dependencies of the decay process in order to find physical conditions that modify or contribute to the decay. The investigations are based on the catalog of the SoHO Debrecen Sunspot Database (SDD) and the Greenwich Photoheliographic Results as well as the Debrecen Photoheliographic Data. Altogether more than 750 sunspot groups were considered. The decay rates have been calculated for the total, umbral, and penumbral area of the groups and in the case of the SDD’s groups they have been calculated for both the leading and the following parts. The decay rates depend linearly on the maximum areas and ranged from 30 to 50 millionths of the solar hemisphere (MSH) day−1 for the sunspot groups and penumbrae and 5–10 MSH day−1 for the umbrae throughout the cycle. The decay rates fall significantly during the Gnevyshev gap and show 4 + 4 Schwabe cyclical variations in the ascending/descending phases, but it is always higher in the northern hemisphere. There is a slight decrease in the decay rates in the activity range toward higher latitudes.

North–south asymmetry in solar activity and Solar Cycle prediction, V: prediction for the north–south asymmetry in the amplitude of Solar Cycle 25

We analyzed the daily sunspot-group data reported by the Greenwich Photoheliographic Results (GPR) during the period 1874-1976 and Debrecen Photoheligraphic Data (DPD) during the period 1977-2017, and the revised Version-2 of ISSN during the period 1874-2017. We determined the amplitude of the Solar Cycles 12-24 and the 13-month smoothed monthly mean corrected areas of the sunspot groups in the Sun's whole-sphere (WSGA), northern hemisphere (NSGA), and southern hemisphere (SSGA) at the epochs of the maxima of the Solar Cycles 12-24. Using all these we obtained the relations similar to that found in our earlier analyzes -- i.e., the existence of a high correlation between the sum of the areas of sunspot groups in the southern-hemisphere near-equatorial band during a small interval (7-9 months) just after a maximum epoch of a solar cycle and the amplitude of next solar cycle -- separately for the Sun's whole-sphere and northern- and southern-hemispheres. By using these relations we predicted ~701 msh (millionth of solar hemisphere), ~429 msh, and ~366 msh for the values of WSGA, NSGA, and SSGA, respectively, at the maximum epoch of the Solar Cycle 25. We predicted 86 + or - 18 for the amplitude of Solar Cycle 25. The 13-month smoothed monthly mean sunspot-group area highly correlate with that of ISSN. Using this relation and the predicted values of WSGA, NSGA, and SSGA we have obtained 68 + or -11 for the amplitude of Solar Cycle 25, which is slightly lower than the aforementioned predicted value, and 39 + or - 4 and 31 + or - 6 for the values of northern- and southern-hemispheres' sunspot numbers at the maximum epoch of Solar Cycle 25. Overall, our results suggest that the amplitude of Solar Cycle 25 would be 25%-40% smaller, and the corresponding north-south asymmetry would be much smaller, than those of Solar Cycle 24.

Long–Term Variations in Solar Differential Rotation and Sunspot Activity, II: Differential Rotation Around the Maxima and Minima of Solar Cycles 12 – 24

Studies of variations in the solar differential rotation are important for understanding the underlying mechanism of solar cycle and other variations of solar activity. We analyzed the sunspot-group daily data that were reported by Greenwich Photoheliographic Results (GPR) during the period 1874 – 1976 and Debrecen Photoheliographic Data (DPD) during the period 1977 – 2017. We determined the equatorial rotation rate [ $A$ ] and the latitude gradient [ $B$ ] components of the solar differential rotation by fitting the data in each of the 3-year moving time intervals (3-year MTIs) successively shifted by one year during the period 1874 – 2017 to the standard law of differential rotation. The values of $A$ and $B$ around the years of maxima and minima of Solar Cycles 12 – 24 are obtained from the 3-year MTIs series of $A$ and $B$ and studied the long-term cycle-to-cycle modulations in these coefficients. Here we have used the epochs of the maxima and minima of the Solar Cycles 12 – 24 that were recently determined from the revised Version-2 international sunspot-number series. We find that there exits a considerably significant secular decreasing-trend in $A$ around the maxima of solar cycles. There exist no secular trends in both $A$ and $B$ around the minima of solar cycles. The secular trend in $B$ around the maxima of solar cycles is also found to be statistically insignificant. We fitted a cosine function to the values of $A$ , and also to those of $B$ , after removing the corresponding linear trends. The cosine-fits suggest that there exist ≈54-year (≈94-year) and ≈82-year (≈79-year) periodicities in $A$ ( $B$ ) around the maxima and minima of solar cycles, respectively. The amplitude of the cosine-profile of $A$ ( $B$ ) around the minima of solar cycles is about 41% (65%) larger than that of $A$ ( $B$ ) around the maxima. In addition, the cosine profiles of $A$ and $B$ suggest a large (up to $180^{\circ }$ ) phase difference between the long-term variations of $A$ , and also between those of $B$ , around maxima and minima of solar cycles. Implications of all these results are discussed briefly.

Long-term Periodicities in North–south Asymmetry of Solar Activity and Alignments of the Giant Planets

The existence of ~12-year and ~51-year periodicities in the north-south asymmetry of solar activity is well known. However, the origin of these as well as the well-known relatively short periodicities in the north-south asymmetry is not yet clear. Here we have analyzed the combined daily data of sunspot groups reported in Greenwich Photoheliographic Results (GPR) and Debrecen Photoheligraphic Data (DPD) during the period 1874-2017 and the data of the orbital positions (ecliptic longitudes) of the giant planets in ten-day intervals during the period 1600-2099. Our analysis suggests that ~12-year and ~51-year periodicities in the north-south asymmetry of solar activity are the manifestations of the differences in the strengths of ~11-year and ~51-year periodicities of activity in the northern- and southern-hemispheres. During the period 1874-2017 the Morlet wavelet power spectra of the north-south asymmetry of sunspot-group area and the mean absolute difference of the orbital positions of the giant planets are found to be similar. Particularly, there is a suggestion that the ~12-year and ~51-year periodicities in the north-south asymmetry of sunspot-group area occurred during approximately the same times as the corresponding periodicities in the mean absolute difference of the orbital positions of the giant planets. Therefore, we suggest that there could be influence of some specific configurations of the giant planets in the origin of the ~12-year and ~50-year periodicities of the north-south asymmetry of solar activity.

A Transit of Venus Possibly Misinterpreted as an Unaided-Eye Sunspot Observation in China on 9 December 1874

Large sunspots can be observed with the unaided eye under suitable atmospheric seeing conditions. Such observations are of particular value because the frequency of their appearance provides an approximate indication of the prevailing level of solar activity. Unaided-eye sunspot (UES) observations can be traced back well before the start of telescopic observations of the Sun, especially in the East Asian historical records. It is therefore important to compare more modern, UES observations with the results of telescopic sunspot observations, to gain a better understanding of the nature of the UES records. A previous comparison of Chinese UES records and Greenwich photo-heliographic results between 1874 and 1918 indicated that a few of the UES were apparently not supported by direct photographic evidence of at least one sunspot with a large area. This article reveals that one of the Chinese unaided-eye observations had possibly captured the transit of Venus on 9 December 1874. The Chinese sunspot records on this date are compared with Western sunspot observations on the same day. It is concluded that sunspots on the solar disk were quite small and the transit of Venus was probably misinterpreted as a sunspot by the Chinese local scholars. This case indicates that sunspots or comparable "obscuring" objects with an area as large as 1000 millionths of the solar disk could easily have been seen with the unaided eye under suitable seeing conditions. It also confirms the visibility of sunspots near the solar limb with the unaided eye. This study provides an explanation of the apparent discrepancy between the Chinese UES observation on 9 December 1874 and the Western sunspot observations using telescopes, as well as a basis for further discussion on the negative pairs in 1900 and 1911, apparently without sufficiently large area.

North–South Asymmetry in Solar Activity and Solar Cycle Prediction, IV: Prediction for Lengths of Upcoming Solar Cycles

We analyzed the daily sunspot-group data reported by the Greenwich Photoheliographic Results (GPR) during the period 1874 – 1976 and Debrecen Photoheliographic Data (DPD) during the period 1977 – 2017 and studied North–South asymmetry in the maxima and minima of the Solar Cycles 12 – 24. We derived the time series of the 13-month smoothed monthly mean corrected whole-spot areas of the sunspot groups in the Sun’s whole sphere (WSGA), northern hemisphere (NSGA), and southern hemisphere (SSGA). From these smoothed time series we obtained the values of the maxima and minima, and the corresponding epochs, of the WSGA, NSGA, and SSGA Cycles 12 – 24. We find that there exists a 44 – 66 years periodicity in the North–South asymmetry of the minimum. A long periodicity (130 – 140 years) may exist in the asymmetry of the maximum. A statistically significant correlation exists between the maximum of SSGA Cycle $n$ and the rise time of WSGA Cycle $n+2$ . A reasonably significant correlation also exists between the maximum of WSGA Cycle $n$ and the decline time of WSGA Cycle $n+2$ . These relations suggest that the solar dynamo carries memory over at least three solar cycles. Using these relations we obtained the values $11.7\pm 0.15~\text{years}$ , $11.2\pm 0.2~\text{years}$ , and $11.45\pm 0.3~\text{years}$ for the lengths of WSGA Cycles 24, 25, and 26, respectively, and hence, July 2020, October 2031, and March 2043 for the minimum epochs (start dates) of WSGA Cycles 25, 26, and 27, respectively. We also obtained May 2025 and March 2036 for the maximum epochs of WSGA Cycles 25 and 26, respectively. It seems during the late Maunder Minimum sunspot activity was absent around the epochs of the maxima of the NSGA-cycles and the minima of the SSGA-cycles, and some activity was present at the epochs of the maxima of some SSGA-cycles and the minima of some NSGA-cycles.

Connection Between Solar Hemispheric Toroidal Cycles and Geomagnetic Variations

The solar activity has hemispheric asymmetries. The levels of activity are different on the two hemispheres on intermediate and longer time scales. During four Schwabe cycles the progress of the northern hemispheric activity precedes the southern one, while in the next four cycles the southern cycle takes over the preceding role (Muraközy and Ludmány, Mon. Not. Roy. Astron. Soc.419, 3624, 2012; Muraközy, Astrophys. J.826, 145, 2016). The interplanetary magnetic field is formed by the distribution of the solar magnetic fields and the outward-streaming solar wind. The present study intends to show how the solar-hemispheric predominance affects the interplanetary and geophysical magnetic field. The interplanetary and geophysical data sets have been chosen from various sources such as the components of the interplanetary magnetic field [B], cosmic-ray data, Ap, aa, and Dst geomagnetic indices, while the solar-hemispheric asymmetry has been examined by using sunspot data from Greenwich Photoheliographic Results (GPR) and Debrecen Photoheliographic Data (DPD).

Stable Sunspot Area Level of Debrecen Photoheliographic Data and Multivariate Correction Factor of SOON Data

We investigate the spatial and temporal variation of sunspot group areas reported by the Greenwich Photoheliographic Results (GPR), the Solar Optical Observing Network (SOON), the Kislovodsk Mountain Astronomical Station (KMAS), and the Debrecen Photoheliographic Data (DPD) databases. We identify improved correction factors for reconciling these individual records to a common scale. Our results show that the DPD sunspot group areas are stable over the studied interval (1974 – 2014). We find an improved fit between GPR and DPD sunspot group areas when using a correction factor such that $\mathrm{GPR} = 0.975(\pm 0.006) \times \mathrm{DPD}$ , independent of the position of the sunspot group on the solar disk. We also find that the scale of KMAS sunspot group areas fits that of DPD well, but has a small position-dependent trend near the limb. However, in order to set SOON sunspot group area records onto the scale of DPD, we find that there is a need for a multivariate correction factor. This multivariate correction factor has a value ranging between 1.1 and 1.9 and is dependent upon the time of the SOON observation, the distance of the group from disk center, and the observatory within the SOON network. Finally, we provide further context to the systematic bias in SOON sunspot group area observations toward lower values relative to those recorded in the GPR and DPD databases that has previously been reported in the literature. We have identified the two main contributors to the SOON area deficit; some penumbral parts are unobserved, and the spot areas are underestimated. Our analysis is vital for studies that require stable, long-term solar activity records such as solar irradiance models that estimate irradiance reduction from records of sunspot group numbers, areas, and locations.

Variations and Regularities in the Hemispheric Distributions in Sunspot Groups of Various Classes

The present study investigates the variations and regularities in the distributions in sunspot groups (SGs) of various classes in the northern and southern hemispheres from Solar Cycles (SCs) 12 to 23. Here, we use the separation scheme that was introduced by Gao, Li, and Li (Solar Phys.292, 124, 2017), which is based on $A/U$ (A is the corrected area of the SG, and U is the corrected umbral area of the SG), in order to separate SGs into simple SGs ($A/U \leq 4.5$) and complex SGs ($A/U > 6.2$). The time series of Greenwich photoheliographic results from 1875 to 1976 (corresponding to complete SCs 12 – 20) and Debrecen photoheliographic data during the period 1974 – 2015 (corresponding to complete SCs 21 – 23) are used to show the distributions of simple and complex SGs in the northern and southern hemispheres. The main results we obtain are reported as follows: i) the larger of the maximum annual simple SG numbers in the two hemispheres and the larger of the maximum annual complex SG numbers in the two hemispheres occur in different hemispheres during SCs 12, 14, 18, and 19; ii) the relative changing trends of two curves – cumulative SG numbers in the northern and southern hemispheres – for simple SGs are different from those for complex SGs during SCs 12, 14, 18, and 21; and iii) there are discrepancies between the dominant hemispheres of simple and complex SGs for SCs 12, 14, 18, and 21.

A Relationship Between the Solar Rotation and Activity Analysed by Tracing Sunspot Groups

The sunspot position from Greenwich Photoheliographic Results (GPR), US Air Force Solar Optical Observing Network and National Oceanic and Atmospheric Administration (USAF/NOAA), and Debrecen Photoheliographic Data (DPD) data bases in the period 1874 to 2016 were used to calculate yearly values of the solar differential-rotation parameters $A$ and $B$. The calculated differential-rotation parameters were compared with the solar-activity level. We found that the Sun rotates more differentially at the minimum than at the maximum of activity during the 1977 - 2016 epoch. An inverse correlation between equatorial rotation and solar activity was found using the recently revised sunspot number. The secular decrease of equatorial rotation rate accompanying the increase of activity stopped in the last part of the 20th century. It was noted that when a significant peak of equatorial rotation velocity is observed during minimum of activity, the strength of the next maximum is smaller than the previous one.

Solar differential rotation in the period 1964–2016 determined by the Kanzelhöhe data set

The main aim of this work is to determine the solar differential rotation by tracing sunspot groups during the period 1964-2016, using the Kanzelh\"ohe Observatory for Solar and Environmental Research (KSO) sunspot drawings and white light images. Two procedures for the determination of the heliographic positions were applied: an interactive procedure on the KSO sunspot drawings (1964 - 2008, solar cycles nos. 20 - 23) and an automatic procedure on the KSO white light images (2009 - 2016, solar cycle no. 24). For the determination of the synodic angular rotation velocities two different methods have been used: a daily shift (DS) method and a robust linear least-squares fit (rLSQ) method. Afterwards, the rotation velocities had to be converted from synodic to sidereal, which were then used in the least-squares fitting for the solar differential rotation law. For the test data from 2014, we found the rLSQ method for calculating rotational velocities to be more reliable than the DS method. The best fit solar differential rotation profile for the whole time period is $\omega(b)$ = (14.47 $\pm$ 0.01) - (2.66 $\pm$ 0.10) $\sin^2b$ (deg/day) for the DS method and $\omega(b)$ = (14.50 $\pm$ 0.01) - (2.87 $\pm$ 0.12) $\sin^2b$ (deg/day) for the rLSQ method. A barely noticeable north - south asymmetry is observed for the whole time period 1964 - 2016 in the present paper. Rotation profiles, using different data sets (e.g. Debrecen Photoheliographic Data, Greenwich Photoheliographic Results), presented by other authors for the same time periods and the same tracer types, are in good agreement with our results. Therefore, the KSO data set is suitable for the investigation of the long-term variabilities in the solar rotation profile.

Meridional Motion and Reynolds Stress from Debrecen Photoheliographic Data

The Debrecen Photoheliographic Data catalogue is a continuation of the Greenwich Photoheliographic Results providing daily positions of sunspots and sunspot groups. We analyse the data for sunspot groups focusing on meridional motions and transfer of angular momentum towards the solar equator. Velocities are calculated with a daily shift method including an automatic iterative process of removing the outliers. Apart from the standard differential rotation profile, we find meridional motion directed towards the zone of solar activity. The difference in measured meridional flow in comparison to Doppler measurements and some other tracer measurements is interpreted as a consequence of different flow patterns inside and outside of active regions. We also find a statistically significant dependence of meridional motion on rotation velocity residuals confirming the transfer of angular momentum towards the equator. Analysis of horizontal Reynolds stress reveals that the transfer of angular momentum is stronger with increasing latitude up to about 40$^{\circ}$ where there is a possible maximum in absolute value.

Short-Term Variations in the Equatorial Rotation Rate of Sunspot Groups

We have detected several periodicities in the solar equatorial rotation rate of sunspot groups in the Greenwich Photoheliographic Results (GPR) during the period 1931-1976, the Solar Optical Observing Network (SOON) during the period 1977-2014, and the Debrecen Photoheliographic Data (DPD) during the period 1974-2014. Our results suggest a ~250-day period in the equatorial rotation rate determined from both the Mt. Wilson Doppler-velocity data and the sunspot-group data during 1986-2007. However, a wavelet analysis reveals that this periodicity appears mostly around 1991 in the velocity data, while it is present in most of the solar cycles covered by the sunspot-group data, mainly near the minimum epochs of the solar cycles. We also found the signature of a period of ~1.4 years period in the velocity data during 1990-1995, and in the equatorial rotation rate of sunspot groups mostly around the year 1956. The equatorial rotation rate of sunspot groups reveals a strong ~1.6-year periodicity around 1933 and 1955 and a weaker one around 1976, and a strong ~1.8-year periodicity around 1943. Our analysis also suggests periodicities of ~5 years, ~7 years, and ~17 years as well as some other short-term periodicities. However, short-term periodicities are mostly present at the time of solar minima. Hence, short-term periodicities cannot be confirmed because of the larger uncertainty in the data.

On-line Tools for Solar Data Compiled at the Debrecen Observatory and Their Extensions with the Greenwich Sunspot Data

The primary task of the Debrecen Heliophysical Observatory (DHO) has been the most detailed, reliable, and precise documentation of the solar photospheric activity since 1958. This long-term effort resulted in various solar catalogs based on ground-based and space-borne observations. A series of sunspot databases and on-line tools were compiled at DHO: the Debrecen Photoheliographic Data (DPD, 1974--), the dataset based on the Michelson Doppler Imager (MDI) of the Solar and Heliospheric Observatory (SOHO) called SOHO/MDI--Debrecen Data (SDD, 1996--2010), and the dataset based on the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) called SDO/HMI--Debrecen Data (HMIDD, 2010--). User-friendly web-presentations and on-line tools were developed to visualize and search data. As a last step of compilation, the revised version of Greenwich Photoheliographic Results (GPR, 1874--1976) catalog was converted to DPD format, and a homogeneous sunspot database covering more than 140 years was created. The database of images for the GPR era was completed with the full-disc drawings of the Hungarian historical observatories \'Ogyalla and Kalocsa (1872--1919) and with the polarity drawings of Mount Wilson Observatory. We describe the main characteristics of the available data and on-line tools.

An Early Sunspot Catalog by Miguel Aguilar for the Period 1914 – 1920

We provide a source of detailed solar parameters spanning the years 1914 – 1920. Although various catalogs containing information on sunspots and sunspot groups have been available for almost 150 years, the contents and conventions can vary greatly from one source to another. Thus, the availability of multiple sources is very important to assess the relative uncertainties in the identified quantities. We provide here a machine-readable version of the sunspot catalog made by M. Aguilar from 1914 to 1920. We show and explain the structure and possible errors found in this catalog. We also try to understand the specific differences of this catalog, i.e. explain the shortcomings and benefits of this catalog versus other available sources of solar information. This catalog, combined with the Valencia catalog, presents a valuable source of comparison with the Royal Greenwich Observatory (RGO or GPR for Greenwich Photoheliographic Results) data, and it helps shed more light on the link between the RGO classification and the more modern classifications of sunspot groups found in the Zurich or McIntosh classifications. We also extend the work started by Carrasco et al. (Solar Phys. 290, 1445, 2015) on the mapping of Cortie types.

North-south asymmetry in small and large sunspot group activity and violation of even-odd solar cycle rule

According to Gnevyshev-Ohl (G-O) rule an odd-numbered cycle is stronger than its preceding even-numbered cycle. In the modern time the cycle pair (22, 23) violated this rule. By using the combined Greenwich Photoheliographic Results (GPR) and Solar Optical Observing Network (SOON) sunspot group data during the period 1874-2015, and Debrecen Photoheliographic Data (DPD) of sunspot groups during the period 1974-2015, here we have found that the solar cycle pair (22, 23) violated the G-O rule because, besides during cycle 23 a large deficiency of small sunspot groups in both the northern and the southern hemispheres, during cycle 22 a large abundance of small sunspot groups in the southern hemisphere. In the case of large and small sunspot groups the cycle pair (22, 23) violated the G-O rule in the northern and southern hemispheres, respectively, suggesting the north-south asymmetry in solar activity has a significant contribution in the violation of G-O rule. The amplitude of solar cycle 24 is smaller than that of solar cycle 23. However, Coronal Mass Ejections (CMEs) rate in the rising phases of the cycles 23 and 24 are almost same (even slightly large in cycle 24). From both the SOON and the DPD sunspot group data here we have also found that on the average the ratio of the number (counts) of large sunspot groups to the number of small sunspot groups is larger in the rising phase of cycle 24 than that in the corresponding phase of cycle 23. We suggest this could be a potential reason for the aforesaid discrepancy in the CME rates during the rising phases of cycles 23 and 24. These results have significant implication on solar cycle mechanism

Indirect comparison of Debrecen and Greenwich daily sums of sunspot areas

Sunspot area data play an important role in the studies of solar activity and its long-term variations. In order to reveal real long-term solar variations precise homogeneous sunspot area databases should be used. However, the measured areas may be burdened with systematic deviations, which may vary in time. Thus, there is a need to investigate the long-term variation of sunspot area datasets and to determine the time-dependent cross-calibration factors. In this study, we investigate the time-dependent differences between the available long-term sunspot databases. Using the results, we estimate the correction factor to calibrate the corrected daily sunspot areas of Debrecen Photoheliographic Data (DPD) to the same data of Greenwich Photoheliographic Results (GPR) by using the overlapping Kislovodsk and Pulkovo data. We give the correction factor as GPR=1.08(\pm 0.11)*DPD

The Greenwich Photo-heliographic Results (1874 – 1976): Summary of the Observations, Applications, Datasets, Definitions and Errors

The measurements of sunspot positions and areas that were published initially by the Royal Observatory, Greenwich, and subsequently by the Royal Greenwich Observatory (RGO), as the Greenwich Photo-heliographic Results (GPR), 1874 – 1976, exist in both printed and digital forms. These printed and digital sunspot datasets have been archived in various libraries and data centres. Unfortunately, however, typographic, systematic and isolated errors can be found in the various datasets. The purpose of the present paper is to begin the task of identifying and correcting these errors. In particular, the intention is to provide in one foundational paper all the necessary background information on the original solar observations, their various applications in scientific research, the format of the different digital datasets, the necessary definitions of the quantities measured, and the initial identification of errors in both the printed publications and the digital datasets. Two companion papers address the question of specific identifiable errors; namely, typographic errors in the printed publications, and both isolated and systematic errors in the digital datasets. The existence of two independently prepared digital datasets, which both contain information on sunspot positions and areas, makes it possible to outline a preliminary strategy for the development of an even more accurate digital dataset. Further work is in progress to generate an extremely reliable sunspot digital dataset, based on the programme of solar observations supported for more than a century by the Royal Observatory, Greenwich, and the Royal Greenwich Observatory. This improved dataset should be of value in many future scientific investigations.