Comparative analysis of Debrecen sunspot catalogues

Abstract

Sunspot area data are important for studying solar activity and its long-term variations. At the Debrecen Heliophysical Observatory, we compiled three sunspot catalogues: the Debrecen Photoheliographic Data (DPD), the SDO/HMI Debrecen Data (HMIDD) and the SOHO/MDI Debrecen Data. For comparison, we also compiled an additional sunspot catalogue, the Greenwich Photoheliographic Data, from the digitized Royal Greenwich Observatory images for 1974-76. By comparing these catalogues when they overlap in time, we can investigate how various factors influence the measured area of sunspots, and, in addition, we can derive area cross-calibration factors for these catalogues. The main findings are as follows. Poorer seeing increases the individual corrected spot areas and decreases the number of small spots. Interestingly, the net result of these two effects for the total corrected spot area is zero. DPD daily total corrected sunspot areas are 5 per cent smaller than the HMIDD ones. Revised DPD daily total corrected umbra areas are 9 per cent smaller than those of HMIDD. The Greenwich photoheliographic areas are only a few per cent smaller than DPD areas. A 0.2 • difference between the north directions of the DPD and MDI images is found. This value is nearly the same as was found (0.22 • ) by us in a previous paper comparing HMI and MDI images. The area measurement practice (spots smaller than 10 mh were not directly measured but an area of 2 mh was assigned to each) of the Solar Observing Optical Network cannot explain the large area deficit of the Solar Observing Optical Network.

Meridional Motion and Reynolds Stress from Debrecen Photoheliographic Data

“…Our dataset is created from positions and times of sunspot groups measured in DPD 1 (Baranyi, Győri, and Ludmány, 2016;Győri, Ludmány, and Baranyi, 2017) determined once per day. We use the daily change in position of each sunspot group to calculate both meridional and rotational speeds:…”

Estimating Solar Irradiance Since 850 CE

“…These compact, dark features are regions where local concentrations of magnetic flux emerge from the convection zone beneath the Sun's surface, the result of twisting and distortion of subsurface magnetic fields by the solar dynamo. Compilation of sunspot catalogs and assessment and validation of records from different observatories is ongoing (Balmaceda et al, 2009;Győri et al, 2017). Systematic observations commenced in the mid-nineteenth century, soon after the discovery of an 11-year cycle in sunspot numbers, and continue to the present.…”

“…The Royal Greenwich Observatory made photographic observations from 1882 to 1986 (Willis et al, 2013), and the Air Force Solar Optical Operational Network (SOON) began collecting information about sunspot areas and locations operationally in the mid-1980s. Compilation of sunspot catalogs and assessment and validation of records from different observatories is ongoing (Balmaceda et al, 2009;Győri et al, 2017).…”

Sunspot observations by Hisako Koyama: 1945–1996

“…Therefore, a thorough revision of the calibration of both series is currently ongoing on the basis of original observations and using new modern methodologies (Clette et al, 2014Vaquero et al, 2016;Svalgaard and Schatten, 2016;Usoskin et al, 2016;Cliver and Ling, 2016;Chatzistergos et al, 2017;Muñoz-Jaramillo and Vaquero, 2019). While observations were conducted over many decades in various institutional observatories such as Greenwich (Willis et al, 2013(Willis et al, , 2016a(Willis et al, , 2016b, Debrecen (Baranyi et al, 2016;Győri et al, 2017), or Mount Wilson (Lefèvre et al, 2005Pevtsov et al, 2019), long-term observations at smaller observatories by individual astronomers -frequently skilled amateur observers -are of particular importance in terms of stability. Indeed, such sunspot time series have been derived from a single observer, often with a unique telescope, in contrast with professional teams working in shifts and with a staff changing over the years (e.g., Clette et al, 2014;Carrasco et al, 2019).…”