Study of differences between sunspot area data determined from ground-based and space-borne observations

The determination of the area of sunspots is important from several points of view, e.g, in study of the evolution of sunspots and their effect on solar irradiance. Automated sunspot area measurements are now replacing time-consuming and subjective hand-made measurements. Also, terrestrial solar observations have been supplemented by observations from space. The resolution of the ground observations is limited by the seeing, while space-borne observations are limited by the size of the CCD array. The use of different data sources, as well as of different region identification algorithms, causes discrepancies in reported sunspot areas. An important task is to determine to what extent these differences can be attributed to different analysis methods and to what extent to different data. It is also important to establish the required spatial resolution of space-based images. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.