THE GROWTH AND DECAY OF SUNSPOTS - COMPARISON BETWEEN THE GREENWICH AND MOUNT WILSON SUNSPOT DATA

The complete sample of the Greenwich Photoheliographic Results (GPR) for the years 1874-1976 was used for the investigation of the growth and decay of sunspot groups. The results were compared with similar findings from the Mt. Wilson sunspot data for the years 1917-1985, which were recently published by R. F. Howard. The results of the absolute umbral area changes are about the same for both sets of data. The main difference between the sets of data occurs for the percentage increase of the umbral areas as a function of latitude. The mean values from the Mt. Wilson data are bigger by a factor of 5 to 7 and show a dependence on the latitude, while the increase of the Greenwich data does not depend on the latitude. The decrease of sunspot areas as a function of latitude is only available from the Greenwich data. There occur higher values for the decrease for higher latitudes from 2.5 up to 42.5 deg.