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

The complete sample of the Greenwich Photoheliographic Results (GPR) f or the years 1874-1976 was used for the investigation of the growth an d decay of sunspot groups. The results were compared with similar find ings from the Mt. Wilson sunspot data for the years 1917-1985, which w ere recently published by R. F. Howard. The results of the absolute um bral area changes are about the same for both sets of data. The main d ifference between the sets of data occurs for the percentage increase of the umbral areas as a function of latitude. The mean values from th e Mt. Wilson data are bigger by a factor of 5 to 7 and show a dependen ce 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 highe r values for the decrease for higher latitudes from 2.5 up to 42.5 deg .