Lifetimes and sizes of supergranular cells

Abstract

Supergranulation is the surface manifestation of large scale solar convection. Since there is a strong correspondence between supergranulation pattern and Ca K chromospheric network, lifetimes and sizes may be obtained from the temporal and spatial autocorrelation functions (ACF), calculated from Ca K filtergrams of the Sun. We have developed a program to study the lifetimes and spatial scales of supergranulation through an extenasive digital analysis. The temporal ACF was calculataed from a 106 hour time-sequence of the data obtained from Antarctica. The lifetimes of quiet cells were found to be about 24-34 hours while that of active cells were about 58-61 hours. The temporal autocorrelation function sometimes showed an oscillataory pattern which may be due to long-term intensity variations or length scale changes associataed with the network. The cell sizes were obtained from Ca K spectroheliograms belonging to the solar minimum phases of 1913-1974 from Kodaikanal Solar Observatory. The average cell size was found to show a curious dependence on solar latitude.