Characteristic size and diffusion of quiet Sun magnetic patterns

Details Characteristic size and diffusion of quiet Sun magnetic patterns Characteristic size and diffusion of quiet Sun magnetic patterns

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995soph..158..213k&link_type=abstract

Solar Physics (ISSN 0038-0938), vol. 158, no. 2, p. 213-225

Physics

18

Diffusion, Magnetic Signatures, Size (Dimensions), Solar Physics, Sun, Cross Correlation, Latitude, Length, Solar Cycles

Scientific paper

We have previously studied large-scale motions using high-resolution magnetograms taken from 1978 to 1990 with the NSO Vacuum Telescope on Kitt Peak. Latitudinal and longitudinal motions were determined by a two-dimensional crosscorrelation analysis of pairs of consecutive daily observations using small magnetic features as tracers. Here we examine the shape and amplitude of the crosscorrelation functions. We find a characteristic length scale as indicated by the Full Width Half Maximum (FWHM) of the crosscorrelation functions of 16.6 +/- 0.2 Mm. The length scale is constant within +/- 45 deg latitude and decreases by about 5% at 52.5 deg latitude; i.e., the characterisic size is almost latitude independent. The characteristic scale is within 3% of the average value during most times of the solar cycle, but it increases during cycle maximum at latitudes where active regions are present. For the time period 1978-1981 (solar cycle maximum), the length scale increases up to 1.7 Mm or 10% at 30 deg latitude. In addition, we derive the average amplitude of the crosscorrelation functions, which reflects the diffusion of magnetic elements and their evolutionary changes (including formation and decay). We find an average value of 0.091 +/- 0.003 for the crosscorrelation amplitude at a time lag of one day, which we interpret as being caused by the combined effect of the lifetime of magnetic features and a diffusion process. Assuming a lifetime of one day, we find a value of 120 sq km/s for the diffusion constant, while a lifetime of two days leads to 230 sq km/s.

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