Characteristic Size and Diffusion of Quiet Sun Magnetic Patterns
Abstract
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 FWHM of the crosscorrelation functions of 16.6 ± 0.2 Mm. The length scale is constant within ±45° latitude and decreases by about 5% at 52.5° latitude; i.e., the characteristic 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° 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 km2 s−1 for the diffusion constant, while a lifetime of two days leads to 230 km2 s−1.
- Publication:
-
Solar Physics
- Pub Date:
- May 1995
- DOI:
- 10.1007/BF00795658
- Bibcode:
- 1995SoPh..158..213K
- Keywords:
-
- Diffusion;
- Magnetic Signatures;
- Size (Dimensions);
- Solar Physics;
- Sun;
- Cross Correlation;
- Latitude;
- Length;
- Solar Cycles;
- Solar Physics;
- Crosscorrelation;
- Solar Cycle;
- Magnetic Feature;
- Daily Observation;
- Characteristic Length Scale