Abstract
Small-scale solar magnetic flux concentrations are studied in two-dimensional G-band images at very high spatial resolution and compared with Ca ii H enhancements. Among 970 small-sized G-band intergranular structures (IgS), 45% are co-spatial with isolated locations of Ca ii H excess and thus considered as magnetic (MIgS); they may be even twice as frequent as the known G-band bright points. The IgS are recognized in the G-band image by a new algorithm operating in four steps: (1) A set of equidistant detection levels yields a pattern of primary “cells”; (2) for each cell, the intrinsic intensity profile is normalized to its brightest pixel; (3) the cell sizes are shrunk by a unitary single-intensity clip; (4) features in contact at an appropriate reference level are merged by removal of the respective common dividing lines. Optionally, adjoining structures may be excluded from this merging process (e.g., chains of segmented IgS), referring to the parameterized number and intensity of those pixels where enveloping feature contours overlap. From the thus recognized IgS pattern, MIgS are then selected by their local Ca ii H contrast and their mean G-band-to-continuum brightness ratio.
Highlights
The majority of solar magnetic flux concentrations appear at scales near the spatial resolution limit hitherto achieved
For a sufficient statistical significance, a pattern recognition method is required that detects intergranular structures (IgS)
Bovelet and Wiehr (2001; hereafter referred to as Paper I) demonstrated that (i) and (ii) are tightly related: It is the finite spatial resolution achieved in solar images that makes small intergranular lanes appear less intensity-depressed; at increasing spatial resolution, small lanes appear as dark as broader ones
Summary
The majority of solar magnetic flux concentrations appear at scales near the spatial resolution limit hitherto achieved. Recognized features often show two deficiencies in describing a realistic pattern of solar structures: (i) a clustering of closely neighboring granules and (ii) too wide intergranular lanes. Bovelet and Wiehr (2001; hereafter referred to as Paper I) demonstrated that (i) and (ii) are tightly related: It is the finite spatial resolution achieved in solar images that makes small intergranular lanes appear less intensity-depressed; at increasing spatial resolution, small lanes appear as dark as broader ones. Adjacent granules, separated by such pale intergranular lanes, are hardly segmented by any plain pattern recognition. Adapting the algorithm to avoid “artificial conglomerates” of adjacent granules (i) requires the segregation process to stop at an intensity level well above that of pale intergranular lanes; as a consequence, the obtained pattern contains bright features that are smaller than realistic granules and intergranular lanes that are much too broad (ii). We present a multiple-scale generalization of MLT for the segmentation of various intensity features from brightest local maxima to faintest structures embedded in the (deep) intergranular lanes
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