Data Analysis

Table 5.1: Details of DST dataset, including an estimation of the height of formation of each bandpass

Line	Wavelength	FWHM	Instrument	Image Scale	Formation
	(Å)	(Å)		( per pixel)	Height (km)
Ca II K3	3933.7	0.30	Halle	0.33	1800-20001
H	6562.8	0.21a	UBFb	0.18	1200-17001
Mg I b2	5172.7	0.13a	UBFb	0.18	700-7502
Mg I b1-0.4 Å	5183.2	0.13a	UBFb	0.18	2003

REFERENCES:
(a) Beckers, Dickson, & Joyce (1975)
(b) Universal Birefringent Filter, Bonaccini et al. (1989)
(1) Vernazza et al. (1981)
(2) Schmieder (1979)
(3) Keller & Koutchmy (1991)

The observational set-up at the DST has been described in detail in Chapter 3. For this study, time series analysis of the Ca II K₃, H core, Mg I b₂, and Mg I b₁-0.4 Å data were used to provide information as a function of height throughout the chromosphere (Table 5.1).

Figure 5.1: Example time-averaged data of the 100"  x  100" FOV in the corona (Fe XV 284 Å), transition region (C IV 1550 Å) and chromosphere (DST wavelengths). The bottom plot is the corresponding magnetogram. The vertical lines show the four stable NBPs analysed in this paper.

A 150-minute sequence of 100  x  100 images were obtained in all wavelengths, centred on a quiet Sun field (Solar_X = -25, Solar_Y = -35) with a 45 s cadence. This provided seven NBPs (Figure 5.1), four of which (NBPs 1, 2, 5 & 7) were distinguishable throughout the entire series in all wavelengths, and hence are used here. As discussed in Chapter 3 the UBF cycle (Table 5.1) also included two Fe I (6302.5 Å) images, linearly polarised at to each other. These images were destretched, integrated and combined to create the magnetogram at the bottom of Figure 5.1. Coalignment of the ground based images with the TRACE data led to a calculated spatial size of 0.33 per pixel in the Ca II K₃ data and 0.18 per pixel for the other wavelengths (Table 5.1). Figure 5.1 shows that the chromospheric NBPs have a one-to-one spatial correlation with the photospheric magnetic field and exist throughout the transition region, and even into the corona.

Analysis of the DST observations was carried out using standard routines within SSW. The data were corrected for CCD readout bias and flat-fielded. Each image was aligned to the first image of the series by means of cross-correlation. TRACE images were reduced using the standard calibration and despiking routines provided. Light curves in each wavelength were then created using the contour and contrast method, high-pass filtered and subjected to a Fourier analysis as described in Chapter 4.