Emission of solar chromospheric and transition region features related to the underlying magnetic field

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Table 2.

Overview of the observations.

Instrument		λ [Å]^a	Line/feature	log T [K]^d	Atmospheric regime^e
SDO	HMI	6173	Magnetogram^b	–	Photosphere
	AIA	1600	Continuum^c	<3.6	Upper photosphere / T-min^f
		2796.9	Mg II k1r	3.6	T-min / lower chromosphere
		2796.6	Mg II k2r	3.8	Middle chromosphere
IRIS		2796.4	Mg II k3	3.9	Upper chromosphere
		1335.7	C II	4.6	Low transition region
		1393.8	Si IV	4.9	Transition region

Notes.

^(a)

The AIA 1600 Å images are acquired in a roughly 50 Å wide wavelength band. For lines observed with IRIS the wavelength of the respective features of the Mg II k line or the rest wavelength of C II and Si IV are given (see Sect. 2.2.1).

^(b)

In active regions HMI can also provide the full vector of the magnetic field. We use the line-of-sight component of the magnetic field from HMI.

^(c)

This 1600 Å band contains also the C IV doublet at 1548 Å and 1550 Å. Except for small patches of strongly enhanced emission around 10⁵ K this band does not show transition region structures on the disc (e.g. compare panels b and d in Fig. 2).

^(d)

The formation temperatures for the 1600 Å continuum and the Mg II k line features are taken from (Vernazza et al. 1981), the values for C II and Si IV are taken from (Peter 2006).

^(e)

This ordering should be a guideline only, in particular when considering the dynamic nature of the solar upper atmosphere.

^(f)

T-min denotes the temperature minimum.

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