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Figure 1: Line radiances of the Mg  X doublet as a function of the radial distance in the equatorial plane (upper pair of graphs). The N  V 123.88 nm height profile near the limb is also shown. The observations have been obtained at two different pointing positions (centre of slit) at   ;   in solar coordinates (: west; : north) with a    slit, and at ; with the    slit. The radiances of the higher range had to be raised by a factor of 1.6 to achieve a smooth transition. A temporal change is the most likely cause of this variation (more than 2 h elapsed between the limb and the coronal observations). Some of the dark pixels of the detector have been shown to demonstrate the signal-to-noise margin. Mg  X radiances are also plotted above a south-polar coronal hole for a pointing positions of and (lower pair). The ratio, L62.50/L60.98, is plotted in the upper section of the diagram and compared with its expected value of 0.5(dashed-dotted line; equatorial ratio: solid line; polar coronal hole: dotted line). The intervals labelled 1 to 5 or A to F define the integration limits used to generate the spectral profiles in Figs. 2 to 4.

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In the text

Figure 2: a) The spectral radiance of the quiet Sun for wavelengths between 60.87 and 61.04 nm. The Mg  X 60.98 nm line in the second order and neighbouring lines are plotted for selected height ranges near the west limb (cf. Fig. 1). The O  V 121.83 nm line and the background are seen in first order, for which the radiance scale is given on the right side. The data points determining the continuum are marked by diamond symbols. The line widths, , obtained by Gaussian fits, refer to the Mg  X-O  III-O  IV blend and the corresponding height ranges. The    slit and the bare detector B were used during the observation. b) The Mg  X 60.98 nm line profiles at greater heights. The observations were performed with the 4 wide slit and the KBr photocathode.

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In the text

Figure 3: a) The spectral radiance near the Mg  X 62.50 nm line for height ranges close to the west limb (cf. Fig. 1). The Mg  X, Si  X and O  IV lines are diffracted in the second order, all the other lines and the continuum are in first order. A few lines blend with the Mg  X line. The values of  are given for the blend. A slit width of 0.3 and the bare portion of detector B were used. b) The Mg  X 62.50 nm and Si  X 62.47 nm lines at greater heights observed with the 4  slit and the bare detector.

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In the text

	Figure 4: The spectral radiance in the Mg  X 60.98 nm window in the second order for selected height ranges above a south-polar coronal hole on 16 May 1997. The display is similar to that of Fig. 2b, but the height ranges D to F are combined to improve the signal-to-noise ratio. A slit width of 1 and the bare section of detector B were used during the observations.
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In the text

Figure 5: Relative line-width variations as a function of radial distance from the Sun. Literature data and results obtained in this work (annotated "SUMER'') are compiled for the Mg  X doublet in equatorial and coronal-hole regions. A classification of the Hassler et al. observations, of which only three typical values are shown, is not defined in the 1990 paper. An approximate scale of 715 km/ has been used for both the SOHO observations and those from the Earth. Integration intervals and the SUMER uncertainty margins are marked by horizontal and vertical bars. Related data points are in some cases connected by lines of various styles. They are meant to improve the orientation of the reader, but not as physical interpolations, in particular, for those points representative of centre-of-disk values displayed here near -80 .

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In the text