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$\begin{figure} \par\includegraphics[width=8cm,clip]{0477fig1.eps} \end{figure}$ Figure 1: Profile of Na D₂ extracted 214 km above Mercury's limb in the northern polar region. Black: original local profile, green: Doppler compensated reference profile, red: local profile, multiplied by a factor f (see Eq. (2)) to match the wing intensities of the reference. Thered and green profile have been cleaned as described in the text. The vertical red line marks the predicted location ofthe line center of the Mercury absorption feature, the vertical green line is the predicted location of the line center of the solar line. The green dashed line indicates the Doppler shift $\delta \lambda$ between local and reference profile. The excess absorption due to Mercury's exosphere is the difference between the green and red profile around the expected central wavelength and is emphasized by the brown area. The red area in the red line wing is the "core-width correction'' (see text). The vertical dashed brown and red lines mark the integration boundaries used to retrieve the equivalent width of the absorption excess and the core-width correction.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{0477fig2.eps} \end{figure}$ Figure 2: Difference between the local and reference profile shown in Fig. 1. The counts have been normalized by the counts of the reference. Positive values indicate excess of absorption. The brown area is proportional to the uncorrected equivalent width W $_\lambda$ of the absorption excess. The red area will be subtracted from W $_\lambda$ to correct for spatial variability of the width of the solar line ("core-width correction'', see text). Around the center of the solar line, the values are very noisy due to the low intensity level (dashed part of the difference profile).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{0477fig3.eps} \end{figure}$ Figure 3: Same as Fig. 2, difference-profile averaged in radial direction over 214 km (0.5'') and median averaged over the 22 selected scans.
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In the text

$\begin{figure} \par\includegraphics[width=13.7cm,clip]{0477fig4.eps} \end{figure}$ Figure 4: Distribution of observed equivalent widths $W_\lambda$ above Mercury's limb. $\Delta {r}$ is the distance from the planetary limb. Inside the disk ( $\Delta {r} < 0$ ), the equivalent widths are multiplied with the relative intensity distribution of the scattered light.
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In the text

$\begin{figure} \par\includegraphics[width=14.8cm,clip]{0477fig5.eps} \end{figure}$ Figure 5: Height dependence of equivalent widths. The black, marked curves are values observed above the northern pole. The non-vanishing values for $\varphi = -31.5^\circ$ and $\Delta {r} > 700$ km can be ascribed to the "streamer'' feature. The unmarked curves have been calculated, as described in the text. The used combinations of scale height H and particle density $n_0(\Delta {r}=0)$ are given in the legend, together with the resulting column densities $n_{{\rm col}}$ and line center optical depths along the grazing line-of-sight, $\Delta \tau _0(\Delta {r}=0)$ . The red curve is the best fit for $\varphi = -16.6^\circ$ , see also Table 2.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{0477fig3.eps} \end{figure}$	Figure 3: Same as Fig. 2, difference-profile averaged in radial direction over 214 km (0.5'') and median averaged over the 22 selected scans.
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$\begin{figure} \par\includegraphics[width=13.7cm,clip]{0477fig4.eps} \end{figure}$	Figure 4: Distribution of observed equivalent widths $W_\lambda$ above Mercury's limb. $\Delta {r}$ is the distance from the planetary limb. Inside the disk ( $\Delta {r} < 0$ ), the equivalent widths are multiplied with the relative intensity distribution of the scattered light.
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