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2 PARSCA93 campaign

The measurements that are analyzed to test the model simulations are the seeing provided by a DIMM-ESO and the $C_{\rm N}^2 \ $ profiles provided by a Classic Scidar adapted to a telescope with diameter D = 84 cm (Département d'Astrophysique-Nice). From the whole PARSCA93 campaign 13-26 May only 8 nights among 14 have been selected. During the nights of 20, 21, 22 and 24 the Antofagasta station did not provide any radiosounding. The nights of 13 and 26 May have been discarded because they gave rise to numerical instabilities. The nights finally selected were those of the 14, 15, 16, 17, 18, 19, 23 and 25 May 1993.

Table 1: PARSCA93 campaign - Seeing measurements from Scidar and ESO-DIMM. In the second column is reported the seeing measured by Scidar. Each value is averaged on the whole night. In the third and fourth column are reported the Scidar and DIMM seeing measuremnts averaged over the same common time range. In the fifth column is reported the time range. In the last column are reported the differences between the measurements from the two instruments. The absolute mean difference is $\vert \Delta \varepsilon \vert =0.15$ and the standard deviation is $\sigma = 0.10$

{\vert c\vert c\vert c\vert c\vert c\vert c\vert}
 ...2.40-4.78 & -0.14 \\  \hline
26/5 & 0.57 & - & - & - & - \\  \hline\end{tabular}

\psfig {figure=ds7968f1.eps,width=8.8cm,angle=-90}
 \end{figure} Figure 1: PARSCA93 campaign - Scidar and DIMM seeing measurements. Statistical analysis. $\sigma$ = standard deviation, $r_{\rm c}$ = correlation coefficient  

In Table 1, averaged values of the Scidar and DIMM observations are shown for each night of the campaign. During the whole campaign, the DIMM-ESO ran during a shorter time than the Scidar. In order to compare measurements provided by the two instruments, we averaged the Scidar and DIMM measurements (third and fourth column) on the same time range (fifth column). As can be seen, comparing the third and fourth column, there is a good correlation for most of the cases, the mean absolute difference is $\langle\Delta 
\varepsilon\rangle =0.15$ with a standard deviation of $\sigma = 0.10$. The correlation between the Scidar and DIMM measurements ($r_{\rm c} = 0.82$) is shown in Fig. 1. This statistical analysis has to be kept in mind when the model simulations are compared with optical measurements in Sect. 5. During the PARSCA93 campaign the Scidar was installed about 300 m below the Paranal peak while the DIMM-ESO is at the Paranal level. The two instruments pointed at the same stars during the measurements. Knowing that the Scidar is not sensitive to the scintillation in the low atmosphere, this particular disposition of the instruments is necessary for a good correlation between Scidar and DIMM measurements.

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