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Precipitable Water Vapor measurements

Millimetric Astronomy from the High Antarctic Plateau: site testing at Dome C

Valenziano L. , Dall'Oglio G., PASA, 16 (2), in press.
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Precipitable Water Vapor measurements

To the best of our knowledge, the first published measurement of the DC PWV content of the atmosphere was performed by the authors in January 1997 (Valenziano et al. 1998). The instrument used was a portable photometer (Volz 1974), with an accuracy of 20 %. The limited sensitivity of the instrument allowed only upper limits to be set in some cases. Data are presented in Figure 8. The average PWV at DC is around 0.6 mm.

Figure 8: Precipitable Water Vapor data measured at DC during January 1997. The continuous line refers to the whole data set (83 measurements), including upper limits. Dashed line histogram is calculated excluding upper limits (50 measurements). Cumulative probabilities are also plotted, with the same line styles.
\begin{figure} \begin{center} \psfig{file=pwv_cumul.plt,angle=90,height=8.5cm} \end{center} \end{figure}

A comparison between DC, SP, Atacama and Mauna Kea sites is reported in Table 1. Data for DC were measured by the authors (in one month), while quartile data for the other site are from Lane (1998). Results for the Vostok station (elevation 3488 m) (Townes & Melnick 1990) in summer do not differ significantly from those reported here, but values of less than 0.1 mm were measured during winter. We have also calculated the 225 GHz and 492 GHz opacities from the 50th percentile PWV data, using a model evaluated from the SP data (Lane 1998). We used the following relations:

$\displaystyle \tau_0 (225 GHz) = 0.030 + 0.069 PWV (mm)$ б  б  (1)
$\displaystyle \tau_0 (492 GHz) = 0.33 + 1.49 PWV (mm)$ б  б  (2)

and we evaluated the corresponding transmissions at the zenith as

$T = \exp^{- \tau_0}$. These values are reported in Table 1, along with available data for other sites (from Lane, 1998).

Table 1: Quartile of PWV, 225 GHz and 492 GHz opacity and transmissions at DC, SP, Mauna Kea and Atacama.
\begin{table} \begin{center} \bigskip\par\begin{tabular*}{\textwidth}{lccccccc} ... ...). $^{2}$PWV values are calculated from 225 GHz opacity (Lane 1998). \end{table}

Next Section: Discussion
Title/Abstract Page: Millimetric Astronomy from the
Previous Section: AWS data analysis
Contents Page: Volume 16, Number 2

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