The results presented in this paper have been obtained using a high resolution
orographic model (500 m 500 m) centered on Paranal mountain (70.40 W, 24.61 S). In
Fig. 1
we display the 2D map of the orographic model related to the total available surface domain.
It corresponds to a domain of 60 km
60 km, that is a 120
120 grid point matrix.
Two horizontal dashed lines mark the extension of a second orographic model related to
a reduced portion, still preserving the general geographic structure of
the region: a sea shore
to the west, a sharp mountain chain along the Chilean coast, a broad mountainous region which includes the peak of
Paranal and a few higher mountains to the east of Paranal. It corresponds to a domain of 60 km
20 km sampled
on 120
40 grid points, which was used for all the simulations
presented in this paper.
The model initialization is critical for the numerical technics. After a simulation,
the quality of the output and the input data are strictly correlated. We used, as input data, the ECMWF analysis taken at the (70.31 W, 23.62 S) grid point
and the radiosounding from Antofagasta station (70.43 W, 23.43 S). The analysis are
3D fields at low
spatial resolution
produced by the meteorological centers for forecast needs. A more detailed analysis of the data
that we used will be given in a further article.
The numerical model is initialized with a vertical profile of P, q, T, U, V (pressure, humidity,
temperature and wind) describing the meteorological situation of a
given night, upstream with respect to the wind direction, from the geographical region analyzed. The forecast values
of the hydrodynamic variables of the prognostic equations provided by the model are produced following
a deterministic computation. One can expect that the higher the spatial vertical resolution
of the different parameters (P, T, ) the better the precision and sensitivity of the
simulations will be. In general, the meteorological radiosoundings have a better vertical resolution
than the analysis but they have a poorer temporal sampling (at the best, only two measurements
are available each day). Moreover the station density is not uniformly distributed over the world.
For all simulations presented in this paper, a computational time step s was found to be
necessary to achieve stable simulations (Masciadri et al. 1997).
We analyzed 60
20 km around the Paranal mountain with an
horizontal resolution of 500 m.
We used the following vertical resolution:
50 m for the first vertical mesh
, a vertical stretching of
over the first 3 km
that is
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