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Analysis of Wind Data Gathered at Chajnantor
ALMA Memo No. 497, (2004)
Аннотация
A general description and statistics of the wind speeds and directions
registered at the ALMA site during 2001 and 2002 are presented. Measurements
from different wind directions within 22.5º (in azimuth), topographic
sectors and two markedly different daily periods were obtained. Spectra
of the wind turbulence are presented for three wind speed conditions.
During the diurnal period the convective turbulence and mean wind
speed determine the shape and magnitude of the wind spectra, whereas
in the nocturnal period the effects of the mechanical turbulence,
such as the wind shear and surface roughness together with the mean
wind speed, become relevant. No significant differences were found
between the spectra obtained from three topographic sectors in the
diurnal period, whereas in the nocturnal period a statistical test
showed a significant difference for a particular topographic sector
and for a given wind speed range, reflecting changes in the wind
spectrum structure due to the local topography. General models of
average spectra were found for three mean wind speeds, in the diurnal
and nocturnal periods. Relations between the models and the mean
wind speed were found. These relations makes it possible to estimate
the spectral behaviour of the wind at the ALMA site for different
mean wind speeds, which will be useful in the study of the wind loading
on the antenna structure and pointing. Based on the results we can
also conclude that the performance of the ALMA antenna regarding
wind load is expected to be better for both day time and nigh time
periods.
