[asac][almanews] ALMA Memo 497 Released

[Stacy Oliver]

ALMA MEMO #497 

ANALYSIS OF WIND DATA GATHERED AT CHAJNANTOR 

Juan Pablo Pérez Beaupuits (ESO), Angel Otárola (ESO), 
Fredrik T. Rantakyrö (ESO),Roberto C. Rivera (ESO)
Simon J. E. Radford (NRAO), Lars-Åke Nyman (ESO) 

2004-05-07 

Keywords: Wind Spectrum – Wind Turbulence – Comparison Test – Site
Testing 

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 daytime and nighttime periods. 

View a pdf version of ALMA Memo #497. 
http://www.alma.nrao.edu/memos/html-memos/alma497/memo497.pdf

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