Description of atmospheric variables measured with a RASS sodar: Cycles and distribution functions

A vertical description of low atmosphere is essential for air pollution analysis, structural design or wind resource assessment. Measurements of horizontal and vertical wind speed and virtual temperature obtained from a Radio Acoustic Sounding System (RASS) sodar below 200 m during 2 years have been considered in this paper with two objectives: the analysis of their yearly and daily cycles and the description of suitable expressions for their distribution functions in the height domain measured. Two prevailing directions have been observed and delimited, East North East (ENE) and West South West (WSW). The first has a yearly evolution and both show a daily cycle in the low atmosphere, where ENE prevails during the night and WSW during the day, resulting in a weak clockwise rotation of median wind vector. Distribution functions for the three variables measured have been proposed using the Chi-square and root mean square errors as goodness of fit estimators. For horizontal wind, the Weibull distribution has been considered during the day and an addition of Weibull and Gaussian distributions during the night. In this period the Weibull distribution has been fitted for the non-prevailing directions. Both functions have been parameterised in height. Two exponential functions have been proposed for vertical wind and triangular functions for virtual temperature.