Atmospheric surface layer in a coastal environment: measurements in a 100 m tower (El Arenosillo)

Abstract

In the southwest of the Iberian Peninsula there is a 100 m high tower, equipped with meteorological instrumentation at the 10, 50 and 100 m levels. The first observations of temperature, relative humidity, wind (direction and speed) and pressure were recorded in 2009. From the original data with a 10-minute resolution, hourly values were calculated applying quality criteria. Using these values, we have obtained various statistical parameters such as percentiles, maxima and minima. The wind regime has also been analyzed. The first 100 m of the atmosphere show an increase in temperature with height, which could be associated with the frequent occurrence of stably stratified conditions. By contrast, the relative humidity has a slight trend to decrease or maintain similar values. As expected, pressure values show a trend to decrease with height. Wind data show flows with similar directions at the three heights and an increase in wind speed. The daily evolution of the atmospheric stratification stability has been estimated using the potential temperature and its difference between levels. As a daily average, in summer the day can be divided into 12 hours of vertical mixing, and thermal inversion for the other 12. In the colder months, 15 hours of stably stratified stability were found. Finally, we have analyzed specific periods, which represent the typical meteorological scenarios of this region, governed by both synoptic and mesoscale processes. In these cases, the stability of atmospheric stratification has been estimated using potential temperature and the Bulk Richardson Number. Under breeze or NE flow conditions, we obtain a daily pattern of atmospheric stratification stability strongly influenced by daytime heating and nighttime cooling, similar to the behavior shown by the planetary boundary layer. However, under SW-W or NW flows, the daily evolution of the potential temperature difference and the Bulk Richardson Number does not present a clear daily cycle, which could be attributed to the influence of the marine boundary layer.