Analysis of four years of ceilometer-derived aerosol backscatter profiles in a coastal site of the western Mediterranean

We present the analysis of four years of measurements by a CL51 ceilometer in Burjassot (39.51 N, 0.42 W), a research station in the western Mediterranean coast. The 1-min resolution profiles of the CL51 are corrected, calibrated, grouped and cloud-screened to create a 1-h resolution database of aerosol backscatter profiles at 910 nm (βa) spanning from July 2013 to August 2017. A total of 21,247 βa profiles are obtained, covering 58% of the considered period. The analysis of the βa profiles as a function of the main aerosol in the atmosphere reveals that dust arrives at Burjassot mainly in the form of elevated layers, with a highest impact between 1 and 4 km. The βa profiles obtained throughout the year show a strong seasonal trend: in summer we obtain, on average, the highest βa coefficients distributed over a stratified profile; on the contrary, in winter the mean βa coefficients have the lowest value and decrease exponentially with height. Our observations indicate that these seasonal changes are related to seasonal changes in the distribution of dust and to the wind direction at surface level. Regarding this last point we observe that conditions favoring aerosol re-circulation and thermal internal boundary layer lead to the highest βa values and to the stratification of the aerosol profile. On the contrary, when these mechanisms are impeded we find lower βa values and no aerosol layering. Finally, we observed that the βa follows a daily cycle that varies depending on the season the wind regime.