| << | Profiling of Aerosols | >> |
Abstract
We performed measurements of the turbulent vertical aerosol mass flux by use of combined measurements with the Doppler wind lidar and with the aerosol Raman lidar of the IfT at Leipzig, Germany (52°N,12°E) in 2006 and 2007. Both instruments were operated closely together in order to observe the same turbulent air volume within the convective boundary layer (CBL) with an equal temporal resolution of 5 s. The eddy-correlation method was applied with the time series of the profiles of the backscatter coefficient at 532 nm and of the vertical wind. Afterwards, the aerosol optical data were converted to the aerosol mass concentration by use of multiwavelength Raman lidar measurements and the application of our inversion scheme. We found that the derived mass concentrations agree well with ground based in situ measurements.
We present a detailed case study of 26 April 2007. A maximum vertical aerosol mass flux of 2.5±0.9 µg m-3s-1 was found in the entrainment zone during the rapid growth of the CBL. This value compares well with the observed CBL growth rate of 300 m h-1 in the morning. Later during the day and at lower heights we found negative values of the aerosol mass flux of -(1.5±0.5) µg m-3s-1 which were most likely caused by aerosol advection towards the upper heights of the CBL.
At all, we applied this method to 7 days (27 time intervals) of dry CBL developments and normalized the flux profiles by the height of the mixing layer zi and by the average aerosol mass concentrations Md. In this way, upward directed entrainment fluxes of (0.045±0.025)Md were found. Additionally, we found the depth of the entrainment zone, i.e. the part of the CBL with significant vertical transport, on the order of 0.5-0.7zi.