Exploring the relationship between relative humidity and aerosol attenuated backscatter ratio
Geoscience & Remote Sensing
C. Braat (TU Delft - Civil Engineering & Geosciences)
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Abstract
Clouds and aerosols continue to contribute to the largest uncertainty to estimates and interpretations of the Earth's changing energy budget. By comparing relative humidity (RH) and attenuated backscatter ratio (ATB) data and deriving scattering hygroscopic enhancement factors at the Cabauw Experimental Site for Atmospheric Physics Research (CESAR), an attempt is made to better understand the process of aerosol hygroscopic growth. This is done by ground based ceilometer, hygrometer and SMPS technology gathering data during the ACCEPT campaign in 2014, resulting in a high temporal resolution, continuous measurements and the possibility to compare the data with ancillary information measured on the same location. Some aerosol number concentration (ANC) data is also taken into account as indication of the influence of ANC on ATB. For the three studied time intervals with a large variation (>30%) in RH, a convincing relation between RH and ATB is found, which can be linked to the Köhler curve when a direct relation between aerosol size and ATB is assumed. For these three time intervals, scattering hygroscopic enhancement factors are derived with similar γ values as reported in previous studies. Further research is required to analyze the correlation between RH and ATB more and rule out other influences on ATB.