Środowiskowe Seminarium Fizyki Atmosfery

Clear experimental evidence of the Twomey effect for shallow trade wind cumuli near Barbados is presented. Effective droplet radius and cloud optical thickness, retrieved from helicopter–borne spectral cloud–reflected radiance measurements, and spectral cloud reflectivity are correlated with collocated in situ observations of the number concentration of aerosol particles from the sub–cloud layer. In situ cloud microphysical and aerosol parameters were sampled by the Airborne Cloud Turbulence Observation System (ACTOS). Spectral cloud–reflected radiance data were collected by the Spectral Modular Airborne Radiation measurements sysTem (SMART-HELIOS). With increasing aerosol number concentration a shift in the probability density functions of optical thickness and reflectivity towards larger values is observed, while the mean values and observed ranges of retrieved effective radius decrease. Relative susceptibilities (RS) are derived for bins of constant liquid water path. Comparisons of RS derived from in situ measurements and from a microphysical parcel model are in close agreement.