Abstract
Abstract. During the CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados) campaign, the interaction between aerosol particles and cloud microphysical properties was investigated in detail, which also includes the influence of clouds on the aerosol formation. During two intensive campaigns in 2010 and 2011, helicopter-borne measurement flights were performed to investigate the thermodynamic, turbulent, microphysical, and radiative properties of trade-wind cumuli over Barbados. During these flights, 91 cases with increased aerosol particle number concentrations near clouds were detected. The majority of these cases are also correlated with enhanced irradiance in the ultraviolet (UV) spectral wavelength range. This enhancement reaches values up to a factor of 3.3 greater compared to background values. Thus, cloud boundaries provide a perfect environment for the production of precursor gases for new particle formation. Another feature of cloud edges is an increased turbulence, which may also enhance nucleation and particle growth. The observed events have a mean length of 100 m, corresponding to a lifetime of less than 300 s. This implies that particles with diameters of at least 7 nm grew several nanometers per minute, which corresponds to the upper end of values in the literature (Kulmala et al., 2004). Such high values cannot be explained by sulfuric acid alone; thus extremely low volatility organic compounds (ELVOCs) are probably involved here.
Highlights
The influence of the number concentration of available cloud condensation nuclei (CCN) on the number concentration of cloud droplets was shown for the first time in Warner and Twomey (1967)
The Fast CPC (FCPC) has its own inlet on Airborne Cloud Turbulence Observation System (ACTOS), which is operated with a higher flow to minimize the residence time between inlet and FCPC
91 events were detected in the cloud layer during measurements flights with valid FCPC data
Summary
The influence of the number concentration of available cloud condensation nuclei (CCN) on the number concentration of cloud droplets was shown for the first time in Warner and Twomey (1967). This study presents results from the CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados) campaign using two helicopter-borne measurement platforms that simultaneously sampled basic meteorological parameters, in situ cloud microphysical and aerosol variables, and cloud-reflected spectral radiation The advantage of these helicopter-borne measurements is the low true air speed of 20 m s−1 combined with a high temporal resolution. Besides providing an investigation in a new geographic environment, these measurements were made with very high spatial resolution (approximately 20 m) and with a lower size limit of 6 nm for aerosol detection This allows for investigation of statistical properties of the NPF events and their correlation with meteorological, microphysical, and radiation variables. An introduction to the CARRIBA project and the scientific goal are given in Siebert et al (2013)
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