Abstract
Abstract. The objective of this study is to validate parameterizations that were recently developed for satellite retrievals of cloud condensation nuclei supersaturation spectra, NCCN(S), at cloud base alongside more traditional parameterizations connecting NCCN(S) with cloud base updrafts and drop concentrations. This was based on the HALO aircraft measurements during the ACRIDICON–CHUVA campaign over the Amazon region, which took place in September 2014. The properties of convective clouds were measured with a cloud combination probe (CCP), a cloud and aerosol spectrometer (CAS-DPOL), and a CCN counter onboard the HALO aircraft. An intercomparison of the cloud drop size distributions (DSDs) and the cloud water content (CWC) derived from the different instruments generally shows good agreement within the instrumental uncertainties. To this end, the directly measured cloud drop concentrations (Nd) near cloud base were compared with inferred values based on the measured cloud base updraft velocity (Wb) and NCCN(S) spectra. The measurements of Nd at cloud base were also compared with drop concentrations (Na) derived on the basis of an adiabatic assumption and obtained from the vertical evolution of cloud drop effective radius (re) above cloud base. The measurements of NCCN(S) and Wb reproduced the observed Nd within the measurements uncertainties when the old (1959) Twomey's parameterization was used. The agreement between the measured and calculated Nd was only within a factor of 2 with attempts to use cloud base S, as obtained from the measured Wb, Nd, and NCCN(S). This underscores the yet unresolved challenge of aircraft measurements of S in clouds. Importantly, the vertical evolution of re with height reproduced the observation-based nearly adiabatic cloud base drop concentrations, Na. The combination of these results provides aircraft observational support for the various components of the satellite-retrieved methodology that was recently developed to retrieve NCCN(S) under the base of convective clouds. This parameterization can now be applied with the proper qualifications to cloud simulations and satellite retrievals.
Highlights
An understanding of cloud formation and its influence on the global hydrological cycle and radiation budget is fundamental for improving weather and climate forecasting models (Ten Hoeve et al, 2011; Jiang and Feingold, 2006; Kohler, 1999; Rosenfeld et al, 2008; Stephens, 1984)
For comparisons between the cloud water content (CWC) estimated from the cloud probe drop size distributions (DSDs) and hot-wire measurements (CWCh), we distinguish between spectra that are dominated by condensational growth and spectra for which coalescence becomes important as well
This study is focused on testing parameterizations used for the recently developed methodology for satellite retrievals of Na, Wb∗, and cloud condensation nuclei (CCN) in convective clouds based on aircraft measurements during the ACRIDICON–CHUVA campaign in the Amazon
Summary
An understanding of cloud formation and its influence on the global hydrological cycle and radiation budget is fundamental for improving weather and climate forecasting models (Ten Hoeve et al, 2011; Jiang and Feingold, 2006; Kohler, 1999; Rosenfeld et al, 2008; Stephens, 1984). Data from aircraft probes provide opportunities to validate and improve cloud models and satellite retrievals of cloud microphysical properties. An assessment of the validity of the cloud probe data is essential before the results can be implemented into cloud models. The number concentration of cloud droplets (Nd) expected at cloud base mainly depends on the atmospheric conditions just below cloud base, i.e., updraft wind speed and the supersaturation (S) activation spectra of cloud condensation nuclei [NCCN(S)] (Pinsky et al, 2012; Reutter et al, 2009; Twomey, 1959). From cloud condensation nuclei counter (CCNC) measurements across a range of supersaturations (S), the parameters N0 and k are estimated from Twomey’s formula (Twomey, 1959): NCCN = N0 · Sk,
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
