Validation of very high cloud droplet number concentrations in air masses transported thousands of kilometres over the ocean

TY - JOUR

T1 - Validation of very high cloud droplet number concentrations in air masses transported thousands of kilometres over the ocean

AU - Martinsson, Bengt G.

AU - Frank, Göran

AU - Cederfelt, Sven Inge

AU - Berg, Olle H.

AU - Mentes, Besim

AU - Papaspiropoulos, Giorgos

AU - Swietlicki, Erik

AU - Zhou, Jingchuan

AU - Flynn, Michael

AU - Bower, Keith N.

AU - Choularton, Tom W.

AU - Mäkelä, Jyrki

AU - Virkkula, Aki

AU - Van Dingenen, Rita

PY - 2000/1/1

Y1 - 2000/1/1

N2 - The microstructure of orographic clouds related to the aerosol present was studied during the second Aerosol Characterisation Experiment (ACE-2). Very high cloud droplet number concentrations (almost 3000 cm -3 ) were observed. These high concentrations occurred when clouds formed on a hill slope at Tenerife in polluted air masses originating in Europe that had transported the order of 1000 km over the Atlantic Ocean. The validity of the measured droplet number concentrations was investigated by comparing with measurements of the aerosol upstream of the cloud and cloud interstitial aerosol. Guided by distributions of the ratios between the measurements, three criteria of typically 30% in maximum deviation were applied to the measurements to test their validity. Agreement was found for 88% of the cases. The validated data set spans droplet number concentrations of 150-3000 cm -3 . The updraught velocity during the cloud formation was estimated to 2.2 m s -1 by model calculations, which is typical of cumuliform clouds. The results of the present study are discussed in relation to cloud droplet number concentrations previously reported in the literature. The importance of promoting the mechanistic understanding of the aerosol/cloud interaction and the use of validation procedures of cloud microphysical parameters is stressed in relation to the assessment of the indirect climatic effect of aerosols.

AB - The microstructure of orographic clouds related to the aerosol present was studied during the second Aerosol Characterisation Experiment (ACE-2). Very high cloud droplet number concentrations (almost 3000 cm -3 ) were observed. These high concentrations occurred when clouds formed on a hill slope at Tenerife in polluted air masses originating in Europe that had transported the order of 1000 km over the Atlantic Ocean. The validity of the measured droplet number concentrations was investigated by comparing with measurements of the aerosol upstream of the cloud and cloud interstitial aerosol. Guided by distributions of the ratios between the measurements, three criteria of typically 30% in maximum deviation were applied to the measurements to test their validity. Agreement was found for 88% of the cases. The validated data set spans droplet number concentrations of 150-3000 cm -3 . The updraught velocity during the cloud formation was estimated to 2.2 m s -1 by model calculations, which is typical of cumuliform clouds. The results of the present study are discussed in relation to cloud droplet number concentrations previously reported in the literature. The importance of promoting the mechanistic understanding of the aerosol/cloud interaction and the use of validation procedures of cloud microphysical parameters is stressed in relation to the assessment of the indirect climatic effect of aerosols.

UR - http://www.scopus.com/inward/record.url?scp=18744429641&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:18744429641

VL - 52

SP - 801

EP - 814

JO - Tellus. Series B: Chemical and Physical Meteorology

JF - Tellus. Series B: Chemical and Physical Meteorology

SN - 1600-0889

IS - 2

ER -