BASE-LINE ATMOSPHERIC CONDENSATION NUCLEI AT CAPE GRIM 1977-1987

The meaning of 'baseline' as applied to measurements of CN, at atmospheric monitoring sites such as Cape Grim, is discussed and the idea that a 'baseline' exists only in a statistical sense advocated. Use of the concentration frequency-distribution geometric-mean is proposed as the best measure of CN concentrations. Variations in CN concentrations at Cape Grim for periods greater than 12 months are derived by Kalman filtering the monthly estimates of geometric mean concentration obtained from 1977 to 1987. Significant variations are shown to be present on this timescale with quasi-periodic oscillations in concentration. Some association between major fluctuations and El-Nino Southern Oscillation perturbations in the regional circulation is suggested. © 1990 Kluwer Academic Publishers.