Airborne measurements of cloud condensation nuclei (CCN) vertical structures over Southern China

Abstract

In this study, the vertical structures of cloud condensation nuclei (CCN) over southern China are investigated with two flight datasets during the period of 16–17 July 2019. The results show that the CCN number concentration (NCCN) increases first with the increasing height, peaking near 1.3 km above the ground, and then decreases sharply to a low value above 2.5 km. Good agreement is obtained by employing a segmentation fitting approach to describe the vertical CCN structure. More specifically a simple linear function is used to fit the NCCN below 1.3 km; a polynomial function is utilized to describe the measurements between 1.3 km and 2.5 km, and, a constant value of 7 cm−3 is assigned above 2.5 km. The CCN particle size distribution (CPSD) presents a unimodal mode with the peak that changes to the direction of larger diameter with growing water vapor supersaturation (SS). As for the effects of SS, NCCN, as well as the diameter of CCN increases with the increasing SS. The CCN spectrum is well represented by the classical Twomey power-law function of NCCN(SS) = C·SSk. Although the values of parameter C are 72 cm−3 and 150 cm−3 in the two measurements, respectively, the paramer k changes a little with its values being 1.5 or so. The results gained herein might be helpful for cloud microphysical parameterization in numerical models and provide a guide for weather modification.