Long-term measurement of daytime atmospheric mixing layer height over Hong Kong

Abstract

Lidar has unique advantages in temporal and spatial resolution to measure the atmospheric mixing layer height (MLH), which is important for analyzing atmospheric phenomena. However, long-term MLH information over several years, which has important significance in air quality and climate studies, is seldom obtained from lidar data due to the scarcity of long-running lidar observations. In this paper, we retrieve and analyze daytime MLH from a data set of a lidar that operated continuously over 6.5 years at Yuen Long, Hong Kong. A new algorithm has been developed for consistently retrieving MLH from this large data set, handling all possible weather conditions and aerosol layer structures. We analyze the diurnal, seasonal and inter-annual variation of MLH over Hong Kong and find a unique phenomenon that the afternoon MLH is higher in autumn than in summer, which is verified by radiosonde results and explained by thermal stability and humidity effect. Moreover, we find a slightly decreasing trend of the daily maximum of MLH, which implies a continually compressed air volume into which pollutants and their precursors are emitted, which is one of the possible factors leading to deteriorated air quality over Hong Kong region. © 2013. American Geophysical Union. All Rights Reserved.