Classification of tropospheric ozone profiles over Johannesburg based on mozaic aircraft data

[摘要] Each ozone profile is a unique response to the photochemical and dynamic processesoperating in the troposphere and hence is critical to our understanding of processesand their relative contributions to the tropospheric ozone budget. Traditionally, meanprofiles, together with some measure of variability, averaged by season or year at aparticular location have been presented as a climatology. However, the mean profile isdifficult to interpret because of the counteracting influences present in the micro-structure.On the other hand, case study analysis, whilst revealing, only applies to isolated conditions. In a search for pattern and order within ozone profiles, aclassification based on a cluster analysis technique has been applied in this study.Ozone profiles are grouped according to the magnitude and altitude of ozoneconcentration.This technique has been tested with 56 ozone profiles at Johannesburg,South Africa, recorded by aircraft as part of the MOZAIC (Measurement of Ozoneand Water Vapor aboard Airbus In-service Aircraft) program. Six distinct groups ofozone profiles have been identified and their characteristics described. The widelyrecognized spring maximum in tropospheric ozone is identified through the classification, but a new summertime mid-tropospheric enhancement due to thepenetration of tropical air masses from continental regions in central Africa has beenidentified. Back trajectory modeling is used to provide evidence of the differentorigins of ozone enhancements in each of the classes. Continental areas over centralAfrica are shown to be responsible for the low to mid-tropospheric enhancement inspring and the mid-tropospheric peak in summer, whereas the winter low-troposphericenhancement is attributed to local sources.The dominance of westerly winds throughthe troposphere associated with the passage of a mid-latitude cyclone gives rise toreduced ozone values.

[学科分类] 大气科学