Rarity of upper-tropospheric low O3 mixing ratio events during MOZAIC flights

[摘要] Only a few previous observations of very lowO₃ mixing ratios in the upper troposphere are available. The aim of this study was to examine the rich MOZAIC data set for more. Flightswith at least 25 4 s averaged mixing ratios less than 8 ppbv at pressures lower than500 hPa measured using commercial aircraft within the MOZAIC project have been analysed. Thereare eleven flights that fulfil these conditions (excluding artefacts as discussed below),representing about 0.001% of all measurements during the analysed period August1994-December 1997. The low O₃events occurred over Southeast Asia, Africa, Brazil and the sea area 200km east of Florida (US) and were all likely to be associated with transport of airmasses from tropical sea areas. These low mixing ratio events occur in the upper troposphereduring periods with generally low mixing ratios. They are not only found over sea, but alsoover land at pressure levels as low as 179 hPa. It could well be that some of the lowO₃mixing ratio events measured during two or more flights belong to the same bigger lowO₃mixing ratio area.

[学科分类] 大气科学