Vertical and latitudinal distributions of tropospheric ozone over the western Pacific: Case studies from the PACE aircraft missions

• Published in: Journal of Geophysical Research - Atmospheres Vol. 108; no. D8; pp. 4251 - n/a
• Main Authors: Tsutsumi, Yukitomo, Makino, Yukio, Jensen, Jørgen B.
• Format: Journal Article
• Language: English
• Published: American Geophysical Union 27-04-2003; Blackwell Publishing Ltd
• Subjects: aerosol; Asia; Atmospheric Composition and Structure; biomass burning; Information Related to Geographic Region; outflow; stratospheric influence; transportation; Troposphere—composition and chemistry; Troposphere—constituent transport and chemistry; typhoon; Southern Hemisphere; Pacific Ocean; Northern Hemisphere; Australia; IW, Pacific
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2001JD001374

Three Pacific atmospheric chemistry experiments (PACE I, II, and III) were conducted each in January 1994, October 1994, and July 1995. The objective was to investigate the latitudinal distribution, transportation, and possible sources of tropospheric ozone over the western Pacific. Measurements of ozone using UV absorption method were taken by an aircraft flying at a maximum altitude of 6000 m between the Southern Hemisphere (SH) and the Northern Hemisphere (NH) (38°S–38°N) and within the longitudinal range of 120°E–150°E. The PACE aircraft missions first provide the middle troposphere (5000–6000 m) ozone distributions in three different seasons over this region in relatively short periods of time (within 9 days). On the basis of one‐minute average data, ozone mixing ratios in the middle troposphere were significantly higher in the NH midlatitudes (39–92 ppbv) and the SH midlatitudes (30–71 ppbv) than in the tropics (10–35 ppbv) during three different seasons. In particular, an air mass with low ozone mixing ratios (2–28 ppbv) extended from 7°S to 29°N in July during PACE III, in contrast to the air mass with higher ozone mixing ratios (39–57 ppbv) observed in the NH midlatitudes (>21°N) in January during PACE I. Several episodes of increased ozone were observed during the PACE missions. In the SH subtropics (16°S–22°S), photochemical ozone production in a biomass‐burning smoke, probably emitted from the northwest part of Australia, caused relatively high ozone mixing ratios (maximum 89 ppbv) at 5200 m during PACE II. In contrast, ozone transport over a long distance from the upper troposphere south of Africa brought about a maximum ozone mixing ratio of 64 ppbv in the same geographical region above 4500 m during PACE III. Large‐scale circulation coupled with a typhoon was found to impact ozone transport from the NH midlatitudes to the tropics. An air mass with ozone mixing ratios averaging about 50 ppbv at 5200 m, which originated over the Asian continent in the NH midlatitudes, was transported to the tropical western Pacific region (9°N–14°N) by a circulation coupled with a typhoon during PACE II. Summer observations of tropopause folding over the western Pacific are rare, yet high potential vorticity (PV) value (>1 PV unit) above 600 hPa level at 35°N shows that the tropopause folding beneath the subtropical jet occurred in the NH midlatitudes over the western Pacific in summer during PACE III. In this measurement, the increased ozone (maximum 92 ppbv) combined with decreased water vapor mixing ratio (<3.0 g/kg) and large potential temperature gradient (0.083 K/m) was observed above 3800 m. These facts suggest stratospheric influenced air descended to 3800 m. The source region of the high ozone observed over the tropical region (5°S–9°S) during PACE II has not been confirmed, but it is thought to have originated from biomass burning and might be influenced by circulation associated with El Nino.