UC Irvine

The MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-service Aircraft) program (Marenco et al., 1998) has archived in situ measurements of temperature, water vapor, and ozone from August 1994 to December 2003. We analyze the trends, seasonality, and interannual variability of these quantities at aircraft cruise levels (7.7–11.3 km) within the tropics (20°S–20°N). Mean lapse rates for temperature and log(water vapor) are nearly identical in both tropics. The root-mean-square variance in temperature over cruise levels, seasons, and years is small, ≤1°C. The seasonal range in water vapor, a factor of 2.5, is much larger than expected from the seasonal range in temperature (1.7°C) if the two scale with the lapse rate relation or the Clausius-Clapeyron equation. The mean ozone abundance in the region sampled is 45 ppb in the north tropics and 50 ppb in the south tropics. This 112-month period shows a clearly linear increase in ozone over the north tropics with a trend fit of 1.12 ± 0.05 ppb/yr. In the south tropics, which has a large seasonal range of over 25 ppb, the trend is less obvious but still robust, 1.03 ± 0.08 ppb/yr. These trends in the upper troposphere are twice as large as reported for surface ozone over the tropical Atlantic (Lelieveld et al., 2004), but this pattern of ozone increases is consistent with projected increases driven by industrial emissions.