Ozone-rich transients in the upper equatorial Atlantic troposphere

Evaluation of a photoacoustic detector for water vapor measurements under simulated tropospheric/lower stratospheric conditions

Although water vapor is one of the most important and certainly the most variable minor constituent of the atmosphere, accurate measurements of p(H20) with high time resolution are difficult, particularly in the cold upper troposphere/lower stratosphere. This work demonstrates that a diode laser-based photoacoustic (PA) water vapor detector is a viable alternative to current water vapor sensors for airborne measurements. The PA system was compared with a high-quality frost point hygrometer (FPH) and with a Lyman-alpha hygrometer in the pressure range of 1000-100 hPa at frost point temperatures between 202 and 216 K. These conditions were simulated in a large environmental chamberfor 14 h. Simultaneous measurements with the three instruments agreed within 6%. Nitric acid vapor interferes with the FPH measurements at low frost point temperatures but does not affect the other instruments. The sensitivity of the PA system is already sufficient for measurements in the upper troposphere, and straightforward improvements can extend its useful range above the tropopause. Rugged construction, extreme simplicity, small size, and potential for long-term automatic operation make the PA system potentially suitable for airborne measurements.

Description and evaluation of a tropospheric ozone lidar implemented on an existing lidar in the southern subtropics

Rayleigh-Mie lidar measurements of stratospheric temperature and aerosol profiles have been carried out at Reunion Island (southern tropics) since 1993. Since June 1998, an operational extension of the system is permitting additional measurements of tropospheric ozone to be made by differential absorption lidar. The emission wavelengths (289 and 316 nm) are obtained by stimulated Raman shifting of the fourth harmonic of a Nd:YAG laser in a high-pressure deuterium cell. A mosaic of four parabolic mirrors collects the backscattered signal, and the transmission is processed by the multiple fiber collector method. The altitude range of ozone profiles obtained with this system is 3¿17 km. Technical details of this lidar system working in the southern tropics, comparisons of ozone lidar profiles with radiosondes, and scientific perspectives are presented. The significant lack of tropospheric ozone measurements in the tropical and equatorial regions, the particular scientific interest in these regions, and the altitude range of the ozone measurements to 16¿17 km make this lidar supplement useful and its adaptation technically conceivable at many Rayleigh-Mie lidar stations.