| Ozone profiles from 10 to 26km have been obtained at almost constant
latitude (20 ± 5° S) in the tropics using SAOZ UV-vis spectrometers
flown onboard long duration balloons in 2001 and 2003. The precision of the
measurements is estimate to be better than 2% in the stratosphere
(3.5% accuracy) and 5-6% in the troposphere (12% and 25%
accuracy at 15km and 10km respectively) with an altitude uncertainty of
-30 ± 25m. The variability of ozone concentration along a latitudinal
circle at 20° S in the SH summer is found smaller than 3-4% above 20km,
but increasing rapidly below in the Tropical Tropopause Layer (TTL). The
high correlation between PV and ozone suggests that most of this variability
can be attributed to quasi-horizontal exchange with the mid-latitude
stratosphere.
The performances of the SHADOZ ozonesonde network, HALOE and SAGE II in the
tropics have been studied by comparison with SAOZ measurements. In the
stratosphere, the main discrepancies arise from differences in altitude
registration, particularly sensitive between 20 and 26km in the tropics
because of the strong gradient of ozone concentration. In the upper
troposphere, the SAOZ measurements are consistent with those of the sondes
and the lidar in cloud free conditions, but biased high by 60% on average
compared to ozonesondes over the Western Pacific, at American Samoa and
Fiji. The likely explanation is the frequent occurrence of near zero ozone
layers in the convective clouds of the South Pacific Convergence Zone which
cannot be seen by SAOZ as well as all ground-based and space borne remote
sensing instruments. Compared to SAOZ, SAGE II displays a 50-60% low bias
similar to that already known with the ozonesondes, and a larger zonal
variability. However, the significant correlation with PV suggests that
useful information on tropospheric ozone could be derived from SAGE II.
Finally, the unrealistic large offsets and variability in the HALOE data
compared to all others, indicates that the measurements of this instrument
are of limited use below 17km. |