Abstract:
In this paper, tropopause characteristics observed from tropical to subtropical Southern Hemisphere stations
using Southern Hemisphere Additional Ozonesonde (SHADOZ) data are presented for the 11-yr
period of 1998–2008. Three different definitions of tropopause—cold-point tropopause (CPT), lapse-rate
tropopause (LRT), and ozone tropopause (OT)—are determined, and their variability for nine different
SHADOZ sites is studied for the purpose of evaluating their usefulness as indicators of possible tropopause
trends. For each station, the OT is uniquely defined by the ozone gradient and is found to be more variable
than either LRT or CPT. The OT roughly coincides with the upper boundary of the region of most active
convective mixing over the western Pacific Ocean and with the lower boundary of the transition region from
the troposphere to the lower stratosphere that is generally referred to as the tropical tropopause layer. The
monthly and year-to-year variations in the tropopause are examined, and the annual cycle in OT, the dominant
signal, is described. The distance of separation of the OT from the CPT or LRT is smaller for the tropics
(stations at 08–158S) than for the subtropics (158–258S). The decadal trend in tropopause heights is measured
using a statistical model that accounts for natural variations expressed in El Nin˜ o–Southern Oscillation, the
quasi-biennial oscillation, and the Indian Ocean dipole. The decadal trend estimation shows no statistically
significant trend for the CPT and LRT in the tropics, in contrast to other studies.Adecrease in altitude for the
OT is significant. In the subtropics, the CPT and LRT decline significantly, by 2240 and 2190 m (10 yr)21,
respectively, but the OT increases.
