Regional and Seasonal Trends in Tropical Ozone from SHADOZ Profiles:
Reference for Models and Satellite Products
Abstract
Understanding lowermost stratosphere (LMS) ozone variability is an
important topic in the trends and climate assessment communities because
of feedbacks among changing temperature, dynamics and ozone. LMS
evaluations are usually based on satellite observations. Free
tropospheric (FT) ozone assessments typically rely on profiles from
commercial aircraft. Ozonesonde measurements constitute an independent
dataset encompassing both LMS and FT. We used Southern Hemisphere
Additional Ozonesondes (SHADOZ) data (5.8°N to 14°S) from 1998-2019 in
the Goddard Multiple Linear Regression model to analyze monthly mean FT
and LMS ozone changes across five well-distributed tropical sites. Our
findings: (1) both FT (5-15 km) and LMS (15-20 km) ozone trends show
marked seasonal variability. (2) All stations exhibit FT ozone increases
in February-May (up to 15%/decade) when the frequency of
convectively-driven waves have changed. (3) After May, monthly ozone
changes are both positive and negative, leading to mean trends of
+(1-4)%/decade, depending on station. (4) LMS ozone losses reach
(4-9)%/decade mid-year, correlating with an increase in TH as derived
from SHADOZ radiosonde data. (5) When the upper FT and LMS are defined
by tropopause-relative coordinates, the LMS ozone trends all become
insignificant. Thus, the 20-year decline in tropical LMS ozone reported
in recent satellite-based studies likely signifies a perturbed
tropopause rather than chemical depletion. The SHADOZ-derived ozone
changes highlight regional and seasonal variability across the tropics
and define a new reference for evaluating changes derived from models
and satellite products over the 1998 to 2019 period.