Model-based climatology of diurnal variability in stratospheric ozone as a data analysis tool
Abstract. Observational studies of stratospheric ozone often
involve data from multiple instruments that measure the ozone at different
times of day. There has been an increased awareness of the potential impact
of the diurnal cycle when interpreting measurements of stratospheric ozone
at altitudes in the mid- to upper stratosphere. To address this issue, we
present a climatological representation of diurnal variations in ozone with
a 30 min temporal resolution as a function of latitude, pressure and
month, based on output from the Goddard Earth Observing System (GEOS)
general circulation model coupled to the NASA Global Modeling Initiative
(GMI) chemistry package (known as the GEOS-GMI chemistry model). This
climatology can be applied to a wide range of ozone data analyses, including
data intercomparisons, data merging and the analysis of data from a single
platform in a non-sun-synchronous orbit. We evaluate the diurnal climatology
by comparing mean differences between ozone measurements made at different
local solar times to the differences predicted by the diurnal model. The
ozone diurnal cycle is a complicated function of latitude, pressure and
season, with variations of less than 5 % in the tropics and subtropics,
increasing to more than 15 % near the polar day terminator in the upper
stratosphere. These results compare well with previous modeling simulations
and are supported by similar size variations in satellite observations. We
present several example applications of the climatology in currently
relevant data studies. We also compare this diurnal climatology to the
diurnal signal from a previous iteration of the free-running GEOS Chemistry
Climate Model (GEOSCCM) and to the ensemble runs of GEOS-GMI to test the
sensitivity of the model diurnal cycle to changes in model formulation and
simulated time period.