Undergraduate Student-Researcher: Robert Carver
Increasing atmospheric burdens of the trace gases
CH4, N2O, and chlorofluorocarbons
can have a significant impact on the infrared radiation budget
and photochemistry of the atmosphere.
One element of this project involves
application of UARS measurements of these
gases to accurately evaluate
the infrared radiative forcing at the tropopause level and
heating rates in the stratosphere. Variations
in the radiative forcing with respect to latitude and
season, both related to changes in the trace gas distributions
in the lower stratosphere and to variations in temperature
and tropospheric cloud fraction, thickness, and height,
are being studied using longwave radiation code initialized
with complementary satellite climatologies
(for example, cloud properties from the International
Satellite Cloud Climatology Project).
The second part of the project
involves UARS distributions of N2O, CFC11 and CFC12
to determine global destruction rates and
instantaneous lifetimes based on rates of stratospheric photolysis.
These calculations incorporate
solar irradiances measured by UARS instruments and include
a line-by-line representation of
opacity in the oxygen Schumann-Runge (S-R) system, as well
as a precise treatment of UV scattering in the
region of S-R/Herzberg overlap near 200 nm.
The new evaluations of radiative forcing and lifetimes
will allow for improved estimates for the Global
Warming Potentials (GWPs) of these gases. The
lifetime for CFC11 has further implications
for the Ozone Depletion Potential (ODP) of replacement
chemicals for the CFCs.
The figure shown below displays the June-July average distribution
of CF2Cl2 (CFC-12)
computed from daily vertical profiles obtained by the
Cryogen Limb Array Etalon Spectrometer (CLAES).
The dashed white line is the climatological tropopause;
the dashed black line corresponds to the lower boundary of
the CLAES observations. The tropospheric distribution is
set by surface measurements, and the region between the dashed
curves is set by cubic spline interpolation.
The next figure shows the calculated distribution of radiative
forcing by CFC-12 on the basis of the observed seasonal and latitudinal
distribution (as shown above for June-July). The highest values occur
in the summertime subtropical regions, primarily as a result of i) the
vertical distribution of CF2Cl2, ii) the high, cold tropopause, and
iii) the low fraction of high cloud.
These results are still preliminary, but clearly demonstrate the
utility of the UARS data to compute global fields of relevance to
global change issues.
This information is being made available by
at New Mexico Institute of Mining and Technology's