Verlag des Forschungszentrums Jülich
JUEL-4207
Hoffmann, Lars
Schnelle Spurengasretrieval für das Satellitenexperiment Envisat MIPAS
153 S., 2006
Remote sensing measurements are most important to understand the complicated
dynamical and chemical processes occurring in the Earth's atmosphere. Only
the measurements made by space-borne experiments can give a continuous and glo
bal overview of the atmospheric state. Most exact and comprehensive measurements
made by such experiments are necessary to validate and improve atmospheric models
which combine the knowledge on numerous mechanisms in the atmosphere.
Since March 2002 the instrument MIPAS (Michelson Interferometer for Passive
Atmospheric Sounding) is operating aboard Envisat, which is the largest and most
ambitious satellite ever built by the European Space Agency. MIPAS measures the
thermal emissions of atmospheric constituents like trace gases, aerosols and clouds
arising from the atmospheric limb. Within the retrieval process geophysical parameters
like pressure, temperature, and trace gas concentrations are derived from these
measurements. A special feature of MIPAS is its high spectral resolution which allows
to gather information on a large number of atmospheric trace species.
The analysis of remote sensing measurements made by satellite experiments is
an extensive task as time-consuming radiative transfer calculations and substantial
amounts of data are typically involved. Envisat MIPAS provides 300 megabyte of
measurement data during a single orbit. For future experiments, e. g. the GLORIA
instrument (Global Limb Radiance Imager for the Atmosphere) recently proposed
by the research centers Juelich and Karlsruhe, the amount of data may even increase
by several orders of magnitude. A very important component in the analysis of
atmospheric remote sensing measurements is the forward model. It is used to simulate
the measurements of an instrument for a given atmospheric state. The rapid
and flexible forward model JURASSIC (Juelich Rapid Spectral Simulation Code)
was developed as part of this thesis. An innovative retrieval processor was created
based on JURASSIC that allows for the analysis of current satellite measurements,
as e. g. made by Envisat MIPAS, but is also suited to be a basic module in the analysis
of future experiments. The description of structure and possible applications
of JURASSIC and the retrieval system are a principal topic of this thesis.
The JURASSIC retrieval system has been applied to derive the global distribution
of the chlorofluorocarbons CFC-11 and CFC-12 from Envisat MIPAS measurements.
These trace species are not part of the ESA operational retrieval at all.
Scientific retrievals carried out by other working groups cover only rather limited
sets of CFC-11 and CFC-12 data. Here, in contrast, the full measurement period
from July 2002 to March 2004 is analyzed comprehensively. This could only be done,
since the JURASSIC retrieval system allows for a very rapid processing of all these
measurements. The derived CFC-11 and CFC-12 data are compared to external MIPAS
retrievals and successfully validated using independent measurements. Hence,
they are suited for further scientific analysis.
Being long-lived trace species, CFC-11 and CFC-12 are most useful for dynamical
studies in the upper troposphere and lower stratosphere region. Zonal means and
variances of these species have been analyzed. They are mainly influenced by the
residual mean circulation of the stratosphere and the activity of planetary waves.
MIPAS measurements are most useful as they allow to study the seasonal behavior
of these processes. In addition, the derived CFC-11 and CFC-12 distributions are
ideally suited to investigate strongly disturbed dynamical situations. An example is
the antarctic major warming in September 2002, which led to a split of the antarctic
polar vortex. Such an event has never been observed before. CFC-11 and CFC-12
measurements during this period compare well to simulations made by the atmospheric
model CLaMS (Chemical Lagrangian Model of the Stratosphere), which
allows to study the processes occurring in such events in great detail.
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