A thorough understanding of the radiation budget of water vapor
and cirrus clouds in the upper troposphere (UT) is crucial
for climate research. Such understanding requires the spatial
distribution of these constituents to be much better known than
is currently the case.
In fact, the uncertainties in the upper tropospheric humidity
(UTH) currently dominate the overall uncertainty of climate
models. The impact of cirrus clouds on the UTH channels in the
millimeter wave range (the subset of the instrument called
AMSU-B) is not accounted for, although aircraft data clearly show
that this impact is not negligible.
The Advanced TIROS Operational Vertical Sounder (ATOVS)instrument
has an excellent potential to measure UTH and also to a certain
degree cirrus cloud parameters. However, to make full use of the
data, considerable work has to be done and retrival algorithms
have to be developed.
Therefore, the aim of this PhD thesis is to model the radiative
effects of cirrus clouds and to develop a "cloud aware" retrival
scheme for UTH from the AMSU-B data. This scheme will also, to
some extent, yield information about the clouds themselves.
On one hand, the cloud aware UTH retrival scheme is a
requirement in order to derive the interesting climatological UTH
data; on the other hand, it is in itself of great value to the
Numerical Weather Prediction (NWP) community.
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It is planned to acheive the objective of this PhD thesis by
making use of the global data set that is provided by operational
meteorological sensors.
Planned approach to the solving of the problem is:
-Getting acquainted with the physics of radiative transfer and
with models used in operational satellite data analysis:
1.RTTOV-5 [Saunders et al., 1999]
2.EUMETSAT ATOVS and AVHRR Processing Package (AAPP)
3.The 1 Dvar retrireview scheme (included in AAPP)
- Learning to use the standard ATOVS data analysis tools.
- Preparing a scenario for the cirrus cloud impact study. This
will contain a range of typical cirrus cloud cases for a range of
latitudes and seasons (tropical to polar winter).
- Develop a fast model based on RTTOV-5 that includes a cirrus
cloud parameterization (RTTOV-5-S).
- Cirrus cloud impact study, using the cloud scenario and
RTTOV-5-S. Make an outline for a cirrus cloud correction scheme
in a 1 Dvar retrival.
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