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Planetary Atmospheric Data Assimilation System
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| We propose to develop a planetary atmospheric data assimilation system for the global extrapolation of spacecraft remote sensing
datasets. Planetary atmospheric datasets amenable to assimilation now include a multi-year dataset for Mars, and potentially mapping
data from Jupiter and Venus. Data assimilation improves the utility and interpretability of spacecraft data by essentially performing a
"four-dimensional retrieval": The physics inherently contained in a numerical model of an atmosphere allows an assimilation system
to globally extrapolate a sparse observational dataset and to convert observed fields (radiances) into physically consistent
meteorological fields (e.g., winds and temperature). However, it should be emphasized that the information content of the data is not
increased by data assimilation - the procedure simply maximizes the interpretability and information extraction from the data. As a
technique, data assimilation has been used for study of the terrestrial atmosphere for many years. The challenges for planetary
application of data assimilation include the very sparse observation patterns (compared to those of the Earth's atmosphere) and the
lack of an extensive, empirical climatological database with which to guide the relationship between the observed fields and model
variables. Consequently, "off the shelf" assimilation schemes cannot be directly employed in the planetary arena. Hence, we propose to
implement and test an ensemble-based scheme, which has the advantage of requiring minimal empirical knowledge of the target
atmosphere and better exploiting sparse observational sampling. Such techniques have shown great promise in terrestrial data
assimilation (though not widely or regularly employed operationally). Technical challenges include algorithm refinement and testing,
efficient implementation of the assimilation system, and various improvements in the forward numerical model. This forward model
will be the planetary version of the NCAR Weather Research and Forecasting model, previously developed with AISR funds. This
project will be a collaborative effort between Caltech and NCAR. |
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