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C.E. Newman, M.I. Richardson (California Institute of Technology), A.D. Toigo (Kobe University)
Some big questions relating to Titan's atmosphere are: How much equatorial superrotation occurs? What determines the way in which albedo patterns change over time at different wavelengths? and What determines the size, frequency and location of the recently observed southern hemisphere clouds?
To investigate such questions properly requires a three-dimensional model of Titan's thick atmosphere, which can examine different scenarios in multi-year simulations. Such simulations are computationally demanding due to Titan's long radiative and seasonal timescales, as well as its slow rotation rate, all of which mean a long time is required to spin up then conduct each run. This demands the use of an efficient, accurate, and mass- and momentum-conserving model.
One such model is the newly developed Planetary Weather Research and Forecasting model (PWRF), which is based on a pre-existing terrestrial mesoscale model (WRF). WRF is a highly parallelized and numerically efficient model, which is also able to place high resolution 'nests' (with information passing both inwards and outwards) over selected regions where resolving small-scale features is most necessary. This is very useful, as increasing the resolution everywhere would slow the model considerably. PWRF retains these features, but extends to using a global mother domain (no separate global model required), and has also been adapted to include a planetary timing system (using areocentric longitude) and other planetary options (such as radiation schemes).
We will present results from the Titan version of PWRF to demonstrate how well the model reproduces key aspects of Titan's circulation (e.g. superrotation, temperature structure). We will describe our plans to include aerosol transport, and our eventual aim to model the recently observed (telescopically from Earth, e.g. Griffith et al. Nature 1998, Brown et al. Nature 2002, and from Cassini, e.g. Porco et al. Nature 2005) methane clouds.
This work is funded by NASA.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.