Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p32c..07n&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P32C-07
Physics
[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [3346] Atmospheric Processes / Planetary Meteorology, [5445] Planetary Sciences: Solid Surface Planets / Meteorology, [6281] Planetary Sciences: Solar System Objects / Titan
Scientific paper
We have developed two 3D Titan general circulation models (GCMs): TitanWRF, based on NCAR's WRF model [Newman et al., 2011], and a Titan version of the MITgcm [Adcroft et al., 2004]. We will present and compare the stratospheric superrotation and tropospheric methane cycle produced using these GCMs, and compare results with observations. Original TitanWRF simulations were unable to produce significant stratospheric superrotation, however we later found that simulations performed without any explicitly imposed sub-grid-scale horizontal diffusion were able to reproduce far greater latitudinal temperature gradients and superrotation (see Figure), similar in many respects to that observed [e.g., Flasar et al., 2005; Achterberg et al., 2011]. Diagnostics show that equatorial superrotation is generated during episodic angular momentum 'transfer events' during model spin-up, and maintained by similar (yet shorter) events once the model has reached steady state. We suggest that these transfer events are produced by barotropic waves, generated at low latitudes then propagating poleward through a critical layer, thus accelerating low latitudes while decelerating the mid-to-high latitude jet in the late fall through early spring hemisphere. We will present these and more recent results from the Titan MITgcm, examining the waves and mechanisms driving superrotation in both models, and discussing the importance of both implicit and explicit horizontal diffusion on model stability and superrotation. We have also used both GCMs to examine Titan's tropospheric methane cycle: parameterizing surface evaporation of methane according to boundary layer humidity, wind speed and atmospheric stability; using a simple parameterization of cloud formation and precipitation; including latent heat effects; and allowing surface regions to be depleted of methane if evaporation exceeds precipitation over time. We will present and compare simulations of cloud locations and timings with those observed, and compare predictions of precipitation and surface methane changes with respectively observations suggesting current/past precipitation and the latitudinal distribution of lakes. Figure Caption: Zonal-mean temperatures in deg K (left) and zonal-mean zonal winds in m/s (right) for Ls =293-323 deg as a function of latitude (deg N) and pressure (mbar) as simulated by TitanWRF.
Lee Chaohong
Lian Yaogang
Newman Claire E.
Richardson Mark I.
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