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| Titel |
The Effect of Surface Ice and Topography on the Atmospheric Circulation and
Distribution of Nitrogen Ice on Pluto. |
| VerfasserIn |
Scot Rafkin, Alejandro Soto, Timothy Michaels |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125236
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| Publikation (Nr.) |
 EGU/EGU2016-4790.pdf |
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| Zusammenfassung |
| A newly developed general circulation model (GCM) for Pluto is used to investigate the
unexpected and highly heterogeneous distribution of nitrogen surface ice imaged by
the New Horizons spacecraft on the surface of Pluto. The GCM is based on the
GFDL Flexible Modeling System (FMS) dynamical core, solved on a discretized
latitude/longitude horizontal grid and a pressure-based hybrid vertical coordinate. Model
physics include a 3-band radiative scheme, molecular thermal conduction within
the atmosphere, subsurface thermal conduction, and a nitrogen volatile cycle. The
radiative-conductive model takes into account the 2.3, 3.3 and 7.8 μm bands of CH4,
including non-local thermodynamic equilibrium effects. The subsurface conduction model
assumes a water ice regolith. In the case of nitrogen surface ice deposition, additional
super-surface layers are added above the water ice regolith to properly account for
conductive energy flow through the nitrogen ice. The nitrogen volatile cycle is
based on a vapor pressure equilibrium assumption between the atmosphere and
surface.
Prior to the arrival of the New Horizons spacecraft, the expectation was that the volatile
surface ice distribution on the surface of Pluto would be strongly controlled by the
latitudinal temperature gradient resulting primarily from the slow seasonal variations of
radiative-conductive equilibrium. If this were the case, then Pluto would have broad
latitudinal bands of both ice covered surface and ice free surface, as dictated by the season.
Furthermore, the circulation, and thus the transport of volatiles, was thought to be driven
almost exclusively by sublimation and deposition flows (so-called “condensation flows”)
associated with the volatile cycle. In contrast to expectations, images from New Horizon
showed an extremely complex, heterogeneous distribution of surface ices draped over
topography of substantial geologic diversity. To maintain such an ice distribution, the
atmospheric circulation and volatile transport must be more complex than previously
envisioned. Topography, the distribution of nitrogen ice itself, and an overall large-scale
atmospheric circulation at least partially independent of the condensation flows must play a
role.
Simulations where topography, surface ice distributions, and volatile cycle physics are
added individually and in various combinations are used to individually quantify the
importance of the general circulation, topography, surface ice distributions and condensation
flows. It is shown that even regional patches of ice or large craters, much like that of
Tombaugh Regio, can have global impacts on the atmospheric circulation, the volatile cycle,
and hence, the distribution of surface ices. This work demonstrates that explaining Pluto’s
volatile cycle and the expression of that cycle in the surface ice distribution requires
consideration of atmospheric processes beyond simple vapor pressure equilibrium arguments. |
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