Download Shemansky-Saturn upper atmosphere structure

Saturn upper atmosphere
structure
D. Shemansky & X. Liu
SET/PSSD
06/26/11
Occultation results
• The fuv spectrum exclusively provides
hydrocarbon vertical structure.
• The euv spectrum exclusively obtains the
properties of H2 and HI. At the altitude of
the hydrocarbon homopause the H2
opacity removes measureable flux from the
stellar or solar source.
cor50_sat_h2vj25_17b_dm_vs_bcru
10 08
6
4
3
2
cor50_sat_h2vj25_17b
Cru_2009_003_265r2 lat -3.6o
10 -18
[H2 X(v)]
6
4
3
2
h = 2097 km
[H2 ] = 3.8 X 10
16
-2
cm
10 -28
6
4
3
2
10 -38
6
4
3
2
10 -48
6
4
3
2
10 -5
0
2
4
6
8
v
10
12
14
Hydrocarbons and H2O
Vertical distribution
Mixing ratios on a pressure scale
Summary
• H2 vertical structure at low latitude in 2009 shows top of
atmosphere temperature of 450 K. H2 X is non LTE with
evidence of non LTE in rotation. Proximal S/C tumble density
altitude has been provided to project. On basis of -3.6o
latitude observation.
• There is disagreement with CIRS hydrocarbon results partly
stemming from their dependence on the Voyager CH4 UVS
profile. Moses theory also uses the Voyager profile. The UVIS
result shows a much more vertically confined CH4 distribution
indicating probable seasonal change in vertical dynamics.
• The UVIS upper limit on H2O falls below Moore etal 2006, and
at the level of the Moses calculachtion which is based on the
Fru chtgruber etal 1997 observation.
H2O issues at Saturn
• The Moore etal calculations assume
precipitating H2O. This results in a constant
vertical mixing ratio. Their nominal rate is
~4.5 X 1027 s-1. The UVIS result limits to ~1026
s-1, within the range of The Fruchtgruber etal
observation.
• Enceladus appears to be an unlikely source at
a level of ~1026 s-1. Moses etal argue for
meteoritic dust.
Ionospheric Reaction Chemistry
• Electron Sink:
H   H 2 X (v  4)  H 2  H
H 2  H 2 X ( v )  H 3  H

3
H  e  H 2 X (v )  H
H 3  e  H  H  H
• Development of Activated H2 X (v):
– Photoelectron excitation, energetic electron excitation,
solar fluorescence, electron recombination with H3+,
three-body recombination, proton charge-exchange
with H2 X
Summary
• H3+ dominant ionospheres predicted for both
forcing conditions
• Energy deposition from Stevens et al. (1993)
predicted for heterogeneous electron forcing,
solar forcing falls short by 3 orders of magnitude
• Observed H2 EUV band emissions predicted with
heterogeneous electron forcing
• Requirement: H* multi-scattering model to predict
excitation of H2 X (v)
• Requirement: H3+ fine-structure to predict Trafton
et al. (1999) emissions