Saturn's temperature profiles at high,
medium and low latitudes derived from
UVIS EUV solar occultations - updates
Jacques Gustin
LPAP ULg
UVIS team meeting – St George – June 04-06 2013
Observations
Date
Lat. range in -500,4500 km MRH (°)
Lat. @ T=0.5
2008_02_20
-76, -70
-72
2008_01_27
-76, -70
-71
2007_05_10
65, 69
67
2007_09_30
-55, -44
-51
2007_11_17_06
-52, -45
-49
2007_11_17_04
-47, -40
-45
2008_03_02
-51, -30
-37
2010_04_06
32, 35
34
2008_05_25
-42, -28
-33
2010_05_17
28, 32
31
2010_03_20
28, 31
30
2010_02_13
24, 26
25
2010_03_02
18, 20
19
2010_09_22
14, 25
15
14 occs from 2007 to 2010, 7 North, 7 South, 3 high lat., 9 medium lat, 2 low lat.
UVIS team meeting – St George – June 04-06 2013
Principle:
- Solar occs with Cassini/UVIS EUV channel:which absorbing species?
- Absorption dominated by H2 in <1120 Å, HC >1120 Å
Transmission in 1046-1113 Å dominated by H2 bands absorption 
H2 structure and T profile
UVIS team meeting – St George – June 04-06 2013
Transmission in 1046-1113 Å
North: 6 low-med, 1 high lat.
UVIS team meeting – St George – June 04-06 2013
South: 5 low-med, 2 high lat.
UVIS team meeting – St George – June 04-06 2013
All:
UVIS team meeting – St George – June 04-06 2013
Model:
- synthetic T profile (300  5000 km):
T(z)  T0 
T  T0
1  e  ( z  z m )
- 0  130 km: Cassini/CIRS T profile (Fletcher et al. 2010)
T

Zm
T0
CIRS

(s)  absorbed
profile  each MRH
spectrum  synthetic transmission  parameters vary until min 2
- First T profile  H2 density
UVIS team meeting – St George – June 04-06 2013
Problem: merging between synth. & CIRS profiles
"Gap” between synth. & CIRS profiles:
TCIRS (300)
T0
2 solutions:
1. Impose T0 to CIRS(300 km): MODEL 1
2. Allow a slant between synth. & CIRS: i) remove values<700 km from synth. profile, i
ii) take the CIRS profile till 300 km, join the 2 profile with a line, iiii) smooth the new profile:
MODEL 2
MODEL 3:
Some cases (N): bad fit at the start of transmission: too much absorption -> too much H2 molecules
-> density constrained by CIRS profile (low alt) -> cannot be controlled by the synthetic T profile.
Solution: shift the whole transmission in MRH
Justifications: 1. MRH calculated assuming Saturn 1 bar = oblate spheroid. In reality: zonal winds
affect this level.
2. Pointing uncertainty: ~ 1 mr; LOS distance from 195000 to 500000 km 
195 to 500 km uncertainty…
 Model3: model 2 + new parameter: shift of transmission (includes 1 & 2)
Fit results:
One or more between M1, M2, M3 lead to good fit AND realistic T profile
model 1
model 2
model 3
M1: average fit, M2: good fit but strange T profile, M3: FIT + T profile OK
 M3
model 1
model 2
model 3
M1, M2 , M3 FIT + T profile OK
 M1, M2, M3
Results: best T profile vs altitude from best model (M1 or M2 or M3)
ACS
(800-1200km,
Gerard 2009)
FUSE
(400–500K,
Gustin 2009)
VIMS
(450K,
Melin 2011)
UKIRT
(380-420K,
Melin 2007)
VIMS
(560-625K 30,
Stallard, 2012
UVIS team meeting – St George – June 04-06 2013
T vs Pressure (M1 or M2 or M3)
FUSE
(400K P<0.2b
500K P=0.1 b
Gustin 2009)
UVIS team meeting – St George – June 04-06 2013
Parameters overview: all satisfactory model (M1 and/or M2 and or M3)
model 1
model 2
model 3
model 1
model 2
model 3
model 1
model 2
model 3
UVIS team meeting – St George – June 04-06 2013
Conclusions:
- Transmissions significantly  (N-S, lat)  real parameters variab.
- Exo T . higher than previous values
. Increase with latitude – linear relationship
- Alt. Grad. lower for high lats  homopause lower near poles
- Aurora: . P-T: new high lat T profiles meet the obs. constraints
. Problem: alt-T: observed T suggest lower alt. (~700 km)
than observations (~1000 km), or observed aur. altitude
suggest T equal or higher than what is observed.
Next:
-3 occs need more work, then publication
-3 new high lat. obtained recently: more work to do…
-
T profiles  derive HC profiles  apply to auroral spectra 
derive altitude & Ee
UVIS team meeting – St George – June 04-06 2013