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 -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

North: 6 low-med, 1 high lat. 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

First T profile  H2 density profile  each MRH  absorbed Model: - synthetic T profile (300  5000 km): - 0  130 km: Cassini/CIRS T profile (Fletcher et al. 2010) T  Zm T0 CIRS First T profile  H2 density profile  each MRH  absorbed spectrum  synthetic transmission  parameters vary until min 2 UVIS team meeting – St George – June 04-06 2013

2 solutions: 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 3 model 1 model 3 model 2 model 2 M1: average fit, M2: good fit but strange T profile, M3: FIT + T profile OK M1, M2 , M3 FIT + T profile OK  M3  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) Moses: t too low a 0.1 microB  UVIS team meeting – St George – June 04-06 2013

Parameters overview: all satisfactory model (M1 and/or M2 and or M3) UVIS team meeting – St George – June 04-06 2013

- Transmissions significantly  (N-S, lat)  real parameters variab. 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