Cassini Team Meeting June 2008
INTRODUCTION:
Slide 1-INTRODUCTION
-Present Limb Profiles of 13Dec04 since controversial VI work 25 years ago (SS=1100 km, Hunten 1300km, on c’ bands), which may have been mostly NI lines indicated ME (exobase) originally and later was leaning to solar PEs
-Establish limb profiles of LBH NI and other lines and Rayleigh Scattering
-Model approach includes laboratory data.
Slide 2-GEOMETRY
Trajectory 160,000 to 85,000 km limb to limb over 4 hours
-overhead sun and 90o emission angle
Inbound orbit is one of a dozen or so observations to date Titan B orbit on 13dec2004, second initial orbit . orbit grazes the magnetopause Titan Tb observations take place inside the magnetosphere. We see fully illuminated disk and limb
Slide 3-LIMB SPECTRA AT 9 ALTITUDES
Limb spectra 90o emission and solar incidence angles
Note regions of strong solar reflectance near surface and strong LBH near 1100km
Slide 4-REVIEW OF DISK REGRESSION
Review of FUV results explains modeling technique solar angles are average over disk
the UVIS disk airglow spectrum and regression model fit over the spectral range of 1150-1750 Å is shown in Figure. It is observed that there are about 20 well-defined emission features from the LBH bands of N2 and the atomic multiplets of H, C and N from 1150-1570 Å along with about a half-dozen solar chromospheric lines from 1570-1750 Å
excellent fit verifying spectrally the appearance of tholins
FUV spectra
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-Day or night
-Bright on dayside and dark on nightside-hint of NI 1200.
-Day intensities w/o Rayleigh scattering using my lab spectrum to normalize out the LBH band system-deep in atmosphere=300m
-LBh =44 R PE (optically forbidden) =hi in atmosphere
-NI =30R\
-HI =170 R PDI
In order
-Rayleigh scattering
-LBH PEs
-NI Lines PDI
-H Ly
-two strong vectors LBH and Rayleigh scattering
Solar spectrum is TIMED SEE from 13dec04
Reflectance spectra is now SORCE SOLSTICE TIEM SHIFTED TO -2.3 DAYS=-31 DEG so use dec 11 SORCE spectrum
Slide 5-MIXING RATIOS ARE PARAMAERS IN MODEL COMPARE TO WILSON AND ATREYA AND LIANG
Compare to other results at 300 km Liang et al and Wilson and Atreya
-1723 pixels with average u and u0 of ~45 deg is modeled separately and is average disk spectrum
-Main HCs in stratosphere are c2h2, c2h4(ethylene), c4h2(diacetylene) that absorb 1500-1800
-Need tholin to fit
-first vector
Interaction between solar XUV radiation field shortward of 1500A produces a) ionosphere at 900 km and shortward of 1000A photodissociates N2 and shortward of 1350 photdissociated CH4 to produce radicals like HC polymers while longward of 1400 a not involved in chemistry and penetrates deeper and is Rayleigh scattered at unit optical depth ~1 x 10(24) cm-2 and absorbed by c2h2 and others at ~300 km
-we are probing to 300 km
-reflected lite depends on mixing ratio at 300 km thru the albedo for single scattering
-tried to fit with and without tholins
-Lommel-Seeliger law)
spectral vector is created from best fit of HCs and tholins by modeling long wavelength is second verifications of tholins from a spectrum using Liang et al cross sections fro 125 A particles
-1723 pixels with average u and u0 of ~45 deg is modeled separately and is average disk spectrum
-Main HCs in stratosphere are c2h2 ACETYLENE, c2h4(ethylene), c4h2 (DI-ACETYLENE) that absorb 1500-1800
-Need tholin to fit
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Slide 6 TITAN REFLECTIVITY INTO FUV
-IUE and UVIS decrease due to HC and tholin extinction 3% at 3000A to 1.5% at 1500A
-Function of phase angle –not corrected to zero phase angle?
-C2h2 bands are strongest absorption feature
mcGrath et al. mention bi-modeal distribution
geometric albedo is the most useful way for studying the nature of the haze (McKay et al., 2001). We can show for the first time the FUV geometric albedo of Titan from 1500-1900 Å in Fig. 4. We plot in Fig. 4 the modeled geometric albedo and the UVIS FUV integrated intensity divided by the TIMED SEE solar flux (4I/F) and compare the results to complementary results for the middle ultraviolet (MUV) from International Ultraviolet Explorer (IUE) (McGrath et al., 1998) and for visible near IR (based on spacecraft and ground-based results compiled by McKay et al., 2001). The modeled geometric FUV albedo (inset: Fig. 4) indicates a value of 0.017 at about 1850 Å with a general trend to decline with decreasing wavelength.
Slide7REPEAT OF LIMB SPECTRA
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SLIDE 8-ALTITUDE DISTRIBUTION OF THE 4-MAIN VECTORS/SPECTRAL COMPONENTS
Slide 9 MODEL OF LONG WAVELENGTH FUV REFLECTANCE BY ALTITUDE
"bestfit_titan_limb_200_250.idl" is the result for emission
>from the pixels at rayheight
>from 200 km to 250 km. Each file has:
>- TITAN_FUV_LAMBDA: wavelength
>- TITAN_FUV_KR_A: limb observation
>- SYNTH: best fit
>- RESULT: contains the best values: result(0): N2 mixing ratio, result(1):
>C2H2 mixing ratio,
>result(2): tholin mixing ratio, result(3): C2H4 mixing ratio, result(4):
>C4H2 mixing ratio.
>The S/N ratio is still good for 50km bins, so I guess that's the spatial
>resolution we should use.
-reflected lite depends on mixing ratio at MINIMUM RAY HEIGHT altitude km thru the albedo for single scattering
fit with tholins
-Lommel-Seeliger law)
Second spectral vector is created from best fit of HCs and tholins by modeling long wavelength is second verifications of tholins from a spectrum using Liang et al cross sections fro 125 A particles
16 strongest blended features ID based on lab spectra and FUSE Ajello et al.,
- Feature 6 in detail with red cassini and black 20 ev lab low res and blue 100 eV high res 0.2 A FWHM
Slide 10-LOWER ATMOSPERE 100 KM
STRONGEST IS BUE=RAYLEIGH scattering
Lyman alpha is green
LBH is red
Atomic N is purple
Regression is orange
Deficits are 1561, 1597, 1657, 1722A
Slide 11-MIDDLE ATMOSPERE
STILL STRONG Rayleigh scattering
SLIDE 12-UPPER ATMOSPHERE AT 1100 KM
Long wavelength deficit in LBH bands
MODELS AT 0 and 40% enhancement beyond 1400 A CH4 methane edge
SLIDE 13 LBH BANDS LAB SPECTRUM
HIGH VIBRATIONAL NUMBER OR LONG WAVELENGTHS ARE ENHANCED
LBH first vector
-LBH band system extends from 1250-2600 A
-complicated system (mag dipole+ electric quadrupole uused lab spectra at high resolution to convolve with UVIS 5A FWHM
-strongest 1300-1500A ~ as PE flux ie solar XUV
-source of Space Weather on Nitrogen bearing planets TIMED=10% accuracy based on Q
Slide 14MODEL INCLUDING SCATTERED LIGHT FOV TO 0.6 O
FUV last line-of-sight that sees full column is at 1200 km then we see near field near S2 only for short wavelengths and full column till 1024 for long wavelengths whch reaches iptical depth unity at minimum ray height of 200-300km
Fuv allows lite shortward of 1400A come from slant columns of 4.* 1016 while long wavelengths come from 1024
FOV allow lower atmosphere signal to contribute Rayleigh scattering and LBH from Lower atmosphere
Slide 15MODEL WITH FULL SLANT COLUMN DENSITIES OF STELLAR OCCULTATION FROM TABLE 1 OF LIANG.
UVBL does not see far field S1 only near field S2 to 10-3 level of principal ray
We do not see to 1019 column density of CH4 since optical depth unity occurs at 1016-17 or 1/100 of full slant column
SLIDE 16 SUMMARY OF LIMB PROFILES
Mystery line seems a lower atmosphere phenomena
SLIDE 17 – THE STRENGTH OF Rayleigh scattering at the long FUV wavelengths
SLIDE 18 –LIMB MIXING RATIOS
What do they mean. We are seeing high in the atmosphere on the average above the minimum ray height altitudes
Chapman factor is 20 at 1000 km
SLIDE 19 -summary
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