HR: 1330h
AN: A12A-0073    [PDF]
TI: Deuterated Methane and Ethane in the Atmosphere of Jupiter
AU: * Parkinson, C D
EM: chris.parkinson@jpl.nasa.gov
AF: Caltech, MS150-21 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: * Parkinson, C D
EM: chris.parkinson@jpl.nasa.gov
AF: JPL, MS183-501 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Yung, Y L
AF: Caltech, MS150-21 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Lee, A Y
AF: Caltech, MS150-21 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Crisp, D
AF: JPL, MS183-501 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AB: CH$_3$D and C$_2$H$_5$D are isotopic tracers in the deep Jovian atmosphere and susceptible to transport and chemical effects. It is expected that the tropospheric ([D]/[H])$_{CH_4}$ ratios determined from the various observations made should be relatively invariable, yet previous determinations of this quantity for Jupiter have given results inconsistent with experimental error bars. This suggests that there may be a problem with the interpretion of some of the observations, or that the apparent CH$_3$D column abundance is variable. We report on the effects of varying important parameters over this pressure regime on the CH$_3$D and C$_2$H$_5$D mixing ratios, CH$_3$D and C$_2$H$_5$D fractionation, the ([D]/[H])$_{CH_4}$, ([D]/[H])$_{C_2H_6}$ and D/H (= ([D]/[H])$_{H_2}$) ratios and compare with the various CH$_3$D and HD observations. Our results show that since the CH$_3$D and C$_2$H$_5$D mixing ratios are strongly dependent upon $K(z)$ in the region of interest where temporal or latitudinal variations in $K(z)$ could significantly impact the measured ([D]/[H])$_{CH_4}$ ratio. The $K(z)$ adopted represents complex upward convection and downdraft mixing that occurs in the Jovian atmosphere as evidenced by recent observations (Gierasch et al., 2000; Ingersoll et al., 2000; Roos-Serote et al., 2000; Vincent et al., 2000). Using our technique allows for the first time a way to explain the discrepancies in the ([D]/[H])$_{CH_4}$ ratio observations by offering a plausible link between the CH$_3$D and C$_2$H$_5$D observations and upper tropospheric dynamical processes. In any case our calculations show how ([D]/[H])$_{CH_4}$ and ([D]/[H])$_{C_2H_6}$ can be used as a diagnostic tracer to constrain $K(z)$ and to better understand the dynamics of the atmosphere in this pressure regime. Additionally, we have made calculations of the C$_2$H$_5$D in the thermosphere of Jupiter. The principal reactions determining the D abundance appear to be generation by reaction of H with vibrationally hot HD and loss by reaction of D with H$_2$($v$=0,1) and CH$_3$. The H, CH$_3$D and C$_2$H$_5$D distributions have been calculated using the Caltech/JPL KINETICS 1-D photochemistry-diffusion model with the column H constrained using the H lyman-alpha airglow. Reactions involving C$_2$H$_5$D are described by Parkinson (2002). Performing sensitivity studies, we have found an enhancement of greater than two orders of magnitude in C$_2$H$_5$D due to the vibrational chemistry, which is significantly larger than that for CH$_3$D enhancement reported by Parkinson et al (2003). This is of great interest and suggests that C$_2$H$_5$D should be detectable in the lower thermosphere: we propose that observations of this species should be made. Enhancement of deuterated hydrocarbons indicates that there may be exchange of these species between the statosphere and troposphere and further show their usefulness as isotopic tracers in the Jovian atmosphere.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0317 Chemical kinetic and photochemical properties
DE: 0355 Thermosphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting