Y. L. Yung, X. Zhang, J. M. Ajello, 2009, Atomic Carbon In The Upper Atmosphere Of
Titan, Bull. Am. Astron. Soc., 41, 30.08.
Abstract: The atomic carbon emission CI line at 1657 Å (3PoJ - 3PJ) in the upper
atmosphere of Titan is first identified from the airglow spectra obtained by the Cassini
Ultraviolet Imaging Spectrometer (UVIS). A one-dimensional photochemical model of
Titan is used to study the photochemistry of atomic carbon on Titan. Reaction between
CH and atomic hydrogen is the major source of atomic carbon and reactions with
hydrocarbons (C2H2 and C2H4) are the most important loss processes. Resonance
scattering of sunlight by atomic carbon is the dominant emission mechanism and the
calculated emission intensity shows good agreement with the observations.
M. R. Line, M. C. Liang, Y. L. Yung, G. Tinetti, 2009, CO2 Chemistry in the
Atmosphere of HD189733b, Bull. Am. Astron. Soc., 41, 42.04.
Abstract: Recent infrared spectroscopy of hot exoplanets has opened up the door to their
atmospheric composition. Atmospheric composition is controlled by thermochemical
equilibrium deep in the planetary atmosphere and photochemistry higher up in the
atmosphere at levels above ~2 bars. These two chemistries interact near ~100 bars in
Jupiter-like atmospheres. HD189733b provides an excellent laboratory to study the
consequences of this hot atmospheric chemistry. The recent spectrum of HD189733b
obtained by Swain et al., 2009 shows absorption features of CO2, CO and H2O. These
observations suggest that the observable atmosphere of HD189733b is dominated
primarily by CO2 chemistry. Here we explore thermochemical equilibrium chemistry
using the NASA-Goddard Chemical Equilibrium with Applications (CEA) code and the
CO2 photochemistry with JPL/Caltech KINETICS code and how these chemistries
manifest themselves in the observed spectrum using a radiative transfer code. We will
also explore techniques for retrieving temperatures and mixing ratios from observed
spectra.
M. C. Liang, H. Yeh, Y. Yung, 2009, Isotopic Fractionation Of Trace Molecules In The
Atmosphere Of Titan And Implications For The Evolution Of The Atmosphere, Bull.
Am. Astron. Soc., 41, 33.09.
Abstract: High precision measurements of the isotopic compositions of H, C, N and O in
several molecules in the atmosphere of Titan have recently been obtained by the CassiniHuygens instruments. We developed a one-dimensional photochemistry-transport model
that includes photolytic and chemical processes for methane, ethane, water, nitrogen and
their isotopologues. Transport is parameterized by eddy diffusion. Most of the
observations can be explained by our model. In addition, a hydrodynamic model is
developed for studying the escape that could have occurred in the early history of Titan.
Implications of our current model for the chemical evolution of Titan are discussed.
C. Parkinson, A. Brecht, S. Bougher, F. Mills, Y. Yung, 2009, Night OH In The
Mesosphere Of Venus and Earth: A Comparative Planetology Perspective, Bull. Am.
Astron. Soc., 41, 63.06.
Abstract: Satellite measurements of the terrestrial nightside mesosphere from the
MLS/Aura MLS instrument show a layer of OH near 82 km. This layer confirms earlier
measurements by ground-based UVFTS. The MLS and UVFTS observations measure
OH in the lowest vibrational state and are distinct, but related chemically, from
vibrationally-excited emission from the OH Meinel bands in the near infrared. The
Caltech 1-D KINETICS model has been extended to include vibrational dependence of
OH reactions and shows good agreement with MLS OH data and with observations of the
Meinel bands. The model shows a chemical lifetime of HOx that increases from less than
a day at 80 km to over a month at 87 km. Above this altitude transport processes become
an important part of HOx chemistry. The model predicts that ground state OH represents
99% of the total OH up to 84 km.
Similarly, Venus airglow emissions detected at wave-lengths of 1.40−1.49 and 2.6−3.14
μm in limb obser-vations by the Visible and Infrared Thermal Imaging Spectrometer
(VIRTIS) on the Venus Express space-craft are attributed to the OH (2−0) and (1−0)
Meinel band transitions as well. The integrated emission rates for the OH (2−0) and (1−0)
bands were measured to be 100±40 and 880±90 kR respectively, both peaking at an
altitude of 96±2 km near midnight local time for the considered orbit. We use the same
Caltech 1-D KINETICS model to model these observations for Venus as was used for the
Earth and discuss the conclusions from a comparative planetology perspective,
highlighting the similarities and differences between Venus and Earth.
F. P. Mills, A. G. Munoz, Y. L. Yung, M. Allen, G. Piccioni, P. Drossart, 2009, Oxygen
Chemistry and Airglow in Venus' Atmosphere, Bull. Am. Astron. Soc., 41, 48.02.
Abstract: Airglow in a planetary atmosphere is diagnostic of the combined effects of
transport, both vertical and horizontal, and chemistry. Airglow emission on the night side
in the OH (3-2, 2-1, 2-0, and 1-0), O2(c-X and a-X), and NO(C-A) bands has been
reported in the past two years based on observations by VIRTIS on Venus Express
[1,2,3]. Previous observations had also identified airglow emission in the O2(a-X) band
on the day side [4]. Vertical profiles from limb observations indicate the OH and O2
nightglow emissions are typically most intense at 95-100 km altitude [1,5] while the NO
nightglow emission is most intense at about 110 km altitude [2]. All of these airglow
emissions are directly or indirectly connected to the atomic oxygen abundance at these
altitudes and vertical profiles of the O2 (a-X) nightglow emission as observed by VIRTIS
on Venus Express have been used to infer the atomic oxygen profile [6]. The expected
connections among these day and night side airglow emissions based on photochemical
modelling will be discussed along with their implications for oxygen chemistry in the 90110 km altitude range in Venus' atmosphere. This work was partially supported by the
Australian Research Council.
[1] Piccioni et al, A&A 483, L29, 2008
[2] García Muñoz et al, PNAS 106, 985, 2009
[3] García Muñoz et al, JGR, in revision, 2009
[4] Connes et al, ApJ 233, L29, 1979
[5] Piccioni et al, JGR 114, E00B38, 2009
[6] Gérard et al, GRL 35, L02207, 2008
X. Zhang, R. A. West, G. S. Orton, A. J. Friedson, C. A. Nixon, Y. L. Yung, 2009,
Radiative Modeling of the Stratosphere of Jupiter, Bull. Am. Astron. Soc., 41, 10.12.
Abstract: Based on the recent 2D retrievals for temperature profiles and abundances of
ethane (C2H6) and acetylene (C2H2) in the stratosphere of Jupiter from Cassini
observations, the short wavelength heating and long wavelength cooling rates are
calculated by correlated-k method. The Methane (CH4) k-distribution parameters from
Irwin et al. (Icarus, 176, 255, 2006) and Karkoschka and Tomasko (Icarus, in press,
2009) and H2-H2 continuum absorption coefficients from Borysow et al. (A&A, 390, 779,
2002) are used for the heating rates calculations, covering all the CH4 bands from 0.5 µm
to 5 µm. The heating rates due to stratospheric aerosol layers are also calculated based on
the 2D aerosol distribution from Banfield et al. (Icarus, 134, 11, 1998). In the long
wavelength region from 5 µm to 10 µm, the spectroscopic parameters are computed from
the HITRAN 2008 database (Rothman et al., JQSRT, 110, 533, 2009), hydrogenbroadening coefficients for hydrocarbons (e.g., Varanasi et. al., JQSRT, 47, 263, 1992),
and the recent H2-H2 and H2-He continuum absorption coefficients by Orton et al. (Icarus,
189, 544, 2007). A line-by-line radiative calculation is used to test the accuracy of our
method. The quantitative modeling of the aforementioned species is important for
constraining the 2D transport and chemistry of Jupiter. The major heat sources (short
wavelength CH4 bands and aerosol absorption) and dominant coolants in the long
wavelength spectral region for different pressure levels are studied.
G. S. Orton, L. Fletcher, T. Stallard, K. Baines, K. Sayanagi, D. Huestis, Y. Yung, S.
Edgington, S. Gulkis, J. Moses, F. Martin-Torres, 2009, Saturn Atmospheric Science in
the Next Decade, Bull. Am. Astron. Soc., 41, 16.03.
Abstract: Although observed from the Earth, Pioneer 11, Voyagers 1 and 2, and now
Cassini in its primary and 2-year extended mission, the characterization of fundamental
atmospheric properties and processes in Saturn remains incomplete. Many open questions
about the atmosphere could be addressed in the next decade:
- SEASONS: How do seasons affect (a) the global distribution of gaseous constituents
and aerosols; and (b) temperatures and the stability against convection and large scaleatmospheric transport? Will a warm polar vortex appear at the northern pole with greater
radiative input?
- HEXAGON: What is the vertical structure of the hexagon, what is driving and
maintaining it; and why is there no feature of similar longevity at the south pole?
- COMPOSITION AND CHEMISRY: What are the noble gas and oxygen abundances?
What is the relation of stratospheric hydrocarbon distributions to radiative climate
influences and photochemistry? What is the rate of influx of ring and other exogenic
materials into the atmosphere?
- CLOUDS AND HAZES: What is the tropospheric cloud inventory, and what are the
different cloud compositions and optical properties? What is producing the haze material?
What is the relation between observable clouds and lightning discharges? What is the
relation between the fine-scale cloud structure identified at 5 microns and the distribution
of condensates, such as ammonia? Do 5-micron clouds have counterparts at other altitude
levels?
- DYNAMICS: What is the source of the strong equatorial upwelling and strong prograde
jet? What changes when we see the emergence of Great White Storms? How is energy
transported by waves between atmospheric levels, via the SAO and by vertical waves
observed in stellar occultations and RSS profiles? What effect does the ephemeral nature
of Saturn's slowly-moving thermal waves have on the atmosphere? Will the tropospheric
hotspots at each pole persist?