P42B-03The State of the Plasma Sheet and Atmosphere at Europa
Thursday, December 18, 201410:50 AM - 11:05 AM, Moscone West 2009
Donald Shemansky, Yuk Yung, Xianming Liu, Jean Yoshii, Candice Hansen, Amanda
Hendrix, Larry Esposito
The Hall et al. (1995) report announcing the discovery of atomic oxygen FUV emission
from Europa included a conclusion that the atmosphere was dominated by O2. Over the
following 20 years publications referencing the atmosphere accepted this conclusion, and
calculations of rates, particularly mass loading of the magnetosphere depended on a
composition that was of order 90% O2. Analysis of the Europa emission spectrum in the
present work, leads to the conclusion that the O I emission properties were
misinterpreted. The interpretation of the source process depends on the ratio of the O I
1356 and 1304 A multiplet emissions (R(4:5) = (I(1356)/I(1304)). The value of R(4:5)
never reaches the lower limit for electron impact dissociation of O2 for any of the 7
recorded disk averaged measurements between 1994 and 2013. Analysis of the Cassini
UVIS exposures show the 1304 A multiplet to be optically thick, and the emissions are
modeled as direct electron and solar photon excitation of O I. The result is a model
atmosphere dominated by O I and O II, with neutral density a factor of 100 below the
original O2 model. Other considerations show incompatibility with an O2 atmosphere.
Deep exposures using the Cassini UVIS EUV spectrograph provide the state of the
plasma sheet at Europa. The ion species are identified as mainly outwardly diffused mass
from the Io plasma torus with a minor contribution from Europa. Plasma time-constants
are of the order of 200 days. Neutral species in the plasma sheet are not measureable. The
energy flux in the magnetosphere L-shells are mainly responsible for energy deposition
maintaining the plasma sheet. The energy content in the Io and Europa L-shells, as
measured, is similar, but the mean radiative cooling rate in the Io plasma torus at the time
of the Cassini encounter was 565 femtoergs cm-3 s-1, compared to 7.3 at Europa,
reflecting the difference between an active and inactive planetary satellite, particularly
considering the fact that most of the radiation at the Europa plasma sheet is from ions that
originated at the orbit of Io. The stochastic observational evidence in disk averaged
Europa oxygen emission obtained over the 1994 to 2012 period shows no indication of
transient events. A significant neutral transient injection in the Europa plasma sheet
would take of order year time-scales to relax to steady state.
A41I-3177Remote Sensing of CO2, CH4, CO, and H2O from Geostationary Orbit
Thursday, December 18, 201408:00 AM - 12:20 PM, Moscone South
Xi Xi, Vijay Natraj, Ming Luo, Qiong Zhang, Run-Lie Shia, Stanley Sander, Yuk Yung
The Geostationary Carbon Process Investigation (GCPI) combines an imaging Fourier
Transform Spectrometer with a geostationary Earth orbit vantage point to realize a
transformational advance in monitoring carbon-bearing molecules and water vapor
beyond the synoptic capabilities of Low Earth Orbit instruments such as SCIAMACHY,
GOSAT and OCO-2. GCPI is designed to measure, several times every day, high-
resolution spectra of reflected sunlight with a moderate signal to noise ratio in nearinfrared (NIR) bands, that can then be used to obtain simultaneous retrievals of column
averaged CO2, CH4, CO, and H2O. The aim of this project is to explore the potential of
retrieving vertical profiles of CO2, CH4, CO, and H2O from high-resolution NIR spectra.
We perform radiative transfer simulations over clear-sky conditions (as expected to be
observed by GCPI) and estimate prospective performance of retrievals based on results
from Bayesian error analysis and characterization. Through Observing System
Simulation Experiments (OSSEs), we demonstrate the feasibility of retrieving vertical
profiles of CO2 and CH4 and partial columns of CO and H2O with high accuracies and
precisions. GCPI’s unprecedented observations with high temporal and spatial coverage
could be used to drive and constrain Earth system models, improve our understanding of
the underlying carbon cycle and water cycle processes, and evaluate model forecasting
capabilities.
SA53A-4111Response of Middle Atmospheric Hydroxyl Radical to the 27-Day Solar
Forcing
Friday, December 19, 201401:40 PM - 06:00 PM, Moscone South
King-Fai Li, Qiong Zhang, Shuhui Wang, Yuk Yung, Stanley Sander
In this study, we use the Microwave Limb Sound (MLS) data to examine the response of
middle atmospheric hydroxyl radicals (OH) to the 27-day solar rotational variability
during the solar maximum activity year (2004–2005). The results are compared to the
simulations of the 1-D photochemical model KINETICS using different UV variabilities.
Shapiro et al. [Atmos. Chem. Phys., 2012] have examined the 27-day solar cycle
modulation in tropical mesospheric OH measured by MLS, and found that the OH 27-day
solar response is ~1% per 1% change in Lyman-α at 80 km. However, as different bandpass filter is applied, the OH response varies significantly. An optimal filter is selected
based on the convergence of OH response with respect to filter window size. The results
show that in the middle atmosphere model simulations underestimate the hydroxyl
radical variabilities to short term solar forcing by 20%-50%.
A21B-3019Fast and Accurate Radiative Transfer Calculations Using Principal
Component Analysis for Climate Modeling
Tuesday, December 16, 201408:00 AM - 12:20 PM, Moscone South
Pushkar Kopparla, Vijay Natraj, Robert Spurr, Run-Lie Shia, Yuk Yung
Radiative transfer (RT) computations are an essential component of energy budget
calculations in climate models. However, full treatment of RT processes is
computationally expensive, prompting usage of 2-stream approximations in operational
climate models. This simplification introduces errors of the order of 10% in the top of the
atmosphere (TOA) fluxes [Randles et al., 2013].
Natraj et al. [2005, 2010] and Spurr and Natraj [2013] demonstrated the ability of a
technique using principal component analysis (PCA) to speed up RT simulations. In the
PCA method for RT performance enhancement, empirical orthogonal functions are
developed for binned sets of inherent optical properties that possess some redundancy;
costly multiple-scattering RT calculations are only done for those (few) optical states
corresponding to the most important principal components, and correction factors are
applied to approximate radiation fields.
Here, we extend the PCA method to a broadband spectral region from the ultraviolet to
the shortwave infrared (0.3-3 micron), accounting for major gas absorptions in this
region. Comparisons between the new model, called Universal Principal Component
Analysis model for Radiative Transfer (UPCART), 2-stream models (such as those used
in climate applications) and line-by-line RT models are performed, in order for spectral
radiances, spectral fluxes and broadband fluxes. Each of these are calculated at the TOA
for several scenarios with varying aerosol types, extinction and scattering optical depth
profiles, and solar and viewing geometries.
We demonstrate that very accurate radiative forcing estimates can be obtained, with
better than 1% accuracy in all spectral regions and better than 0.1% in most cases as
compared to an exact line-by-line RT model. The model is comparable in speeds to 2stream models, potentially rendering UPCART useful for operational General Circulation
Models (GCMs). The operational speed and accuracy of UPCART can be further
improved by optimizing binning schemes and parallelizing the codes, work on which is
under way.
A41H-3164CO2 Annual and Semiannual Cycles from Satellite Retrievals and Models
Thursday, December 18, 201408:00 AM - 12:20 PM, Moscone South
Xun Jiang, David Crisp, Edward Olsen, Susan Kulawik, Charles Miller, Thomas Pagano,
Yuk Yung
We have compared satellite CO2 retrievals from the Greenhouse gases Observing
SATellite (GOSAT), Atmospheric Infrared Sounder (AIRS), and Tropospheric Emission
Spectrometer (TES) with in-situ measurements from the Earth System Research
Laboratory (NOAA-ESRL) Surface CO2 and Total Carbon Column Observing Network
(TCCON), and utilized zonal means to characterize variability and distribution of CO2.
In general, zonally averaged CO2 from the three satellite data sets are consistent with the
surface and TCCON XCO2 data. Retrievals of CO2 from the three satellites show more
(less) CO2 in the northern hemisphere than that in the southern hemisphere in the
northern hemispheric winter (summer) season. The difference between the three satellite
CO2 retrievals might be related to the different averaging kernels in the satellites CO2
retrievals. A multiple regression method was used to calculate the CO2 annual cycle and
semiannual cycle amplitudes from different satellite CO2 retrievals. The CO2 annual
cycle and semiannual cycle amplitudes are largest at the surface, as seen in the NOAAESRL CO2 data sets. The CO2 annual cycle and semiannual cycle amplitudes in the
GOSAT XCO2, AIRS mid-tropospheric CO2, and TES mid-tropospheric CO2 are
smaller compared with those from the surface CO2. Similar regression analysis was
applied to the Model for OZone And Related chemical Tracers-2 (MOZART-2) and
CarbonTracker model CO2. The convolved model CO2 annual cycle and semiannual
cycle amplitudes are similar to those from the satellite CO2 retrievals, although the model
tends to under-estimate the CO2 seasonal cycle amplitudes in the northern hemisphere
mid-latitudes from the comparison with GOSAT and TES CO2 and underestimate the
CO2 semi-annual cycle amplitudes in the high latitudes from the comparison with AIRS
CO2. The difference between model and satellite CO2 can be used to identify possible
deficiency in the model and improve the model in the future.
P53C-4026Testing a Simple Recipe for Estimating Thermal Hydrodynamic Escape Rates
in Primitive Terrestrial Atmospheres
Friday, December 19, 201401:40 PM - 06:00 PM, Moscone South
Andrew Friedson, Yuk Yung, Pin Chen
During the first billion years of the Sun’s history, the emission of ultraviolet and X-ray
radiation varied from ~100 to ~6 times greater than its present level. The absorption of
this intense radiation in the upper atmospheres of the terrestrial planets is believed to
have driven rapid hydrodynamic escape, either in the form of energy-limited escape or
transonic blow-off. The calculation of escape rates under these circumstances, and in
particular the nature of the correct condition to apply at the upper boundary, depends on
whether or not the flow remains subsonic below the exobase. If the flow remains
subsonic, the kinetic Jeans equations may be applied at the exobase; otherwise, the radius
of the sonic point must be located and then appropriate boundary conditions applied at
this radius. This seems to suggest that the full hydrodynamic escape problem needs to be
solved iteratively to determine where the sonic radius falls and the type of boundary
conditions that should be applied. Such an arduous undertaking is generally impractical
for standard application in chemical evolution models or related studies. Fortunately, a
much easier but still accurate approach to determining whether the flow remains subsonic
below the exobase for a given amount of energy deposition has been provided by Johnson
et al. (2013, Ap. J. Lett. 768:L4), who base their results on rigorous Discrete Simulation
Monte Carlo models. Their model provides the ratio of the escape rate to the energylimited value as a function of the total XUV heating. The XUV heating, however, is itself
coupled to the escape rate through the radial structure of the upper atmosphere, which can
become greatly distended for large heating rates. Here we present a simple recipe for
estimating the hydrodynamic escape rate that includes the coupling between the escape
rate, the radial structure, and the XUV heating while avoiding the use of demanding
numerical calculations. The approach involves an iterative semi-analytical method for
determining the effective radius of energy deposition, from which the escape rate, radial
structure, and other parameters can be derived. We test its performance against some
more elaborate, rigorous calculations of primitive-atmosphere hydrodynamic escape that
are available in the literature.
P53C-4029Venus Then and Now: Simulating Sulfuric Acid Clouds Using Latitudinally
Dependent VIRA and VeRA Temperature Profiles
Friday, December 19, 201401:40 PM - 06:00 PM, Moscone South
Peter Goa, Christopher Parkinson, Charles Bardeen, Yuk Yung
Observations from the Pioneer Venus Orbiter (PVO) and from SPICAV/SOIR aboard
Venus Express (VEx) have shown the upper haze (UH) of Venus to be highly spatially
and temporally variable. Previous models of this system, using typical temperature
profiles representative of the Venus atmosphere as a whole, did not investigate the effects
of temperature variations on the UH particle distributions. Parkinson et al. (2014,
submitted) showed that the inclusion of latitudinally dependent temperature profiles
retrieved from SPICAV/SOIR observations in the Venus cloud model of Gao et al.
(2014) resulted in markedly different cloud distributions between the different latitude
cases, such as a lowered cloud base near the equator and a slightly thicker UH at the
poles. Thus, temperature variations across Venus could help explain spatial variations in
the atmospheric aerosol distribution. In this work, we expand on the aforementioned
study by including VIRA temperature profiles derived from Venera and PVO
observations (Kliore et al. 1985) at similar latitudes as the SPICAV/SOIR profiles to
assess how the aerosol distribution varies spatially and temporally. By comparing the
simulated cloud and haze distributions arising from the two sets of temperature profiles,
we can evaluate whether secular changes have occurred in the ~30 years between the
PVO and VEx epochs.
A12E-07An Analysis of Interannual Variabilities in High Cloud Cover from AIRS Data:
Imprints of the El Niño-Southern Oscillation and Comparison to Models
Monday, December 15, 201411:50 AM - 12:05 PM, Moscone West
Yuk Yung, Katie Antilla, Sze Ning Mak, Tiffany Chang, King-Fai Li, Hui Su, Sun
Wong, Jonathan Jiang
Using data from the Atmospheric Infrared Sounder (AIRS), we examine how global high
cloud cover varies over time in the decade from 2003 to 2012, with a focus on identifying
dominant modes of variabilities and associated spatial patterns, and relate them to sea
surface temperature (SST). By performing Empirical Orthogonal Function (EOF)
analysis on satellite observations of high cloud cover, the El Niño-Southern Oscillation
(ENSO) — including both EP-ENSO (canonical ENSO) and CP-ENSO (ENSO Modoki)
— is found to be the leading source of variability in high cloud cover. High cloud
distributions are further shown to be closely associated with SST variations. The
observations are compared to simulations from 20 AMIP5 models. In general, the models
are able to simulate the first EOF, the EP-ENSO, in the data. However, only about half of
the AMIP5 models could realistically reproduce the second EOF, the CP-ENSO.
Improved understanding of high cloud variabilities will advance climate model
simulations and facilitate more accurate predictions of future climate, specifically the
climate response to increasing greenhouse gases such as CO2.
A53L-3361Seasonal and Diurnal Variations in Anthropogenic Sources of CO2 in the Los
Angeles Megacity
Friday, December 19, 201401:40 PM - 06:00 PM, Moscone South
Sally Newman, Jade Larriva-Latt, Ying Hsu, Clare (Kam Weng) Wong, Stanley Sander,
Xiaomei Xu, Yuk Yung
Greenhouse gas emissions in urban regions comprise the bulk of anthropogenic
contributions to the atmosphere. Governments compile bottom-up inventories from the
different source sectors, but top-down measurements of the individual species, such as
CO2, are totals. Top-down measurements are required to verify bottom-up inventories
based on economic data. We must use other methods, such as analysis of ratios between
species and ratios between isotopologues, in addition to model calculations, in order to
determine the contributions of the various sectors that are actually observed in the
atmosphere. Because of the very large signal in megacities, due to large anthropogenic
emissions, these are the ideal regions to study to disentangle the signals from such
sources as fossil fuel combustion, including identifying gasoline and natural gas
signatures, and the biosphere. In this study, we extend our isotopic study of midafternoon flask samples in Pasadena, CA to continuous measurements of CO2 mixing
ratios and δ13C in order to understand how the relative contributions of different sources
vary with time of day and with time of year. Summers are characterized by larger
contributions from natural gas combustion during the afternoons and evenings than
during the mornings.
P21D-3960NOx in the atmospheres of aquaplanets as electron acceptors for life
Tuesday, December 16, 201408:00 AM - 12:20 PM, Moscone South
Michael Wong, Yuk Yung, Michael Russell
A high potential electron acceptor is required to drive the highly endergonic reactions at
the entry points to the autotrophic metabolic pathways that would lead to life on any wet
rocky world. Nitrate and nitrite in the earliest oceans are the most attractive candidates
(Ducluzeau et al., 2009, 2014). It has been estimated that, given a CO2 and N2
atmosphere, lightning (a proportion of it volcanic), meteorite impacts and volcanic gases
would have produced enough NOx in a million years or so (>1018 g) to generate
micromolar amounts of NO3- and NO2- in the ocean (Yung and McElroy, 1979; Kasting,
1990; Navarro-González et al., 1998; Martin et al., 2007). It is notable that lightning has
been detected on Venus and Mars along with evidence of atmospheric NO.
Because a figure 1018 g of nitrate/nitrite is controversial, we will present new
calculations based on 10 atmospheres of CO2, two atmospheres of N2 and stepped
concentrations of water vapor dependent on surface temperatures.
P31E-07Pluto Photochemical Models for the New Horizons Flyby
Wednesday, December 17, 201409:24 AM - 09:36 AM, Moscone West
Randy Gladstone, Michael Wong, Yuk Yung
During the New Horizons flyby of the Pluto system on July 14, 2015 a number of
observations will be made to determine the structure, composition, and variability of
Pluto’s atmosphere. A key observation of this type is the Alice solar occultation, which
will measure the full disk ultraviolet (52-187 nm) spectral flux from the Sun through
ingress and egress behind Pluto, about one hour after closest approach. This observation
will be used to determine the temperature and vertical density profiles of N2, CH4, and
various minor species above two regions of very different surface albedo. Nearly
simultaneous Earth ingress and egress occultations observed in X-band uplink will
provide profiles of temperature and pressure in Pluto’s lower atmosphere, and electron
densities in the ionosphere. Wave structures in both the solar and radio occultation data
will provide constraints on atmospheric dynamics. In order to interpret and understand
these data sets, we have modified a 1-D Titan photochemical model to Pluto, for the
epoch of the New Horizons flyby. The model uses a similar, but updated reaction list to
that of Krasnopolsky and Cruikshank [1999] and Wong et al. [2014], and adopts the
results of Zhu et al. [2014] for the background atmosphere. We present here initial results
for several assumed eddy diffusion profiles.
Krasnopolsky, V. A., and D. P. Cruikshank, J. Geophys. Res., 104, 21,979, 1999.
Wong, M. L., Y. L. Yung, and G. R. Gladstone, Icarus, in press, 2014.
Zhu, X., D F. Strobel, and J. T. Erwin, Icarus, 228, 301, 2014.
A41H-3169Retrieval of CO2 Mixing Ratios from CLARS Measurements: Correcting
Aerosol Induced Biases
Thursday, December 18, 201408:00 AM - 12:20 PM, Moscone South
Qiong Zhang, Vijay Natraj, Run-Lie Shia, Coleen Roehl, Yuk Yung, Stanley Sander
A Fourier transform spectrometer at the California Laboratory for Atmospheric Remote
Sensing (CLARS) on the top of Mt Wilson, California, measures greenhouse gas
concentrations in the Los Angeles basin using reflected sun light. Observations include
those with large viewing zenith angles (up to 83.1), making the measurements very
sensitive to aerosol scattering. A previous study by the authors shows the ratioing of CO2
and O2 slant column densities (SCDs) can largely cancel the effect of aerosol scattering,
but biases still exist due to the wavelength dependence of aerosol scattering.
In this study, biases caused by different types of aerosols are analyzed. Preliminary
results indicate that the information from CLARS-FTS spectra is not sufficient to
constrain all the free parameters, including the aerosol single scattering albedo (SSA),
aerosol optical depth, surface albedo, etc. In order to mitigate the influence of aerosol
scattering, a few effective aerosol parameters are retrieved simultaneously with absorbing
gas abundances. The corrected SCDs show reasonable variabilities from the morning to
the afternoon in the presence of aerosols. The column-averaged dry air mole fraction of
CO2 (XCO2) products are compared to measurements from the Total Carbon Column
Observing Network (TCCON) at Caltech. By retrieving aerosol parameters in the CO2
and O2 absorption bands, biases in XCO2 caused by wavelength dependence of aerosol
scattering can be considerably reduced.
P31D-4017Carbon Reservoir History of Mars Constrained by Atmospheric Isotope
Signatures
Wednesday, December 17, 201408:00 AM - 12:20 PM, Moscone South
Renyu Hu, David Kass, Bethany Ehlmann, Yuk Yung
The evolution of the atmosphere on Mars is one of the most intriguing problems in the
exploration of the Solar System, and the climate of Mars may have evolved from a
warmer, wetter early state to the cold, dry current state. Because CO2 is the major
constituent of Mars’s atmosphere, its isotopic signatures offer a unique window to trace
the evolution of climate on Mars. Here we use a box model to trace the evolution of the
carbon reservoir and its isotopic signature on Mars, with carbonate deposition and
atmospheric escape as the two sinks and magmatic activity as the sole source. We derive
new quantitative constraints on the amount of carbonate deposition and the atmospheric
pressure of Mars through time, extending into the Noachian, ~3.8 Gyr before present.
This determination is based on recent Mars Science Laboratory (MSL) isotopic
measurements of Mars’s atmosphere, recent orbiter, lander, and rover measurements of
Mars’s surface, and a newly identified mechanism (photodissociation of CO) that
efficiently enriches the heavy carbon isotope. In particular, we find that escape via CO
photodissociation on Mars has a fractionation factor of 0.6 and hence, photochemical
escape processes can effectively enrich 13C in the Mars’s atmosphere during the
Amazonian. As a result, modest carbonate deposition must have occurred early in Mars’s
history to compensate the enrichment effects of photochemical processes and also
sputtering, even when volcanic outgassing up to 200 mbar occurred during the Hesperian.
For a photochemical escape flux that scales as the square of the solar EUV flux or more,
at least 0.1 bar of CO2 must have been deposited as carbonates in the Noachian and
Hesperian. More carbonate deposition would be required if carbonate deposition only
occurred in the Noachian or with low fractionation factors.
A41A-3009Decadal Variability of Clouds and Comparison with Climate Model
Simulations
Thursday, December 18, 201408:00 AM - 12:20 PM, Moscone South
Tsaepyng Shen, Hui Su, Jonathan Jiang, Yuk Yung
An apparent climate regime shift occurred around 1998/1999, when the steady increase
of global-mean surface temperature appeared to hit a hiatus. Coherent decadal variations
are found in atmospheric circulation and hydrological cycles. Using 30-year cloud
observations from the International Satellite Cloud Climatology Project, we examine the
decadal variability of clouds and associated cloud radiative effects on surface warming.
Empirical Orthogonal Function analysis is performed. After removing the seasonal cycle
and ENSO signal in the 30-year data, we find that the leading EOF modes clearly
represent a decadal variability in cloud fraction, well correlated with the indices of
Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). The
cloud radiative effects associated with decadal variations of clouds suggest a positive
cloud feedback, which would reinforce the global warming hiatus by a net cloud cooling
after 1998/1999. Climate model simulations driven by observed sea surface temperature
are compared with satellite observed cloud decadal variability.
A53L-3371Estimating Top-down Emissions (2011-2014) of CH4 and CO2 From Los
Angeles by an FTS Atop Mount Wilson
Friday, December 19, 201401:40 PM - 06:00 PM, Moscone South
Clare (Kam Weng) Wong, Dejian Fu, Thomas Pongetti, Sally Newman, Eric Kart, Riley
Duren, Ying Hsu, Charles Miller, Yuk Yung, Stanley Sander
Megacities, such as Los Angeles, emit significant amount of anthropogenic greenhouse
gases (GHGs). As the world’s population in urban regions is expected to increase from
over 50% now to 70% by 2050, monitoring the temporal trends of urban GHG emissions
are necessary to verify regulation policy. Since megacities tend to have large spatially
and temporally varying GHG emission characteristics, it is important to perform
measurements which provide continuous spatio-temporal coverage of the domain. In this
study, we demonstrate the ability to track major greenhouse gases, methane (CH4) and
carbon dioxide (CO2) using ground-based remote sensing technique from Mount Wilson.
Since 2010, in Los Angeles, a Fourier Transform Spectrometer (FTS) has been deployed
on Mount Wilson to measure CO2, CH4, carbon monoxide (CO), the combustion tracer,
and other tracer gases using reflected sunlight in the near-infrared spectral regions.
Combining the unique vista from Mount Wilson and high-precision measurements from
the FTS, the slant column abundances of these trace gases above and within the urban
dome of Los Angeles are acquired. Within the urban dome, continuous daytime temporal
and spatial measurements are recorded for 28 reflection points which are strategically
located across the basin. Here we analyze the path-averaged dry air mixing ratios XCH4,
XCO2 and XCO acquired by the FTS during a three-year period from 2011 to 2014.
Using tracer-to-tracer correlation analysis, we investigate the ratios of XCH4:XCO2,
XCH4:XCO and XCO:XCO2 in excess of the background values. Significant spatiotemporal variability in all three ratios is observed across the Los Angeles megacity during
this measurement period. We then derive the top-down estimates of basin total CH4 and
CO2 emissions between 2011 and 2014 using the existing bottom-up emission database
of CO2and CO, and compare our estimates to the emissions reported by the state
government and previous studies.
P53C-4033Photochemical Control of the Distribution of Water and Sulphuric Acid
Aerosols in the Clouds and Upper Haze of Venus with Comparison to Venus Express
SOIR Observations
Friday, December 19, 201401:40 PM - 06:00 PM, Moscone South
Christopher Parkinson, Peter Gao, Yuk Yung, Stephen Bougher, Charles Bardeen
Observations of the middle and lower cloud layers of Venus has established the water
vapour mixing ratio there as ~ 30-35 ppm (Ignatiev et al. 1997), while more recent data
suggests that the water vapor mixing ratio of the upper haze of Venus is ~ 1 ppm
(Bertaux et al. 2007). The transition region between these two regimes, the upper cloud,
is an active site of photochemistry and production of sulfuric acid, which occurs through
the formation of SO3 from the oxidation of SO2, and subsequent reactions between SO3
and water. These reactions have been shown by Parkinson et al. (2014a, submitted) as
capable of causing an order of magnitude decrease of the water vapor mixing ratio in the
upper cloud and upper haze if the SO2 mixing ratio at the upper cloud base were
increased by only ~20%, as the resulting high SO3 concentrations rapidly react with any
available water to form sulfuric acid. The opposite is true when water is in high
abundance. This is likely to have profound effects on the sulfuric acid clouds and hazes
themselves, as 1) the depletion of either species will decrease the production rate of
sulfuric acid and 2) the saturation vapor pressure of the cloud droplets increases with
decreasing water fraction, and thus a "drying" of the clouds may result in decreased cloud
thickness. In this work we will use the Venus microphysical cloud models of Gao et al.
(2014) and Parkinson et al. (2014b, submitted) to simulate the sulfuric acid clouds and
hazes of Venus from 40 to 100 km altitude and evaluate how their structure and particle
sizes depend on the background water vapor profile and sulfuric acid production rate as
determined by Parkinson et al. (2014a, submitted). We also show how they respond to
transient episodes of increased/decreased SO2/H2O mixing ratios and discuss the
plausibility of possible causes, such as volcanic activity.
SA53A-4106Solar Cycle Induced Variability in Middle Atmospheric HOx —
Abundances and Partitioning
Friday, December 19, 201401:40 PM - 06:00 PM, Moscone South
Shuhui Wang, Luis Millan Valle, King-Fai Li, Stanley Sander, Yuk Yung, Natheniel
Livesey, Michelle Santee, Moo-Chang Liang
Solar UV irradiance variability during the 11-year solar cycle has strong impacts on
Earth’s atmospheric composition and climate. The odd hydrogen species HOx (primarily
OH and HO2), which plays a key role in controlling middle atmospheric ozone, are
expected to show distinct variability following the solar cycle. Previous investigations
based on total OH abundances from long-term ground-based observation and 5.5 year
Aura/Microwave Limb Sounder (MLS) OH data and model calculations suggest that the
HOx solar cycle variability may dominate the ozone solar cycle variability above 40 km.
In the present study, we expand the investigation to both HO2 and OH, as well as the
partitioning between them, which is important in the catalytic HOx cycle. With the newly
developed MLS offline HO2 product that has significantly improved data quality and
better vertical and diurnal coverage, we examine the vertical and latitudinal distribution
of the solar cycle signals in HO2 (~10 year data) and compare it with OH. Model
simulations using the Caltech/JPL 1-D photochemical model are used to understand the
detailed mechanisms controlling the variability in HOx abundances and partitioning. The
results of using different solar spectral irradiance (SSI) variabilities in models and the
comparison with observations will be discussed.
In addition, while the continuous MLS OH data record is only 5.5 year, the MLS THz
sub-system was turned back on for a 30-day OH measurement in every August since
2011. Using the most recent version of MLS retrieval software (v4.1x, to be released),
some first OH data for selected months will be presented, suggesting reliable quality of
the “THz restart” observations and making it promising to combine such OH data with
earlier OH data to build a longer-term record.