Meridional Transport in the Stratosphere of Jupiter

The Cassini measurements of C$_2$H$_2$ and C$_2$H$_6$ at $\sim$5 mbar provide a constraint on meridional transport in the stratosphere of Jupiter. We performed a two-dimensional photochemical calculation coupled with mass transport due to vertical and meridional mixing. The modeled profile of C$_2$H$_2$ at latitudes less than 70$^\circ$ follows the latitude dependence of the solar insolation, while that of C$_2$H$_6$ shows little latitude dependence, consistent with the measurements. In general, our model study suggests that the meridional transport timescale above 5-10 mbar altitude level is $\gtrsim$1000 years and the time could be as short as 10 years below 10 mbar level, in order to fit the Cassini measurements. The derived meridional transport timescale above the 5 mbar level is a hundred times longer than that obtained from the spreading of gas-phase molecules deposited after the impact of Shoemaker-Levy 9 comet. There is no explanation at this time for this discrepancy.Comment: 11 pages, 3 figures, 1 table. ApJL in pres

Pressure Line Broadening and Feasibility of CO_2 Profile Retrieval using Near Infrared Observations of an Absorption Line

Analytic expressions are derived for the transmittance and reflectance of sunlight and their Jacobians for an absorption line with Lorentz line broadening. Rodgers information analysis is applied to calculate the information content, the degrees of freedom and the averaging kernel for a simple atmospheric model to investigate the feasibility of retrieving the profile of CO_2 using near-infrared (NIR) measurements over a single absorption line. The results have implications for the design of future space instruments with high spectral resolution and high signal to noise ratios to obtain global scale information on the CO_2 vertical distribution which is important for inferring the sources, sinks, and transport of CO_2

Simulation of the transport of halogen species from the equatorial and mid-latitude stratosphere to the polar stratosphere in a two-dimensional model

The bulk of O sub 3 destruction in the Antarctic stratosphere takes place in the lower stratosphere between 15 and 25 km. Both O sub 3 and the halogen reservoir species have their origins in the higher altitude region (20 to 30 km) in the equatorial and mid-latitude stratosphere. Using the Caltech-JPL two-dimensional residual circulation model, researchers investigate the growth of stratospheric halogen due to the increase of CFCl sub 3 and CF sub 2 Cl sub 2

Stratospheric aircraft exhaust plume and wake chemistry studies

This report documents progress to date in an ongoing study to analyze and model emissions leaving a proposed High Speed Civil Transport (HSCT) from when the exhaust gases leave the engine until they are deposited at atmospheric scales in the stratosphere. Estimates are given for the emissions, summarizing relevant earlier work (CIAP) and reviewing current propulsion research efforts. The chemical evolution and the mixing and vortical motion of the exhaust are analyzed to track the exhaust and its speciation as the emissions are mixed to atmospheric scales. The species tracked include those that could be heterogeneously reactive on the surfaces of the condensed solid water (ice) particles and on exhaust soot particle surfaces. Dispersion and reaction of chemical constituents in the far wake are studied with a Lagrangian air parcel model, in conjunction with a radiation code to calculate the net heating/cooling. Laboratory measurements of heterogeneous chemistry of aqueous sulfuric acid and nitric acid hydrates are also described. Results include the solubility of HCl in sulfuric acid which is a key parameter for modeling stratospheric processing. We also report initial results for condensation of nitric acid trihydrate from gas phase H2O and HNO3

New Insights into Martian Atmospheric Chemistry

HO_x radicals are produced in the Martian atmosphere by the photolysis of water vapor and subsequently participate in catalytic cycles that recycle carbon dioxide (CO_2) from its photolysis product carbon monoxide (CO), providing a qualitative explanation for the stability of its atmosphere. Balancing CO_2 production and loss based on our current understanding of Martian gas-phase chemistry has, however, proven to be difficult. The photolysis of O_3 produces O(^1D), while oxidation of CO produces HOCO radicals, a new member of the HO_x family. The O(^1D) quantum yield has recently been updated, which quantifies nonzero quantum yields in the Huggins bands. In Earth’s atmosphere HOCO is considered to be unimportant since it is quickly removed by abundant oxygen molecules. The smaller amount of O_2 in the Mars’ atmosphere causes HOCO’s lifetime to be longer in Mars’ atmosphere than Earth’s (3 × 10^(-5) seconds to 1.2 days from Mars’s surface to 240 km, respectively). Limited kinetic data on reactions involving HOCO prevented consideration of its reactions directly in atmospheric models. Therefore, the impact of HOCO reactions on Martian chemistry is currently unknown. Here, we incorporate new literature rate constants for HOCO chemistry and an updated representation of the O(^1D) quantum yield in the Caltech/JPL 1-D photochemical model for Mars’ atmosphere. Our simulations exemplify perturbations to NO_y, HO_x, and CO_x species, ranging from 5 to 50%. The modified O(^1D) quantum yield and new HOCO chemistry cause a 10% decrease and a 50% increase in OH and H_2O_2 total column abundances, respectively. At low altitudes, HOCO production contributes 5% towards CO_2 production. Given recent experimentally-obtained branching ratios for the oxidation of CO, HOCO may contribute up to 70% toward the production of NO_y, where HO_x and NO_y species are enhanced up to a factor 3, which has implications for rethinking the fundamental understanding of NO_y, HO_x, and CO/CO_2 cycling on Mars. Two new reaction mechanisms for converting CO to CO_2 using HOCO reactions are proposed, which reveal that H_2O_2 is more intimately coupled to CO_x chemistry. Our simulations are in good agreement with satellite/spacecraft measurements of CO and H_2O_2 on Mars

On the information content of the thermal infrared cooling rate profile from satellite instrument measurements

This work investigates how remote sensing of the quantities required to calculate clear-sky cooling rate profiles propagates into cooling rate profile knowledge. The formulation of a cooling rate profile error budget is presented for clear-sky scenes given temperature, water vapor, and ozone profile uncertainty. Using linear propagation of error analysis, an expression for the cooling rate profile covariance matrix is given. Some of the features of the cooling rate covariance matrix are discussed, and it is found that nonzero error correlations in the temperature, water vapor, and ozone retrieval profiles must be considered to produce an unbiased estimate of cooling rate profile variance and the covariance structure. To that end, the exclusion of the details of this error correlation leads to an underestimation of the cooling rate profile uncertainty. This work then examines the assumptions made in the course of deriving the expression for the cooling rate covariance matrix by using ERA-40 Reanalysis data. It is established that the assumptions of linear error propagation and Gaussian statistics are generally tenable. Next, the information content of thermal infrared spectra with respect to clear-sky cooling rate profiles is investigated. Several formerly- and currently-operational spectrometers are compared with different spectral coverage, resolution, signal-to-noise ratio. Among these, IASI is found to have the ability to provide the greatest amount of information on the cooling rate profile. Also, it may be scientifically useful to develop far-infrared missions in terms of cooling rate profile analysis

Simulated retrievals for the remote sensing of CO_2, CH_4, CO, and H_2O from geostationary orbit

The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution spectra of reflected sunlight in three near-infrared bands centered around 0.76, 1.6, and 2.3 μm and to deliver simultaneous retrievals of column-averaged dry air mole fractions of CO_2, CH_4, CO, and H_2O (denoted XCO_2, XCH_4, XCO, and XH_2O, respectively) at different times of day over North America. In this study, we perform radiative transfer simulations over both clear-sky and all-sky scenes expected to be observed by GeoFTS and estimate the prospective performance of retrievals based on results from Bayesian error analysis and characterization. We find that, for simulated clear-sky retrievals, the average retrieval biases and single-measurement precisions are < 0.2 % for XCO_2, XCH_4, and XH_2O, and < 2 % for XCO, when the a priori values have a bias of 3 % and an uncertainty of 3 %. In addition, an increase in the amount of aerosols and ice clouds leads to a notable increase in the retrieval biases and slight worsening of the retrieval precisions. Furthermore, retrieval precision is a strong function of signal-to-noise ratio and spectral resolution. This simulation study can help guide decisions on the design of the GeoFTS observing system, which can result in cost-effective measurement strategies while achieving satisfactory levels of retrieval precisions and biases. The simultaneous retrievals at different times of day will be important for more accurate estimation of carbon sources and sinks on fine spatiotemporal scales and for studies related to the atmospheric component of the water cycle

Continued development and validation of the AER two-dimensional interactive model

Results from two-dimensional chemistry-transport models have been used to predict the future behavior of ozone in the stratosphere. Since the transport circulation, temperature, and aerosol surface area are fixed in these models, they cannot account for the effects of changes in these quantities, which could be modified because of ozone redistribution and/or other changes in the troposphere associated with climate changes. Interactive two-dimensional models, which calculate the transport circulation and temperature along with concentrations of the chemical species, could provide answers to complement the results from three-dimension model calculations. In this project, we performed the following tasks in pursuit of the respective goals: (1) We continued to refine the 2-D chemistry-transport model; (2) We developed a microphysics model to calculate the aerosol loading and its size distribution; (3) The treatment of physics in the AER 2-D interactive model were refined in the following areas--the heating rate in the troposphere, and wave-forcing from propagation of planetary waves

Isotopic fractionation of nitrous oxide in the stratosphere: Comparison between model and observations

We investigate the mass dependent isotopic fractionation mechanisms, based on photolytic destruction and reaction with O^1D, to explain the ^(15)N/^(14)N and ^(18)O/^(16)O fractionation of stratospheric N_2O and reconcile laboratory experiments with atmospheric observations. The Caltech/JPL two-dimensional (2-D) model is utilized for detailed studies of N_2O and its isotopologues and isotopomers in the stratosphere. We compare model results with observations of isotopic enrichment using three different methods of calculating photolytic cross-sections for each of the major isotopologues and isotopomers of N_2O. Although the Yung and Miller [1997] successfully modeled the pattern of enrichments for each isotopologue or isotopomer relative to each other, their approach underestimated the magnitude of the enrichments. The ab initio approach by Johnson et al. [2001] provides a better fit to the magnitudes of the enrichments, with the notable exception of the enrichment for the ^(15)N^(14)N^(16)O. A simpler, semi-empirical approach by Blake et al. [2003] is able to model the magnitude of all the enrichments, including the one for ^(15)N^(14)N^(16)O. The Blake et al. [2003] cross-sections are temperature-dependent, but adjustments are needed to match the measurements of Kaiser et al. [2002a] . Using these modified cross-sections generally improves the agreement between model and mass spectrometric measurements. Destruction of N_2O by reaction with O(^1D) results in a small but nonnegligible isotopic fractionation in the lower stratosphere. On a per molecule basis, the rates of destruction of the minor isotopologues or isotopomers are somewhat less than that for ^(14)N^(14)N^(16)O. From our 2-D model we infer the relative rates for isotopologues and isotopomers ^(14)N^(14)N^(16)O (446), ^(14)N^(15)N^(16)O (456), ^(15)N^(14)N^(16)O (546), ^(14)N^(14)N^(17)O (447) and ^(14)N^(14)N^(18)O (448), to be 1, 0.9843, 0.9942, 0.9949, and 0.9900, respectively. Thus the destruction of N_2O in the atmosphere results in isotopic fractionations of (456), (546), (447) and (448) by 19.4, 9.5, 5.5 and 12.0‰. If we do not distinguish between the (456) and (546) isotopomers, the mean isotopic fractionation for ^(15)N is 14.5‰. If we assume that the mean tropospheric values for δ_(456), δ_(546_, δ^(15)N and δ^(18)O are 16.35, −2.35, 7.0 and 20.7‰, respectively, we infer the following isotopic signature for the integrated sources of N_2O: δ_(456) = − 2.9‰, δ_(546) = −11.7‰, δ^(15)N = −7.3‰ and δ^(18)O = 8.7‰

Stratospheric aircraft exhaust plume and wake chemistry

Progress to date in an ongoing study to analyze and model emissions leaving a proposed High Speed Civil Transport (HSCT) from when the exhaust gases leave the engine until they are deposited at atmospheric scales in the stratosphere is documented. A kinetic condensation model was implemented to predict heterogeneous condensation in the plume regime behind an HSCT flying in the lower stratosphere. Simulations were performed to illustrate the parametric dependence of contrail droplet growth on the exhaust condensation nuclei number density and size distribution. Model results indicate that the condensation of water vapor is strongly dependent on the number density of activated CN. Incorporation of estimates for dilution factors into a Lagrangian box model of the far-wake regime with scale-dependent diffusion indicates negligible decrease in ozone and enhancement of water concentrations of 6-13 times background, which decrease rapidly over 1-3 days. Radiative calculations indicate a net differential cooling rate of the plume about 3K/day at the beginning of the wake regime, with a total subsidence ranging between 0.4 and 1 km. Results from the Lagrangian plume model were used to estimate the effect of repeated superposition of aircraft plumes on the concentrations of water and NO(y) along a flight corridor. Results of laboratory studies of heterogeneous chemistry are also described. Kinetics of HCl, N2O5 and ClONO2 uptake on liquid sulfuric acid were measured as a function of composition and temperature. Refined measurements of the thermodynamics of nitric acid hydrates indicate that metastable dihydrate may play a role in the nucleation of more stable trihydrates PSC's