Greenhouse effect due to atmospheric nitrous oxide

The greenhouse effect due to nitrous oxide in the present atmosphere is about 0.8°K. Increase in atmospheric N_2O due to perturbation of the nitrogen cycle by man may lead to an increase in surface temperature as large as 0.5°K by 2025, or 1.0°K by 2100. Other climatic effects of N_2O are briefly discussed

Methyl bromide: Ocean sources, ocean sinks, and climate sensitivity

The oceans play an important role in the geochemical cycle of methyl bromide (CH_3Br), the major carrier of O_3-destroying bromine to the stratosphere. The quantity of CH_3Br produced annually in seawater is comparable to the amount entering the atmosphere each year from natural and anthropogenic sources. The production mechanism is unknown but may be biological. Most of this CH_3Br is consumed in situ by hydrolysis or reaction with chloride. The size of the fraction which escapes to the atmosphere is poorly constrained; measurements in seawater and the atmosphere have been used to justify both a large oceanic CH_3Br flux to the atmosphere and a small net ocean sink. Since the consumption reactions are extremely temperature-sensitive, small temperature variations have large effects on the CH_3Br concentration in seawater, and therefore on the exchange between the atmosphere and the ocean. The net CH_3Br flux is also sensitive to variations in the rate of CH_3Br production. We have quantified these effects using a simple steady state mass balance model. When CH_3Br production rates are linearly scaled with seawater chlorophyll content, this model reproduces the latitudinal variations in marine CH_3Br concentrations observed in the east Pacific Ocean by Singh et al. [1983] and by Lobert et al. [1995]. The apparent correlation of CH_3Br production with primary production explains the discrepancies between the two observational studies, strengthening recent suggestions that the open ocean is a small net sink for atmospheric CH_3Br, rather than a large net source. The Southern Ocean is implicated as a possible large net source of CH_3Br to the atmosphere. Since our model indicates that both the direction and magnitude of CH_3Br exchange between the atmosphere and ocean are extremely sensitive to temperature and marine productivity, and since the rate of CH_3Br production in the oceans is comparable to the rate at which this compound is introduced to the atmosphere, even small perturbations to temperature or productivity can modify atmospheric CH_3Br. Therefore atmospheric CH_3Br should be sensitive to climate conditions. Our modeling indicates that climate-induced CH_3Br variations can be larger than those resulting from small (±25%) changes in the anthropogenic source, assuming that this source comprises less than half of all inputs. Future measurements of marine CH_3Br, temperature, and primary production should be combined with such models to determine the relationship between marine biological activity and CH_3Br production. Better understanding of the biological term is especially important to assess the importance of non anthropogenic sources to stratospheric ozone loss and the sensitivity of these sources to global climate change

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

Adsorption of HO_x on Aerosol Surfaces: Implications for the Atmosphere of Mars

The potential impact of heterogeneous chemistry on the abundance and distribution of HO_x in the atmosphere of Mars has been assessed by combining observational data of dust and ice aerosol distributions with an updated photochemical model. Critical parameters include the altitude distributions of aerosols, and the surface loss coefficients (γ) of HO_2 on dust and ice in the lower atmosphere, and H on ice above 40 km. We find that adsorption of HO_2 on dust (γHO_2 ≥ 0.01), or ice near 30 km (γHO_2 ≥ 0.1), can deplete OH abundances in the lower atmosphere by 10% or more. Such depletions approach those obtained by lowering the water vapor abundance by an order of magnitude below the global average observed by Viking (≈ 25%). Since the oxidation of CO is catalyzed by HO_x in the lower atmosphere via the reaction CO + OH → CO_2 + H, loss of OH due to adsorption of HO_2 on dust or ice at low altitudes could have a significant effect on the ratio CO : CO_2. The adsorption of H on ice at 50 km (γ_H ≥ 0.01) can result in even larger OH depletions. However, this effect is localized to altitudes > 40 km, where CO oxidation is relatively unimportant. Laboratory data suggest that γHO_2 ≈ 0.01 is a reasonable estimate for adsorption on dust. Larger values are plausible, but are not strongly supported by experimental evidence. The reactivity of HO_2 on ice is unknown, while γH on ice appears to be < 0.001. There is a need for measurements of HO_x adsorption on surfaces representative of Martian aerosols at temperatures < 220 K

Chemical dynamics of triacetylene formation and implications to the synthesis of polyynes in Titan's atmosphere

For the last four decades, the role of polyynes such as diacetylene (HCCCCH) and triacetylene (HCCCCCCH) in the chemical evolution of the atmosphere of Saturn's moon Titan has been a subject of vigorous research. These polyacetylenes are thought to serve as an UV radiation shield in planetary environments; thus, acting as prebiotic ozone, and are considered as important constituents of the visible haze layers on Titan. However, the underlying chemical processes that initiate the formation and control the growth of polyynes have been the least understood to date. Here, we present a combined experimental, theoretical, and modeling study on the synthesis of the polyyne triacetylene (HCCCCCCH) via the bimolecular gas phase reaction of the ethynyl radical (CCH) with diacetylene (HCCCCH). This elementary reaction is rapid, has no entrance barrier, and yields the triacetylene molecule via indirect scattering dynamics through complex formation in a single collision event. Photochemical models of Titan's atmosphere imply that triacetylene may serve as a building block to synthesize even more complex polyynes such as tetraacetylene (HCCCCCCCCH)

Io, its Atmosphere and Optical Emissions

Io is surrounded by a halo of atoms which radiate in emission lines. This was discovered by groundbased observations in 1973, a year before Pioneer 10 passed through the Jovian system. Earlier optical and radio observers had reported other anomalies associated with Io, and the Pioneer spacecraft discovered an ultraviolet emission cloud around the satellite and a substantial ionosphere. A new field of planetary research is dedicated to integrating these phenomena into a model of Io and of the Jovian environment with which it strongly interacts. Sodium dominates the optical emission cloud around Io. The production rate is very large and has not yet been satisfactorily explained. Sputtering by charged particle bombardment may play an important role. The primary excitation mechanism is the resonant scattering of sunlight. While the sodium cloud is brightest near Io, it extends around the entire orbit and is present at low levels in the general Jovian environment. The ionospheric electron density on Io is comparable to that on Mars, a surprising result since the solar flus is much weaker. Here, again, Io’s charged particle environment may play an important part. The observed electron profiles plus the constraints provided by the emission cloud are consistent with at least two models of Io’s neutral atmosphere

Magnetically Levitated Autoparametric Broadband Vibration Energy Harvesting

Some of the lingering challenges within the current paradigm of vibration energy harvesting (VEH) involve narrow operational frequency range and the inevitable non-resonant response from broadband noise excitations. Such VEHs are only suitable for limited applications with fixed sinusoidal vibration, and fail to capture a large spectrum of the real world vibration. Various arraying designs, frequency tuning schemes and nonlinear vibratory approaches have only yielded modest enhancements. To fundamentally address this, the paper proposes and explores the potentials in using highly nonlinear magnetic spring force to activate an autoparametric oscillator, in order to realize an inherently broadband resonant system. Analytical and numerical modelling illustrate that high spring nonlinearity derived from magnetic levitation helps to promote the 2:1 internal frequency matching required to activate parametric resonance. At the right internal parameters, the resulting system can intrinsically exhibit semi-resonant response regardless of the bandwidth of the input vibration, including broadband white noise excitation

Heavy ozone enrichments from ATMOS infrared solar spectra

Vertical enrichment profiles of stratospheric ^(16)O^(16)O^(18)O and ^(16)O^(18)O^(16)O (hereafter referred to as ^(668)O_3 and ^(686)O_3 respectively) have been derived from space-based solar occultation spectra recorded at 0.01 cm^(−1) resolution by the ATMOS (Atmospheric Trace MOlecule Spectroscopy) Fourier-transform infrared (FTIR) spectrometer. The observations, made during the Spacelab 3 and ATLAS-1, -2, and -3 shuttle missions, cover polar, mid-latitude and tropical regions between 26 to 2.6 mb inclusive (≈ 25 to 41 km). Average enrichments, weighted by molecular ^(48)O_3 density, of (15±6)% were found for ^(668)O_3 and (10±7)% for ^(686)O_3. Defining the mixing ratio of ^(50)O_3 as the sum of those for ^(668)O_3 and ^(686)O_3, an enrichment of (13±5)% was found for ^(50)O_3 (1σ standard deviation). No latitudinal or vertical gradients were found outside this standard deviation. From a series of ground-based measurements by the ATMOS instrument at Table Mountain, California (34.4°N), an average total column ^(668)O_3 enrichment of (17±4)% (1σ standard deviation) was determined, with no significant seasonal variation discernable. Possible biases in the spectral intensities that affect the determination of absolute enrichments are discussed

A New Understanding of the Europa Atmosphere and Limits on Geophysical Activity

Deep extreme ultraviolet spectrograph exposures of the plasma sheet at the orbit of Europa, obtained in 2001 using the Cassini Ultraviolet Imaging Spectrograph experiment, have been analyzed to determine the state of the gas. The results are in basic agreement with earlier results, in particular with Voyager encounter measurements of electron density and temperature. Mass loading rates and lack of detectable neutrals in the plasma sheet, however, are in conflict with earlier determinations of atmospheric composition and density at Europa. A substantial fraction of the plasma species at the Europa orbit are long-lived sulfur ions originating at Io, with ~25% derived from Europa. During the outward radial diffusion process to the Europa orbit, heat deposition forces a significant rise in plasma electron temperature and latitudinal size accompanied with conversion to higher order ions, a clear indication that mass loading from Europa is very low. Analysis of far ultraviolet spectra from exposures on Europa leads to the conclusion that earlier reported atmospheric measurements have been misinterpreted. The results in the present work are also in conflict with a report that energetic neutral particles imaged by the Cassini ion and neutral camera experiment originate at the Europa orbit. An interpretation of persistent energetic proton pitch angle distributions near the Europa orbit as an effect of a significant population of neutral gas is also in conflict with the results of the present work. The general conclusion drawn here is that Europa is geophysically far less active than inferred in previous research, with mass loading of the plasma sheet ≤4.5 x 10^(25) atoms s^(-1) two orders of magnitude below earlier published calculations. Temporal variability in the region joining the Io and Europa orbits, based on the accumulated evidence, is forced by the response of the system to geophysical activity at Io. No evidence for the direct injection of H_2O into the Europa atmosphere or from Europa into the magnetosphere system, as has been observed at Enceladus in the Saturn system, is obtained in the present investigation