A numerical response of the middle atmosphere to the 11-year solar cycle

A two-dimensional numerical model with coupled photochemistry and dynamics has been used to investigate the response of the middle atmosphere (16–116 km) to changes in solar activity over the 11-year solar cycle. Model inputs that vary with solar cycle include solar radiation, cosmic ray and auroral ionization rates and the flux of NO_x at the model's upper boundary.In this study, the results of model runs for solar cycle minimum and maximum conditions are compared. In the stratosphere, using currently accepted estimates of changes in solar radiation at wavelengths longer than 180 nm, only small responses in ozone, temperature and zonal winds are obtained. On the other hand, changes at shorter wavelengths, and the effects of particle precipitation, lead to large variations in the abundances of trace species in the thermosphere and upper mesosphere. In particular, very large abundances of NO_x are produced above 90 km by auroral particle precipitation. Considerable amounts of NO_x are transported subsequently to the stratosphere by the global mean meridional circulation. It is shown that this excess NO_x can lead to significant decreases in ozone concentrations at high latitudes and that it may explain observations of nitrate deposition in Antarctic snow.     

Sulfide Oxidation across Diffuse Flow Zones of Hydrothermal Vents

The sulfide (H₂S/HS^?) that is emitted from hydrothermal vents begins to oxidize abiotically with oxygen upon contact with ambient bottom water, but the reaction kinetics are slow. Here, using in situ voltammetry, we report detection of the intermediate sulfur oxidation products polysulfides [ $ {\text{S}}_{\text{x}}^{2 - } $ ] and thiosulfate [ $ {\text{S}}_{ 2} {\text{O}}_{ 3}^{ 2- } $ ], along with contextual data on sulfide, oxygen, and temperature. At Lau Basin in 2006, thiosulfate was identified in less than one percent of approximately 10,500 scans and no polysulfides were detected. Only five percent of 11,000 voltammetric scans taken at four vent sites at Lau Basin in May 2009 show either thiosulfate or polysulfides. These in situ data indicate that abiotic sulfide oxidation does not readily occur as H₂S contacts oxic bottom waters. Calculated abiotic potential sulfide oxidation rates are <10^?3 ??M/min and are consistent with slow oxidation and the observed lack of sulfur oxidation intermediates. It is known that the thermodynamics for the first electron transfer step for sulfide and oxygen during sulfide oxidation in these systems are unfavorable, and that the kinetics for two electron transfers are not rapid. Here, we suggest that different metal catalyzed and/or biotic reaction pathways can readily produce sulfur oxidation intermediates. Via shipboard high-pressure incubation experiments, we show that snails with chemosynthetic endosymbionts do release polysulfides and may be responsible for our field observations of polysulfides.     

Comparison of polar mesospheric cloud measurements from the Cloud Imaging and Particle Size experiment and the solar backscatter ultraviolet instrument in 2007

We compare measurements from the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) experiment to the NOAA-17 solar backscatter ultraviolet (SBUV/2) instrument during the 2007 Northern Hemisphere polar mesospheric cloud (PMC) season. Daily average Rayleigh scattering albedos determined from identical footprints from the CIPS nadir camera and SBUV/2 agree to better than ～5% throughout the season. Average PMC brightness values derived from the two instruments agree to within ±10%. PMC occurrence frequencies are on average ～5% to nearly a factor of two higher in CIPS, depending on latitude. Agreement is best at high latitudes where clouds are brighter and more frequent. The comparisons indicate that AIM CIPS data are valid for scientific analyses. They also show that CIPS measurements can be linked to the long time series of SBUV/2 data to investigate long-term variability in PMCs.     

Use of Rhodamine water tracer in the marshland upwelling system

Rhodamine water tracer (RWT) was used to characterize the migration of waste water within the saline subsurface of a marshland upwelling system (MUS), which is an alternative on-site waste water treatment system for coastal areas. Field tracer studies were performed to investigate the fresh waste water plume movement within the saline ground water. Pore velocities were calculated using first detection times and ranged from 0.68 to 10.7 x 10(-4) cm/sec for the loamy sandy soil matrix present at the site. Use of RWT in the field also allowed determination of main and preferential flowpaths. One- and two-dimensional laboratory experiments were performed using silica sand to investigate the interactions of the organically rich waste water with RWT within the zone surrounding the point of injection (one-dimensional) and the impact of background salinity on plume movement (two-dimensional). The results from these studies were used to help explain the field data. One-dimensional breakthrough curves revealed retardation factors for the RWT in the waste water mixture of 1.73 to 1.90. These results were similar to other researchers, indicating little interaction between the waste water and RWT. Variations in pore water salinity (5, 15, 25, and 35 ppt) were found to have a significant effect on pore water velocities of the fresh water plume (two-dimensional), indicating the need to incorporate background salinities into the design process for MUS.     

Reactive transport of gentisic acid in a hematite-coated sand column: Experimental study and modeling

The adsorption of gentisic acid (GA) by hematite nano-particles was examined under static and dynamic conditions by conducting batch and column tests. To simulate natural sediments, the iron oxide was deposited on 10 μm quartz particles. The GA adsorption was described by a surface complexation model fitted to pH-adsorption curves with GA concentrations of 0.1-1 mM in a pH range of 3-10. The surface was described with one type of site (FeOH°), while gentisic acid at the surface was described by two surface complexes (FeLH₂°, log K_int = 8.9 and FeLH⁻, log K_int = −8.2). Modeling was conducted with PHREEQC-2 using the MINTEQ database. From a kinetic point of view, the intrinsic chemical reactions were likely to be the rate-limiting step of sorption (∼10⁻³ s⁻¹) while external and internal mass transfer rates (∼10² s⁻¹) were much faster. Under flow through conditions (column), adsorption of GA to hematite-coated sand was about 7-times lower than under turbulent mixing (batch). This difference could not be explained by chemical adsorption kinetics as shown by test calculations run with HYDRUS-1D software. Surface complexation model simulations however successfully described the data when the surface area was adjusted, suggesting that under flow conditions the accessibility to the reactive surface sites was reduced. The exact mechanism responsible for the increased mobility of GA could not be determined but some parameters suggested that decreased external mass transfer between solution and surface may play a significant role under flow through conditions.     

Scientific objectives of the Solar Mesosphere Explorer mission

The 1981–82 Solar Mesosphere Explorer (SME) mission is described. The SME experiment will provide a comprehensive study of mesospheric ozone and the processes which form and destroy it. Five instruments will be carried on the spinning spacecraft to measure the ozone density and its altitude distribution from 30 to 80 km, monitor the incoming solar ultraviolet radiation, and measure other atmospheric constituent which affect ozone. The polar-orbiting spacecraft will be placed into a 3pm-3 am Sun-synchronous orbit. The atmospheric measurements will scan the Earth's limb and measure: (1) the mesospheric and stratospheric ozone density distribution by inversion of Rayleigh-scattered ultraviolet limb radiance, and the thermal emission from ozone at 9.6 m; (2) the water vapor density distribution by inversion of thermal emission at 6.3 m; (3) the ozone photolysis rate by inversion of the O₂(¹g) 1.27 m limb radiance; (4) the temperature profile by a combination of narrow-band and wide-band measurements of the 15 m thermal emission by CO₂; and, (5) theNO₂ density distribution by inversion of Rayleighscattered limb radiance at 0.439 m. The solar ultraviolet monitor will measure both the 0.2–0.31 m spectral region and the Lyman-alpha (0.1216 m) contribution to the solar irradiance. This combination of measurements will provide a rigorous test of the photochemical equilibrium theory of the mesospheric oxygen-hydrogen system, will determine what changes occur in the ozone distribution as a result of changes in the incoming solar radiation, and will detect changes that may occur as a result of meteorological disturbances.     

The effect of particle precipitation events on the neutral and ion chemistry of the middle atmosphere: II. Odd hydrogen

A one dimensional time-dependent model of the neutral and ion chemistry of the middle atmosphere has been used to examine the production of odd hydrogen (H, OH, and HO₂) during charged particle precipitation. At altitudes above about 65 km, odd hydrogen production depends on the ionization rate, and the atomic oxygen and water vapor densities. Odd hydrogen production is shown to exhibit diurnal and other time dependent variations during such an event at these altitudes, and the assumption that two odd hydrogen particles are always produced per ionization is reexamined.     

Tidal and Groundwater Fluxes to a Shallow, Microtidal Estuary: Constraining Inputs Through Field Observations and Hydrodynamic Modeling

Increased nutrient loading to estuaries has led to eutrophication, degraded water quality, and ecological transformations. Quantifying nutrient loads in systems with significant groundwater input can be difficult due to the challenge of measuring groundwater fluxes. We quantified tidal and freshwater fluxes over an 8-week period at the entrance of West Falmouth Harbor, Massachusetts, a eutrophic, groundwater-fed estuary. Fluxes were estimated from velocity and salinity measurements and a total exchange flow (TEF) methodology. Intermittent cross-sectional measurements of velocity and salinity were used to convert point measurements to cross-sectionally averaged values over the entire deployment (index relationships). The estimated mean freshwater flux (0.19?m³/s) for the 8-week period was mainly due to groundwater input (0.21?m³/s) with contributions from precipitation to the estuary surface (0.026?m³/s) and removal by evaporation (0.048?m³/s). Spring?Cneap variations in freshwater export that appeared in shorter-term averages were mostly artifacts of the index relationships. Hydrodynamic modeling with steady groundwater input demonstrated that while the TEF methodology resolves the freshwater flux signal, calibration of the index?Csalinity relationships during spring tide conditions only was responsible for most of the spring?Cneap signal. The mean freshwater flux over the entire period estimated from the combination of the index-velocity, index?Csalinity, and TEF calculations were consistent with the model, suggesting that this methodology is a reliable way of estimating freshwater fluxes in the estuary over timescales greater than the spring?Cneap cycle. Combining this type of field campaign with hydrodynamic modeling provides guidance for estimating both magnitude of groundwater input and estuarine storage of freshwater and sets the stage for robust estimation of the nutrient load in groundwater.     

The cloud imaging and particle size experiment on the Aeronomy of Ice in the mesosphere mission: Instrument concept,design, calibration,and on-orbit performance

The Cloud Imaging and Particle Size Experiment (CIPS) is one of three instruments aboard the Aeronomy of Ice in the Mesosphere spacecraft. CIPS provides panoramic ultraviolet images of the atmosphere over a wide range of scattering angles in order to determine the presence of polar mesospheric clouds, measure their spatial morphology, and constrain the parameters of cloud particle size distribution. The AIM science objectives motivate the CIPS measurement approach and drive the instrument requirements and design, leading to a configuration of four wide-angle cameras arrayed in a ‘+’ arrangement that covers a 120° (along orbit track)×80° (across orbit track) field of view. CIPS began routine operations on May 24, 4 weeks after AIM was launched. It measures scattered radiances from PMCs near 83 km altitude to derive cloud morphology and particle size information by recording multiple exposures of individual clouds to derive PMC scattering phase functions and detect nadir horizontal spatial scales to approximately 3 km. This paper describes the instrument design, its prelaunch characterization and calibration, and flight operations. Flight observations and calibration activities confirm performance inferred during ground test, verifying that CIPS exceeds its measurement requirements and goals. These results are illustrated with example flight images that demonstrate the instrument measurement performance.