bluuebunny/crossref_metadata_2025 huggingface dataset:
The distribution of helium 3 in the deep western and southern Indian Ocean
Authors: Jamous Daniel , Mémery Laurent , Andrié Chantal , Jean‐Baptiste Philippe , Merlivat Liliane
Published: February 2008

Almost a decade after the Geochemical Ocean Sections Study Indian Expedition, the new deep 3He data from the INDIGO program give a further insight into the distribution of this tracer in the Indian Ocean. This distribution exhibits some major features related on one hand to a hydrothermal 3He input in the Gulf of Aden and on the Mid‐Indian Ocean Ridge, and on the other to the origin of the water masses and to the characteristics of the deep circulation. The main pattern is a significant north‐south 3He gradient, with deep waters of the southern ocean showing δ3He values around 8–9% due to the influence of the Atlantic deep waters poor in 3He and relatively high values in the northern and central regions (15% to 18% between 2000 m and 3000 m depth) originating from the hydrothermal activity. In the easternmost part of the basin, the 3He values exhibit a significant increase at shallower depths (around 1000 m) probably due to the Pacific water flow through the Indonesian sills, whereas the data in the Indian sector of the Antarctic ocean show a maximum of the order of 10%, south of the Polar Front, interpreted as showing the presence of the Pacific deep waters in the Antarctic Circumpolar Current. These different aspects are summarized by mapping the horizontal distribution of the δ3He maxima all over the Indian basin. This map points out some characteristics of the deep circulation but also stresses the need for further measurements in order to clarify the description of this tracer in several key areas.
Assessment of the air‐sea exchange of CO2 in the south Pacific during austral autumn
Authors: Murphy Paulette P. , Feely Richard A. , Gammon Richard H. , Harrison D. E. , Kelly Kimberly C. , Waterman Lee S.
Published: February 2008

Measurements of CO2 concentrations in the atmosphere and in the surface waters of the South Pacific Ocean were made by NOAA scientists between 1984 and 1989. These basin‐wide measurements were all taken during austral autumn and provide data for evaluation of the seasonal flux of CO2 from this region. The sensitivity of this flux to the uncertainty in the CO2 gas exchange coefficient was evaluated using four different wind data sets and two formulations for the wind dependence of gas transfer velocity. The integrated net flux of CO2 to the atmosphere during austral autumn (February to May) ranges from −0.03 (ocean influx) to +0.09 (ocean efflux) GT of carbon depending on the combination of wind field and wind‐dependent exchange coefficient used.
An acoustic backscatter thermometer for remotely mapping seafloor water temperature
Authors: Jackson Darrell R. , Dworski J. George
Published: February 2008

A bottom‐mounted, circularly scanning sonar operating at 40 kHz has been used to map changes in water sound speed over a circular region 150 m in diameter. If it is assumed that the salinity remains constant, the change in sound speed can be converted to a change in temperature. For the present system, the spatial resolution is 7.5 m and the temperature resolution is 0.05°C. The technique is based on comparison of successive sonar scans by means of a correlation algorithm. The algorithm is illustrated using data from the Sediment Transport Events on Slopes and Shelves (STRESS) experiment.
Evaluation of multichannel sea surface temperature product quality for climate monitoring: 1982–1988
Authors: Bates John J. , Diaz Henry F.
Published: February 2008

Satellite‐derived multichannel sea surface temperature (MCSST) data are evaluated for the period 1982–1988 relative to in situ data from the comprehensive ocean‐atmosphere data set (COADS). A number of statistical methods are used to assess the quality of the MCSST data. Temporal anomaly cross correlations are significant at the 95% confidence level for all basins and subregions examined, except for the North Atlantic Ocean. Biases in the MCSST product, caused by volcanic aerosols and by use of the wrong satellite calibration tables, cause problems in the utility of the MCSST data for climate monitoring. Signal‐to‐noise variance ratios range from 0.49 in the North Atlantic Ocean to above 4 in the equatorial Pacific. Mean differences between MCSST and COADS show that the MCSST values are lower than COADS by 0.19° to 0.64°C. The mean differences are found to have an annual cycle that varies with latitude and season. The mean MCSST standard deviations are always lower than those of COADS (except again for the North Atlantic Ocean), ranging from 0.03° to 0.45°C. Accurate monitoring of SST variability in the southern oceans is not possible without the use of satellite data. Because of the stringent accuracy requirements of SST data for climate monitoring, however, the utility of MCSST data alone for this purpose is only marginal.
The influence of stable stratification on small‐scale anisotropy and dissipation in turbulence
Authors: Thoroddsen S. T. , Van Atta C. W.
Published: February 2008

Small‐scale turbulence measurements in stably stratified grid‐generated turbulence show that strong stable stratification induces large anisotropies in the mean‐square strain rates ∂v/∂x and ∂w/∂x, relative to ∂u/∂x. This effect is magnified with increased strength of stratification. Froude number scaling is partially successful in collapsing the data. Anisotropies of the strain rates associated with the small scales are found to develop relatively faster than the anisotropy of the large‐scale energy containing eddies. The mean‐square magnitude of the ∂w/∂x strain rate is up to 4 times lower than the level predicted from ∂u/∂x based on isotropy. These results cast doubt on the accuracy of employing conventional dissipation estimates based on the assumption of local isotropy in stratified turbulence, at least for the low Reynolds numbers characterizing these experiments. These results are especially relevant to ocean microscale measurements, as buoyancy affected turbulence with similar dynamical character, i.e., ε/νN2 of similar magnitudes, has been observed in the thermocline (see Gregg and Sanford, 1988; Yamazaki, 1990). Estimates of dissipation rates based on the formulations of Stillinger et al. (1983) and Yamazaki and Osborn (1990) are shown to disagree by as large as a factor of 2. The measurements also show that stable stratification induces anisotropy in the lateral horizontal rms velocity component in addition to the well‐known vertical anisotropy. The lateral anisotropy is about half of the vertical anisotropy. Measured spectral relations between the stream wise and lateral velocity components in the horizontal plane were compared with relations predicted by the two‐ and three‐dimensional (2‐D and 3‐D) isotropic theories. Comparison of measured and calculated lateral spectra indicate no tendency toward the development of 2‐D turbulence in the range of Froude numbers studied.
A perturbation simulation of CO2 uptake in an ocean general circulation model
Authors: Sarmiento Jorge L. , Orr James C. , Siegenthaler Ulrich
Published: February 2008

The uptake of anthropogenic CO2 by the ocean is simulated using a perturbation approach in a three‐dimensional global general circulation model. Atmospheric pCO2 is prescribed for the period 1750–1990 using the combined Siple ice core and Mauna Loa records. For the period 1980 to 1989, the average flux of CO2 into the ocean is 1.9 GtC/yr. However the bomb radiocarbon simulation of Toggweiler et al. (1989b) shows that the surface to deep ocean exchange in this model is too sluggish. Hence the CO2 uptake calculated by the model is probably below the actual value. The observed atmospheric increase in 1980 to 1989 is 3.2 GtC/yr, for a combined atmosphere‐ocean total of 5.1 GtC/yr. This is comparable to the estimated fossil CO2 production of 5.4 GtC/yr, implying that other sources and sinks (such as from deforestation, enhanced growth of land biota, and changes in the ocean carbon cycle) must be approximately in balance. The sensitivity of the uptake to the gas exchange rate is small: a 100% increase in gas exchange rate gives only a 9.2% increase in cumulative oceanic uptake. Details of the penetration into different oceanic regions are discussed.
An energy‐salinity balance climate model: Water vapor transport as a cause of changes in the global thermohaline circulation
Authors: Wang Huaxiao , Birchfield G. Edward
Published: February 2008

The connection between water vapor transport and the thermohaline circulation is examined with a simple global coupled ocean‐atmosphere energy‐salinity balance model (ESBM). Both latitudinal intrabasin and interbasin water vapor fluxes are considered. It is demonstrated that interbasin and intrabasin water vapor fluxes play interdependent and competitive roles in affecting the state of the thermohaline circulation. Increasing intrabasin water vapor flux in the North Atlantic, by decreasing water density in the high latitudes, decreases the North Atlantic deep water production and hence the thermohaline circulation, while increasing interbasin water vapor flux from the Atlantic to the Pacific, by increasing the mean density of the Atlantic and decreasing that of the Pacific, increases the strength of the global thermohaline circulation. The global thermohaline circulation and its asymmetry are sensitive to the latitudinal hydrological cycle in the North Atlantic because of the large water vapor flux from the Atlantic to Pacific Ocean. Global thermohaline circulation exhibits bimodal equilibria as a consequence of imbalances in rates of change of advective and eddy freshwater fluxes in the high‐latitude North Atlantic. One equilibrium mode resembles the modern ocean circulation with a strong global asymmetric thermohaline circulation associated with dominant deep water production in the North Atlantic and an effective “heat pump” operating in the Atlantic Ocean. In the other equilibrium, deep water is produced primarily in the Southern Ocean; in particular, North Atlantic deep water is replaced by Southern Ocean deep water. Deep water is produced in the North Pacific in this mode, but is, for reasonably large interbasin water vapor transport, insufficient to reverse the direction of deep water flow into the South Pacific. Based on estimated water vapor fluxes for the present climate, our study suggests that the present thermohaline circulation is dynamically stable, i.e., far from the critical regions of rapid transition between two modes.
Measurements of nitrogen oxides at Barrow, Alaska during spring: Evidence for regional and northern hemispheric sources of pollution
Authors: Jaffe D. A. , Honrath R. E. , Herring J. A. , Li S.‐M. , Kahl J. D.
Published: February 2008

Total reactive nitrogen oxide (NOy) and NO were measured at the National Oceanic and Atmospheric Administration Geophysical Monitoring for Climatic Change (NOAA GMCC) site at Barrow, Alaska, for 5 weeks during the spring of 1989. The data demonstrate the existence of a complex array of pollution sources which influence arctic air chemistry. During periods when 10‐day back‐trajectories indicated southerly flow, median NOy concentrations ranged from 284 to 467 ppt. When the 10‐day back‐trajectories originated in the Arctic, median NOy, concentrations ranged from 617 to 734 ppt, providing evidence for the long‐range transport of pollutants to the Arctic known as “arctic haze.” The NOy concentrations observed during the spring background periods are significantly higher than previous measurements of NOy at Barrow taken during summer, regardless of where the air mass originated. These observations provide evidence for a greatly increased NOy lifetime during the colder months over a large region of the background troposphere as well as the presence of much higher NOy concentrations in the Arctic. During four 12–60 hour events, substantially elevated NOy were observed in air not impacted by emissions from the town of Barrow. During these four events, peak NOy concentrations of 3 to 16 ppb were observed. Other data, including NO, SO2, SO4, and meteorology, were used to help identify the source region for the elevated NOy levels. These data present a consistent picture which indicates that during certain periods, elevated NOy levels are associated with air coming from the Prudhoe Bay industrial area approximately 300 km to the ESE and demonstrate that this facility is a major source of nitrogen oxides, and possibly other air pollutants, to the Alaskan Arctic.
Stratospheric photochemical studies with Atmospheric Trace Molecule Spectroscopy (ATMOS) measurements
Authors: Natarajan Murali , Callis Linwood B.
Published: February 2008

The photochemical partitioning of stratospheric odd nitrogen and odd chlorine is examined using diurnal model calculations and data from the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment. This experiment, conducted during April–May 1985, used a solar occultation technique to obtain vertical profiles of temperature and various other trace constituents at 30°N and 48°S latitudes. The knowledge of total odd nitrogen and odd chlorine levels is a major advantage provided by this data set. We have conducted model calculations for different altitudes at 30°N to evaluate photochemical parameters of interest. Calculated NO2 and NO profiles at sunset are compared with the ATMOS observations. The calculated ratio NO2/NO at sunset is smaller than the observed value by about 27% at 40 km. This difference could be explained by uncertainties in the data and model parameters. The ATMOS data set confirms the presence of N2O5 in the stratosphere; however, the observed mixing ratios at sunset are more than a factor of 2 smaller than the calculated values. We have used recent information on the sticking coefficient for N2O5 on sulfuric acid aerosol surfaces and background aerosol surface area density distribution to estimate the lifetime of N2O5 against removal by heterogeneous reaction. It is shown that the conversion of N2O5 into HNO3 could take place in the presence of aerosol surface rapidly enough to affect the N2O5 mixing ratio below 30 km. The inclusion of the heterogeneous reaction brings the calculated N2O5 profile below 30 km into better agreement with the ATMOS data. The present calculations give lower HCl mixing ratios compared to the ATMOS data in the 30‐to 43‐km region. We have examined the effects of a secondary path for the reaction OH + ClO, leading to the production of HCl. With a branching ratio of 8% for this path we find that the discrepancy between the calculated and measured HCl is essentially removed. This modification reduces the chlorine‐catalyzed destruction of odd oxygen and has the potential to significantly improve agreement between measured and modeled O3 in the middle stratosphere.
Further study of a saturated gravity wave spectrum in the mesosphere
Authors: Wu Yong‐Fu , Widdel H.‐U.
Published: February 2008

Mesospheric wind profiles with a height resolution of 25 m derived from five foil chaff experiments performed during the last salvo of the MAC/SINE (Middle Atmosphere Cooperation/Summer in Northern Europe) campaign in the summer of 1987 at Andøya Rocket Range, in Northern Norway (69°17′N, 16°01′E), allow us to study the character of the motion spectrum in the mesosphere. The wind data have shown that (1) the average slope of the five vertical wave number spectra was −3.0 ± 0.2 for wavelengths in the range from 6.4 km to 100 m; (2) a dominant vertical wavelength of more than 6.4 km was found; and (3) there was good agreement between the observed spectrum and the saturated spectrum presented by Dewan and Good (1986) and Smith et al. (1987). In this paper, we further show that (1) very large wind shears, as high as 50–90 m s−1 km−1, are observed to be present at various heights (such large shears yield Richardson numbers smaller than 0.25, suggesting that the saturated gravity wave spectrum is associated with the shear instabilities); and (2) when the Richardson number profile is compared with the altitude profile of the mesosphere‐stratosphere‐troposphere (MST) radar (SOUSY) echo power, the low Richardson numbers are observed in the region of most intense backscatter. It is suggested from our measurements that the enhanced echo power is linked to wave saturation processes.
Stratospheric Aerosol and Gas Experiment II measurements of the quasi‐biennial oscillations in ozone and nitrogen dioxide
Authors: Zawodny Joseph M. , McCormick M. Patrick
Published: February 2008

The first measurements ever to show a quasi‐biennial oscillation (QBO) in NO2 have been made by the Stratospheric Aerosol and Gas Experiment II (SAGE II) and are presented in this work along with observations of the well‐known QBO in stratospheric ozone. The SAGE II instrument was launched aboard the Earth Radiation Budget satellite near the end of 1984. Measurements of ozone and nitrogen dioxide through early 1990 are analyzed for the presence of a quasi‐biennial oscillation. The measurements show the global extent of both the O3 and NO2 QBO in the 25‐ to 40‐km region of the stratosphere. The SAGE II QBO results for ozone compare favorably to theory and previous measurements. The QBO in NO2 is found to be consistent with the vertical and horizontal transport of NOy. Both species exhibit a QBO at extratropical latitudes consistent with strong meridional transport into the winter hemisphere.
Calibration of a magnetic direction finding network using measured triggered lightning return stroke peak currents
Authors: Orville Richard E.
Published: February 2008

Peak currents from 18 triggered lightning return strokes lowering negative charge have been measured at the NASA Kennedy Space Center, Florida. These strokes are correlated with simultaneous measurements by six Lightning Location and Protection (LLP) Inc. wideband magnetic direction finders (DFs) in Georgia and Florida operating at high gain from 1985 through 1988. The following have been determined: (1) The normalized signal strength amplitudes, in LLP units, can be used to estimate the peak current in lightning return strokes by the relation, I(kA) = 2.3+0.19(Normalized Amplitude), where the amplitude is range‐normalized to 100 km. An approximation of the form, I(kA) = 0. 2(Normalized Amplitude) is also valid, introducing errors of typically less than 6 %. (2) Range‐normalized signal strength amplitudes, in LLP units, for individual DFs have been examined as a function of the measured return stroke peak currents. It is found that a DFs normalized amplitude has a higher correlation with peak currents, the further the DF site is from the triggered lightning. The correlation coefficients range from 0.53 to 0.93, At a DF site the standard deviation of the normalized amplitudes from the best fit line to the measured peak currents are independent of the DF site's distance from the triggered lightning, averaging 28 LLP units, which corresponds to 6 kA. (3) Signal strength amplitudes, which are proportional to the peak magnetic radiation fields, have been examined for seven triggered lightning return strokes. The signal strength amplitudes decay with distance, D, as D−1.13. (4) An evaluation of the error in the mean range‐normalized signal strength amplitude caused by lightning location errors reveals that the mean amplitude is typically in error by less than 2% from the value calculated using the exact location of the triggered flash.
Determination of the isotopic composition of atmospheric methane and its application in the Antarctic
Authors: Lowe David C. , Brenninkmeijer Carl A. M. , Tyler Stanley C. , Dlugkencky Edward J.
Published: February 2008

A procedure for the determination of the 13C/12C ratio and the 14C abundance in atmospheric methane is presented. The method is based on the collection of air samples in stainless steel tanks at a pressure of 7 bar. The air is processed in the laboratory by cryogenic removal of condensibles, followed by oxidation of the methane content after which the resulting CO2 is collected. Also CO is removed prior to oxidation. The 13C/12C ratio is determined on the CO2 sample by stable isotope ratio mass spectrometry. The 14C content is determined by means of accelerator mass spectrometry. The overall precision of the technique is 0.1‰ for δ13C and 1.5 pMC for 14C. The method has been used to determine the carbon isotopic composition of methane in air collected at Baring Head, New Zealand, and also in air collected on aircraft flights between New Zealand and Antarctica. No gradient in the carbon isotopic composition between Baring Head and South Pole station was detected. The annual mean δ13C value at Baring Head was −47.13±0.20‰ for 1989 which includes seasonal effects probably due to OH variations and local meteorology. The annual mean 14C value at Baring Head in 1989 was 118.3 percent modern (pMC).
Infrared measurements of HF and HCl total column abundances above Kitt Peak, 1977–1990: Seasonal cycles, long‐term increases, and comparisons with model calculations
Authors: Rinsland C. P. , Levine J. S. , Goldman A. , Sze N. D. , Ko M. K. W. , Johnson D. W.
Published: February 2008

Series of high‐resolution (∼0.01 cm−1) solar absorption spectra recorded with the McMath Fourier transform spectrometer on Kitt Peak (altitude 2.09 km, 31.9°N, 111.6°W) have been analyzed to deduce total column amounts of HF on 93 different days and HCl on 35 different days between May 1977 and June 1990. The results are based on the analysis of the HF and H35Cl (1–0) vibration‐rotation band R(1) lines which are located at 4038.9625 and 2925.8970 cm−1, respectively. All of the data were analyzed using a multilayer, nonlinear least squares spectral fitting procedure and a consistent set of spectroscopic line parameters. The results indicate a rapid increase in total HF and a more gradual increase in total HCl with both trends superimposed on short‐term variability. In addition, the total columns of both gases undergo a seasonal cycle with an early spring maximum and an early fall minimum, with peak‐to‐peak amplitudes equal to 25% for HF and 13% for HCl. In the case of HF, the changes over the 13 years of measurement are sufficiently large to determine that a better fit is obtained assuming a linear rather than an exponential increase with time. For HCl, linear and exponential models fit the data equally well. Referenced to calendar year 1981.0 and assuming a sinusoidal seasonal cycle superimposed on a linear total column increase with time, HF and HCl increase rates of (10.9±1.1)% yr−1 and (5.1±0.7)% yr−1 and total columns of (3.17±0.11)×1014 and (1.92±0.06)×1015 molecules cm−2 (2 sigma) are derived, respectively; the corresponding best fit mean exponential increase rates are equal to (7.6±0.6)% yr−1 and (4.2±0.5)% yr−1 (2 sigma). Over the 13‐year observing period, the HF and HCl total columns increased by factors of 3.2 and 1.8, respectively. Based on HF and HCl total columns deduced from measurements on the same day, the HF/HCl total columns ratio increased from 0.14 in May 1977 to 0.23 in June 1990. Short‐term temporal variations in the HF and HCl total columns are highly correlated; these fluctuations are believed to be caused by dynamical variability in the lower stratosphere. The results of this investigation are compared with previously reported measurements and with time‐dependent, two‐dimensional model calculations of HF and HCl total columns based on emission histories and photo‐oxidation rates for the source molecules.
A comparison of sulfur‐free and ambient air enclosure techniques for measuring the exchange of reduced sulfur gases between soils and the atmosphere
Authors: Castro Mark S. , Galloway James N.
Published: February 2008

The exchange of reduced sulfur gases between the atmosphere and forest soils in the Shaver Hollow watershed (Shenandoah National Park, Virginia) were measured with sulfur‐free and ambient air enclosures at least twice a month from March through November 1989. Soils within sulfur‐free enclosures were sources of carbonyl sulfide (COS) and carbon disulfide (CS2). Atmospheric fluxes of COS and CS2 ranged from 0.77 to 13.03 ng COS‐S/m2‐min and from 2.04 to 15.74 ng CS2‐S/m2‐min. In contrast, soils within ambient air enclosures were sinks for COS and CS2. Uptake rates of COS and CS2 ranged from 2.78 to 16.20 ng COS‐S/m2‐min and from 3.42 to 26.62 ng CS2‐S/m2‐ min. The discrepancy in the direction of these fluxes was caused by the flux measurement techniques.
Atmospheric methane: A global three‐dimensional model study
Authors: Tie XueXi , Alyea Fred N. , Cunnold Derek M. , Kao C.‐Y. Jim
Published: February 2008

We have developed a three‐dimensional model to study global methane distributions and the transport of methane. The model includes transports, chemical reactions, and global methane sources. The calculations provide a fairly good simulation of the observed latitudinal gradient of methane and its global mean distribution in the stratosphere. The model results also suggest that rice paddies in Southeast Asia and wetlands in the high latitudes of North America can contribute to required sources for maximum of methane. The simulation also models the positive vertical gradients of methane in the troposphere of the southern hemisphere, which was observed by Fraser et al. (1984). The model analyses show that this positive gradient is the result of the interhemispheric transport of methane at upper levels of the troposphere.
Nonlocal thermodynamic equilibrium processes in ozone: Implications for the energy budget of the mesosphere and lower thermosphere
Authors: Mlynczak Martin G.
Published: February 2008

The conversion of chemical potential energy and infrared radiative energy to kinetic energy by nonlocal thermodynamic equilibrium (non‐LTE) processes involving ozone is a potentially significant source of heat in the terrestrial upper mesosphere and lower thermosphere. Heating rates in excess of 6 K d−1 could occur near the mesopause if all potential energy is converted to heat. Calculation of the heating rate requires knowledge of the processes which convert chemical potential energy to internal energy of ozone during the exothermic recombination reaction that forms ozone. In addition, the rates at which ozone exchanges internal energy with its surroundings through collisional and radiative processes must be known. The lack of a detailed data base of kinetic and spectroscopic information limits the ability to accurately model the heating by ozone. Therefore heating rates are calculated and compared using two different statistical equilibrium models previously applied in the analysis of measurements of limb emission from ozone. The calculated heating depends strongly on the assumed distribution and relaxation of energy in the quasi‐nascent ozone molecule. Finally, in the absence of a detailed data base of rate coefficients it may be possible to estimate the heating rate due to non‐LTE processes in ozone from appropriate satellite measurements of the ozone concentration and of the infrared emission from ozone in the 9–12 μm spectral interval.
Shortwave, longwave, and net cloud‐radiative forcing as determined from Nimbus 7 observations
Authors: Ardanuy Philip E. , Stowe Larry L. , Gruber Arnold , Weiss Mitchell
Published: February 2008

We studied the effect of clouds on the Earth's radiation budget at the top of the atmosphere. Both the northern hemisphere summer and winter are considered in terms of cloud‐radiative forcing, which describes the total effect of clouds on the Earth's radiation budget components. The cloud forcing is obtained by using statistically generated models correlating simultaneous observations of cloud properties and radiation budget parameters obtained from observations from Nimbus 7 satellite observations. The models estimate the broadband albedo and longwave flux throughout the range of variation, including periods of extensive to near‐total cloud cover where more simplistic representations fail. As such, the models are used to estimate period‐averaged clear‐sky radiation budget components. Knowledge of the cloudy‐sky and clear‐sky radiation budget components permits the computation of cloud‐radiative forcing. We show that the net effect of clouds is to cool the Earth. On the average, for an Earth observed to be 52.1% cloud covered, the net cloud forcing is −26.8 Wm−2. This net cooling is obtained from a longwave warming of 24.1 Wm−2 and a shortwave cooling of −50.9 Wm−2. Over much of the Earth there is a general compensation between the warming and cooling effects of clouds. However, over the middle‐ and high‐latitude oceans the albedo effect of clouds is dominant. This is particularly true in each summer hemisphere, where the effects of persistent cloudiness, low oceanic albedos, and high solar insolation combine to drive the net cloud forcing strongly negative. The net effect of cloud forcing cools the Earth, primarily due to the effect of clouds in the summer hemisphere oceans.
Multilevel measurement of the electric field underneath a thundercloud: 2. Dynamical evolution of a ground space charge layer
Authors: Soula Serge , Chauzy Serge
Published: February 2008

In August 1989 the electric field was measured below a thunderstorm at Kennedy Space Center for more than 1 hour at several levels up to 800 m. No substantial precipitation reached the ground at the experimental site until after this data collection period, which included the thunderstorm approach and the triggering of four lightning flashes. The sensors at altitude were suspended from a tethered balloon and that at the surface was a standard field mill. The maximum value detected was 65 kV/m at 603 m while at the same time the steady surface field did not exceed 5 kV/m. Applying Gauss's law to the electric field data, we have calculated average charge densities within the layers formed by the levels where the sensors were located. Corona ions produced at the surface were detected up to the upper layer between 436 m and 603 m, and the densities calculated reached values close to 1 nC m−3 within each layer. The current densities were also evaluated at the sensor levels; the one calculated at 436 m ranges about 1.4 nA m−2 which means that a large proportion of corona ions were carried up to several hundreds of meters above ground.
An upper limit for the rate coefficient of the reaction of NH2 radicals with O2 using FTIR product analysis
Authors: Tyndall G. S. , Orlando J. J. , Nickerson K. E. , Cantrell C. A. , Calvert J. G.
Published: February 2008

Fourier transform infrared spectrometry has been used to study the products of the photooxidation of ammonia in the presence of oxygen at 296 K. The data have been used to derive an upper limit of 6×10−21 cm3 molecule−1 s−1 for the reaction of NH2 radicals with O2 to produce NOχ at 296 K. This upper limit, which is 3 orders of magnitude lower than previous estimates based on the kinetics of NH2 loss, rules out the importance of this reaction in the atmosphere and suggests that NH2 will be oxidized by O3 or NO2. The effect on the NOχ and N2O budgets depends critically on the products of the NH2 + O3 reaction. Simulations of the experimental product yields also allow an evaluation of possible product channels for the reaction of NH2 with HO2.
Na Doppler/temperature lidar: Initial mesopause region observations and comparison with the Urbana medium frequency radar
Authors: Bills Richard E. , Gardner Chester S. , Franke Steven J.
Published: February 2008

Meteoric ablation in the upper atmosphere is the source of a dense layer of atomic Na between about 80 and 105 km altitude. Peak densities are typically several thousand atoms/cm3, and the total abundance varies seasonally at mid‐latitudes with the maximum in winter. The Na layer is a sensitive tracer of the thermal and density structure of this region of the atmosphere and can be probed with exceptional accuracy and resolution using resonance fluorescence lidar techniques. We report the first observations of vertically resolved Na density, temperature, and wind profiles in the mesopause region using a new four‐frequency Doppler/temperature lidar. The initial zonal wind and temperature observations were obtained with a resolution of 30 min and 1.5 km and rms accuracies of 12 m/s and 2 K. These measurements were conducted simultaneously with the medium frequency (MF) radar at the Urbana Atmospheric Observatory (40°N, 88°W) during the night of March 14–15, 1991. The mean temperature profile exhibits a well‐defined mesopause at 95.5 km with a temperature of 181 K. The mean zonal wind profile exhibits a strong 58 m/s westward jet at 97 km which appears to be related to the mesopause. During the 6‐hour and 45‐min observation period the Na Doppler winds, averaged between 88 and 98 km, exhibit the same general trends as the MF radar apparent and true winds in this same region. However, the lidar and radar velocity estimates differ by as much as 40 m/s at some times during the night.
Transport of N2O in the stratosphere related to the equatorial semiannual oscillation
Authors: Choi Woo Kap , Holton James R.
Published: February 2008

A two‐dimensional time‐dependent tracer model was constructed to study the double‐peak structure (equatorial minimum and subtropical maxima) observed in the distribution of nitrous oxide during the spring equinoctial condition. The meridional transport circulation was determined from computed diabatic heating rates, and the horizontal eddy diffusion coefficients were computed as residuals by potential vorticity conservation, using observed mean winds to compute the budget of zonal mean potential vorticity. This model was used to predict the 30‐day evolution of the observed nitrous oxide field. The integrated results were generally in good agreement with observed tracer fields up to the midstratosphere. However, the agreement between the model calculations and the observed mixing ratios was not as good in the equatorial upper stratosphere at the equinoxes. Stronger downward motion compared to motion derived from diabatic heating rates based on climatological temperature and ozone fields is required in the equatorial region in order to simulate the observed double‐peak structure. To intensify the equinoctial subsidence, the semiannual oscillation in the zonal mean wind and temperature fields were enhanced to double the climatological values in the equatorial region. The diabatic vertical velocity fields produced in this way significantly changed the resulting tracer patterns. The double‐peak structure produced by the model with the modified meridional circulation was much closer to the observed double peak than the one produced by the model based on the original diabatic circulation. A possible change of the ozone concentration associated with the specified temperature change was estimated. The effect of this ozone change on transport was to enhance the strength of the semiannual oscillation, although the magnitude was very small. This work indicates that standard climatologies may underestimate the strength of the equatorial semiannual oscillation. The diabatic circulation must be stronger than implied by these climatologies. Otherwise, it does not seem possible to account for the observed evolution of the nitrous oxide mixing ratio distribution.
Spectral line shape considerations for limb temperature sounders
Authors: Edwards David P. , Strow L. Larrabee
Published: February 2008

The sensitivity of radiative transfer calculations to spectral line shape models is investigated for two CO2 spectral regions used by instruments aboard the Upper Atmosphere Research Satellite for making low‐altitude temperature and pressure retrievals. Line shape models have been tested by comparing calculated spectra with observations made by the Atmospheric Trace Molecule Spectroscopy experiment. Spectral line mixing is discussed and shown to be important at the 617 cm−1 Q branch where its inclusion in the radiative transfer model can lead to differences of more than 2 K in brightness temperature at low tangent heights. The sub‐Lorentzian line wings of the CO2 ν2 band must be correctly modeled in calculations at the 791 cm−1 Q branch otherwise equivalent brightness temperatures for a 15 km limb view will be in error by as much as 10 K.
The subsurface character of Meteor Crater, Arizona, as determined by ground‐probing radar
Authors: Pilon J. A. , Grieve R. A. F. , Sharpton V. L.
Published: February 2008

Ground‐probing radar has provided new two‐dimensional stratigraphic and structural information on Meteor Crater, Arizona. Four 50‐MHz transects inside the crater and one 100‐MHz transect on a northeast radial across the exterior ejecta blanket were carried out. The frequencies used were in relation to the desired depth of investigation: greater than 50 m at 50 MHz and ∼30 m for 100 MHz. The results obtained inside the crater show that the water table can be clearly detected at depths of ∼65 m, as can the contact between the crater wall and the infilling allochthonous breccia lens. In addition, we were able to detect (1) point reflectors from relatively coherent blocks (>1.5m) within the breccia lens, (2) a zone ∼7 m thick relatively free of point reflectors from the immediate fall back unit, (3) a series of subhorizontal reflectors a few meters apart due to bedding in the post impact crater sediments, and (4) five separate subhorizontal reflectors from what we interpret to be a series of postimpact paleo‐water table levels in the breccia lens. The ejecta blanket transect indicates a ∼4–10 m thick ejecta layer and the underlying Moenkopi Formation sandstone, as well as the Moenkopi‐Kaibab contact and bedding within the Kaibab Formation. In addition, reverse faults with displacements up to 4 m were detected in the bedrock, as well as changes from subhorizontal to ∼30° in the dip of the bedrock as the crater rim is approached from the northeast. Beneath the ejecta blanket, the total uplift observed at the crater rim is around 55 m. The radar data indicate uplift effects out to a radial distance of ∼400 m from the rim, farther than that determined from drilling (∼300 m). The results demonstrate the utility of continuous ground‐probing radar cross sections in studying the near‐subsurface (∼50 m) character at Meteor Crater. This relatively rapid, low cost technique can be extended to other structures, but confident interpretation requires supplemental ground truth constraints.
Editorial
Authors: Chapman Clark R.
Published: February 2008

No abstract is available for this article.
Laboratory measurement of the millimeter wave properties of liquid sulfuric acid (H2SO4)
Authors: Fahd Antoine K. , Steffes Paul G.
Published: February 2008

Recent observations of the millimeter wave (2.6 mm) emission from Venus have shown significant variations in its continuum flux emission (de Pater et al., 1991). Some of this change in emission may be attributed to variability in the abundance of Venus cloud constituents, specifically H2SO4 condensates. In order to evaluate this hypothesis, a knowledge of the dielectric properties of liquid sulfuric acid at millimeter wave frequencies (30 < f < 300 GHz) is needed. The dielectric constants can then be used to determine the expected absorptivity from such a condensate and hence the effect of H2SO4 droplets on the millimeter wave emission from Venus. Therefore we have performed laboratory measurements of the complex dielectric constant of liquid sulfuric acid between 30–40 and 90–100 GHz. The methodology and the results are reported in this paper along with a calculation of the absorption properties of H2SO4 droplets under Venus‐like conditions. In addition, this paper discusses the effects of these condensates on the variation in the flux emission of Venus and compares the effect of H2SO4 droplets with other absorbers in the atmosphere of Venus such as gaseous SO2. We conclude that this condensate does affect the brightness temperature of Venus and its effect cannot be omitted in future modeling of the atmosphere of Venus.
Optical constants of solid methane and ethane from 10,000 to 450 cm−1
Authors: Pearl J. , Ngoh M. , Ospina M. , Khanna R.
Published: February 2008

We made thin film transmission measurements of solid CH4 (phases I and II) and C2H6 (phase II). From these, the complex indices of refraction at near‐ and mid‐infrared wavelengths were determined by using a combined least squares and Kramers‐Kronig analysis.
A mantle plume model for the equatorial highlands of Venus
Authors: Kiefer Walter S. , Hager Bradford H.
Published: February 2008

The Equatorial Highlands of Venus consist of four main structures, Atla, Beta, Ovda, and Thetis regiones. Each has a circular to oval‐shaped planform and rises 4–5 km above the mean planetary radius. These highlands are associated with long‐wavelength geoid highs, with amplitudes ranging from 35 m at Ovda to 120 m at Atla. They also contain topographic valleys, interpreted as extensional rift zones, and Beta is known to contain shield volcanoes. These characteristics are all consistent with the Equatorial Highlands being formed by mantle plumes. An alternative model, in which Ovda and Thetis are interpreted as spreading centers analogous to terrestrial mid‐ocean ridges, fails to explain most of the observed geoid anomalies and topography in these regions. Some smaller highlands, such as Bell Regio, Eistla Regio, and the Hathor/Innini/Ushas region, may also be plume related, but most coronae are unlikely to be the direct result of plume activity. We have modeled plumes using a cylindrical, axisymmetric finite element code and a depth‐dependent, Newtonian rheology. We compare our model results with profiles of geoid and topography across Atla, Beta, Ovda, and Thetis; our best model fits are for Beta and Atla. Assuming whole mantle convection and that Earth and Venus have similar mantle heat flows, Venus must lack an Earth‐like low‐viscosity zone in its upper mantle in order satisfy the observed geoid and topography for these features. This conclusion is consistent with the long‐wavelength admittance spectrum of Venus and with the observed differences in the slopes of the geoid spectra for the two planets. One explanation for the different viscosity structures of the two planets could be that the mantle of Venus is drier than Earth's mantle.
Structural development of Coprates Chasma and Western Ophir Planum, Valles Marineris Rift, Mars
Authors: Schultz Richard A.
Published: February 2008

A portion of Valles Marineris was mapped in detail in order to clarify the dominant processes responsible for the formation of Coprates Chasma. New crater counts indicate that the caprock on western Ophir Planum plateau has a Late Hesperian crater age, whereas trough floor preserved in western Coprates Chasma has an Early to Late Hesperian crater age. Caprock on western Ophir Planum correlates in relative age with the Syria Planum Formation, and the caprock may overlie Lower Hesperian ridged plains material. The conspicuous absence of wrinkle ridges on Ophir Planum may reflect burial by this later material. Trough floor material in Coprates Chasma correlates in relative age with ridged plains material on the adjacent Lunae Planum and Coprates plateaus and represents a structurally coherent block displaced downward by normal faulting. The crater counts and detailed structural relationships demonstrate the commonly accepted view that Coprates Chasma occupies a graben. The floor of this graben is only thinly mantled by intratrough deposits and is relatively intact; the trough shows no evidence for a chaotically broken and jumbled floor, as required by genesis models of collapse and subsurface drainage. Formation of Coprates Chasma by keystone collapse of locally elevated topography is not supported by available topographic data, but a general association between the trough and volcanotectonic activity in the Tharsis region is considered to be a likely explanation for the trough forming stresses. Subtle asymmetries in topography and boundary fault development across Coprates Chasma may imply a gentle, down‐to‐the‐north half‐graben geometry for the trough. Normal faults that define the northern margin of western Coprates Chasma and those that deform the adjacent Ophir Planum plateau change trend systematically with position, implying a 30° rotation of the local horizontal principal stresses in this region during trough growth. Faulting on Ophir Planum appears related to the faulting that created the Coprates Chasma trough. The geology and structure of Coprates Chasma are comparable to those of other troughs such as Melas, Ius, and perhaps Candor chasmata, suggesting that these troughs may also have formed as grabens. The revised crater age for western Ophir Planum indicates that the initiation of trough faulting and subsidence in the Valles Marineris system is early Late Hesperian and may have been synchronous across the system relative to the prevailing cratering rate.
Late Pleistocene Continental Climate and Oceanic Variability Recorded in Northwest Pacific Sediments
Authors: Hovan S. A. , Rea D. K. , Pisias N. G.
Published: February 2008

Core V21‐146 provides a continuous record of northwest Pacific pelagic sedimentation spanning the past 530,000 years. Downcore variations of δ18O from benthic foraminiferal calcite were correlated to the SPECMAP record to provide an age model for late Pleistocene paleoclimatic and paleoceanographic variation. Fluxes of CaCO3 and eolian material have been determined by combining information about linear sedimentation rates, bulk densities and component percentages. The mass accumulation rate (MAR) of CaCO3 varies from 58 to 1435 mg(cm² kyr)−1 and exhibits the Pacific Ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record. However, the pattern of CaCO3 accumulation appears to shift during the mid‐Brunhes so that prior to 350,000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods. The flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess‐soil stratigraphy in China. Dust fluxes range from 43 to 718 mg(cm² kyr)−1 and are greater by a factor of about 4 during glacial times. Cross‐spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100, 41, and 19 kyr. Eolian grain sizes, generally used as a proxy record of wind intensity, range from 8.4ф (2.9 µm) to 6.2ф (13.6 µm). A change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower‐frequency and higher‐amplitude fluctuations than the younger portion. Power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25–35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities. The phase relationship for eccentricity between the eolian grain size and δ18O records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions.