bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic simulation of plasma flows in the inner magnetosphere
Authors: Miller Ronald H. , Rasmussen Craig E. , Gombosi Tamas I. , Khazanov Georgi V. , Winske Dan
Published: February 2008

A one‐dimensional hybrid particle code is used to study the interactions between upflowing thermal ions from conjugate ionospheres. The simulation model allows for multiple species, convection of plasmaspheric flux tubes, and Coulomb self‐collisions which conserve momentum and energy locally. The model incorporates a variable‐flux boundary condition where the flux, at the boundaries, approaches zero as the plasmasphere fills and equilibrium conditions are reached. The effects of two important processes on plasmaspheric refilling have been considered. The first includes convection of the plasmaspheric flux tube. The second is the interaction of ionospheric thermal plasma and particle injection from an external source. Particle injection seems to play an important role in the evolution of the total particle distribution on the early timescales (t < 1 hour); however, for late timescales (t > 8 days) the thermal plasma from the ionosphere dominates the particle distribution.
Limb view spectrum of the Earth's airglow
Authors: Mende S. B. , Swenson G. R. , Geller S. P. , Viereck R. A. , Murad Edmond , Pike C. P.
Published: February 2008

Sometimes the Earth's airglow layer, when observed in the limb view, appears to be a double layer. During one of these occasions we were able to obtain absolute spectral intensity and altitude profiles for most well‐known airglow features from the space shuttle on the STS‐37 mission. The lower of the two airglow layers consisted of the OH Meinel bands, the ground state of the O2 atmospheric band at 762 nm and an intense nighttime sodium layer at 598 nm peaking near 92 km. The upper airglow layer consists of the atomic oxygen lines at 557.7, 630, and 636.4 nm, and a blue green continuum. Significant 557.7, 630, and 636.4 nm OI emissions were observed to extend above 110 km into the lower F region. The volume emission rate distribution as a function of altitude was modeled, and the model limb intensity distribution was compared to the data. From the spectral profile of the modeled volume emission distribution, the green continuum located at 103 km ± 2 km altitude was identified as recombination emission of NO2 produced by a dense NO layer. Another layer which was present at each of the modeled wavelength regions had a volume emission peak at 90 km. Our observations did not show the presence of continuum emission with increasing intensity toward the near infrared. The observed regions were quite near the equator.
Ionospheric wave emissions passively detected by the OEDIPUS A Tether
Authors: James H. G.
Published: February 2008

The tethered sounding rocket payload OEDIPUS A was launched over aurora in the evening of January 30, 1989. A conducting tether between the instrumented subpayloads was extended to 958 m during the flight which attained an apogee altitude of 512 km. Electron fluxes of up to ∼2 × 108 cm−2 s−1 sr−1 were recorded by an onboard energetic particle detector throughout much of the flight. Electron density measurements were made by the bistatic transmitter‐receiver set high‐frequency exciter (HEX) and receiver for exciter (REX) using a special technique based on the characteristics of the Z mode of propagation. This electron density information was used to identify the frequency limits of propagation of various emissions in the 0‐5 MHz bandwidth of the receiver REX which was configured for passive detection of rf current induced in the tether. On two occasions in the flight, sharply delimited depletions of ambient density correlated closely with enhancements of radio noise, notably in the whistler mode at frequencies below 800 kHz. These depletions were located on the flanks of “inverted‐V” structures in the precipitating electron fluxes. The whistler mode emissions were very weak compared with what can be observed at greater heights in the auroral topside ionosphere. However, their detection apparently was enhanced by a resonance condition between the tether length and the wavelength of sheath waves. By ray tracing analysis, depletions were found incapable of trapping the whistler mode Waves, which exhibited levels 8‐10 dB higher than those outside the depletion, or of rendering them more detectable by the tether than unguided waves. The tether resonance may compensate for the tether's relative inefficiency as a receiving antenna because of its orientation along the magnetic field direction. It is inferred that the waves are generated close to the payload by suprathermal electrons.
Giotto's second encounter: The mission to comet P/Grigg‐Skjellerup
Authors: Grensemann M. G. , Schwehm G.
Published: February 2008

July 10, 1992, saw the second highlight in the life of the Giotto spacecraft which was originally designed for a short 8‐month lifetime, the main mission of which was to explore andphotograph comet Halley. Not only did Giotto survive the harsh environment around Halley but it was also able, after more than 7 years in orbit around the Sun, to pass within about 200 km of a second comet, P/Grigg‐Skjellerup, to provide exciting scientificmeasurements about the environment close to the comet.
Ulysses measurements of energetic H3 molecules in Jupiter's magnetosphere
Authors: Lanzerotti L. J. , Maclennan C. G. , Feldman D. M.
Published: February 2008

The Voyager 2 measurements of energetic (∼1 MeV/nucleon) H3 molecules in Jupiter's magnetosphere provided strong evidence that the planet's ionosphere is an important plasma source in the Jovian environment (Hamilton et al., 1980). During the Ulysses spacecraft encounter with Jupiter in February 1992 the Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energies (HI‐SCALE) on this satellite also detected significant fluxes of energetic H3 molecules. These molecules were measured throughout the dayside inbound pass (near the plasma sheet) as well as during the outbound pass at high Jovian latitudes on the duskside. The spectral shapes of the energetic 4He and the H3 are found to be similar over the range ∼0.6‐1.6 MeV/nucleon, with a power law spectral slope of n∼3. The abundance ratio R (≡H3/4He) is found to be ∼0.1 over this energy range for the inbound pass and to vary from ∼0.2 at ∼0.6 MeV/nucleon to ∼0.1 at ∼1.6 MeV/nucleon at duskside high latitudes. These observations, especially those from high latitudes, confirm that the energetic molecules must be accelerated out of the Jovian topside ionosphere into the magnetosphere.
Oceanic transform earthquakes with unusual mechanisms or locations: Relation to fault geometry and state of stress in the adjacent lithosphere
Authors: Wolfe Cecily J. , Bergman Eric A. , Solomon Sean C.
Published: February 2008

On oceanic transforms, most earthquakes are expected to occur on the principal transform displacement zone (PTDZ) and to have strike‐slip mechanisms consistent with transform‐parallel motion. We conducted a search for transform earthquakes departing from this pattern on the basis of source mechanisms and locations taken from the Harvard centroid moment tensor catalogue and the bulletin of the International Seismological Centre, respectively. Events with unusual mechanisms occur on several transforms. We have determined the source mechanisms and centroid depths of 10 such earthquakes on the St. Paul's, Marathon, Owen, Heezen, Tharp, Menard, and Rivera transforms from inversions of long‐period body waveforms. Relative locations of earthquakes along these transforms have been determined with a multiple‐event relocation technique. Much of the anomalous earthquake activity on oceanic transforms is associated with complexities in the geometry of the PTDZ or the presence of large structural features that may influence slip on the fault. Reverse‐faulting earthquakes occur at a compressional bend in the Owen transform in the area of Mount Error and at the St. Paul's transform near St. Peter's and St. Paul's Rocks. A normal‐faulting earthquake on the Heezen transform is located at the edge of a pull‐apart basin marking an extensional offset of the fault. Normal‐faulting earthquakes along the Tharp, Menard, and Rivera transforms may also be related to extensional offsets. Some events with unusual mechanisms occur outside of the transform fault zone, however, and do not appear to be related to fault zone geometry. For instance, earthquakes with mechanisms indicating reverse‐faulting on ridge‐parallel fault planes are located near the ridge‐transform intersections of the St. Paul's and the Marathon transforms. Possible additional contributors to the occurrence of anomalous earthquakes include recent changes in plate motion, differential lithospheric cooling, and the development of a zone of weakness along the fault zone, but we do not find strong evidence to confirm the influence of these processes.
Upper mantle compressional velocity structure beneath the northwest Atlantic Ocean
Authors: Zhao Lian‐She , Helmberger Don V.
Published: February 2008

A compressional velocity model for the northwest Atlantic Ocean is derived by modeling waveform and travel time data from long‐period and short‐period World‐Wide Standard Seismograph Network and Canadian network station recordings. A 90‐km‐thick lid with a velocity of 8.1 km/s at the top gradually increasing to 8.3 km/s at the bottom is obtained by fitting the travel time data of first arrivals and waveform data of almost purely oceanic paths at distances of 8°–20°. Triplication P waveform data constrain the structure below the lid. A distinct but smooth low‐velocity zone is located at a depth of 170 km. Combining these results with the shear wave structure derived by Grand and Helmberger (1984a) for the same region, we suggest an olivine‐rich mineralogy in the upper 100 km and partial melting possibly extending as deep as 300 km based on low seismic velocities and high Vp/Vs
Micromagnetic study of the influence of crystal defects on coercivity in magnetite
Authors: Moskowitz Bruce M.
Published: February 2008

A one‐dimensional micromagnetic model is used to calculate the thermal dependence of microcoercivity (hc) produced by the unpinning of a domain wall (DW) from various types of defects in magnetite. Equilibrium solutions are found that minimize the magnetoelastic, anisotropy, exchange, magnetostatic, and external field energies with respect to the wall width (w) and position of the wall relative to the defect. The defect may be a single dislocation, dislocation dipole, planar defect, or planar defect bounded by two parallel dislocations. Wall pinning is produced by (1) microstress fields of dislocations, (2) local changes in exchange and anisotropy constants within a planar defect region, or (3) a combination of both effects. The calculations, using temperature‐dependent parameters, predict the thermal dependence of hc (T) as a function of grain size, domain wall width, defect spacing, and type of defect. Results show that, for grain sizes between 1 and 100 μm, hc(T) is usually a function of the wall width raised to some power n. The particular value of n is found to be a function of the DW‐defect interaction spacing (d/w), type of defect, and grain size. Also, within this size range, the wall width expands with temperature more gradually than classical theory predicts. The microcoercivity results are used with the theory of Xu and Merrill (1990) to predict the thermal dependence of the macroscopic coercivity Hc in magnetite. For grains with low defect densities, such as recrystallized magnetites, negative dislocation dipoles with d/w≈0.1–1 produce a thermal dependence of coercivity that agrees with experimental results. In the high defect density limit, a population of positive and negative dislocation dipoles with a distribution of dipole widths produce an Hc (T) dependence consistent with experimental data from crushed and glass ceramic magnetites.
A fractal analysis of Quaternary, Cenozoic‐Mesozoic, and Late Pennsylvanian sea level changes
Authors: Hsui Albert T. , Rust Kelly A. , Klein George D.
Published: February 2008

Sea level changes are related to both climatic variations and tectonic movements. The fractal dimensions of several sea level curves were compared to a modern climatic fractal dimension of 1.26 established for annual precipitation records. A similar fractal dimension (1.22) based on δ(18O/ 16O) in deep‐sea sediments has been suggested to characterize climatic change during the past 2 m.y. Our analysis indicates that sea level changes over the past 150,000 to 250,000 years also exhibit comparable fractal dimensions. Sea level changes for periods longer than about 30 m.y. are found to produce fractal dimensions closer to unity and Missourian (Late Pennsylvanian) sea level changes yield a fractal dimension of 1.41. The fact that these sea level curves all possess fractal dimensions less than 1.5 indicates that sea level changes exhibit nonperiodic, long‐run persistence. The different fractal dimensions calculated for the various time periods could be the result of a characteristic overprinting of the sediment record by prevailing processes during deposition. For example, during the Quaternary, glacio‐eustatic sea level changes correlate well with the present climatic signature. During the Missourian, however, mechanisms such as plate reorganization may have dominated, resulting in a significantly different fractal dimension.
The statistical distribution of swash maxima on natural beaches
Authors: Holland K. T. , Holman R. A.
Published: February 2008

Cartwright and Longuet‐Higgins (1956) describe the statistical distribution of maxima that would result from the linear superposition of random, Gaussian waves. The distribution function depends solely upon the relative width of the power spectrum and root‐mean‐square value of the process time series. Runup field data from three experiments are presented to determine the extent to which the distribution of swash maxima can be approximated using the Cartwright and Longuet‐Higgins probability density function. The model is found to be satisfactory for describing various distribution statistics including the average maxima, the proportion of negative maxima, and the elevation at which one third of the swash maxima are exceeded. However, systematic discrepancies that scale as a function of time series skewness are observed in the statistics describing the upper tail of the distributions. Although we conclude that the linear model is incapable of delineating these apparent nonlinearities in the swash time series, the extent of the deviation can be estimated empirically for the purpose of constraining nonlinear models and nearshore engineering design.
Arctic sea ice signatures for passive microwave algorithms
Authors: Thomas D. R.
Published: February 2008

Passive microwave satellite data can be used to estimate the concentrations of three surface types: open water, first‐year ice, and multiyear ice. These estimates are made with an algorithm that requires knowing the microwave signatures of each of these three surface types. For the Scanning Multichannel Microwave Radiometer, the algorithm proposed by Cavalieri et al. (1984), known as the SMMR Team algorithm, is widely used. Two unsatisfying properties of this algorithm are (1) its estimates of multiyear ice concentrations are much lower than its estimates of summer ice concentrations and are also significantly lower than independent estimates of Arctic Ocean multiyear ice, and (2) it produces variations in estimated concentration that appear to be caused by spatial and temporal variations in the signatures. We examine two alternative sets of signatures. One set varies temporally but not spatially and is defined by the modes of major peaks in histograms of brightness temperature. The other set is defined as the overall means of the temporally varying signatures; we call these “new constant signatures.” An estimate of the average bias of the winter multiyear ice is derived and a corresponding correction applied to the new constant signatures. Both sets of new signatures have essentially the same precision: 0.05 (fractional area) for winter ice concentration, 0.10 for summer ice concentration, and 0.15 to 0.3 for winter multiyear ice concentration. These error estimates are upper bounds to the true precision, especially for multiyear ice for which some true concentration changes are included in the variability. The precision estimates include all spatial and temporal signature variability, and are compatible with estimates of sea ice emissivity variability given in the literature. Because the temporally varying signatures provide only a slightly better precision, we prefer the new constant signatures. Both sets of new signatures result in about 0.6 to 0.7 winter multiyear ice for the Arctic Ocean, substantially more than the 0.3 to 0.4 computed using the original Team algorithm signatures, and in the same range as several independent estimates of the multiyear ice, 0.54 to 0.75.
Wave effects on ocean‐ice interaction in the marginal ice zone
Authors: Liu Antony K. , Häkkinen Sirpa , Peng Chih Y.
Published: February 2008

The effects of wave train on ice‐ocean interaction in the marginal ice zone are studied through numerical modeling. A coupled two‐dimensional ice‐ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics. The sea ice model is coupled to the reduced‐gravity ocean model through interfacial stresses. The main dynamic balance in the ice momentum is between water‐ice stress, wind stress, and wave radiation stresses. By considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves, a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed. The numerical results show significant effects from wave action. The ice edge is sharper, and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days. Upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action; wave action sharpens the ice edge and can produce ice meandering, which enhances local Ekman pumping and pycnocline anomalies. The resulting ice concentration, pycnocline changes, and flow velocity field are shown to be consistent with previous observations.
Physical processes of microwave backscattering from laboratory wind wave surfaces
Authors: Ebuchi Naoto , Kawamura Hiroshi , Toba Yoshiaki
Published: February 2008

Physical processes of microwave backscattering from wind wave surfaces are investigated in a wind wave tunnel by using a X‐band (9.6 GHz) microwave scatterometer. Detailed analysis of time series of the backscattered intensity and Doppler spectrum shows that the physical processes of microwave backscattering are closely associated with the processes of the wind wave field. At slant incidence (45°) the backscattered intensity is in phase with the wave profile, and the Doppler velocity also follows the phase of the individual waves with high Doppler velocity observed at the crests of the individual waves. This velocity is equal to the propagating speed of the crests. It is concluded that the fine structures of wind wave surfaces, which are trapped near the crests and propagating with the crests, are the main contributor to microwave backscattering. It is also pointed out that the effect of wave breaking with bubble entrainment on the microwave backscattering is not significant under the condition of the present experiment. At normal incidence the backscattered intensity has a different phase relationship with the wave profile. The intensity has two peaks, one at the crest and the other at the trough of the individual waves. The peak at the trough is stronger than that at the crest. This result is consistent with specular point scattering and also with the asymmetrical features of young laboratory wind waves. At intermediate incident angles, backscattering processes are rather complicated because both specular point scattering and Bragg resonance scattering contribute to the radar backscattering.
On mean and seasonal currents and transports at the western boundary of the equatorial Atlantic
Authors: Schott Friedrich , Fischer Jürgen , Reppin Jörg , Send Uwe
Published: February 2008

Current measurements from two consecutive yearlong deployments of three moored stations at the western end of the equator in the Atlantic, along 44°W, are used to determine the northwestward flow of warm water in the upper several 100 m and of the southeastward counterflow of North Atlantic Deep Water (NADW). Measurements from three acoustic Doppler current profilers (ADCPs) looking upward from 300 m toward the surface allowed calculation of a time series of upper layer transports over 1 year. Mean transport through the array for the upper 300 m is 23.8 Sv with an annual cycle of only ±3 Sv that has its maximum in June‐August and minimum in northern spring. Estimated additional mean northwestward transport in the range 300–600 m is 6.7 Sv, based on moored data and shipboard Pegasus and lowered ADCP profiling. In the depth range 1400–3100 m a current core with maximum annual mean southeastward speed of 30 cm s−1 is found along the continental slope that carries an estimated upper NADW transport of 14.2–17.3 Sv, depending on the extrapolation used between the mooring in the core and the continental slope. This transport is higher than off‐equatorial estimates and suggests near‐equatorial recirculation at the upper NADW level, in agreement with northwestward mean flow found about 140 km offshore. Below 3100 m and above the 1.8°C isotherm, only a small core of lower NADW flow with speeds of 10–15 cm s−1 is found over the flat part of the basin near 1.5°N, clearly separated from the continental slope by a zone of near‐zero mean speeds. Estimated transport of that small current core is about 4.5 Sv, which is significantly below other estimates of near‐equatorial transport of lower NADW and suggests that a major fraction of lower NADW may cross the 44°W meridian north of the Ceara Rise. Intraseasonal variability is large, although smaller than observed at 8°N near the western boundary. It occurs at a period of about 1 month when it is dominant in the near‐surface records and corresponds to earlier observations in the equatorial zones of all oceans and at a period of about 2 months when it is dominant at the NADW level and could be imported either from the north along the boundary or from the east along the equator. The existence of an annual cycle in the deep currents of a few centimeters per second amplitude, as suggested by high‐resolution numerical model results, could neither be proven nor disproven because of the high amount of shorter‐period variability.
Open boundary conditions for the extended Kalman filter with a quasi‐geostrophic ocean model
Authors: Evensen Geir
Published: February 2008

The formulation of consistent boundary conditions for the quasi‐geostrophic (QG) model with an extended Kalman filter in a data assimilation scheme is discussed. To form a well‐posed boundary value problem for the QG model, the stream function must be specified at all boundaries and the vorticity must be specified at the inflow boundaries. The situation becomes significantly more complicated when proper boundary conditions are to be specified for the error covariance evolution equation. For closed or periodic boundaries no severe problems occur, but in general cases with open boundaries, only approximative methods can be used. Here a scheme is presented which allows for the stream function to be updated on the boundaries, e.g., from the use of measurements located close to the boundaries, or from meanders and eddies approaching the boundaries from the interior of the domain. Further, the boundary value problem for the error covariance evolution equation is treated extensively. It is demonstrated that numerical discretization of the error covariance evolution equation leads to severe numerical difficulties when open boundaries are used. An approximate numerical scheme that can be used to handle open boundaries with inflow and outflow is proposed, and examples are given to illustrate the method. Is is shown that the boundary scheme is consistent and can be used even with data located at inflow boundaries. However, the approximations used in the scheme may lead to loss of positive definiteness for the error covariance matrix and an algorithm must be used to ensure positive definiteness for long time integrations.
Calibration of advanced very high resolution radiometer infrared channels: A new approach to nonlinear correction
Authors: Brown James W. , Brown Otis B. , Evans Robert H.
Published: February 2008

A detailed reanalysis of the calibration procedures for the National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) based on thermal‐vacuum test data was performed as part of the National Air and Space Administration/NOAA AVHRR Pathfinder Project. This effort, a followup to work by Brown et al. (1985), was motivated by the finding that the AVHRR instruments on several NOAA platforms have been routinely operated outside the range of thermal‐vacuum test results, and thus one could not interpolate nonlinear corrections directly from earlier methods. These new calibration procedures permit calculation of nonlinear temperature corrections for any AVHRR operating temperature based on a second‐order polynomial regression with a total calibration accuracy relative to an external calibration standard of less than two digital counts (±0.2°C). Such an improvement is quite important to the absolute accuracy of surface thermal fields, which are derived from these data utilizing various multichannel atmospheric water vapor correction schemes. We find systematic differences in the newly derived nonlinear correction results and those reported previously by Weinreb et al. (1990) and the original reference material in the various addenda to NOAA NESS Technical Memorandum 107 (Lauritson et al., 1979). Calibration results for various AVHRR radiometers show instrument‐similar corrections for each band. Radiometers on NOAA platforms 8‐12 demonstrate similar nonlinearities.
The effect of averaging on bulk estimates of heat and momentum fluxes for the tropical western Pacific Ocean
Authors: Ledvina D. V. , Young G. S. , Miller R. A. , Fairall C. W.
Published: February 2008

The magnitudes of bulk air‐sea surface flux estimates calculated using three temporal averaging methods were compared. The reference method is a simple average of fluxes computed from hourly values of bulk meteorological parameters termed the sampling method (SM). In contrast, the scaler averaging method (SAM) computes the average flux from the average of the bulk data; thus it ignores correlations between variables. The vector averaging method (VAM) is similar to the SAM but uses the magnitude of the average wind vector rather than the average magnitude of the hourly wind vectors. The data used in this study were collected during the Tropical Ocean and Global Atmospheric pilot cruise of the R/V Wecoma in the equatorial Pacific Ocean near 0°N, 145°E from February 17 to March 10,1990. The ratios of the SAM and VAM values relative to the SM values were studied as a function of averaging periods from 2–72 hours. The ratios vary little for times exceeding 36 hours. For averaging periods of 72 hours, the SAM estimates of QE, QH, τx, and τy were 102%, 61%, 21%, and 69% of the SM estimates, respectively; the VAM ratios were even lower. These results suggest that air‐sea surface sealer fluxes and stress components computed from monthly, weekly, and even daily averaged bulk meteorological parameters can be seriously in error in equatorial, temporally variable wind regimes.
Longshore current on a barred beach: Field measurements and calculation
Authors: Smith Jane McKee , Larson Magnus , Kraus Nicholas C.
Published: February 2008

Measurements of the longshore current on a barred beach made during the 1990 Duck Experiment on Low‐Frequency and Incident‐Band Longshore and Across‐Shore Hydrodynamics (DELILAH) field data collection project conducted at Duck, North Carolina, revealed an unexpected and persistent broad peak in the current velocity in the trough between the nearshore bar and the shore. This paper introduces longshore current and associated wave measurements from DELILAH together with a numerical model capable of describing the field observations. An existing numerical model of the mean current is modified to include a general transport equation for the mean turbulent kinetic energy created by wave breaking, and Reynolds stress components needed to calculate the longshore current and mean water level are reexpressed to include the turbulent momentum transport. In comparison to predictions from the original model, the modified model produces much improved agreement with the measured current velocity on the barred profiles in the field measurements and with the velocity profile and mean water level generated on a uniformly sloping laboratory beach by monochromatic waves. Three forms of a bottom friction coefficient are examined, and the open‐channel‐flow Manning friction coefficient is selected because of best agreement and consistency. Values of the Manning friction coefficient required to calibrate the model agree with values normally assigned to the related bottom roughness in open‐channel flow.
Absorption of solar radiation by O2: Implications for O3 and lifetimes of N2O, CFCl3, and CF2Cl2
Authors: Minschwaner K. , Salawitch R. J. , McElroy M. B.
Published: February 2008

An accurate line‐by‐line model is used to evaluate effects of absorption in the Schumann‐Runge bands of O2 on transmission of ultraviolet radiation. Allowing also for absorption in the Herzberg continuum, the model is shown to provide a reliable simulation of observed transmission in the spectral interval 192 to 200 nm. The model is used to evaluate rates for photolysis of N2O, CFCl3, and CF2Cl2, and to infer global loss rates (1.22×l010 kg N yr−1, 7.21×107 and 3.04×l07 kg Cl yr−1, respectively) and instantaneous lifetimes (123, 44, and 116 years, respectively) appropriate for 1980. A parameterized version of the line‐by‐line model enabling rapid evaluation of transmission in the Schumann‐Runge region is described. Photochemical calculations employing the parameterization and constrained by data from the Atmospheric Trace Molecule Spectroscopy experiment are used to examine the budget of odd oxygen. Consistent with previous studies, it is shown that photochemical loss of odd oxygen exceeds production by photolysis of O2 for altitudes above 40 km. The imbalance between production and loss is shown to be consistent with a source of odd oxygen proportional to the product of the mixing ratio and photolysis rate of ozone, which suggests that processes involving vibrationally excited O2 may play an important role in production of odd oxygen.
Estimates of the stratospheric residual circulation using the downward control principle
Authors: Rosenlof Karen H. , Holton James R.
Published: February 2008

The transformed Eulerian‐mean momentum and continuity equations are used to calculate the residual mean meridional circulations for the lower stratosphere and troposphere. Momentum and temperature fluxes required for the computation are estimated from U.K. Meteorological Office (UKMO) analyzed geopotential heights. National Center for Atmospheric Research (NCAR) CCM2 model output is used to assess the errors associated with the calculation. The model comparisons showed that the method works reasonably well for solstice seasons, but is inadequate for equinox seasons. In addition, it is found that some parameterization of gravity wave drag needs to be included with the planetary wave forcing to accurately estimate the residual mean circulation using this method.
Solar‐Stellar Irradiance Comparison Experiment 1: 1. Instrument design and operation
Authors: Rottman Gary J. , Woods Thomas N. , Sparn Thomas P.
Published: February 2008

The main objective for the Solar‐Stellar Irradiance Comparison Experiment (SOLSTICE) is to accurately measure the full disk solar spectral irradiance in the ultraviolet (UV) spectral region over a long time period. To meet this objective, SOLSTICE has the unique capability of making routine observations of the UV radiation from a set of early‐type stars, using the identical optical elements and detectors employed for the solar observations. The stars selected for this calibration are assumed, on the basis of stellar evolution theory, to be extremely stable in the UV spectral region. Moreover, it is the average flux from a number of stars, perhaps from as many as 25, that is assumed to be stable. The SOLSTICE 1 is on the Upper Atmosphere Research Satellite (UARS), and the overall design and operation of the instrument are discussed. The quality of the solar and stellar data is extremely high and preliminary results indicate that the technique is working well.
Diurnal and seasonal variations of the small‐, intermediate‐, and large‐ion concentrations and their contributions to polar conductivity
Authors: Dhanorkar Savita , Kamra A. K.
Published: February 2008

Simultaneous measurements of the concentrations of small, intermediate and large ions and of polar conductivity of both polarities were made at a height of 1 m above ground at Pune (18° 32′N, 73° 51′E, 559 m above msl), India during February 1990 to January 1991. Diurnal and seasonal variations of concentrations of ions of all three categories show their peak values in the morning hours throughout the year. Concentrations of all categories of ions are higher during the nighttime as compared to that during the daytime and are higher in winter than in other seasons. Although small‐ion concentrations show only a small change, intermediate‐ and large‐ion concentrations undergo a change of up to 1 to 2 orders of magnitude over a period of a year. Most of the time, our observations do not exhibit any inverse relationship between the small‐ and large‐ion concentrations. The results have been explained in terms of the stability of the lower atmosphere and accumulation of radioactive gases, aerosols, etc., below nocturnal inversions. The diurnal and seasonal variations of the percentage contribution of three different categories of ions to the polar conductivity show that although contribution of small ions is dominant for most of the day, contributions of intermediate and large ions become very large in the morning hours, especially in winter. Diurnal variations of the mean values of polar conductivity calculated from the ion concentrations are compared with those of the measured values of polar conductivity. The two values show good agreement during the daytime when the polar conductivity is small. However, the measured values of polar conductivity are always higher than its calculated values during nighttime or in the morning hours when polar conductivity is large.
The cryogenic limb array etalon spectrometer (CLAES) on UARS: Experiment description and performance
Authors: Roche A. E. , Kumer J. B. , Mergenthaler J. L. , Ely G. A. , Uplinger W. G. , Potter J. F. , James T. C. , Sterritt L. W.
Published: February 2008

The cryogenic limb array etalon spectrometer (CLAES) is one of 10 experiments launched in September 1991 on the NASA Upper Atmosphere Research Satellite (UARS). CLAES measures altitude profiles of temperature, pressure, O3, H2O, CH4, N2O, NO, NO2, N2O5, HNO3, ClONO2, HCl, CFC 11, CFC 12, and aerosol absorption coefficients. These data are obtained between 10 and 60 km with 2.5‐km vertical resolution and 500‐km horizontal grid size and between latitudes 80° north and south. Since CLAES actually measures infrared spectral earthlimb emissions, it can operate continuously throughout the diurnal cycle. The on‐orbit lifetime as dictated by stored cryogens which cool optics and detectors is estimated to be 21 months. The experiment will perform the first global mapping of stratospheric ClONO2, CFC 11, CFC 12, and N2O5, and these data, along with the simultaneous measurement of temperature and the other constituents listed above, should contribute to a significant improvement in our understanding of stratospheric and mesospheric photochemistry, radiative structure, and dynamics. CLAES began viewing the atmosphere in early October 1991, and the first several months of observations will be discussed. Examples of atmospheric spectral emission profiles for a number of constituents are presented as well as responsivity and noise parameters. These data show the instrument performance to be excellent and close to prelaunch predictions. An overview of the experiment and instrumentation is presented, various scientific observational modes are described, and the algorithms and software used to retrieve atmospheric parameters from emission spectra are discussed.
Nitric oxide production by lightning discharges
Authors: Goldenbaum G. C. , Dickerson R. R.
Published: February 2008

We have investigated NO production in the expansion phase of a lightning discharge using a hydrodynamic model coupled with the chemical rate equations for the two Zel'dovich reactions and oxygen dissociation. We have found that most of the NO production occurs early in the discharge, prior to shock wave formation, and that the rapid drop in density, not temperature, controls NO formation. The number of molecules per Joule (P) depends strongly on the energy per unit volume in the initial heated channel: this dependence is nonlinear with a maximum value of 26 × 1016 molecules NO/J. For a representative discharge at a pressure of 1 atm, the number produced is 15 × 1016/J. Initial investigation indicates that for a constant energy density (estimated to be about 6 MJ/m3) the rate of production drops off rapidly with decreasing air density and thus altitude. Use of P appropriate for sea level pressure may lead to a major overestimate of the rate of NO formation in atmospheric lightning, much of which occurs at high altitude. We present suggestions for new laboratory experiments to quantify global NO production by lightning.
Possibilities of cirrus particle sizing from dual‐frequency radar measurements
Authors: Matrosov S. Y.
Published: February 2008

This paper considers possibilities of estimating the sizes of ice particles in cirrus clouds using measurements at two radar millimeter wavelengths. The radar frequencies considered are those at the transparency “windows”: 35, 94, 140, and 215 GHz. It is shown that measurements of reflectivity differences at 35 and 215 GHz and at 94 and 215 GHz could potentially be used to estimate particle median sizes from about 0.2 to 0.4 mm. However, the sensitivity of reflectivity differences to particle shapes and orientations will keep the expected error of such an estimation at not less than about 0.1 mm. Measurements of differences in circular depolarization ratios at 35 and 94 GHz, 35 and 215 GHz, 94 and 215 GHz, and 35 and 140 GHz can also be used to estimate particle sizes, and the combination of 35 and 215 GHz can lower the limit of estimated median sizes to about 0.1 mm. It is also shown in the paper that an equal volume sphere approach, being a reasonable approximation for describing backscatter by small ice nonspherical particles, gives larger errors when describing backscatter by larger non‐Rayleigh particles. Backscatter by these bigger particles shows significant dependence on particle orientation, which results in relatively large errors of sizing.
Estimation of the global average temperature with optimally weighted point gauges
Authors: Hardin James W. , Upson Robert B.
Published: February 2008

This paper considers the minimum mean squared error (MSE) incurred in estimating an idealized Earth's global average temperature with a finite network of point gauges located over the globe. We follow the spectral MSE formalism given by North et al. [1992] and derive the optimal weights for N gauges in the problem of estimating the Earth's global average temperature. Our results suggest that for commonly used configurations the variance of the estimate due to sampling error can be reduced by as much as 50%.
Morphology and time variation of the Jovian far UV aurora: Hubble space telescope observations
Authors: Gérard Jean‐Claude , Dols Vincent , Paresce Francesco , Prangé Renée
Published: February 2008

High spatial resolution images of the north polar region of Jupiter have been obtained with the Faint Object Camera on board the Hubble Space Telescope. The first set of two images collected 87 min apart in February 1992 shows a bright (≃180 kR) emission superimposed on the background in rotation with the planet. Both Ly α images show common regions of enhanced emission but differences are also observed, possibly due to temporal variations. The second group of images obtained on June 23 and 26, 1992 isolates a spectral region near 153 nm dominated by the H2 Lyman bands and continuum. Both pictures exhibit a narrow arc structure fitting the L = 30 magnetotail field line footprint in the morning sector and a broader diffuse aurora in the afternoon. They show no indication of an evening twilight enhancement. Although the central meridian longitudes were similar, significant differences are seen in the two exposures, especially in the region of diffuse emission, and interpreted as signatures of temporal variations. The total power radiated in the H2 bands is ≃ 2 × 1012 W, in agreement with previous UV spectrometer observations. The high local H2 emission rates (∼450 kR) imply a particle precipitation carrying an energy flux of about 5 × 10−2 W m−2.
A series solution for diffraction over terrain modeled as multiple bridged knife edges
Authors: Whitteker J. H.
Published: February 2008

The multiple knife edge model for terrain diffraction problems is extended to apply to solid terrain. The model is constructed by bridging over the spaces between diffracting screens with perfectly reflecting plane surfaces that connect the tops of the diffracting screens. In this way the diffracting screens are hidden from view, and the plane surfaces become a solid, reflecting, model of terrain. Nevertheless, there remains a mathematical similarity with multiple knife edges, and a series solution already known for multiple knife edges can be adapted to the new model. Although bridging over the knife edges adds new modes of propagation, many of these modes make identical contributions to the field, and the final series contains no more terms than for knife edges only. As with knife edges, computing time increses rapidly as a function of the number of knife edges, and the series may not converge if the terrain profile contains valleys. However, valleys can always be removed by means of Babinet's principle. Sample results show that bridging over knife edges results in increased attenuation and a smoother variation with terrain height. A round hill can be approximated, and the resulting attenuation approaches the known attenuation for a round hill, as the number of bridged knife edges increases.
A model with ellipsoidal scatterers for polarimetric remote sensing of anisotropic layered media
Authors: Nghiem S. V. , Kwok R. , Kong J. A. , Shin R. T.
Published: February 2008

This paper presents a model with ellipsoidal scatterers for applications to polarimetric remote sensing of anisotropic layered media at microwave frequencies. The physical configuration includes an isotropic layer covering an anisotropic layer above a homogeneous half space. The isotropic layer consists of randomly oriented spheroids. The anisotropic layer contains ellipsoidal scatterers with a preferential vertical alignment and random azimuthal orientations. Effective permittivities of the scattering media are calculated with the strong flucutation theory extended to account for the nonspherical shapes and the scatterer orientation distributions. On the basis of the analytic wave theory, dyadic Green's functions for layered media are used to derive polarimetric backscattering coefficients under the distorted Born approximation. The ellipsoidal shape of the scatterers gives rise to nonzero cross‐polarized returns from the untilted anisotropic medium in the first‐order approximation. Effects of rough interfaces are estimated by an incoherent addition method. Theoretical results and experimental data are matched at 9 GHz for thick first‐year sea ice with a bare surface and with a snow cover at Point Barrow, Alaska. The model is then used to study the sensitivity of polarimetric backscattering coefficients with respect to correlation lengths representing the geometry of brine inclusions. Polarimetric signatures of bare and snow‐covered sea ice are also simulated based on the model to investigate effects of different scattering mechanisms.
Macrodispersivity Tensor for Nonreactive Solute Transport in Isotropic and Anisotropic Fractal Porous Media: Analytical Solutions
Authors: Zhan Hongbin , Wheatcraft Stephen W.
Published: February 2008

Using spectral stochastic theory, macrodispersivity tensors are developed for one‐, two‐, and three‐dimensional isotropic and anisotropic fractal porous media. Since natural geologic aquifers are always bounded, we introduce the concept of a maximum length scale ((Lmax). In the one‐dimensional case, the asymptotic (long‐time) longitudinal macrodispersivity (A∞) is proportional to Lmax2, and in the multidimensional cases, A∞ ∝ Lmax. In the multidimensional cases, as the fractal dimension increases, A∞ decreases, because a larger fractal dimension means the tortuosity of solute particles is larger, leading to more mixing in the transverse direction, which in turn reduces longitudinal spreading. The transverse macrodispersivities are shown to be analogous to traditional spectral stochastic results. In the multidimensional cases, Lmax is shown to be controlled by the aquifer thickness. As a result, ergodic conditions may be reached in relatively thin aquifers, allowing the use of the asymptotic macrodispersivity expressions obtained here for single realizations.
Inorganic germanium and silica in the Indian Ocean: Biological fractionation during (Ge/Si)OPAL formation
Authors: Froelich P. N. , Mortlock R. A. , Shemesh A.
Published: February 2008

Hydrographic profiles of inorganic germanium and silica in the western Indian Ocean confirm the silicalike behavior of inorganic germanium in seawater. Combining all existing oceanic data (Indian, Atlantic, Pacific, Bering Sea and Antarctic), these new data provide an improved oceanic Ge to Si relationship: Ge(pM) = 0.699±0.004 × Si(μM) + 3.6±0.4. Simple box models of the ocean demonstrate that the positive Ge intercept in this relationship results from biological fractionation of the Ge/Si ratio: Siliceous organisms discriminate against germanium during production of biogenic opal. This result is confirmed by (Ge/Si)Opal analyses of diatoms and radiolaria separated from siliceous oozes of Holocene core tops. A rapid rise in diatom‐(Ge/Si)Opal recorded in an Antarctic piston core over the interval from the Last Glacial (18 thousand years before present) to the Holocene (present) suggests that biosiliceous productivity was lower and preformed silica concentrations were higher in Southern Ocean surface waters during glacial times.
Iron addition experiments in the Antarctic: A reanalysis
Authors: Dugdale Richard C. , Wilkerson Frances P.
Published: February 2008

In an accompanying paper, Martin et al. [this issue] interpret the results of four iron enrichment experiments using Antarctic seawater to indicate iron limitation of phytoplankton growth and nitrate uptake and suggest that Fe additions may contribute to reducing atmospheric CO2 and the greenhouse problem. We have published a review [Dugdale and Wilkerson, 1989] of nitrogen uptake measurements using 15N in Antarctic waters and here reanalyze the nitrate depletion data of Martin et al. [this issue], reported as absolute uptake rates (ρ with units of concentration per unit time), in the context of previous investigations by converting the data to nitrogen‐specific uptake rates (V, in reciprocal time units). We conclude that Fe addition to the enclosed water does not affect the algal growth terms due to nitrate uptake per se, but apparently influences loss terms enabling phytoplankton biomass to accumulate in the experimental bottles.