bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic reconnection in collisionless field reversals the universality of the ion tearing mode
Authors: Kuznetsova M. M. , Zelenyi L. M.
Published: February 2008

A theoretical analysis of the stability of a quasi‐neutral sheet with small normal magnetic component Bn is presented. It is demonstrated that contrary to the statement of Pellat et al. [1991], pitch angle diffusion (PAD) can remove the stabilizing effect of Bn. The PAD results in the escape of electrons to the region of negligibly small wave—particle interactions which decreases the electron contribution to the energy balance equation. In the limit of strong PAD the ion tearing mode growth rate gives the universal upper estimate of the rate of collisionless spontaneous reconnection.
Simultaneous optical observations of transpolar arcs in the two polar caps
Authors: Craven J. D. , Murphree J. S. , Frank L. A. , Cogger L. L.
Published: February 2008

Optical observations with DE 1 and Viking demonstrate conclusively that transpolar arcs can be present simultaneously at polar latitudes in both hemispheres. The arcs observed here are aligned parallel to one another on opposite sides of the magnetic pole, and relative to the noon‐midnight meridian are rotated slightly in the counterclockwise direction when viewed from above the North Pole.
Additional complexity in the lunar crust: Petrology of sodic anorthosites and sulfur‐rich, ferroan noritic anorthosites
Authors: Norman Marc D. , Taylor G. Jeffrey , Keil Klaus
Published: February 2008

Lunar breccia 67016 contains two suites of unusual highlands rocks: sulfur‐rich, noritic anorthosites, and sodic anorthosites. Mineral compositions of the sulfur‐rich noritic anorthosites closely match those of ferroan anorthosites. Unusually large amounts of sulfides, and sulfidation reactions involving olivine in these clasts probably reflect endogenous volatile transfer. The sodic anorthosites are mafic‐poor, with mineral compositions intermediate between those of pristine ferroan and alkali anorthosites. Rare examples of pristine rocks with similar mineral compositions are known, and may represent a distinct class of lunar crustal rocks.
Analysis of standing wave patterns in VLF transmitter signals: Effects of sporadic E layers and in situ measurements of low electron densities
Authors: Siefring Carl L. , Kelley Michael C.
Published: February 2008

An analysis of standing waver patterns formed by the reflection of VLF transmitter signals incident upon a sporadic E layer is presented. The patterns were detected by electric field sensors on a sounding rocket designed to study the upward propagation of lightning‐induced electric fields. To model the measured standing wave patterns, it was necessary to have an accurate electron density profile. However, it has always been difficult to make accurate measurements of the low electron densities in the nighttime D and E regions. We devise a unique method to determine the electron concentration from the measured vertical wavelength of the standing wave patterns. The data from this analysis are then used to calibrate Langmuir probe measurements which, in turn, give a reasonable (but not perfect) electron density profile to use for full‐wave modeling of the transmitter signals. This analysis yields several interesting characteristics, including the possibility that some energy is trapped in the sporadic E layer. The amplitude‐versus‐frequency characteristics of upgoing electromagnetic waves are also modeled. It is discovered that a sporadic E layer can act as a half‐wave window at appropriate frequencies. A method for using VLF signals to measure electron densities without the existence of a standing wave pattern is also derived. Such a method is ideally suited for measuring the low electron densities in the nighttime D and E regions.
Observation of electron bunching during Landau growth and damping
Authors: Ergun R. E. , Carlson C. W. , McFadden J. P. , TonThat D. M. , Clemmons J. H. , Boehm M. H.
Published: February 2008

A high‐frequency wave‐particle correlator instrument has been flown for the first time on a recent auroral sounding rocket. The direct observation of electron bunching showed that large‐amplitude Langmuir waves were resonant with low‐energy, field‐aligned electrons, roughly corresponding to expectations. The observed electron bunching, however, appeared to be in phase (or 180° out of phase) with the electric field signal rather than the wave potential, indicating that an energy exchange was occurring. An elementary energy transfer analysis shows that Landau growth or damping could account for the electron bunching. A Monte Carlo test particle simulation supports this model. The simulation shows a perturbation of the electron distribution function in phase with the electric field for roughly half of a bounce period after the particles interact with the wave, followed by particle trapping in the wave potential. The latter effect was not observed, for which we offer two interpretations. Either the particle trapping did not occur due to finite frequency bandwidths and changing wavelengths, or the physical size of the wave packet was too small to establish particle trapping.
Field‐aligned dynamics of chemically induced perturbations to the ionosphere
Authors: Bernhardt P. A. , Rodriguez P. , Siefring C. L. , Lin C. S.
Published: February 2008

Ionospheric modification using photochemically reactive vapors is studied with a one‐dimensional, multi‐ion, fluid model of plasma flow along magnetic field lines. The magnitudes of ion and electron density changes are determined by considering both chemical processes (i.e., photoionization, ion‐molecule reactions, dissociative recombination, electron attachment) and transport processes (i.e., multispecies diffusion, electric currents, ambipolar electric fields). The numerical treatment in the model is not specific to any type of release or any interaction chemistry. It has been used to simulate releases of Ba, CO2, and CF3Br in the ionosphere, but generalization to other species may be easily accomplished. The results of the calculations are found to be in good agreement with experimental observations. The feasibility of modifying the parallel current paths in the auroral F region is examined.
Measurement of the direction of the auroral kilometric radiation electric field inside the sources with the Viking satellite
Authors: Hilgers A. , de Feraudy H. , Le Quéau D.
Published: February 2008

The spin modulation of the high‐frequency noise from one electric antenna of the Viking satellite has been used to determine for the first time the direction of the polarization plane of the auroral kilometric radiation (AKR) inside the sources of the radiation (i.e., at the local frequency of generation). The observations show a clear difference between the modulation patterns obtained inside the AKR sources and the ones obtained far from them. The chi‐square goodness of fit test has been used to compare the measurements made during 36 AKR source crossings with a theoretical model accounting for the specific Viking antenna equipment. This statistical study shows that, inside the sources, the wave electric field is directed perpendicular to the static magnetic field, within 10°. This observation, consistent with a wave generation by the cyclotron maser instability, is also a fundamental constraint on any model attempting to relate the wave observations far from the sources to the physical characteristics of the sources.
Distributed two‐dimensional region 1 and Region 2 currents: Model results and data comparisons
Authors: Siscoe George , Maynard Nelson
Published: February 2008

We combine the one‐dimensional, distributed region 1 current model of Lotko et al. (1987) with the two‐dimensional, distributed region 2 current model of Vasyliunas (1972) to produce the first model to distribute both region 1 and region 2 currents in two dimensions (no sheet currents) and to calculate both currents mutually consistently from a single applied transpolar potential. The solutions give ionospheric equipotentials and electric field profiles for all local times and latitudes and Birkeland current contours and profiles everywhere within the auroral annulus. The Birkeland current contours comprise a symmetrical pair of spirals unwinding counterclockwise with region 0, 1, and 2 segments. The model predictions are compared with DE 2 data with noted points of agreement and disagreement. We list steps needed to develop the model further.
High spectral resolution measurement of gamma ray lines from the Earth's atmosphere
Authors: Willett J. B. , Mahoney W. A.
Published: February 2008

A search for gamma ray line features from the Earth's atmosphere has been conducted using data from the third High Energy Astronomy Observatory (HEAO 3) high spectral resolution gamma ray spectrometer. In addition to the strong line at 0.511 MeV, other intrinsically broadened line features have been observed at 1.63, 2.31, 3.67, 4.43, 5.09, and 6.13 MeV. Since the spectral resolution of the instrument is much finer than the width of the observed line features, the intrinsic width as well as the energy and intensity of each of these lines are reported. Several other predicted lines have also been observed. The characteristics of the lines seen by HEAO 3 are generally consistent with theoretical predictions as well as with previous measurements.
A global simulation of the magnetosphere with a long tail: No interplanetary magnetic field
Authors: Kageyama A. , Watanabe K. , Sato T.
Published: February 2008

A global simulation of the magnetosphere with a long tail (∼100 RE) is performed. A magnetosphere with a neutral sheet is constructed from a dipole field by solar wind dynamic pressure (no interplanetary magnetic field (IMF)). Concentration of the plasma sheet current occurs preferentially at 14–18 RE on the tail side of the Earth, which is an indication that, magnetically, this is the most fragile region of the tail structure. It is the demarcation region between the dipolar and streaming field line structures. Therefore, in the presence of resistivity, magnetic reconnection can be preferentially driven here by a compressional disturbance of some sort. In the present initial value problem, reconnection occurs at 15–20 RE in the tail and develops into a large lump of plasma surrounded by reconnected field lines, a plasmoid, which is ejected tailward. The time scale of the plasmoid formation and ejection process is very slow, of the order of several hours, when no IMF exists. After ejecting one plasmoid, reconnection occurs again in the plasma sheet, and a second plasmoid is formed and ejected. This result shows that a magnetosphere that has a sufficiently long tail and a neutral sheet is fragile and subject to plasmoid formation. We also show that the hot plasma, when mapped down to the ionosphere along the field lines, encompasses the auroral oval in agreement with the DE satellite observations.
Modeling the magnetic signature of impact‐generated plasma clouds
Authors: Wagner B. , Neubauer F. M.
Published: February 2008

A theoretical model has been developed to evaluate the magnetic field disturbances due to plasma clouds formed by hypervelocity (68 km/s) impacts of milligram mass dust particles on the Giotto spacecraft at comet P/Halley. The model is partly analytical and assumes unmagnetized ions and frozen‐in electrons as suggested by the high time‐resolution magnetic field observations. It treats the cloud development after an initial phase with unfrozen plasma ending a few milliseconds after impact. Fitting the model to the observed magnetic field signature of the impacts allows the determination of the center‐of‐mass velocity and the expansion velocity as well as the total number of particles in the expanding cloud, which leads to an estimate for the mass of the dust particle.
Marine transgression, shoreline emergence: Evidence in seabed and terrestrial ground temperatures of changing relative sea levels, Arctic Canada
Authors: Taylor Alan E.
Published: February 2008

Precise temperatures to depths of several hundred meters have been measured in abandoned petroleum exploration wells in coastal and offshore areas of the Canadian Arctic. In these regions, changes in relative sea level during the Quaternary have left a strong thermal signature on deep ground temperatures. Surface temperature changes of the order of 10–20 K accompanied shoreline emergence due to uplift in some regions and marine transgression due to eustatic changes in sea levels in others. Classical, analytic techniques are used to demonstrate that these anomalous features are a direct consequence of recent changes in sea level. In coastal areas of the Queen Elizabeth Islands, modelling of the large, near‐surface temperature‐depth gradients and the distinct curvature in the measured profiles yield emergence times in general agreement with dates taken from emergence curves. The analysis suggests that surface temperatures of these coastal areas were 16–19 K higher than at present from the Late Wisconsinan until emergence in the Holocene, suggesting either marine conditions for this period or glacial ice cover with basal temperatures near the pressure melting point. In contrast, at two offshore wells on the Beaufort Shelf, analyses of the negative temperature‐depth gradients below the seabed and profile curvature yield times of marine transgression generally consistent with the published sea level curve for the area. The analyses suggest that surface temperatures of some present offshore areas were 10–16 K lower than today's sea bottom temperatures from the Late Wisconsinan until marine transgression in the Holocene. The characteristic ground temperature profiles measured in such arctic areas provide independent evidence for the relative changes in sea level indicated by proxy data. It is especially valuable for these areas, where there is little historical record and from which datable material, such as shells, driftwood, and pumice fragments, may be scarce or ambiguous. These effects may not be observable in temperate areas because of the smaller contrast in sea bottom and terrestrial temperatures.
The equation of state of a molten komatiite: 2. Application to komatiite petrogenesis and the Hadean Mantle
Authors: Miller Gregory H. , Stolper Edward M. , Ahrens Thomas J.
Published: February 2008

New experimental data for the equation of state of a komatiitic liquid were used to model adiabatic melting in a peridotitic mantle. If komatiites are formed by >30% partial melting of a peridotitic mantle, then komatiites generated by adiabatic melting come from source regions that began their unmelted ascent in the lower transition zone (≈500–670 km) or the lower mantle (>670 km). The great depth of incipient melting implied by this model suggests that komatiitic liquids may form in a pressure regime where they are denser than their coexisting crystals, possibly the bulk mantle. Although komatiitic magmas are thought to separate from residual crystals in the mantle at a temperature ≈200°C greater than modem mid‐ocean ridge basalts (MORBs), their ultimate sources are predicted to be diapirs that, if adiabatically decompressed from initially solid mantle, were more than 700°C hotter than the sources of MORBs and were derived from great depth. We also studied the evolution of an initially molten mantle, i.e., a magma ocean. Our model considers the thermal structure of the magma ocean, density constraints on crystal segregation, and approximate phase relationships for a nominally chondritic mantle. Crystallization will begin at the core‐mantle boundary. Perovskite buoyancy at >70 GPa may lead to a compositionally stratified lower mantle with iron‐enriched magnesiowüstite content increasing with depth. Large convective velocities in the magma ocean would prohibit crystal‐liquid fractionation by settling or flotation until quiescent boundary layers form. Such boundary layers could form when the crystal content of the magma reaches a critical value (near 44 vol %) and, in the late stages of crystallization, around unmelted blocks of foundered protocrust. Matrix compaction and diapirism could also lead to fractionation effects. The upper mantle could be depleted or enriched in perovskite components relative to the bulk mantle. Olivine neutral buoyancy may lead to the formation of a dunite septum in the upper mantle, partitioning the ocean into upper and lower reservoirs, but this septum must be permeable.
Application of the global positioning system to crustal deformation measurement: 2. The influence of errors in orbit determination networks
Authors: Larson Kristine M. , Webb Frank H. , Agnew Duncan C.
Published: February 2008

Global Positioning System (GPS) measurements of a geodetic network in southern and central California have been used to investigate the errors introduced by adopting different sets of stations as fixed. Such fixed points, called fiducial stations, are necessary to eliminate the errors of imprecise satellites orbits, which otherwise would dominate the error budget for distances greater than tens of kilometers. These fiducial stations also define the reference frame of the crustal deformation network. Establishing the magnitude of the effect of changing the fiducial network is essential for crustal deformation studies, so that these artifacts of the differences between fiducial networks used for the data analyses are not interpreted as geophysical signals. Solutions for a crustal deformation network spanning distances up to 350 km were computed with a variety of fiducial networks. We use fiducial coordinates determined from very long baseline interferometry (VLBI). We compare these solutions by computing the equivalent uniform strain and rotation that best maps one solution into another. If we use a continental‐scale fiducial network with good geometry, the distortions between the solutions are about 10−8, largely independent of the exact choice of stations. The one case of a large‐scale fiducial network where the distortions are larger is when the three fiducial stations chosen all lie close to a great circle. Use of a fiducial network no larger than the crustal deformation network tan produce apparent strains of up to 10−7. Our work suggests that fiducial coordinates determined from GPS data analysis may be used, although they should be determined using a consistent reference frame, such as provided by VLBI and satellite laser ranging.
Kinematic framework of the Cocos‐Pacific Plate Boundary from 13°N to the Orozco TRANSFORM FAULT: RESULTS FROM AN EXTENSIVE MAGNETIC AND SEAMARC II SURVEY
Authors: Madsen John A. , Fornari Daniel J. , Edwards Margo H. , Gallo David G. , Perfit Michael R.
Published: February 2008

During the summer of 1987, magnetic anomaly data were collected by surface ship as part of an extensive SeaMARC II investigation of the East Pacific Rise (EPR) from 13°N to the Orozco transform. The survey extended to either side of the rise axis onto seafloor at least 1.8 million years (m.y.) in age, enabling the recent evolution of the structural and kinematic framework of the plate boundary to be studied in detail. North of 13°50′N there has been a major perturbation in the evolution of the plate boundary. Swaths of lineaments that trend oblique to EPR‐parallel topography form a north pointing, V‐shaped discordant zone on the Pacific and Cocos plates that is broadly symmetric about the EPR axis. On the Pacific plate a zone of discordant morphology 130 km long and between 6 and 14 km wide with a structural grain that is highly oblique to the present‐day spreading direction is observed on seafloor 0.9–1.8 m.y. in age. A similar but more subtle feature of the same age is also present on the Cocos plate. These zones of discordant lineaments can be correlated with changes in the magnetic lineation pattern. On the Pacific plate the disturbed zone lies between anomalies J and 2, creating greater than normal distance between the anomalies. On the Cocos plate the disturbed zone is characterized by a distinct, high‐amplitude, northwestward trending magnetic anomaly. The observed structural grain and the changes in the magnetic anomaly patterns associated with the disturbed zones are very similar to those observed at propagating ridges. Based on the magnetic anomalies, a propagation rate of 10.8 cm/yr in a N10°W direction is estimated for the past 1.8 m.y. A detailed examination of the structures developed within the disturbed zone on the Pacifc plate indicates that the rift propagation in this area can best be explained by the model of Wilson (1990) which involves cyclic rift failure with inward curvature of both rift tips. Plate adjustment to the propagation event is ongoing. There is a pronounced change in the morphology of the rise axis with distance from the propagation event. Close to and for ∼100 km behind the propagator tip, the EPR crest is not well developed and is characterized by a series of low (relief of 100–200 m) ridges and troughs with a poorly defined neovolcanic zone. Further away (>100 km) from the propagator tip the rise crest is a single, linear, horst‐shaped ridge with a well‐developed narrow axial graben at the axis of the ridge. Regional morphologic and magnetic data suggest that this cycle of rift propagation may have begun approximately 2.5 million years before present (m.y.B.P.) near the eastern ridge‐transform intersection of the paleo‐O'Gorman transform and is continuing today at the Orozco transform.
Seismic Gap Hypothesis: Ten years after
Authors: Kagan Yan Y. , Jackson David D.
Published: February 2008

The seismic gap hypothesis states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries. One of the earliest and clearest applications of the seismic gap theory to earthquake forecasting was by McCann et al. (1979), who postulated zones of high, medium, and low seismic potential around the Pacific rim. In the 10 years since, there have been over 40 large (M ≥ 7.0) earthquakes, enough to test statistically the earlier forecast. We also analyze another forecast of long‐term earthquake risk, that by Kelleher et al. (1973). The hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence. The data suggest that, contrary to these forecasts, places of recent earthquake activity have larger than usual seismic hazard, whereas the segments of the circum‐Pacific belt with no large earthquakes in recent decades have remained relatively quiet. The “clustering” of earthquake times does not contradict the plate tectonic model, which constrains only the long‐term average slip rate, not the regularity of earthquakes.
The basal stress distribution of Ice Stream E, Antarctica, inferred by control methods
Authors: MacAyeal Douglas R.
Published: February 2008

The irregular spatial distribution and velocity independence of basal friction derived from Landsat measured surface velocity suggests that ice stream flow is not controlled by the properties of a deformable basal till alone. Rigid bedrock substrata may contact the base of the ice stream in small (<100 km2) areas where the velocity field displays strong vorticity and where the ice stream surface appears rumpled in Landsat images.
Subducting slabs stagnant in the mantle transition zone
Authors: Fukao Yoshio , Obayashi Masayuki , Inoue Hiroshi , Nenbai Masakazu
Published: February 2008

The P wave velocity structure beneath the Western Pacific is found from the International Seismological Center first arrival data. Special attention was paid to the deep structure beneath the Wadati‐Benioff zone. We discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks. This way of discretization minimizes a problem with tomographic studies of regional scale: difficulty in making corrections for the effects outside the region of interest. Our solution is iterative with the alternate step of the relocation of earthquakes, using the whole mantle model of Inoue et al. (1990) as a starting model. A first‐order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model. The essential result depends little on whether the reference spherical model is smooth or discontinuous near 400‐ and 670‐km depths. We examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere. The resolution is depth dependent but in general good enough to see the slab configuration beneath the Southern Kurile‐Japan‐Izu‐Bonin arcs and the Java arc. It is relatively poor beneath the Northern Kurile and Mariana arcs. The seismic image of subducting slab beneath the Southern Kurile to Bonin arcs bends to subhorizontal near the leading edge of the Wadati‐Benioff zone and extends continentward over a distance of more than 1000 km. The subhorizontal portion of the slab connects a high‐velocity blob to the bottom that reaches a depth of at least 800 km across the 670‐km discontinuity under the Japan arc. Although the image of the Java slab directly penetrates the 670‐km discontinuity, it then bends to a shallow dip with a considerable spread, reaching a depth of about 1200 km. These results suggest that descending slabs of lithosphere in the Western Pacific tend to be stagnant in the transition zone under a subtle control of the 670‐km discontinuity. Although stagnant slab materials eventually descend into the lower mantle, they no longer maintain their original configuration below the 670‐km discontinuity.
The barotropic response of the subpolar North Pacific to stochastic wind forcing
Authors: Cummins Patrick F.
Published: February 2008

In a recent observational study, Koblinsky et al. (1989) attempted to demonstrate that the topographic Sverdrup balance can account for mesoscale current fluctuations with periods between 10 and 100 days in the abyssal North Pacific. However, the topographic Sverdrup balance proved difficult to verify systematically over the North Pacific. In this paper the conditions required to obtain the topographic Sverdrup balance are investigated through numerical experiments with a stochastically forced, barotropic, quasi‐geostrophic numerical model of the subpolar North Pacific. In the numerical experiments the topographic Sverdrup balance emerges from area averages of the terms in the vorticity equation, but only for periods longer than about 40 days when the averages are taken over 4°×4° region. This period increases when averages are taken over progressively smaller regions. An examination of vorticity balances at individual points along sections through the model domain indicates that the topographic Sverdrup balance is not obtained at individual points, even for very long period motions. The possibility of verifying topographic Sverdrup dynamics with oceanic data is considered. It is argued that topographically generated small scales in the velocity field reduce the likelihood that the topographic Sverdrup balance can be systematically observed in velocity measurements from individual current meter moorings. The results suggest that the vorticity balance is complex and that topographic Sverdrup dynamics cannot be expected to provide an adequate explanation for the seasonal modulation of the abyssal eddy kinetic energy that is observed with moored instrumentation in the North Pacific.
The jet off Point Arena, California: Its role in aspects of secondary production in the copepod Eucalanus californicus Johnson
Authors: Smith Sharon L. , Lane Peter V. Z.
Published: February 2008

The most abundant large herbivorous copepod in the jet off Point Arena, California, was Eucalanus californicus. In July 1988, females were actively laying eggs and also had a sac of stored lipid. If egg production is a function of present food supply, food concentrations within the jet become the primary factor governing egg laying. However, if stored lipid is the nutritive source for egg production, the critical food supply governing egg laying can be quite distant in space and time from the actual egg laying. In this jet, present food concentration was the factor governing egg production. The size of the lipid sac was also positively correlated with egg production, suggesting that lipid was not being used for oogenesis. Such a life history strategy, in which egg laying and lipid storage are proceeding concurrently in females, has not been described before. Reproductive females were found primarily nearshore and along the southern edge of the jet; highest rates of egg laying and largest lipid reserves were also in these areas. We speculate that temperature affinities of Eucalanus californicus result in maximized abundance, egg production, and lipid sequestration at temperatures below approximately 13°C. In the Point Arena region, this results in a nearshore portion of the population inhabiting surface layers and showing potential for very high rates of secondary production. The jet acts to transport E. californicus from the nearshore zone into its offshore habitat on a regular basis. Eddies in the region may be the mechanism by which E. californicus is returned to the nearshore zone.
Structure and dynamics of a coastal filament
Authors: Dewey Richard K. , Moum James N. , Paulson Clayton A. , Caldwell Douglas R. , Pierce Stephen D.
Published: February 2008

Repeated microstructure transects across filaments in the coastal transition zone (CTZ) have revealed fundamental structure and dynamics of the complicated features. The measurements allow detailed momentum and vorticity analyses and provide a possible explanations for structural asymmetry of the fronts. Observations made between July 2 and July 23, 1988, along the central meridional CTZ survey line were used to estimate terms in the meridional momentum equation. The analysis indicates geostrophic flow along the axes of the fronts with the across‐front pressure gradient explaining as much as 87% of the variance in the balance. Significant ageostrophic flow in the across‐front coordinate was found, with the along‐front pressure gradient explaining only 71% of the variance in the momentum balance. The fronts were found to be asymmetric in relative vorticity, with stronger positive vorticity on the cooler side of the front and weaker negative vorticity on the warm side. Mean vertical velocities were estimated from the repeated transects of acoustic Doppler current profiles and the rapid sampling vertical profiler hydrographic and turbulence measurements. Regions of upwelling and downwelling are likely associated with adjustments in the relative vorticity, resulting in maximum vertical velocities of 40 m d−1. Asymmetry in the near‐surface temperature and salinity extrema are explained by cross‐frontal exchange. This cross‐frontal exchange modifies the relative roles of salinity and temperature in determining the density away from the coastal upwelling region, a dynamically important characteristic not revealed by advanced very high resolution radiometer imagery.
Energetics of global ocean tides from Geosat altimetry
Authors: Cartwright David E. , Ray Richard D.
Published: February 2008

The authors' global ocean tide maps derived from Geosat altimetry are here improved in quality and coverage; they compare favorably with ground truth data at about the same rms level as Schwiderski's models, slightly better in lunar than in solar tides. Diurnal admittances clearly show Kelvin wave structure in the southern ocean and confirm Platzman's resonant mode at 28.5±0.1 hours with an apparent Q of about 4. Driving energy enters dominantly in the North Pacific for the daily tides and is strongly peaked in the tropical oceans for the half‐daily tides. Global rates of working on all major tide constituents except S2 agree well with independent results from analyses of gravity through satellite tracking. Comparison at S2 is improved by allowing for the air tide in gravitational results but suggests deficiencies in all solar tide models. Estimates of Q factors based on potential energy (approximately 8 for daily tides and 13 for half‐daily tides) agree reasonably well with hydrodynamic models.
A diagnostic study of the wind‐ and buoyancy‐driven North Atlantic circulation
Authors: Spall Michael A.
Published: February 2008

A two‐moving‐layer diagnostic model with a variable depth mixed layer on top is applied to the annual mean climatology of the North Atlantic. Estimates of the annual mean mass flux from the mixed layer into the upper thermocline (called mixed layer pumping) and subsurface heating rates are obtained on the basin scale from hydrographic data alone. No independent measures of wind stress or other surface forcings are required. In addition, it is shown that the nonlinear terms in the vorticity equation are critical to balance the subsurface heat flux in the Gulf Stream and over most of the subtropical gyre. Evidence is presented for the existence of interior, southeastern, northeastern, and recirculation regimes in the North Atlantic. These regimes are distinguished by the behavior of the characteristic trajectories of the system and by whether the flow is a direct cell (interfacial flux and vertical velocity have the same sign) or indirect cell (interfacial flux and vertical velocity have the opposite sign). It is demonstrated here that one can make use of analytic approaches in the analysis of historical data sets to yield relatively simple solutions that give a direct link between theory and observations.
Primary production estimates from recordings of solar‐stimulated fluorescence in the equatorial Pacific at 150°W
Authors: Stegmann P. M. , Lewis M. R. , Davis C. O. , Cullen J. J.
Published: February 2008

Biological, optical, and hydrographical data were collected on the WEC88 cruise along 150°W and during a 6‐day time series station on the equator during February/March 1988. This area was characterized by a subsurface chlorophyll maximum (SCM), located at 50–70 m depth at the equator and descending down to 120–125 m at the north and south end of the transect. Highest primary production rates were near‐surface and confined to the equatorial region and stations between 7° and 11°N. To determine the relationship between solar‐stimulated fluorescence (centered at 683 nm wavelength) and primary production, a production‐fluorescence model based on phytoplankton physiology and marine optics is described. Results of model calculations predict that there is a linear relation between production and fluorescence. A comparison between morning and midday measurements of the production‐fluorescence relation showed that there was some difference between the two, whereas evening measurements, on the other hand, were distinctly different from the morning/midday ones. This seems to suggest that diurnal variations contribute significantly to variability in the quantum yield of photochemical processes. The ratio of the quantum yield of photosynthesis to the quantum yield of fluorescence (Φc/Φƒ), the parameter which will determine how well production can be estimated from optical recordings, ranged between 0.24 and 0.44 molC Ein−1 (an Einstein equals a mole of photons) for all stations. The highest value for this ratio occurred at the equatorial stations, indicating that interstation (i.e., latitudinal) variability could have an effect on the production‐fluorescence relation. Measured (with 14C incubations) and predicted production compared quite well, although high measured production rates for near‐surface samples were underestimated in most cases. Since both production and fluorescence were nonlinear at high irradiance intensities, we recommend in the future that a nonlinear component be incorporated into our model to take this effect into account and thus allow us to refine our estimates of nonlinear data.
Stratospheric dynamical effects of solar ultraviolet variations: Evidence from zonal mean ozone and temperature data
Authors: Hood L. L. , Jirikowic J. L.
Published: February 2008

Cross‐spectral analysis of low‐latitude average Nimbus 7 stratospheric and mesospheric sounder (SAMS) temperature deviations versus Nimbus 7 solar backscattered ultraviolet (SBUV) solar 205 nm flux measurements in the 1–3 mbar pressure range yields significant coherence at periods near 27 and 13 days. This supports earlier correlative evidence that the ozone response to solar ultraviolet variations is supplemented by a coupled temperature response in the upper stratosphere. Comparisons of improved one‐dimensional radiative photochemical model calculations with ozone and temperature response measurements at low latitudes yields agreement only in the case of ozone at levels below 3 mbar. An additional, presumably dynamical, component of the upper stratospheric response is suggested. Cross‐spectral analysis of low‐latitude average SAMS temperature deviations versus higher‐latitude temperature fluctuations of opposite sign in the winter hemisphere also yields significant coherency at periods near 27 and 13 days. Latitudinal temperature oscillations of this type result from interference between stationary and traveling wave components at stratospheric heights. It is therefore hypothesized that solar ultraviolet variations may force or modulate traveling waves with periods near 27 and 13 days in the upper stratosphere. The existence of such waves with higher amplitude near solar maximum than near solar minimum may help to explain observed solar cycle variations of zonally averaged winds and temperature in the upper stratosphere.
Field study of environmental variables controlling the NO emissions from soil and the NO compensation point
Authors: Slemr F. , Seiler W.
Published: February 2008

The NO flux rates were measured on a sandy loam at Haxthäuser Hof near Mainz in summer 1983. Significant emissions of NOy species other than NO were also occasionally measured. The data show that the NO and NOy emission rates are dependent on soil temperature, soil moisture, soil porosity, fertilization, plant cover, soil organic matter content, and NO and NOy mixing ratios in ambient air. Generally, one of these variables dominated and masked the influence of the others. In some cases the soil treatment led to the replacement of one dominating controlling factor by another one. In most cases, NO and NOy emission was observed at low, and deposition at high, mixing ratios of NO and NOyin the ambient air. The compensation points, i.e., the mixing ratios at which the flux from the soil is zero, varied between 0–5.5 parts per billion by volume (ppbv) for NO and 0–16.3 ppbv for NOy depending on the plant cover, soil temperature, soil organic matter content, and fertilization. Because the compensation points are of the same order of magnitude as the NO and NOy mixing ratios in ambient air, knowledge of the variables controlling them is essential for creditable estimations of the global NOx emissions by soils.
Two‐dimensional model calculation of fluorine‐containing reservoir species in the stratosphere
Authors: Kaye Jack A. , Douglass Anne R. , Jackman Charles H. , Stolarski Richard S. , Zander R. , Roland G.
Published: February 2008

Two‐dimensional model calculations have been carried out of the distributions of the fluorine‐containing reservoir species HF, CF2O, and CFClO. HF constitutes the largest fluorine reservoir in the stratosphere, but CF2O also makes an important contribution to the inorganic fluorine budget. CFClO amounts are most important in the tropical lower stratosphere. HF amounts increase with altitude throughout the stratosphere, while those of CF2O and CFClO fall off above their mixing ratio peaks due to photolysis. The model is in good qualitative agreement with observed vertical profiles of HF arid CF2O but tends to underestimate the total column of HF. The calculated CFClO distribution is in good agreement with the very limited data. The disagreement in the HF columns is likely due to small inaccuracies in the model's treatment of lower stratospheric photolysis of chlorofluorocarbons. The model results support the suggestion that CF2O may be heterogeneously converted to HF on the surface of polar stratospheric cloud particles. The model results also suggest that the quantum yield for photolysis of CF2O is near unity.
The attenuation of fluctuations in scalar concentrations through sampling tubes
Authors: Lenschow D. H. , Raupach M. R.
Published: February 2008

We present results of a laboratory investigation of the attenuation of humidity fluctuations in tubing. The purpose is to obtain simple formulations for use in turbulent flux measurement applications, where the measurement of a trace species may be remote from the sampling point so that the sample must be transported through a tube to the sensor. The laboratory data are compared to the attenuation predicted from Taylor's (1953 and 1954) formulations for the virtual longitudinal eddy diffusivity of a constituent introduced into a pipe, for both laminar and turbulent flow, by plotting the normalized half‐power frequency against Reynolds number. Results were first obtained for fully developed equilibrium flow (both laminar and turbulent) through a straight tube. The following modifications were then studied: an intake section, a 90° elbow bend, and curved tubes (bending through 90°) with tube‐radius to radius‐of‐curvature ratios of a/R = 0.034 and 0.081. The effect, if any, of these modifications is to increase the half‐power frequency over that of the equivalent length of straight tubing. Applying this analysis to a situation where a sample is collected on a tower and transported to an instrument at the base of the tower, we find that as long as the flow in the tube is turbulent, the attenuation in the tubing should not be a significant factor for introducing errors in flux measurements in the unstably stratified atmospheric surface layer.
Outgoing longwave radiation and its diurnal variation from combined ERBE and Meteosat observations: 1. Estimating OLR from Meteosat data
Authors: Cheruy F. , Kandel R. S. , Duvel J. P.
Published: February 2008

Radiative transfer calculations show that measurements in two relatively narrow spectral domains, corresponding to the atmospheric infrared window and to a band of water vapor absorption, can account for nearly all of the variance of outgoing longwave radiation integrated over the entire thermal spectrum. Statistical analyses of simultaneous colocated Meteosat radiance and Earth Radiation Budget Experiment (ERBE) radiant exitance data, for the months of November 1984 and April and July 1985, yield regression coefficients for estimating longwave radiant exitance MLW from radiances observed in the Meteosat infrared (IR) window and water vapor (WV) channels, with root‐mean‐square errors of the order of or less than 10 W m−2. The coefficients thus obtained are in good agreement with coefficients relating MLW, IR and WV from analysis of results of radiative transfer calculations. Meteosat data can then be used to estimate MLW at times not sampled by ERBE. Although some biases appear to exist over areas of heterogeneous cloud cover, they should not significantly affect studies of strong diurnal variations.
Climatological statistics of stratospheric inertia‐gravity waves deduced from historical rocketsonde wind and temperature data
Authors: Hamilton Kevin
Published: February 2008

Ten years of rocketsonde observations of wind and temperature in the 28–57 km height range at 12 stations (spanning 8°S to 76°N) were analyzed. The aim was to determine the geographical and seasonal variation of statistics relating to the propagation of inertia‐gravity waves. As noted by earlier investigators, there is a clear tendency for the rocketsonde hodographs to display clockwise rotation with height in the extratropical northern hemisphere. This is consistent with the notion that the variations are dominated by inertia‐gravity waves with upward energy propagation. By using the wind and temperature data simultaneously it was possible to determine a dominant direction of horizontal wave propagation for each profile. This quantity has an impressive seasonal variation in mid‐latitudes, with strong eastward propagation apparent in summer and generally westward propagation in winter. This seasonal cycle is consistent with theoretical notions of how the mean flow ought to affect wave propagation. Two stations within 10° of the equator are included in this analysis. The results at these near‐equatorial stations contrast strongly with those at higher latitudes. There is a clear tendency for the hodographs at these stations to display quite linear polarization (rather than the systematic rotation generally seen at higher latitudes). The wind variations also show a remarkable tendency to align themselves in the zonal direction. When the wind and temperature variations are used together, it can be shown that the variations seen are consistent with a clear dominance of eastward propagation.
Modeling of Jupiter's millimeter wave emission utilizing laboratory measurements of ammonia (NH3) opacity
Authors: Joiner Joanna , Steffes Paul G.
Published: February 2008

Radiative transfer models which have been used to compute Jupiter's millimeter wave emission do not agree well with the existing radio astronomical observations (e.g., de Pater and Massie, 1985). This apparent discrepancy has gone largely unexplained due to a lack of laboratory absorption data at these wavelengths coupled with uncertainties in the calibration of millimeter wave observations. Gaseous ammonia (NH3) is the largest source of millimeter wave opacity on Jupiter. Previous laboratory measurements at 7.5‐ to 9.38‐mm were inconclusive as to which theoretical line shape most accurately describes the millimeter absorptivity of NH3 (Joiner et al., 1989). We have made additional laboratory absorption measurements of gaseous ammonia at a shorter wavelength (3.2 mm) where the theoretical line shapes can be better evaluated. We have conducted measurements at a temperature of 210 K, at pressures ranging from 1 to 2 atm, and in a mixture consisting of 85.56% hydrogen (H2), 9.37% helium (He), and 5.07% ammonia (NH3). We give a revised formalism for computing NH3 absorption in an H2/He atmosphere using the Ben‐Reuven line shape. We investigate several other potential millimeter wavelength absorbers and give revised formalisms for computing their absorption. We have compiled a list of Jupiter's reliable millimeter wavelength observations. We compare our list of observations with synthetic emission spectra utilizing our revised expressions for computing absorption.