bluuebunny/crossref_metadata_2025 huggingface dataset:
Episodic inputs of atmospheric nitrogen to the Sargasso Sea: Contributions to new production and phytoplankton blooms
Authors: Michaels Anthony F. , Siegel David A. , Johnson Rodney J. , Knap Anthony H. , Galloway James N.
Published: February 2008

Atmospheric wet deposition rates of nitrate and ammonia on Bermuda collected in the Atmosphere Ocean Chemistry Experiment (AEROCE) are compared with the synoptic measurements of carbon and nitrogen cycling from the U.S. Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time Series Study (BATS) station, 75 km southeast of Bermuda. Measurable deposition events were found on 23.8% of the days between October 1, 1988 and June 30, 1991. However, only a few of these events significantly contributed to the standing stocks of nitrogen and phytoplankton or rates of primary production. For 1.7% of the days each year, the atmospheric nitrogen deposition would have equaled the sinking particulate nitrogen flux as estimated by sediment traps. For only 0.2% of the time, would adequate nitrogen be deposited to a 20 m mixed layer to change the surface concentrations of particulate organic nitrogen by 10%. The results are dramatically different if all of the deposition remains confined to the upper l m of the water column enabling intense, surface phytoplankton blooms to occur. The occurrence of these near‐surface blooms may be an important signal in the interpretation of satellite ocean color imagery, particularly when the satellite data are used to infer whole water‐column phytoplankton stocks or productivity. Numerical simulations of the evolution of the near‐surface mixed layer after a rainfall event indicate that low salinity surface waters would be mixed to the upper 10 m or so within 2‐4 hours, except for wind speeds less than approximately 5m s−1. Thus, wet deposition induced surface algae blooms should only be observed under relatively calm meteorological conditions. In summary, wet deposition of nitrogen is a relatively unimportant process in affecting upper ocean nitrogen cycling for the Sargasso Sea off Bermuda, although in oceans with lower productivity and areas where deposition may increase with future industrial development, episodic deposition events may eventually have some short‐term impacts on the local nitrogen cycle. To assess the total impact of atmospheric deposition of nitrogen will require additional information on dry deposition and the organic nitrogen content of rainwater.
Is carbon accumulating in the northern temperate zone?
Authors: Houghton R. A.
Published: February 2008

The current imbalance in the global carbon budget (“missing carbon”) is approximately 1.5 to 2.0 PgC/yr. The study by Tans et al. [1990], based on geographically based estimates of industrial emissions, atmospheric data, and a model of atmospheric transport, suggested that the missing carbon was accumulating in terrestrial ecosystems of the northern hemisphere's temperate zone. Two recent analyses of forest growth in this region have reported an accumulation of carbon that approaches 1 PgC/yr, and on the basis of these three studies one might conclude that the carbon budget is close to balanced. These recent analyses are incomplete, however. They included the accumulation of carbon in regrowing forests logged during the last several decades but not the emissions of carbon from plant material initially held in those forests before logging. When all of the carbon is accounted for, the net flux of carbon (to forests as well as from forest products and logging debris) is close to zero in these regions. Thus the recent analyses have not uncovered a missing sink for carbon, as claimed. On the contrary, they seem to have confirmed that the current imbalance in the carbon budget cannot be explained by the net accumulation of wood in northern forests. If the entire global imbalance is accumulating in the biomass of these forests, the required accumulation rate is too large to have been missed by forest surveys. An annual flux of 1.5 to 2.0 PgC/yr seems too large to be accommodated in aboveground vegetation anywhere.
Dissolved organic matter and the glacial‐interglacial pCO2 problem
Authors: Paillard Didier , Ghil Michael , Le Treut Hervé
Published: February 2008

Two box models, one analytical and one numerical, are used to investigate systematically a broad range of oceanic circulation changes on the atmospheric carbon dioxide (CO2) concentration. A number of oceanic carbon cycle models have failed to reproduce the 30% increase in CO2 partial pressure (pCO2) during the last deglaciation as reconstructed from polar ice cores. We apply therefore this approach of exploring the model's parameter space to examine the effect of long‐lived dissolved organic matter on the system. The results from the two models complement each other, in terms of insight versus detail. Carbon is usually assumed to be transported from the surface into the deep ocean through the sedimentation of particulate matter. If there exists in the ocean a pool of dissolved organic matter (DOM) with a regeneration time comparable with the advection time, then the associated carbon can also be advected, resulting in a different distribution. Such a DOM reservoir acts as a smoother on the spatial distribution of nutrients in the sea, particularly in the equatorial intermediate waters. We establish the role of intermediate waters as one of the key components of the oceanic carbon cycle and show that DOM reduces the sensitivity of the carbon cycle to oceanic circulation pattern changes, mainly because of its smoothing effect. Consequently, the possible existence of DOM species with a time constant of the order of a century tends to reduce, rather than enhance, the glacial‐interglacial difference in pCO2 levels due to changes in the thermohaline circulation.
Annual cycles of phytoplankton chlorophyll concentrations in the global ocean: A satellite view
Authors: Yoder James A. , McClain Charles R. , Feldman Gene C. , Esaias Wayne E.
Published: February 2008

Conceptual and mathematical models show that annual cycles of phytoplankton biomass are different within different regions of the ocean. The purpose of this manuscript is to use coastal zone color scanner chlorophyll imagery (CZCS‐Ch1) to determine annual cycles in phytoplankton chlorophyll (biomass) averaged over very large areas of the global ocean. A possible result is that large‐scale averaging of CZCS‐Ch1 will yield no interpretable signals because of spatial variability in annual cycles at scales much smaller than our averaging scale. Alternatively, if our analyses show regular and persistent global patterns, then our results will jprovide a basin‐scale overview of phytoplankton biomass seasonally for comparison with model results or with other large‐scale oceanographic measurements. Our results show that monthly mean CZCS‐Ch1 imagery (and using in situ concentrations for winter at latitudes poleward of 40 deg) resolves important differences in annual phytoplankton chlorophyll cycles for different ocean basins and latitude belts. As predicted by simple models of plankton dynamics, our results show: (1) global subtropical waters have circa 2X higher CZCS‐Ch1 concentrations in winter than in summer and (2) subpolar waters in the northern hemisphere (NH) have mean monthly CZCS‐Ch1 concentrations during May and June that are manyfold higher than in winter, particularly in the North Atlantic. Our results also show: (1) Northern Indian Ocean is the major subtropical anomaly, (2) subpolar waters in the SH do not show differences between spring maxima and winter minima as large as those in the subpolar NH and (3) larger ocean area in the SH is compensated by higher mean annual CZCS‐Ch1 concentrations in the NH, so that annual hemispherical integrals (mean annual concentrations multiplied by ocean areas) are very similar. The simple patterns we report imply that mean annual cycles in phytoplankton biomass averaged over very large areas of the global ocean are largely explainable by very simple mathematical models such as those presented several decades ago by Cushing, Riley, Steele, and others.
Effect of mantle plumes on the growth of D” by reaction between the core and mantle
Authors: Kellogg L. H. , King S. D.
Published: February 2008

The core‐mantle boundary is a fundamental compositional discontinuity in the Earth, where molten iron alloy from the core meets solid silicate minerals from the mantle. Heat flow from the core to the mantle creates a thermal boundary layer at the base of the mantle. At the same time, chemical reactions may create a layer of different composition and density than the overlying mantle. Using a finite element model of convection in a spherical shell that includes formation of dense material at the base of the shell, we investigate how a layer forms at the base of the mantle. Development of a layer at the base of the mantle by this method depends both on the composition of the material forming at the core‐mantle boundary and on the rate at which the material diffuses into the mantle. If the material is less than 3–6% denser than the overlying mantle, assuming reasonable choices of lower mantle thermodynamic parameters, the reactant material will be swept away by upwelling plumes. More dense material, on the other hand, forms an internally convecting layer that entrains material from above. The varying thickness and composition of the layer is consistent with geophysical observations of the characteristics of the deep mantle.
Nonlinear dynamics established in the ENSO
Authors: Elsner J. B. , Tsonis A. A.
Published: February 2008

A time series describing the El‐Nino ‐ Southern Oscillation (ENSO) is analyzed using the latest techniques of chaos theory. The methods which rely on resampling statistics were developed to more finely distinguish between nonlinearity and linear correlated noise. From the results significant nonlinear structure arising from ENSO dynamics on the monthly time scale is established.
On the voltage and distance across the low latitude boundary layer
Authors: Hapgood Mike , Lockwood Mike
Published: February 2008

A pass of the AMPTE‐UKS satellite through the low‐latitude boundary layer (LLBL) at 8:30 MLT is studied in detail. The magnetosheath field is predominantly northward. It is shown that multiple transitions through part or all of the layer of antisunward flow lead to overestimation of both the voltage across this layer and its width. The voltage is estimated to be only about 3 kV and this implies that the full LLBL is about 1200 km thick, consistent with previous studies.
Observations of suprathermal ions in association with SLAMS
Authors: Giacalone Joe , Schwartz Steven J. , Burgess David
Published: February 2008

We present observations of 1.4–20 keV ions in association with short large amplitude magnetic structures (SLAMS) using high time resolution AMPTE/UKS data near the quasi‐parallel Earth's bow shock. The observations show a strong temporal gradient in the suprathermal ion pressure as the convecting SLAMS passes. We discuss these observations in the context of recent simulation studies which predict that SLAMS are the result of the steepening of a ULF wave as it passes through an energetic particle pressure gradient and present a simple picture illustrating the relationship between this spatial gradient and the observed temporal one.
on scaling temporal variations in cosmic ray intensity
Authors: Kudela K. , Venkatesan D.
Published: February 2008

We have examined the time series of hourly values of cosmic ray intensity over the years 1974–1990, observed by neutron monitors at Calgary and Lomnicky Stit, for the scaling properties. The scaling is shown to exist in intervals of 32–256 hours in data over several years. Fractal structure is deduced with statistically insignificant evidence of multifractal behaviour. The higher moments of the distribution have, in many years, symmetric properties, i.e., the scaling is similar for the same order (positive and negative).
A survey and new measurements of ice vapor pressure at temperatures between 170 and 250K
Authors: Marti James , Mauersberger Konrad
Published: February 2008

Saturated vapor pressures of ice at temperatures below 200K have become more important since the discovery of ice clouds in the polar stratosphere and upper mesosphere. Direct measurements of ice vapor pressures at such low temperatures are sparse and unreliable. This paper summarizes published vapor pressure data and presents new measurements at temperatures between 170 and 250K, extending the range of measured ice vapor pressures by three orders of magnitude. A simple empirical vapor pressure equation is derived which permits prediction of vapor pressures between 170K and the triple point of water, with an accuracy of about 2%: log P = A/T + B, with A = −2663.5 ± 0.8, B = 12.537 ± 0.011, P in Pa and T in kelvins. Predictions by this empirical equation agree, within experimental uncertainty, with the most reliable equation derived from thermodynamic principles.
New advances for paleomagnetic studies of sediment cores using U‐Channels
Authors: Nagy Elizabeth A. , Valet Jean‐Pierre
Published: February 2008

Accurate and detailed paleomagnetic data can be obtained from continuous measurements of U‐channels extracted from sedimentary cores using a small‐diameter pass‐through magnetometer and high resolution signal‐response pick‐up coils. The spatial resolution is not significantly lower than that obtained by measuring standard paleomagnetic samples and features on the order of 3–5 cm can be confidently resolved. We propose a method to analyze the demagnetization data based on the angular dispersion of the directions between successive demagnetization steps and the downcore changes in the rate of intensity decrease. This technique allows us to distinguish very rapidly between intervals with well‐identified characteristic magnetic components and zones characterized by a more complex behavior during demagnetization. It is also possible to directly measure the magnetic susceptibility, and to induce and measure most rock magnetic properties along the U‐channels. Thus all parameters necessary for a complete paleomagnetic study of sediment cores can be confidently obtained directly from U‐channels without extracting individual samples. Finally this equipment makes possible the measurement and complete demagnetization of up to 10 single samples at a time in less than one hour by using techniques similar to those developed for the U‐channels.
The effect of ocean tides on the Earth's rotation as predicted by the results of an ocean tide model
Authors: Gross Richard S.
Published: February 2008

The published ocean tidal angular momentum results ofSeiler[1991] are used to predict the effects of the most important semidiurnal (M2,S2,N2), diurnal (K1,O1,P1), and long period (Mf,Mf′,Mm, andSsa) ocean tides on the Earth's rotation. The separate, as well as combined, effects of ocean tidal currents and sea level height changes on the length‐of‐day, UT1, and polar motion are computed. The predicted polar motion results reported here account for the presence of the free core nutation and are given in terms of the motion (within the rotating, body‐fixed terrestrial reference frame) of the celestial ephemeris pole so that they can be compared directly to the results of observations. Outside the retrograde diurnal tidal band, the summed effect of the semidiurnal and diurnal ocean tides studied here predict peak‐to‐peak polar motion amplitudes as large as 2 mas. Within the retrograde diurnal tidal band, the resonant enhancement caused by the free core nutation leads to predicted polar motion (or, equivalently, nutation) amplitudes as large as 9 mas (at the unobservable retrogradeK1tidal frequency).
Source parameters of small earthquakes recorded at 2.5 km depth, Cajon Pass, southern California: Implications for earthquake scaling
Authors: Abercrombie Rachel , Leary Peter
Published: February 2008

A 2.5 km deep triaxial seismometer at Cajon Pass in southern California has recorded several hundred earthquakes <ML4.0 occurring within the San Andreas fault system. At 2.5 km seismic background noise is below amplifier sensitivity and the 2–250 Hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs. Compared with downhole recorded motion, seismic amplitudes at the surface are amplified below 10 Hz and severely attenuated above 30 Hz. We estimate that QS is at least 1000 for wave motion at 2.5 km and below and QP is over 2000. The range of source dimensions in the downhole recorded catalog is ∼10 m to ∼70 m (ML∼−2.0, Mo∼108 Nm to ML∼2.7, Mo∼1013 Nm). The plot of log(source‐radius) vs log(moment) has a straight line trend compatible with earthquake scaling at constant stress drop; inferred stress drops are scattered between 1 and 500 bars. There is no evidence in the catalog for the proposed minimum source dimension at ∼100 m. When the Cajon Pass borehole catalog, containing some of the smallest recorded natural earthquakes, is combined with 800 larger events from previous studies, the moment‐radius trend suggests that natural earthquakes are self‐similar over a magnitude range M∼−2 to ∼8. We suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust.
Methanesulfonic acid in coastal Antarctic snow related to sea‐ice extent
Authors: Welch K. A. , Mayewski P. A. , Whitlow S. I.
Published: February 2008

Proxy records of biogenic sulfur gas obtained from ice cores suggest that variability in marine biogenic sulfur emissions may reflect changes in climate [Saigne and Legrand, 1987; Legrand et al., 1988, Legrand et al., 1991; Anderson and Charlson, 1991]. Increased sea‐ice extent has previously been proposed as one cause of relatively high methanesulfonic acid (MSA) in glacial‐age ice core samples [Gibson et al., 1990]. We have analyzed MSA, one of the oxidation products of the biogenic sulfur gas dimethylsulfide [Hatakeyama et al., 1985], from snowpit samples recovered from a coastal site in Southern Victoria Land, Antarctica. Time series of MSA correlate significantly with the longest continuous record available of Southern Ocean sea‐ice extent (two decades) [Jacka, 1990].
Melting of iron‐magnesium‐silicate perovskite
Authors: Sweeney Jeffrey S. , Heinz Dion L.
Published: February 2008

Iron‐magnesium‐silicate perovskite was melted in a laser‐heated diamond anvil cell and monitored by thermal analysis. Two signals were identified at each pressure: a lower temperature signal and a higher temperature signal.

The lower signal may correspond to the temperature where iron diffuses rapidly. The higher signal would then correspond to melting of magnesium‐enriched silicate perovskite. Alternatively, the lower signal may be the solidus where (Fe.14Mg.86)SiO3 undergoes incongruent melting to an iron‐magnesium‐enriched solid plus a silica‐enriched liquid. Then, the higher signal would be the liquidus.

The slope for the melting curve (the higher signal) between 30GPa and 94GPa is slightly negative. Fitting to a straight line gives a value for the slope of −2.5 ± 0.6K/GPa. At 30GPa, the lower signal is ≈300K below the melting curve. They converge slightly at higher pressures and differ by ≈140K at 94GPa. Our melting curve is several hundred degrees (K) below previous estimates.
High ice crystal production in winter cumuli over the Japan Sea
Authors: Takahashi Tsutomu
Published: February 2008

An aircraft equipped with a new video camera designed to count ice crystals flew into the Hokuriku winter cumulus clouds which developed over the Japan sea during typical Monsoon weather. On one day we encountered cumulus clouds which formed many small ice crystals. There, a very high concentration of ice crystals in the size of 60/100 μm in diameter was measured when both large and small graupel were observed, while medium‐sized graupel were missing. It was proposed that ice crystals were shattered in the collision of large and small graupel, which have different ice surfaces formed by different modes.
On the origin of short large‐amplitude magnetic structures upstream of quasi‐parallel collisionless shocks
Authors: Dubouloz N. , Scholer M.
Published: February 2008

In order to model the development of the turbulence upstream of quasi‐parallel shocks, one‐dimensional hybrid simulations have been performed of the injection of a very hot ion population into a cold incident flow. ULF electromagnetic waves are initially generated in the right‐hand resonant ion beam mode. As these waves are convected to the injection source and encounter larger beam densities, they grow in amplitude and scatter the beam ions. Beam ion clumps characterized by distributions with a significant fraction of ions having velocities antiparallel to the beam bulk velocity are generated, and destabilize the left‐hand resonant ion beam mode. This process enables the formation of enhanced magnetic field structures which, like the short large‐amplitude magnetic structures (SLAMS) observed upstream of the quasi‐parallel Earth's bow shock, show scale lengths smaller than the ULF waves wavelength, have magnetic amplitudes up to a few times the ambient magnetic field, are left‐hand polarized in the plasma rest frame, and often possess attached whistler waves.
Venus bow shocks at unusually large distances from the planet
Authors: Steinolfson R. S. , Cable S.
Published: February 2008

Recent analysis of data from the Pioneer Venus Orbiter (PVO) has shown that the bow shock often travels to unusually large distances from the planet when the solar wind magnetosonic Mach number is near unity. We suggest that distant bow shocks can be explained as an integral part of the response of the global solar wind/Venus interaction to the anomalous local solar wind conditions that existed during the time of these observations. The lower than normal plasma beta and magnetosonic Mach number are in a parameter regime for which the usual fast‐mode bow shock close to the planet may not provide the necessary compression and deflection of the solar wind. Using MHD simulations we show that, for these conditions, the usual fast shock is replaced by a bow shock consisting of an intermediate shock near the Sun‐Venus line and a fast shock at large distances from the Sun‐Venus line. This composite bow shock propagates upstream away from the planet at a low speed and appears to be approaching a new equilibrium stand‐off location at a large distance from the planet.
The spatial distribution of coronae and related features on Venus
Authors: Squyres Steven W. , Janes Daniel M. , Schubert Gerald , Bindschadler Duane L. , Moersch Jeffrey E. , Turcotte Donald L. , Stofan Ellen R.
Published: February 2008

Coronae are large quasi‐circular geologic features that are common on Venus. They appear to be the surface tectonic and volcanic expressions of mantle diapirs that have impinged on the underside of the venusian lithosphere. We have investigated the spatial distribution of 335 coronae and related features identified in Magellan radar data. It is more clustered than a Poisson distribution, with a statistical certainty of more than 99%. It is dominated by a single large cluster centered near the equator at about 245° longitude. The features are preferentially found at elevation and geoid values close to the planetary mean, with a paucity at both the highest and lowest levels of topography and geoid. Some coronae appear aligned in quasi‐linear chains. We attribute the clustering of coronae and related features to preferential formation of these features above regions of broad‐scale mantle upwelling, and suggest that a major mantle upwelling underlies the one large cluster. We suggest that coronae are rare at the lowest elevations because these may be regions of mantle downwelling. The shortage of coronae at the highest elevations may result both from obscuration by other intense tectonism there and from suppression there of their formation by an unusually thick crust. Corona chains may be produced by enhanced passive mantle uplift below failed or incipient rifts.
Impact cratering at geologic stage boundaries
Authors: Stothers Richard B.
Published: February 2008

The largest known Cenozoic impact craters with the most accurately measured ages are found to correlate very closely with geologic stage boundaries. The level of confidence in this result is 98–99% even under the most pessimistic assumptions concerning dating errors. One or more large impacts may have led, in at least some cases, to the extinctions and first appearances of biotic species that mark many of the geologic stage boundaries.
The heliospheric cavity radio emission: Generation of discrete tones by Fermi acceleration via oscillating boundary
Authors: Farrell W. M.
Published: February 2008

A theory is presented that describes the formation of the discrete radio tones that could apply to the radio emission observed in the outer heliosphere by the Voyager spacecraft. Specifically, a broadband emission is assumed to be trapped within the heliospheric cavity. If the heliospheric outer boundary, the heliopause, has a large‐scale, monochromatic oscillation, the trapped emission will form intense, discrete tones at wave frequencies where the photon travel time is an integer ratio of the boundary oscillation period. A new set of nonlinear coupled difference equations are presented that describe the interaction of the trapped photon with the boundary, the set appearing similar to that used to model Fermi acceleration of particles via oscillatory boundaries. Results indicate that heliopause oscillation periods on the order of 1000s of seconds could generate tones at frequencies near those observed by Voyager. The tones can also drift in association with the changing cavity size or oscillation period.
A simultaneous measurement of the vertical profiles of sodium nightglow and atomic sodium density in the upper atmosphere
Authors: Clemesha B. R. , Simonich D. M. , Takahashi H. , Melo S. M. L.
Published: February 2008

On May 31, 1992, a rocket payload equipped with 10 airglow photometers was launched from the Alcântara Launch Center in Northern Brazil. The payload was designed to measure sodium, hydroxyl, atomic and molecular oxygen airglow emissions, in addition to electron density and temperature. At the time of launch, a sodium lidar was operated at the same site, giving vertical profiles of atmospheric sodium density. The measured vertical profiles of the Na D line emission and atomic sodium density are remarkably similar, with sharp boundaries at 81 km and 99 km. On the assumption that the Chapman mechanism is responsible for the Na D emission, the measurements imply an almost constant ozone density of 4×107 cm−3 between 87 and 99 km. The unexpectedness of this height independent ozone concentration suggests that our understanding of the sodium excitation mechanism might be inadequate.
A recent sea‐ice retreat west of the Antarctic Peninsula
Authors: Jacobs S. S. , Comiso J. C.
Published: February 2008

Satellite passive microwave data show a record decrease in sea ice extent in the Bellingshausen Sea from mid‐1988 through early 1991. The change coincides with more southerly surface winds, increased cyclonic activity and rising surface air temperatures, which reached historic highs along the west coast of the Antarctic Peninsula in 1989. Preceded by high ice cover in 1986–87, the retreat was most evident during summer in the formerly perennial sea‐ice field over the continental shelf. Ocean heat storage probably contributed to the persistence and coastal propagation of this anomaly.
The Spectra of the topography of the Earth, Venus and Mars
Authors: Balmino G.
Published: February 2008

The global topography of the terrestrial bodies has been more or less determined from past planetary missions and from ground measurements and the behaviour of their spectra studied over the low frequencies only‐except the Earth's case. We here perform new spherical harmonic analysis of the topography of the Earth, Venus and Mars by using existing (sometimes recently made available) data sets, to the highest possible degree and order, so as to establish the decay of these spectra over a larger range of frequencies than before, study the limit of validity of the used data sets, and provide some new inputs to further geophysical analysis.
Five years of ground deformation monitoring on axial seamount using a bottom pressure recorder
Authors: Fox Christopher G.
Published: February 2008

The results of five years of pressure measurements collected by a Bottom Pressure Recorder deployed within the summit caldera of Axial Seamount, on the central Juan de Fuca Ridge, are interpreted for monotonic offsets related to vertical seafloor movements. Results indicate five significant subsidence events during the observation period (3.7 years), or an average of 1.35 events per year. The displacements range from 3–10 cm with durations of 10–14 days. These results indicate an active volcanic system and can be viewed as positive evidence for future attempts at seafloor volcanic observatories and response to active events on oceanic ridge crests. Advanced instrumentation based on multiple sensors has been deployed at the site to reinforce the results of this pilot experiment.
Study of the source process of the 1992 Colombia Ms=7.3 earthquake with the empirical Green's Function Method
Authors: Li Yingping , Toksöz M. Nafi
Published: February 2008

The source time function (STF) of the October 18, 1992 Colombia Ms=7.3 earthquake has been determined using long‐period, teleseismic surface and body waveform data and the Empirical Green's Function (EGF) method. Love and SH waveforms of a Ms=6.7 foreshock were treated as the EGFs and deconvolved from the mainshock waveforms to obtain the relative STF. This indicated that the Ms=7.3 mainshock was a double event followed 100 seconds later by a large aftershock (not previously reported). The source durations for the mainshock and the aftershock are about 45 and 25 seconds, respectively. Based on the source radiation directivity, the rupture directions for the mainshock and aftershock are about S50°W. The total length of the fault for the mainshock and aftershock is about 140 km, which agrees with the fault dimension estimated using the aftershock distribution. The seismic moment releases for the three asperities on the rupture surface are 1.0×1019, 6.9×1019 and 2.3×1019 Nm, with respect to time.
Neutral temperature anomaly in the equatorial thermosphere‐A source of vertical winds
Authors: Raghavarao R. , Hoegy W. R. , Spencer N. W. , Wharton L. E.
Published: February 2008

Data obtained from the WATS (Wind and Temperature Spectrometer) instrument on DE‐2 (Dynamics Explorer) during high solar activity, show new evidence for the presence of vertical winds of a significant magnitude in the equatorial thermosphere. They reveal a latitudinal structure that can be related to the recently discovered phenomena of the Equatorial Temperature and Wind Anomaly (ETWA). In the local evening hours, the vertical winds usually are downward around the dip equator and collocated with the temperature minimum of ETWA. In general, they are upward at about 24° dip latitude away from the dip equator and are collocated with the ETWA temperature crests. The magnitude of the vertical winds is in the 10–40 m/s range. It is proposed that the temperature and pressure ridges, formed by the excess ion drag on the zonal winds around the two crests and ordered by the relatively lower ion drag at the trough of the well known Equatorial Ionization Anomaly (EIA), drive a new wind system in the meridional plane and that the measured vertical winds form part of this wind system.
High resolution observations of 150 km echoes at Jicamarca
Authors: Kudeki Erhan , Fawcett Clinton D.
Published: February 2008

High resolution soundings of equatorial upper E‐region echoes at Jicamarca exhibit gravity wave modulated signal intensity distributions and Doppler velocities corresponding to vertical plasma drifts. A gravity wave wind driven interchange instability is suggested as a possible generation mechanism of the field‐aligned plasma irregularities responsible for the echoes. The echoes may be utilized in gravity wave studies and in zonal electric field measurements by radars with modest sensitivities.
Helium isotope variations in Juan De Fuca Ridge basalts
Authors: Lupton John E. , Graham David W. , Delaney John R. , Johnson H. Paul
Published: February 2008

We have measured ³He/4He ratios and He and Ne concentrations on a suite of 24 basalt glasses from the neovolcanic zone of the Juan de Fuca Ridge (JdFR) from 44.6°N near the Blanco Transform up to 48.0°N on the Endeavour Segment. The helium isotope ratios exhibit a clear geographic variation, with relatively constant values of 7.8 RA along the southern JdFR increasing to a maximum of 8.8 RA at 46.9°N on the Cobb Segment, and then dropping to values of ∼8.0 RA at the Cobb Offset. Ratios along the Endeavour Segment further north are somewhat higher, averaging ∼8.2 RA. Basalts dredged from Axial Seamount have ³He/4He = 7.9–8.4 RA, indicating that the seamount does not have a geochemical or isotopic signature distinct from other portions of the JdFR. This confirms that while Axial Seamount is the locus of excess magma generation, it is devoid of any hotspot or ocean island basalt geochemical signature. For the whole sample set, ³He/4He ratios show a negative correlation with 87Sr/86Sr. We attribute the geographical variations in ³He/4He to broad‐scale heterogeneity in the mantle source region beneath the JdFR. Beginning at Axial Seamount and further north, ³He/4He shows a positive correlation with Fe8.0, suggesting that melting dynamics in the underlying mantle may exert some control on the helium isotope ratios along part of our survey area.
CLAES CH4, N2O and CCL2F2 (F12) Global data
Authors: Kumer J. B. , Mergenthaler J. L. , Roche A. E.
Published: February 2008

Zonal mean comparisons of CH4 (for altitude regions above the 1.35 ppmv contour), of N2O (above the 210 ppbv contour), and of F12 (above the 360 pptv contour) with UARS Pre‐launch Climatology and with recent models shows reasonable agreement, and some interesting differences in the details of equatorial uplift and descent near the winter poles, including apparent north ‐ south differences. Prominent features such as the double peaked uplift structure in the April–May SAMS [Jones and Pyle, 1984; Barnett et al, 1985] data are clearly evident in all three CLAES tracers. Contours of SAMS CH4 and N2O occur mostly at higher pressures than in the CLAES data, presumably due in part to increased tropospheric content of these gasses, and/or perhaps some dynamic difference associated with the 15 years time difference between the data sets. The CLAES F12 are the first long time base global data sets. These show more tropical uplift than climatology or models. This might suggest a somewhat shorter lifetime of F12 in the stratosphere than is currently accepted.
Modeling polar cap F‐region patches using time varying convection
Authors: Sojka J. J. , Bowline M. D. , Schunk R. W. , Decker D. T. , Valladares C. E. , Sheehan R. , Anderson D. N. , Heelis R. A.
Published: February 2008

Creation of polar cap F‐region patches are simulated for the first time using two independent physical models of the high latitude ionosphere. The patch formation is achieved by temporally varying the magnetospheric electric field (ionospheric convection) input to the models. The imposed convection variations are comparable to changes in the convection that result from changes in the By IMF component for southward interplanetary magnetic field (IMF). Solar maximum‐winter simulations show that simple changes in the convection pattern lead to significant changes in the polar cap plasma structuring. Specifically, in winter, as enhanced dayside plasma convects into the polar cap to form the classic tongue‐of‐ionization (TOI) the convection changes produce density structures that are indistinguishable from the observed patches.
Observations and model comparisons of early‐time expansion characteristics of a satellite‐Borne barium‐lithium release at F‐region altitudes
Authors: Szuszczewicz E. P. , Hunton D. E. , Wygant J. R. , Schunk R. W.
Published: February 2008

We describe the very‐early‐time expansion processes (≈0 ‐ 3 s) of the CRRES G‐9 Ba+/Li+ cloud release, as manifested by thermal‐ and photo‐ionization mechanisms, by coupling to the background ionosphere, and by differential acceleration of multi‐ion constituents. In our data analysis we present the very first “in situ” evidence of electrostatic snowplow effects in an expanding plasma cloud, with arguments that these effects are the result of ambipolar fields and that kinetic effects of ion‐neutral collisions have little influence in the G‐9 scenario. In addition to the electrostatic snowplow process, the results show mass‐dependent effects on the expansion of ion and neutral constituents in the cloud. These effects are manifested in the observation that the Li+ ions “outpace” the heavier Ba+ in the expansion process, and take on forerunner characteristics at the cloud's leading edge.
The effect of oxidation on the Verwey transition in magnetite
Authors: Özdemir Özden , Dunlop David J. , Moskowitz Bruce M.
Published: February 2008

At the Verwey transition (Tv≈110–120 K), magnetite transforms from monoclinic to cubic spinel structure. It has long been believed that magnetic remanence and susceptibility would change markedly at Tv in the case of coarse grains but only slightly or inappreciably in the case of fine (<1 µm) grains. We find on the contrary that remanence changes at Tv by 50–80% in both large and small crystals, if they are stoichiometric. However, minor surface oxidation suppresses the transition, and the fact that fine grains oxidize more readily leads to an apparent size dependence. Our experiments used submicron magnetite cubes with mean sizes of 0.037, 0.076, 0.10 and 0.22 µm which were initially non‐stoichiometric (oxidation parameter z from 0.2–0.7). A saturation isothermal remanent magnetization (SIRM) given in a 2.5 T field at 5 K decreased steadily during zero‐field warming to 300 K with little or no indication of the Verwey transition. After the oxidized surface of each crystal was reduced to stoichiometric magnetite, the SIRM decreased sharply during warming by 50–80% around 110 K. The change in SIRM for the 0.22 µm grains was almost identical to that measured for a 1.5 mm natural magnetite crystal. Thus a 1012 change in particle volume does not materially affect the remanence transition at Tv but oxidation to z=0.3 essentially suppresses the transition. The effect of the degree of oxidation on Tv provides a sensitive test for maghemitization in soils, sediments and rocks.
Variations in the period of the sunspot cycle
Authors: Ochadlick Andrew R. , Kritikos Haralambos N. , Giegengack Robert
Published: February 2008

Using a wavelet analysis approach, subtle variations in the solar cycle period were extracted from the yearly means of the sunspot numbers. For the nominal eleven‐year solar cycle, the resulting estimates of the cycle's period are in good agreement with those given by Friis‐Christensen and Lassen. Longer period structures in the solar‐cycle, including the Gleissberg cycle, are also delineated by the wavelet analysis.
Relationships between optical extinction, backscatter and aerosol surface and volume in the stratosphere following the eruption of Mt. Pinatubo
Authors: Brock Charles A. , Jonsson Haflidi H. , Wilson James C. , Dye James E. , Baumgardner Darrel , Borrmann Stephan , Pitts Mike C. , Osborn Mary T. , DeCoursey Robert J. , Woods David C.
Published: February 2008

The eruption of the Mt. Pinatubo volcano in the Philippines in June 1991 has resulted in increases in the surface and mass concentrations of aerosol particles in the lower stratosphere. Airborne measurements made at midlatitudes between 15 and 21 km from August 1991 to March 1992 show that, prior to December 1991, the Pinatubo aerosol cloud varied widely in microphysical properties such as size distribution, number, surface and volume concentrations and was also spatially variable. Aerosol surface area concentration was found to be highly correlated to extinction at visible and near‐infrared wavelengths throughout the measurement period. Similarly, backscatter at common lidar wavelengths was a good predictor of aerosol volume concentrations. These results support the use of satellite extinction measurements to estimate aerosol surface and of lidar measurements to estimate aerosol volume or mass if temporal changes in the relationships between the variables are considered.
Interim standard for the ion‐neutral atomic oxygen collision frequency
Authors: Salah Joseph E.
Published: February 2008

A growing body of evidence based on radar and optical observations of winds in the Earth's upper atmosphere indicates that the commonly utilized value for the ion‐neutral atomic oxygen (O+‐O) collision frequency for momentum transfer is too low by a factor of 1.3–2. A revised standard for the O+‐O momentum transfer collision frequency is therefore recommended based on all the available measurements, in order to facilitate comparisons with thermospheric and ionospheric models and among data sets until future accurate laboratory measurements and more reliable observations can be made. The new interim standard, representing a 70% increase from the previous value, is given by: ν o+−o = 4×10−17 Tr0.5 no, where Tr = (Ti+Tn)/2, Ti being ion temperature, Tn neutral temperature, and no atomic oxygen number density in m−3.
Ion anisotropies in the magnetosheath
Authors: Gary S. Peter , Anderson Brian J. , Denton Richard E. , Fuselier Stephen A. , McKean Michael E. , Winske Dan
Published: February 2008

One‐ and two‐dimensional initial value hybrid computer simulations are used with a magnetosheath parameter model to study the consequences of the growth of the mirror and ion cyclotron anisotropy instabilities. Magnetosheath observations have demonstrated inverse correlations between the proton and helium ion temperature anisotropies and the proton parallel β. Using the maximum growth rate as a fitting parameter, linear Vlasov instability theory for the proton cyclotron and helium cyclotron anisotropy instabilities reproduces both observed correlations. Furthermore, results from the asymptotic states of simulations of the ion cyclotron instabilities qualitatively reproduce both observations.
Record low ozone values over Canada in early 1993
Authors: Kerr J. B. , Wardle D. I. , Tarasick D. W.
Published: February 2008

Measurements of ozone made over Canada during the first four months of 1993 indicate that total ozone has been about 11 to 17% below normal. These low values were recorded, without exception, at all nine of the Canadian mid‐latitude ground‐based monitoring sites. Record low averages for the period from January to April were measured at three of the four mid‐latitude stations where measurements have been made since the 1960’s. Comparison of January to April, 1993 ozonesonde profile measurements with those from earlier years indicates that the ozone deficit is in the lower stratosphere between 40 and 200 mb, the same altitudes where aerosols from the Mount Pinatubo volcanic eruption have been observed. The peak loss is 30% at 100 mb (16 Km).
Remote‐sensing of F‐region ion drifts and ion temperatures at Søndre Strømfjord, Greenland using Doppler measurements of the O+(²P) state
Authors: Carr S. S. , Niciejewski R. J. , Killeen T. L.
Published: February 2008

Ground‐based observations of Doppler line profiles from the F‐Region O+(²P) state, made with the Fabry‐Perot interferometer (FPI) at Søndre Strømfjord, Greenland have been analyzed to provide measurements of the ion convection velocity and ion temperature. The FPI line‐of‐sight (LOS) ion drift and temperature measurements have been compared with simultaneous incoherent scatter radar (ISR) measurements; the results from the two techniques are in good agreement.
Stereoscopic auroral intensity measurements from ground and space
Authors: Oznovich I. , McEwen D. J. , Eastes R. W.
Published: February 2008

Simultaneous measurements of auroral intensities from below and above the emitting layer can be used to verify imager orientation and mapping procedures for satellite auroral images, determine auroral height by stereoscopic methods, and deduce incident particle characteristics. A data reduction approach that achieves optimal spatial and temporal matching of ground and space data sets is presented. We investigate a January 25, 1987, case study of a bright auroral arc using a meridian scanning photometer and an all‐sky camera located at Rabbit Lake, Saskatchewan, and a space imager (AIRS of Polar BEAR). The ground and space latitudinal profiles of arc intensity match best for a peak deposition height of 122±7 km. Theoretical calculations indicate that the observed FUV intensities are due to electrons of average energy 3.1±1.1 keV and a total energy flux of 5.7±1.5 ergs cm−2 s−1.
Tropical mountains and coal formation: A climate model study of the Westphalian (306 MA)
Authors: Otto‐Bliesner Bette L.
Published: February 2008

A global climate model has been used to study the seasonal sensitivity of tropical rainfall and soil moisture to the presence of Himalayan‐scale mountains at tropical latitudes during the Westphalian. These mountains act to retard the northward progression of the Intertropical Convergence Zone in their vicinity during the Northern Hemisphere summer such that there is converging low‐level flow from both the eastern and western Panthalassa Ocean and an eight‐fold enhancement of precipitation over the mountains. The computed annual cycle of soil moisture for these tropical regions concurs with geologic evidence of extensive coal deposits formed in a broad area at tropical latitudes and only small seasonality in either temperature or precipitation in these areas.
An evaluation of O2(b¹Σg) as a possible source of OH and odd‐nitrogen in the stratosphere and mesosphere
Authors: Siskind David E. , Summers Michael E. , Mlynczak Martin G.
Published: February 2008

A one dimensional photochemical model has been used to evaluate the hypothesis that the oxidation of H2 and N2O by O2(b¹Σg) could lead to significant production of OH and odd‐nitrogen in the middle atmosphere. For the reaction with H2, even if all the quenchings lead to oxidation, the change in the OH column is only 13%. This is still too small to resolve the discrepancy between the model and ground based measurements and furthermore could not account for the apparent change in the ground based column with time. For the reaction with N2O, it is possible to produce significant odd‐nitrogen in the lower stratosphere only if the oxidation yield is at least 5–10%. However, one then gets a surplus of odd‐nitrogen in the upper stratosphere unless one makes the additional assumption that the production of O2(b¹Σg) from O(¹D) quenching is small.