bluuebunny/crossref_metadata_2025 huggingface dataset:
The decoupling of production and particulate export in the surface ocean
Authors: Buesseler Ken O.
Published: February 2004

The relationship between primary production in the surface ocean and export of particulate organic carbon (POC) on sinking particles is examined in studies that have utilized 234Th as a tracer of upper ocean export. Comparisons between production and export are made in a wide range of open ocean settings and seasons. The results indicate that much of the ocean is characterized by low POC export relative to primary production (export/production = ThE < 5–10%). Exceptions to this pattern are found during blooms at high latitudes, accompanying spring blooms at midlatitudes, and perhaps in association with more episodic export pulses. These sites of high export are most often characterized by food webs dominated by large phytoplankton, in particular diatoms. These results can be used to better parameterize surface export in biogeochemical models in order to provide a more accurate prediction of the flow of C and associated nutrients in the oceans.
Ion sources and acceleration mechanisms inferred from local distribution functions
Authors: Ashour‐Abdalla M. , El‐Alaoui M. , Peroomian V. , Raeder J. , Walker R. J. , Richard R. L. , Zelenyi L. M. , Frank L. A. , Paterson W. R. , Bosqued J. M. , Lepping R. P. , Ogilvie K. , Kokubun S. , Yamamoto T.
Published: February 2004

This study investigates the sources of the ions making up the complex and nonisotropic H+ velocity distribution functions observed by the Geotail spacecraft on May 23, 1995, in the near‐Earth magnetotail region and recently reported by Frank et al. [1996]. A distribution function observed by Geotail at ∼10 RE downtail is used as input for the large scale kinetic (LSK) technique to follow the trajectories of approximately 90,000 H+ ions backward in time. Time‐dependent magnetic and electric fields are taken from a global magnetohydrodynamic (MHD) simulation of the magnetosphere and its interactions with appropriate solar wind and IMF conditions. The ion population described by the Geotail distribution function was found to consist of a mixture of particles originating from three distinct sources: the ionosphere, the low latitude boundary layer (LLBL), and the high latitude plasma mantle. Ionospheric particles had direct access along field lines to Geotail, and LLBL ions convected adiabatically to the Geotail location. Plasma mantle ions, on the other hand, exhibited two distinct types of behavior. Most near‐Earth mantle ions reached Geotail on adiabatic orbits, while distant mantle ions interacted with the current sheet tailward of Geotail and had mostly nonadiabatic orbits. Ions from the ionosphere, the LLBL, and the near‐Earth mantle were directly responsible for the well‐separated, low energy structures easily discernible in the observed and modeled distribution functions. Distant mantle ions formed the higher energy portion of the Geotail distribution. Thus, we have been successful in extracting useful information about particle sources, their relative contribution to the measured distribution and the acceleration processes that affected particle transport during this time.
Observations of bidirectional electrons in the distant tail lobes: GEOTAIL results
Authors: Baker D. N. , Nishida A. , Mukai T. , Yamamoto T. , Saito Y. , Matsuno Y. , Kokubun S. , Pulkkinen T. I.
Published: February 2004

ISEE‐3 demonstrated the relatively frequent occurrence of low‐energy (50 ∼ 500 eV) electron flux enhancements within the distant magnetotail lobes. These electrons were found to be “bidirectional” in the sense that intensities were highest parallel (and antiparallel) to the lobe magnetic field lines. It was concluded that these electrons must enter the tail lobes along open field lines at the distant magnetopause and that this population would constitute the source for polar rain electrons at low altitudes in the polar cap regions. Similar plasma electron features have been found using the Low Energy Particle (LEP) sensor system onboard the GEOTAIL spacecraft. Remarkably close correspondences of low‐energy (≲ 2 keV) ion tailward flow enhancements are found to occur when bidirectional electron fluxes suddenly intensify. Such ion plasma measurements were not available with ISEE‐3 and, thus, a new aspect of solar wind entry and overall plasma dynamics is revealed by these GEOTAIL measurements in the distant tail. Other ISTP data (e.g., IMP‐8 and CANOPUS) are used to analyze selected periods.
The role of sulfur emission in volatile particle formation in jet aircraft exhaust plumes
Authors: Kärcher B. , Fahey D. W.
Published: February 2004

Recent in‐situ emission measurements of the Concorde in the lower stratosphere point to a surprisingly efficient conversion of fuel sulfur to H2SO4 in the exhaust plume. By means of a comprehensive model, the formation and evolution of aerosol particles and precursors are calculated in the diluting aircraft wake. The results provide strong evidence that high levels of SO3 present in the nascent plume are required to explain the observations of large numbers of nanometer‐sized aerosols. Limiting particle formation at emission to keep potential chemical effects on stratospheric ozone small will require control of the sulfur oxidation kinetics during fuel combustion. The similarities between super‐ and subsonic exhaust plumes suggest that the presence of SO3 in the latter will also be a key limiting factor in new aerosol production.
Compositional analysis of the Orientale Basin using full resolution Clementine data: Some preliminary results
Authors: Bussey D. B. J. , Spudis P. D.
Published: February 2004

Clementine imaged the Moon globally in eleven different wavelengths. We used these data to construct a full resolution (250 m/pixel) multispectral image of the Orientale basin. Using this image in conjunction with other data sets, such as Earth‐based spectra, we mapped the compositional units of the basin to obtain insights into its formation and evolution. The basin ejecta units are largely uniform in composition with the inner, Montes Rook Formation being slightly more mafic than the outer, Hevelius Formation. The Inner and Outer Rook mountains display many outcrops of pure anorthosite. These and other findings are consistent with a three layer model for the lunar crust consisting of a mixed zone (megaregolith) tens of kilometres thick overlying a layer of anorthosite above a basaltic layer.
Why are earthquakes nudging the pole towards 140°E?
Authors: Spada Giorgio
Published: February 2004

Earthquakes have collectively the tendency to displace the pole of rotation of the earth towards a preferred direction (∼140°E'. This trend, which is still unexplained on quantitative grounds, has been revealed by computations of earthquake‐induced inertia variations on both a secular and a decade time‐scale. Purpose of this letter is to show that the above trend results from the combined effects of the geographical distribution of hypocenters and of the prevailing dip‐slip nature of large earthquakes in this century. Our findings are based on the static dislocation theory and on simple geometrical arguments.
Numerical modeling of the 1995 Chilean Tsunami. Impact on French Polynesia
Authors: Guibourg Sandrine , Heinrich Philippe , Roche Roger
Published: February 2004

On the 30th July 1995, an earthquake with magnitude of 8.1 occurred off the coast of Chile. The associated tsunami propagated across the Pacific ocean and reached French Polynesia 10 hours after the seismic event with maximum run‐up heights of about 2.5 meters. The most affected islands in French Polynesia were the Marquesas Islands that present few outer reefs, more gradual bottom slopes and large bays. The tsunami propagation has been modeled from Chile to Polynesian Islands, solving the shallow water equations. The water surface initialisation has been computed from Okada's formulas, using seismic parameters of Ruegg (1996). The tsunami propagation is simulated by a finite‐difference numerical model using a system of multiple grids with different grid sizes. The computed waves are in fair agreement with the recorded waves along the Chilean coasts, in Tahiti and in Nuku Hiva. The numerical results obtained in the Marquesas Islands confirm the observations of numerous eyewitnesses.
Trends in daily wintertime temperatures in the northern stratosphere
Authors: Pawson Steven , Naujokat Barbara
Published: February 2004

Long‐term changes in the extrema reached in 31 years of daily northern stratospheric temperatures (T' are discussed. The lowest T reached at any location on any day (Tmin' show trends of −1.90 and −1.85 K/decade at 50 hPa and 30 hPa. Increases in the maxima (Tmax' are twice as large at 30 hPa as at 50 hPa. The trends are superimposed on a low‐frequency variability of Tmin with clear peaks between 1975/1976 and 1986/1987 and after 1991/1992. Before the middle 1970s no very low Tmin were observed; this is very likely an observational constraint since T=192 K this may be the lowest detectable value in the earliest years. A more robust measure of the coldness of the lower stratosphere is the area with T < 195 K at 50 hPa, which is relevant for PSC formation. It increased considerably over the 31 years owing largely to the persistence of cold days.
The geodetic signature of the M8.0 Oct. 9,1995, Jalisco Subduction Earthquake
Authors: Melbourne T. , Carmichael I. , DeMets C. , Hudnut K. , Sanchez O. , Stock J. , Suarez G. , Webb F.
Published: February 2004

The October, 1995 Mw 8.0 Jalisco subduction earthquake has provided a thorough geodetic observation of the coseismic subduction process. An 11 station regional GPS network located directly onshore of the rupture demonstrates consistent vertical subsidence verified by tide gauge data and southwest‐directed extension, with measured displacements reaching 1 meter. Unusually shallow and non‐uniform faulting is required to explain the displacements. We determine that up to 5 meters of slip occurred within the upper 15 km of the thrust fault zone and 2 meters possibly as shallow as 8 km, and that slip was likely distributed in two main patches. The paucity of continental sediments in this subduction zone could be responsible for the anomalously shallow faulting.
JULIA radar studies of electric fields in the equatorial electrojet
Authors: Hysell D. L. , Larsen M. F. , Woodman R. F.
Published: February 2004

First results from the JULIA radar at Jicamarca are presented. These include coherent scatter observations of the equatorial electrojet and of 150‐km echoes. Interferometry is used to measure the zonal drift rate of kilometer scale waves in the electrojet as functions of altitude. A technique for estimating the background zonal electric field from the interferometry data is described. The electric field estimates can be calibrated against the Doppler speed of the 150‐km echoes when the latter are present. The kilometer‐scale wave drifts sometimes exhibit large‐amplitude, periodic height variations with vertical wavelengths of about 10 km. These signatures are reminiscent of the wind profiles measured with chemical release techniques in the lower thermosphere during the Guará campaign.
Plasma sheet pressure changes during the substorm growth phase
Authors: Nagai T. , Mukai T. , Yamamoto T. , Nishida A. , Kokubun S. , Lepping R. P.
Published: February 2004

This paper reports clear evidence for increases in plasma pressure in the plasma sheet at 20–50 Re during the growth phase of substorms. The spacecraft WIND has provided the IMF Bz and other solar wind conditions, while the spacecraft GEOTAIL has observed plasma and magnetic field in the plasma sheet. We have examined 19 isolated substorms after clear southward turnings of the IMF Bz in steady solar wind conditions. Pressure increases start immediately after the southward turnings of the IMF Bz. Increases in plasma pressure are caused mainly by increases in plasma number density. Temperature does not show any significant changes. These observations suggest that the near‐Earth plasma sheet is compressed by enhanced magnetic field intensity in the tail lobes during the substorm growth phase.
Initial comparison of POLAR UVI and Sondrestrom IS radar estimates for auroral electron energy flux
Authors: Doe Richard A. , Kelly John D. , Lummerzheim Dirk , Parks George K. , Brittnacher Mitchell J. , Germany Glynn A. , Spann James
Published: February 2004

Calibrated images from the POLAR satellite ultraviolet imager (UVI) in the 165.5 to 174.5 nm portion of the N2 Lyman‐Birge‐Hopfield band (LBH‐long) can be used to estimate the energy flux (FE) of auroral electrons precipitating into the high‐latitude ionosphere. Similarly, electron density profiles, as measured by ground‐based incoherent‐scatter radar, can be used to estimate FE and mean energy (Eo) by solving a system of linear equations relating the E‐region ionization rate profile to a family of monoenergetic ion production profiles. A coordinated POLAR/Sondrestrom radar experiment, designed as an initial comparison of POLAR UVI and ground‐based estimates of FE for a stable auroral arc, was executed during a POLAR apogee on May 20, 1996 at the Sondrestrom radar facility (lat. 66.99°N, long. 50.95°W). Reconstructed energy distributions, based on radar‐measured Ne profiles, indicate an approximately 2 keV Maxwellian source with an energy flux of from 6.4 to 14 mW m−2. LBH‐long images, binned over 0.5° of latitude and 1.0° of longitude, were used to derive energy flux as well. The UVI‐derived FE time history agrees favorably with radar estimates both in absolute magnitude and in the trend for this period. This experiment suggests that reliable estimates for the precipitating electron source energy and its ionospheric response can be derived from either ground‐based radar or POLAR UVI images during summertime conditions.
Rapid lateral expansion of optical luminosity in lightning‐induced ionospheric flashes referred to as ‘elves'
Authors: Inan U. S. , Barrington‐Leigh C. , Hansen S. , Glukhov V. S. , Bell T. F. , Rairden R.
Published: February 2004

Data acquired by a new array of horizontally spaced photometers boresighted with a low‐light‐level camera provide the first measurement of the rapid lateral expansion of optical luminosity in lightning‐induced ionospheric flashes referred to as ‘elves', occurring over time scales substantially less than 1 ms. The narrow individual fields‐of‐view of (2.2° × 1.1°' provide a spatial resolution of ∼20‐km at a range of 500 km, enabling the documentation of expansion occurring over a horizontal range of 200 km with a time resolution of ∼30µs. The observed dynamic features of elves are consistent with a model in which the optical output is produced as a result of heating by the electromagnetic pulse (EMP' from a lightning discharge.
Terrestrial 2fp radio source location determined from WIND/GEOTAIL triangulation
Authors: Reiner M. J. , Kasaba Y. , Kaiser M. L. , Matsumoto H. , Nagano I. , Bougeret J.‐L.
Published: February 2004

We combine simultaneous WIND/GEOTAIL direction‐finding analyses of terrestrial 2fp radio emission to provide the first 3‐D source location by two spacecraft triangulation. These observations were made when WIND and GEOTAIL were relatively close to the electron foreshock and to each other. For two cases presented the 2fp radio source centroid was stationary and located in the upstream wing of the electron foreshock region some 15‐50RE from the contact point. In a third case the 2fp source centroid followed the change in orientation of the electron foreshock.
A crustal magnetization model for the magnetic field of Mars: A preliminary study of the Tharsis Region
Authors: Hood L. L. , Hartdegen K.
Published: February 2004

Crustal magnetic field anomalies are calculated at several altitudes above the Tharsis region on Mars assuming a source region consisting of uniformly magnetized subsurface volcanic constructs. The subsurface structure is consistent with a proposed model for the evolution of the Tharsis province based on geologic and tectonic evidence. The maximum thicknesses of subsurface volcanic deposits are constrained by gravity and topography data. Mean magnetization intensities are assumed to be comparable to those of SNC meteorites. Because reversals of the former Martian dynamo are neglected, the calculated field magnitudes may represent an upper limit on actual fields to be expected above the Tharsis region. Maximum field magnitudes at 300 km altitude are in the range 1–5 nT and would be marginally detectable by an orbiting magnetometer.
Tropospheric SF6: Observed latitudinal distribution and trends, derived emissions and interhemispheric exchange time
Authors: Geller L. S. , Elkins J. W. , Lobert J. M. , Clarke A. D. , Hurst D. F. , Butler J. H. , Myers R. C.
Published: February 2004

Sulfur hexafluoride (SF6), an anthropogentically produced compound that is a potent greenhouse gas, has been measured in a number of NOAA GMDL air sampling programs. These include high resolution latitudinal profiles over the Atlantic and Pacific oceans, weekly flask samples from seven remote, globally distributed sites, hourly in situ measurements in rural North Carolina, and a series of archived air samples from Niwot Ridge, Colorado. The observed increase in atmospheric mixing ratio is consistent with an overall quadratic growth rate, at 6.9±0.2% yr−1 (0.24±0.01 ppt yr−1) for early 1996. From these data we derive an early 1996 emission rate of 5.9±0.2 Gg SF6 yr−1 and an interhemispheric exchange time of 1.3±0.1 years.
Synthetic and sedimentary records of geomagnetic excursions
Authors: Vlag P. , Thouveny N. , Rochette P.
Published: February 2004

The geomagnetic excursion recorded in the sediments of Lac St.Front (Massif Central, France) is characterized by shallow and negative inclinations followed by a younger steep inclination interval (Vlag et al., 1996). In the corresponding interval of the nearby Lac du Bouchet only steep inclinations are found. Sedimentary records of the Mono Lake excursion show similar inclination patterns; ‘complete’ records of this excursion show a succession of a shallow by a steep inclination interval, while ‘incomplete’ records only show only steep inclinations (Coe and Liddicoat, 1994). Due to a non‐instantaneous acquisition of the remanence, sedimentary records reflect only a smoothed geomagnetic signal. It will be shown that smoothing of a small low‐intensity ‘reversed’ interval embedded in a non‐antipodal normal field interval may result in records of a shallow inclination interval followed by a steep inclination interval, while further smoothing results in only steep inclinations. Realignment of magnetic grains by the stronger normal field can also produce such records and may explain why such an unusual large lock‐in depth is required by the conventional smoothing model. Whatever the mechanism, the similarities between these synthetic records and the excursional records of Lac St. Front‐Lac du Bouchet and Mono Lake suggest that the latter are more or less affected by vector addition of two non‐antipodal directions.
Non‐Markovian electron diffusion in the auroral ionosphere at high Langmuir‐wave intensities
Authors: Sanbonmatsu K. Y. , Doxas I. , Goldman M. V. , Newman D. L.
Published: February 2004

A generalized non‐Markovian diffusion model which describes the interaction of Langmuir waves with field‐aligned electrons in the auroral ionosphere is found to be relevant to the large amplitude Langmuir waves measured by UC Berkeley sounding rockets and by the Freja satellite. This model is valid for any ordering of the diffusion time and the autocorrelation time (the standard quasilinear diffusion model requires the diffusion time to be much longer than the autocorrelation time). We demonstrate that, while the quasilinear diffusion approximation is valid for the lower altitudes studied by the Berkeley sounding rockets, the non‐Markovian model is needed for the intense waves observed at the higher altitudes probed by Freja. A test particle simulation is employed to quantify our estimates of the relevant timescales.
Evidence of substantial ozone depletion in winter 1995/96 over northern Norway
Authors: Hansen Georg , Svenøe Trond , Chipperfield Martyn P. , Dahlback Arne , Hoppe Ulf‐Peter
Published: February 2004

In winter 1995/96, the stratospheric ozone layer over most of the European Arctic was exposed to extremely low temperatures and strong PSCs. At the same time, total ozone monitoring instruments at Tromsø and Andøya, Northern Norway, observed values up to 50% below the long‐term average values of the Dobson instrument at Tromsø. The deviation increased systematically with time of the year, reaching a maximum in early March. Measurements with the ozone DIAL system at the ALOMAR facility at Andøya showed significant reduction of ozone mixing ratios in the 430 to 580 K potential temperature region. A maximum reduction of almost 50% occurred at about 500 K between early January and early March. Comparison with 3D model calculations revealed large reductions with respect to passive tracer ozone profiles in the 400 to 600 K region, reaching a maximum of about 60% by the end of March at the 475 K level. The 3D chemical model showed ozone depletion in the same altitude region as the measurements but seemed to underestimate the depletion systematically. The comparison also indicated ozone depletion of up to 30% in the 475 to 675 K region in extra‐vortex air which remained close to the vortex edge during a period in mid‐March.
Upper mantle structure in the Southeastern Canadian Cordillera
Authors: Burianyk M. J. A. , Kanasewich E. R.
Published: February 2004

A seismic broadside wide‐angle experiment in Canada's southeastern Cordillera has revealed an anomalous and unexpected seismic arrival. Analysis of the data shows that the arrival is unlikely to be a crustal or shallow mantle phase or multiple or converted waves. The kinematic characteristics of this arrival dictate that it is a reflection from within, or from the base of, a low velocity zone (< 7.8–8.0 km s−1) situated at a depth of 59 to 62 km that we identify as the top of the asthenosphere. This leads to the conclusion that the base of the lithosphere is at a depth of 50±2 km in the region. The interpreted shallow asthenosphere bolsters earlier conclusions of a heat source at depth in the southeastern Canadian Cordillera. The interpretation also shows that stratification in the upper mantle is resolvable by current wide‐angle seismic experiments.
Climate during glaciation and deglaciation identified through chemical tracers in ice‐cores
Authors: Marsh Nigel D. , Ditlevsen Peter D.
Published: February 2004

Presented here are the results and interpretations of an analysis of 8 chemical species obtained from the Greenland Ice Sheet Project 2 (GISP2) [Mayewski et al 1994; Mayewski et al 1993] ice‐core, covering the period 41–0 Kyr BP. A reduction of the system to three distinct base vectors describing the 8 dimensional species space is possible. These are believed to represent the different sources of aerosols that have been transported via the atmosphere, and precipitated onto the Greenland ice‐sheet. Physical reasoning suggests that these are mainly a signature of (1) an ocean source, (2) continental land and exposed continental shelves, and (3) biochemical land sources. Correlations between the resulting time series, describing the temporal contributions from the 3 source areas, reveal five distinct periods over the 41 Kyrs record, each differing dramatically in the contributed abundance of chemical species from the sources. Mechanisms are proposed to explain differences in the climate dynamics over the five periods, with interpretations leading to new information regarding paleo sea level and glacial extent. Such findings are important for reconstructing the climate prior to the Last Glacial Maximum (LGM).
Particle transport in the magnetosphere: A new diffusion model
Authors: Sheldon R. B. , Eastman T. E.
Published: February 2004

Previous transport models of the plasmasphere, ring current and radiation belts have considered either diffusive or convective transport, but not both. Since the ∇B drift speed is proportional to energy, analyses of particles with E > 100 keV have generally used only ∇B drift and diffusive transport. Conversely, particles of E < 30 keV have been treated with only E × B drift and convective transport. The ring current, which lies between these two regimes, cannot be described by either mechanism alone, so that these standard models, though widely used and otherwise applicable, fail in detail to describe the trapped ion population as observed with modern instrumentation. We develop a formalism that can describe both diffusive and convective transport in a completely general way, including UT, LT, radial, and pitch angle dependence, with arbitrary magnetic and electric field models. The formalism is general enough to rederive the electric or magnetic diffusion coefficients for trapped particles without the simplifying assumption of axial symmetry or a vanishing convection electric field, thus improving on the standard coefficients derived nearly 30 years ago. More importantly, we include the previously neglected diffusion term due to a localized, non‐global perturbation of the fields, and show that under some circumstances this term may dominate over the resonant diffusion caused by global perturbations.
Simulations of tropospheric joint distributions in the UW θ‐σ model and CCM2
Authors: Zapotocny Tom H. , Johnson Donald R. , Schaack Todd K. , Lenzen Allen J. , Reames Fred M. , Politowicz Philip A. , Yuan Zhuojian
Published: February 2004

Results are presented for experiments which examine the ability of the University of Wisconsin (UW) hybrid isentropic‐sigma (θ‐σ) and sigma (σ) coordinate models and the NCAR Community Climate Model 2 (CCM2) to transport and conserve the joint distributions of potential temperature (θ) or equivalent potential temperature (θe) and a source‐free inert trace constituent identical to the respective initial distribution (tθ or tθe). Under the idealized isentropic conditions of these experiments, the governing equations for the atmospheric continuum require that the joint distributions (θ, tθ or θe, tθe) be conserved throughout the integration. Deviation in the paired values is an objective measure of a model's skill to conserve the joint distributions. Results show that conservation remains higher in the UW θ‐σ model than in the other models, even near the interface between isentropic and sigma model domains.
homogenization of Manning's Formula for modeling surface runoff
Authors: Hergarten Stefan , Neugebauer Horst J.
Published: February 2004

Surface runoff during excessive rainfalls is one of the most important processes contributing to soil erosion. Recent physically based soil erosion models (watershed models) use a modified Manning formula describing sheet flow for the calculation of the runoff. But in cropland, surface runoff is dominated by flow in rill systems. Based on the original Manning formula, we investigate the influence of rill geometry and spacing on runoff and erosion. The results differ significantly from those of sheet flow. Moreover, significant differences occur between wide, shallow rills and v‐shaped rills. The apparent overall roughness coefficient decreases with increasing rill spacing.
A wintertime in situ profile of BrO between 17 and 27 km in the Arctic vortex
Authors: McKinney Karena A. , Pierson James M. , Toohey Darin W.
Published: February 2004

The vertical profile of bromine oxide (BrO) was measured in situ from a balloon launched near Kiruna, Sweden (68°N, 21°E) at sunrise on February 3, 1995. BrO mixing ratios of 10±2 parts per trillion by volume (pptv) were observed at high solar zenith angles (90–92°) between 20 and 23 km in a layer that coincided with significantly enhanced abundances of ClO. Above 23 km, where ClO mixing ratios typical of midlatitudes were observed, BrO mixing ratios ranged from 5 to 11 pptv, increasing nearly monotonically with increasing altitude and decreasing solar zenith angle. The measurements indicate that 30 to 60% of the total bromine (assuming 18 pptv total bromine) is in the form of BrO between 23 and 27 km at these latitudes in winter. These results are consistent with lower altitude measurements of BrO from the NASA ER‐2 at similar latitudes and season. Observations of higher fractions of BrO (50 to 95% of total bromine) in the chemically perturbed region at sunrise imply the rapid release of bromine from a photolabile reservoir species, such as BrCl.
Tomographic reconstruction of 630.0 nm emission structure for a polar cap arc
Authors: Doe Richard A. , Kelly John D. , Semeter Joshua L. , Steele David P.
Published: February 2004

Monochromatic imagers located at two sites in the Canadian Arctic were operated concurrently during the poleward transit of a duskside sun‐aligned polar cap arc on 19 February 1996. The arc was observed by both stations in 630.0 nm images over a 5‐min period. Profiles of 630.0 nm brightness versus elevation angle were extracted from pairs of images along a great circle defined by the two ground stations. These data were then supplied as inputs to a tomographic reconstruction for the arc‐related 630.0 nm volume emission rate in a vertical (latitude vs. altitude) plane: η630 (lat,z). The time evolution of η630 (lat,z) structure for this polar cap arc indicates that a modification to the electron source energy distribution and not a thermospheric process (such as neutral heating and plasma diffusion/decay) controlled the arc‐related 630.0 nm emission.
Remote determination of auroral energy characteristics during substorm activity
Authors: Germany G. A. , Parks G. K. , Brittnacher M. , Cumnock J. , Lummerzheim D. , Spann J. F. , Chen L. , Richards P. G. , Rich F. J.
Published: February 2004

Ultraviolet auroral images from the Ultraviolet Imager (UVI) onboard the POLAR satellite can be used as quantitative remote diagnostics of the auroral regions, yielding estimates of incident energy characteristics, compositional changes, and other higher order data products. Here incident energy estimates derived from UVI are compared with in situ measurements of the same parameters from an overflight by the DMSP F12 satellite coincident with the UVI image times during substorm activity occurring on May 19, 1996. This event was simultaneously observed by WIND, GEOTAIL, INTERBALL, DMSP and NOAA spacecraft as well as by POLAR.
the phase evolution of Young Sea Ice
Authors: Wettlaufer J. S. , Worster M. Grae , Huppert Herbert E.
Published: February 2004

Sea ice forms as a porous matrix consisting of pure ice crystals in equilibrium with brine. We present an experimental and theoretical study that reveals that the brine expelled by growing sea ice initially remains trapped within the crystalline interstices but that drainage into the underlying water is ultimately triggered abruptly due to the onset of buoyancy‐driven convection. The onset is quantified by a critical porous‐medium Rayleigh number, and we present an empirical marginal stability diagram that defines the transition.
Reaction of N2O5 with H2O on bulk liquids and on particles and the effect of dissolved HNO3
Authors: Hanson D. R.
Published: February 2004

Measurements of the reaction probability (γ) of N2O5 on ∼60 wt% H2SO4 were performed at 201 to 230 K on bulk liquids and at 230 K on aerosol particles. The bulk and aerosol results are in good agreement (less than 10% difference). The measurements on bulk liquids show very little change in γ with temperature from 201 to 230 K. HNO3 was added to the bulk liquids at ∼201 K and to aerosol particles at 230 K (the H2SO4‐content was decreased to keep water activity approximately constant). For [HNO3] levels of 1‐to‐15 wt %, the N2O5 reaction probability decreased by ∼15% from that measured on HNO3‐free 60 wt% H2SO4. For 60 wt% H2SO4 aerosol in the stratosphere ([HNO3] ∼0.3 wt%) the decrease in the N2O5 hydrolysis reaction probability due to HNO3 would be small.
High resolution measurements in the summer polar mesosphere
Authors: Rüster R.
Published: February 2004

VHF radar measurements with high temporal and vertical resolution of 4 s and 75 m, respectively, have been carried out in northern Norway (69°N) in the summer of 1987 to study the structure of polar mesospheric summer echoes as well as dynamical processes involved. The results, which have been analysed using bispectral methods, reveal nonlinear interactions to exist in the gravity wave period range. Iso‐lines of conserved quantities deduced from the vertical velocity field show strong resemblance with simultaneously observed echo power variations. The results indicate a correlation between signal‐to‐noise ratio and the vertical gradient of the temperature.
The state of stress near the Mendocino Triple Junction from inversion of earthquake focal mechanisms
Authors: Schwartz Susan Y. , Hubert Aurélia
Published: February 2004

Focal mechanisms of 70 earthquakes occurring in the region of the Mendocino triple junction between 1977 and 1995 are inverted to obtain the regional stress orientations and relative magnitudes in this technically complex area. A diverse set of earthquake geometries is consistent with a single stress field characterized by north‐northwest, horizontal, maximum principal compressive stress. Although this stress direction is almost perpendicular to convergence between the North American and Gorda plates, it is consistent with the stress direction inferred within the Gorda plate northwest of the triple junction. A maximum compressive stress direction nearly parallel to strike of the Cascadia subduction zone implies very low resolved shear stress across this plate boundary. Evidence for failure along the southernmost section of the Cascadia subduction zone comes from the occurrence of the recent 1992 (Ms=7.1) Cape Mendocino underthrusting earthquake as well as from measurements of Holocene surface uplift consistent with the 1992 coseismic uplift pattern. Rupture of the Cascadia subduction zone under this stress regime requires that the southernmost region of the Gorda‐North American Plate boundary is weak.
Trends in the surface meridional temperature gradient
Authors: Gitelman Alix I. , Risbey James S. , Kass Robert E. , Rosen Richard D.
Published: February 2004

Given the presence of a meridional temperature gradient (MTG) across midlatitudes, large‐scale eddies transport heat poleward, thereby shaping Earth's climate. Defining an MTG index here as the difference in surface temperature between the 30°–35°N belt and the 50°–55°N belt, we use a temperature record compiled from observations over a 110‐year period to determine a trend in the MTG in the last century. We find a significant decreasing trend in the MTG over this period of 0.4±0.1°C per 100 years, along with indications of substantial multidecadal variability.
Ozone variability in the high latitude summer stratosphere
Authors: Natarajan Murali , Callis Linwood B.
Published: February 2004

Observations made by the HALOE instrument aboard UARS show very low stratospheric ozone in the Arctic and Antarctic summers of 1992 and 1993 [Park and Russell, 1994]. Large longitudinal variability is seen in ozone between 8 and 45 mb, poleward of 60° during late summer. This paper examines the cause of this variability using isentropic trajectory analysis and photochemical calculations. According to trajectory analysis using UKMO wind fields, air parcels with higher ozone mixing ratios move to 73°N from lower latitudes in the longitude sector 180°E ‐ 225°E over a 9 day period beginning on 10 August, 1993. Low ozone values seen in the HALOE data around 100°E at 73°N correspond to air parcels that remain mostly in higher latitudes. We present results from photochemical calculations conducted in conjunction with UARS data, and conclude that the longitudinal asymmetry in ozone can be be explained by transport along isentropic trajectories with standard chemistry.
Extension of coronal structure into interplanetary space
Authors: Woo Richard , Habbal Shadia Rifai
Published: February 2004

We investigate the extension and evolution of the solar corona into interplanetary space by comparing 1995 Ulysses radio occultation measurements of path‐integrated electron density and density fluctuations measured between 21 and 32 Ro, with simultaneous white‐light measurements made by the HAO Mauna Loa K‐coronameter below 2.5 Ro. The surprising picture of the extended corona to emerge from this comparison is one in which stalks of streamers, occupying a small fraction of volume in interplanetary space, are superimposed on a background corona distinguished by a plethora of ray like structures, often referred to as plumes in polar coronal holes. The radial preservation of the boundary between polar coronal holes and the base of streamers implies that the solar wind from polar coronal holes expands radially rather than undergoing any significant divergence as previously thought. Combining this picture of the extended corona with in situ velocity measurements made by Ulysses throughout its two polar passages, we conclude that the raylike structures, except for the stalks of streamers, seem to be the source of the fast wind. The existence of the fast wind at low latitudes can be attributed to these raylike structures, rather than the expansion of the boundaries of polar coronal holes to low latitudes.
Mid‐latitude observations of the seasonal variation of BrO: 2. Interpretation and modelling study
Authors: Fish D. J. , Aliwell S. R. , Jones R. L.
Published: February 2004

A 1‐D photochemical model, initialised with output from a chemical transport model and coupled to a radiative transfer model, is used to calculate BrO slant columns. Calculated BrO slant columns are shown to be in good agreement with measured values, which supports our current understanding of stratospheric bromine chemistry at middle latitudes, and argues against the need to invoke new chemistry or a new photolabile night‐time bromine reservoir. The model calculations show that the seasonal variation of BrO slant columns results from seasonal variations in NO2 abundances. The occurrence of BrONO2 hydrolysis on sulphate aerosols is found to affect twilight BrO abundances, but no other heterogeneous reactions involving bromine species are important under the range of stratospheric conditions sampled. The zenith‐sky measurements from Aberdeen in the winter of 1994–5 can be explained with present photochemical schemes and current estimates of approximately 20 pptv for the bromine content of the stratosphere.
“Non‐collisional” ionization and temperature layers in the auroral E/F1 layer: EISCAT observations
Authors: Schlesier Anke , Mishin Evgeny , Schlegel Kristian
Published: February 2004

EISCAT observations of thin layers of enhanced ionization and elevated electron temperature during auroral precipitations, similar to the phenomenon of the ‘Enhanced Aurora', are presented and described. Being well narrower than those predicted by the conventional collisional approach, the layers are likely caused by plasma turbulence generated by precipitating electrons and field‐aligned currents in the altitude range 110–170 km. The results are in a qualitative agreement with the model of the plasma turbulence layer which takes the influence of collisions upon the beam‐plasma interaction into account.
Ocean chemistry of the fossil fuel CO2 signal: The haline signal of “business as usual”
Authors: Brewer Peter G.
Published: February 2004

The increasing fossil fuel CO2 signal in surface ocean waters, superimposed upon the natural background, has now reached the level of about 2mg kg−1, and thus, if we were to conceive of this as a separate signal, it has become a new component of the salinity of sea water in its own right. By the year 2100, under the IPCC “Business as Usual” scenario, the fossil fuel signal will exceed in mass the contributions of fluoride, boron, or strontium ions to the salinity of the surface ocean waters, and will reduce the pre‐industrial carbonate iron concentration by about 55%. However the net effect of this massive chemical transfer to the ocean has not been to cause a haline contraction, but to increase the volume of the ocean by about 330 × 109 m³ today. The water flux from fossil combustion, of about 10.5 × 109 m³ yr−1, adds to this volume change.
Enhanced ELF wave generation efficiency using ‘O' mode HF heating
Authors: Barr Richard , Stubbe P. , Rietveld M. T. , Nielsen E.
Published: February 2004

We present here signals received near the Tromsø ionospheric heater facility when the heater was modulated with a 505Hz square wave. We found that whereas the harmonics of the square wave (≥ 1515 Hz) showed the accepted behaviour of reduced wave excitation on switching from ‘X' to ‘O' mode HF heating, the fundamental frequency showed enhanced excitation of more than 10dB with ‘O' mode heating. The phase of the 505 Hz signals changed by typically 90° when the HF wave polarization was switched from ‘X' to ‘O' mode, but the phase of the harmonics was continuous through HF mode switching. We consider that these results indicate that during ‘O' mode heating the fundamental current was sourced in the upper D/E region, where the Pedersen current dominated, whereas the harmonic currents were sourced around 80 km where the Hall current maximised. The amplitude of the signal at the fundamental frequency was very unstable during ‘O' mode heating. This together with the fact that STARE data showed clear echos over Tromsø during ‘O' mode heating, which disappeared on switching to ‘X' mode, leads us to conclude that parametric instabilities, modulated by the HF heater, were responsible for this enhanced ELF excitation.
Electromagnetic hybrid‐code simulation of magnetic reconnection: Velocity distribution functions of accelerated ions
Authors: Nakabayashi J. , Machida S.
Published: February 2004

A 2‐1/2 dimensional electromagnetic hybrid simulation was conducted to explore particle acceleration in the magnetic reconnection process in the Earth magnetotail. By adding a localized anomalous resistivity to the neutral sheet of initial static Harris solution, we realized a spontaneous magnetic reconnection. We found that two kinds of characteristic electric fields were generated in addition to the conventional dawn‐to‐dusk electric field after the reconnection commenced. The first type of the electric field is directed toward the neutral sheet in the expanded plasma sheet boundary layer (PSBL), resulting in a dawnward drift of cold ions. The second type of electric field was directed as the conventional dawn to dusk component in the plasma sheet, but with a significantly large component away from the diffusion region. Though well‐developed slow mode shocks were not formed, this field played a significant role in plasma jet formation. The energy transfer from the electric field to the ions with the first type electric field was three times higher than with that the second type field. In addition to these perpendicular electric fields, the field‐aligned electric field in front of expanding plasma sheet (early‐phase plasmoid) caused a parallel ion acceleration. The dawnward plasma drift in the expanded plasma sheet and PSBL yielded a nonzero By field whose polarity showed an octupole structure with respect to the central diffusion region.

The relevant forms of ion distribution functions predicted by the present model are also considered in this study. This model can be applied to the transient phase of the magnetic reconnection, i.e., the expansion phase of the magnetospheric substorms.
High resolution OI (630 nm) image measurements of F‐region depletion drifts during the Guará Campaign
Authors: Taylor M. J. , Eccles J. V. , LaBelle J. , Sobral J. H. A.
Published: February 2004

A high performance, all‐sky, imaging system has provided data on the evolution and drift motions of F‐region depletions above the magnetic dip equator at Alcântara, Brazil, (2.3°S, 44.5°W). Monochromatic images of depletions in the OI(630 nm) nightglow were recorded on eight nights during 1‐16 October, 1994, as part of the Guará campaign. The drift motions of the depletions were typically 80–100 m/s eastward prior to local midnight and reduced to a minimum of ∼30–50 m/s in the morning hours, in accord with previous observations. However, on October 2–3 and 12–13 the depletions were observed to reverse direction for ∼60–90 min, achieving westward speeds of ∼30 m/s before the motion reverted to eastward around 0100 LT and accelerated to 35–45 m/s near dawn. Magnetic activity and other evidence suggests that these reversals in the motion of the airglow depletions probably result from reversals in the F‐region dynamo rather than from shifts in the altitude of the shear in the nighttime F‐region plasma drift.
DC electric field measurements with the Guará Spread‐F Rocket
Authors: Jahn J.‐M. , LaBelle J. , Pfaff R. F.
Published: February 2004

Data presented in this paper provide the first high‐altitude (> 600 km) rocket measurements of electric fields associated with spread‐F plumes measured simultaneously with a VHF coherent backscatter radar. In regions outside of spread‐F plasma depletions the electric field is primarily vertical, implying zonal plasma flow. The mean zonal drifts of the ambient plasma inferred from the rocket data are larger than average quiet time values, which can be attributed to the presence of active spread‐F irregularities. Within the spread‐F depletions, the vertical electric field becomes comparable to the zonal component, and individual plasma depletions are found to rise with speeds of up to 100 m/s. No large (> 10 mV/m) electric fields are observed in the plume region.
UV and optical light transmission properties in deep ice at the South Pole
Authors: Askebjer P. , Barwick S. W. , Bergström L. , Bouchta A. , Carius S. , Dalberg E. , Erlandsson B. , Goobar A. , Gray L. , Hallgren A. , Halzen F. , Heukenkamp H. , Hulth P. O. , Hundertmark S. , Jacobsen J. , Kandhadai V. , Karle A. , Liubarsky I. , Lowder D. , Miller T. , Mock P. , Morse R. , Porrata R. , Price P. B. , Richards A. , Rubinstein H. , Schneider E. , Spiering Ch. , Streicher O. , Sun Q. , Thon Th. , Tilav S. , Wischnewski R. , Walck C. , Yodh G.
Published: February 2004

Both absorption and scattering of light at wavelengths 410 to 610 nanometers were measured in the South Pole ice at depths 0.8 to 1 kilometer with the laser calibration system of the Antarctic Muon And Neutrino Detector Array (AMANDA). At the shortest wavelengths the absorption lengths exceeded 200 meters—an order of magnitude longer than has been reported for laboratory ice. The absorption shows a strong wavelength dependence while the scattering length is found to be independent of the wavelength, consistent with the hypothesis of a residual density of air bubbles in the ice. The observed linear decrease of the inverse scattering length with depth is compatible with an earlier measurement by the AMANDA collaboration (at ∼515 nanometers).
Lithospheric thinning and chemical buoyancy beneath the Hawaiian Swell
Authors: Moore William B. , Schubert Gerald
Published: February 2004

The source of the buoyancy that supports the Hawaiian Swell is not well understood. The swell may be supported by replacement of negatively buoyant lithosphere with buoyant mantle or by emplacement of buoyant material beneath lithosphere of normal thickness. These mechanisms can be distinguished by examining the quadratic relationship between geoid height and bathymetry. At the Hawaiian Swell, the curvature of the geoid height vs. swell topography relationship is negative, indicating that the swell is supported by thinned lithosphere. The magnitude of the curvature suggests that the mantle filling in the region of thinned lithosphere is both thermally and chemically buoyant.