bluuebunny/crossref_metadata_2025 huggingface dataset:
Grammatical Framework
Authors: RANTA AARNE
Published: January 2004

Grammatical Framework (GF) is a special-purpose functional language for defining grammars. It uses a Logical Framework (LF) for a description of abstract syntax, and adds to this a notation for defining concrete syntax. GF grammars themselves are purely declarative, but can be used both for linearizing syntax trees and parsing strings. GF can describe both formal and natural languages. The key notion of this description is a grammatical object, which is not just a string, but a record that contains all information on inflection and inherent grammatical features such as number and gender in natural languages, or precedence in formal languages. Grammatical objects have a type system, which helps to eliminate run-time errors in language processing. In the same way as a LF, GF uses dependent types in abstract syntax to express semantic conditions, such as well-typedness and proof obligations. Multilingual grammars, where one abstract syntax has many parallel concrete syntaxes, can be used for reliable and meaning-preserving translation. They can also be used in authoring systems, where syntax trees are constructed in an interactive editor similar to proof editors based on LF. While being edited, the trees can simultaneously be viewed in different languages. This paper starts with a gradual introduction to GF, going through a sequence of simpler formalisms till the full power is reached. The introduction is followed by a systematic presentation of the GF formalism and outlines of the main algorithms: partial evaluation and parser generation. The paper concludes by brief discussions of the Haskell implementation of GF, existing applications, and related work.
Constructed product result analysis for Haskell
Authors: BAKER-FINCH CLEM , GLYNN KEVIN , JONES SIMON PEYTON
Published: January 2004

Compilers for ML and Haskell typically go to a good deal of trouble to arrange that multiple arguments can be passed efficiently to a procedure. For some reason, less effort seems to be invested in ensuring that multiple results can also be returned efficiently. In the context of the lazy functional language Haskell, we describe an analysis, Constructed Product Result (CPR) analysis, that determines when a function can profitably return multiple results in registers. The analysis is based only on a function's definition, and not on its uses (so separate compilation is easily supported) and the results of the analysis can be expressed by a transformation of the function definition alone. We discuss a variety of design issues that were addressed in our implementation, and give measurements of the effectiveness of our approach across a substantial benchmark set. Overall, the price/performance ratio is good: the benefits are modest in general (though occasionally dramatic), but the costs in both complexity and compile time, are low.
The Functional “C” experience
Authors: HARTEL PIETER , MULLER HENK , GLASER HUGH
Published: January 2004

A functional programming language can be taught successfully as a first language, but if there is no follow up the students do not appreciate the functional approach. Following discussions concerning this issue at the 1995 FPLE conference (Hartel & Plasmeijer, 1995), we decided to develop such a follow up by writing a book that teaches C to students who can write simple functional programs. This paper summarises the essence of our approach, which is based on program transformation, and presents our experience teaching functional C at the Universities of Southampton and Bristol.
An empirical model of the high‐latitude magnetopause
Authors: Boardsen S. A. , Eastman T. E. , Sotirelis T. , Green J. L.
Published: February 2004

A quantitative, static, empirical model of the high‐latitude magnetopause is developed for GSM coordinates and parameterized by dipole tilt angle (ψ), solar wind pressure, and interplanetary magnetic field (IMF) Bz. We fit 691 high‐latitude magnetopause crossings by the Hawkeye 1 spacecraft to a generalized second‐order surface using only crossings for which both solar wind pressure and IMF data are available. These Northern Hemisphere crossings are shown to lie within the spatial coverage of Hawkeye for different bins of ψ spanning the range of −35° to 35°, demonstrating that the independence of the crossings is not due to a bias in coverage. At high latitudes, solar wind pressure and ψ are found to be of major and equal importance in modeling magnetopause position. In the Northern Hemisphere the high‐latitude magnetopause is displaced outward for positive ψ and inward for negative ψ. Additional inward displacement of the magnetopause surface is reduced for extreme negative ψ values. IMF Bz dependence is separable only after the effects of ψ and pressure are removed. The radial dependence on IMF Bz weakens near the cusp and becomes stronger antisunward of the cusp, where the magnetopause is displaced outward for negative IMF Bz, and inward for positive IMF Bz. This is consistent with findings along the low‐latitude flanks. Both AE and Dst dependencies are found in the high‐latitude magnetopause crossings after removing ψ and pressure dependencies from the crossings. This model is only valid at high latitudes, antisunward of the cusp, out to a xGSM value of about −5 Rε. The ψ dependence of the nose is also modeled using a subset of magnetopause crossings from Roelof and Sibeck [1993] along with Hawkeye crossings below the cusp region. For positive ψ the most Sunward point of the nose is displaced below the xGSM‐yGSM plane. Both the nose model and the high‐latitude model are in reasonable agreement with the theoretical model of Sotirelis and Meng [1999].
The ramp widths of high‐Mach‐number, quasi‐perpendicular collisionless shocks
Authors: Newbury J. A. , Russell C. T. , Gedalin M.
Published: February 2004

The shock ramp is traditionally defined as the narrow region over which the magnetic field primarily jumps from upstream to downstream conditions. Although narrow in comparison to other features in the shock profile, the ramp plays the most important role in providing the necessary dissipation of the incident solar wind flow. However, its features are not well understood, particularly for shocks observed when the upstream solar wind has a high Mach number and high plasma β. Using the ISEE 1 and 2 spacecraft to measure the spatial scales in supercritical, quasi‐perpendicular bow shock profiles, we examine the scale size of the ramp and pay particular attention to features found within the ramp. It is shown that the ramp can usually be characterized by two different scales: (1) a large scale (or global ramp width) within which the main transition from the upstream to downstream magnetic field occurs and (2) a thinner subramp scale which contains steep jumps in the magnetic field magnitude with amplitudes comparable to the overall change in magnetic field at the shock. It is shown that both scales are characteristic of the quasi‐stationary shock profile (and are stationary within an ion gyroperiod), which allows for a reliable conversion from measured temporal durations to spatial lengths in the shock profile. In most shocks the global ramp width is 0.4–1 ion inertial lengths (c/ωpi), and the subramp scale is about 0.1–0.2 c/ωpi We argue that presence of these small‐scale, large‐amplitude, quasi‐stationary structures in the ramp may be important for ion dynamics. An oscillatory behavior of the ramp is also observed in some shocks. Also, the global ramp width and subramp scales show little dependence on upstream parameters: The global ramp scale thins as θBn approaches 90°, but not as much as predicted, and there is little overall correlation between ramp scales and either Mach number or β. Future multispacecraft observations of the bow shock will require high‐temporal‐resolution measurements and close spatial separations to address the problem of shock structure. Present plans for the Cluster mission will provide little data at the close separations needed for such a study.
Geomagnetic field intensity from 71 to 12 ka as recorded in deep‐sea sediments of the Blake Outer Ridge, North Atlantic Ocean
Authors: Schwartz Martha , Lund Steve P. , Johnson Thomas C.
Published: February 2004

In this paper we estimate relative geomagnetic field paleointensity between 71 and 12 kyrs BP as recorded in three deep sea sediment cores from the Blake Outer Ridge, western North Atlantic Ocean. Paleointensities were estimated by normalizing sediment natural remanant magnetization separately to (1) magnetic susceptibility, (2) anhysteretic remanant magnetization and (3) saturation isothermal remanent magnetization (SIRM). In one core, paleointensities were estimated within short time windows which display uniform sediment magnetic characteristics, and offsets between windows were removed to minimize environmental biases. We find that most features of our records are preserved regardless of normalizer choice, but we chose SIRM as the best normalizer for the final paleointensity estimates. Our three records preserve and agree upon a number of short‐duration (∼103 years) paleointensity features even though the cores are separated by almost 250 km. We conclude that these are real geomagnetic field signals of at least local extent. We also identify a number of differences between our records which must be artifacts of sediment remanence acquisition or paleointensity normalization. Such artifacts occur as either (1) baseline shifts between time intervals with slightly different sediment magnetic characteristics or (2) differences in amplitude of short duration events. In spite of these environmental biases, the number and ages of relative paleointensity highs and lows are preserved. Thus sediment paleointensity estimates may be used locally for high‐resolution chronostratigraphic correlation. Correlation of our paleointensity records with other records from the same extended region (North Atlantic Ocean‐western Europe) indicates that major paleointensity features appear in all regional records. However, differences in the ages and disagreement in magnitude and number of individual features call into doubt the use of these relative paleointensity records for high‐resolution chronostratigraphic correlation on a broader regional scale or for quantitative estimation of past geomagnetic field variability.
Effects of magnetic anomalies discovered at Mars on the structure of the Martian ionosphere and solar wind interaction as follows from radio occultation experiments
Authors: Ness N. F. , Acuña M. H. , Connerney J. E. P. , Kliore A. J. , Breus T. K. , Krymskii A. M. , Cloutier P. , Bauer S. J.
Published: February 2004

The slopes of the electron density profiles obtained by radio occultation experiments at Mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of Venus. The results obtained by the Mars‐Global‐Surveyor (MGS) spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin at Mars. Addressing the difference between the ionosphere at Venus and Mars, the scale heights of electron density profiles obtained by radio occultation methods onboard Mariner 9 and Viking 1 are analyzed at altitudes higher than the topside boundary of the photoequlibrium region in the magnetic field‐free ionosphere. The local increase of the mean scale height in the altitude region 180–250 km is assumed to be either an effect of a nonhorizontal magnetic field associated with the magnetic anomalies or diffusive equilibrium in the magnetic field free ionosphere. The areas where the scale height of electron density profile is increased in comparison with average one have been selected. The angle between the magnetic field measured by MGS MAG/ER at altitudes 120–250 km and local zenith direction is investigated throughout these selected areas.
Imaging electron density and magnetic field distributions in the magnetosphere: A new technique
Authors: Ganguly S. , Van Bavel G. H. , Brown A.
Published: February 2004

The current collection of magnetospheric observations consists almost entirely of in situ measurements at isolated spacecraft positions. A novel remote sensing technique for simultaneously imaging the plasma density N and the magnetic field B is proposed. The imaged region of the magnetosphere can be several Earth radii in extent. Simultaneous measurements of both group delay and Faraday rotation of radio waves propagating through the magnetosphere yield both total electron content (TEC) and Faraday rotation angle, which is the integral of electron density weighted by some known function of the magnetic field and ray path. These data can then be inverted to obtain estimates of the three‐dimensional spatial distribution of N and B. The geometry of the ray paths determines the number of components of B that can be resolved. Simple multisatellite simulations and common data processing techniques introduce this new application of tomography: Magnetospheric TEC measurements yield a map of N, which is then combined with Faraday rotation angle measurements to produce a two‐component map of B in the plane of observation. The successful tomographic reconstructions provide a straightforward illustration of the practicality of using this technique to map the magnetospheric plasma density and magnetic field in two or three dimensions. Furthermore, simultaneous images of N and B are of great topical interest to geospace science because of their direct and immediate relevance to current questions regarding magnetospheric structure and dynamics.
Airglow observations of mesoscale low‐velocity traveling ionospheric disturbances at midlatitudes
Authors: Garcia F. J. , Kelley M. C. , Makela J. J. , Huang C.‐S.
Published: February 2004

This paper presents a summary of 630.0 nm emission observations made by the Cornell All‐Sky Imager that have revealed an abundance of structure in the midlatitude thermosphère. Some events were so bright that the weaker 557.7 nm thermospheric line was readily visible and produced sharper images because of the shorter excitation lifetime. Global Positioning System observations show that the airglow features are traveling ionospheric disturbances (TIDs). The remarkable feature of the data is the overwhelming tendency for these low‐velocity TIDs to develop with a northwest to southeast orientation and to propagate in the southwest direction. Speeds ranged from 50 to 170 m/s, and wavelengths ranged from 50 to 500 km. The Perkins instability is investigated as a possible explanation for the structures. The linear theory, including both winds and electric fields, predicts a positive but small growth rate. However, the real part of the dispersion relation gives the wrong sign for the wave propagation. Furthermore, the growth rate seems too small to amplify a seed gravity wave significantly during one period of neutral gas oscillation. We conclude that this class of low‐velocity TID is not yet explained theoretically.
Cross‐field diffusion of charged particles and the problem of ion injection and acceleration at quasi‐perpendicular shocks
Authors: Scholer M. , Kucharek H. , Giacalone J.
Published: February 2004

It is an open question how charged particles are injected at quasiperpendicular shocks into a first‐order Fermi acceleration mechanism. Crossfield diffusion of solar wind ions is a possible injection process. However, in a system with at least one ignorable spatial dimension, charged particles moving in fluctuating fields are tied to the magnetic field lines. We have therefore determined the cross‐field diffusion coefficient of charged particles in self‐consistently generated turbulence by three‐dimensional hybrid simulations. The initial setup consists of a homogeneous magnetic field with an isotropic core plasma plus a second, nongyrotropic ion distribution. The combined distributions resemble the distribution found immediately downstream of the quasi‐perpendicular Earth bow shock: Part of the solar wind is transmitted (core) and part is specularly reflected and subsequently convected downstream (nongyrotropic part). Such a particle distribution excites the Alfvén ion cyclotron and mirror mode instability. The turbulence scatters the nongyrotropic ions both parallel and perpendicular to the field. The perpendicular and the parallel diffusion coefficients have been determined for two values of the density of the nongyrotropic distributions, nb. The ratio of the two diffusion coefficients is smaller than the value predicted by hard sphere scattering theory, i.e., parallel scattering is considerably stronger than scattering perpendicular to the field. The power in the magnetic field fluctuations in the high nb case is comparable to the power obtained in a two‐dimensional quasiperpendicular shock simulation immediately behind the shock ramp. On the basis of perpendicular scattering time it is suggested that cross‐field diffusion in the turbulent wave field generated by the specularly reflected ions is sufficient to inject and accelerate these ions efficiently at quasi‐perpendicular shocks.
On the limitation of the current sheet approximation in estimation of the northward Bz associated field‐aligned currents
Authors: Yamamoto T. , Inoue S. , Ozaki M.
Published: February 2004

This paper calls attention to the limitation of the current sheet approximation, which has commonly been used in deducing the field‐aligned currents (FACs) from the field‐perpendicular components of magnetic field disturbances detected from low‐altitude/midaltitude (below a few Earth radii) satellites. We focus our study on the current system involved in the northward interplanetary magnetic field associated FAC (so‐called northward Bz (NBZ)). Assuming a numerical model for the total system of the region 1, region 2, and NBZ FACs, plus the associated ionospheric currents, the dusk‐to‐dawn and sunward components of the resulting magnetic disturbance δBx and δBy are calculated. In contrast to the commonly adopted hypothesis that the field‐perpendicular magnetic disturbances as observed from the low‐altitude (a few hundred kilometers) satellites are attributed primarily to the FACs, it is found that the ionospheric currents can make a significant contribution to those disturbances. Particularly, in the central part of the region of NBZ FACs, δBx from the ionospheric currents dominates δBx from the FACs. Next, for a simple discussion on the limit of the current sheet approximation we consider the magnetic disturbances at altitudes higher than several hundred kilometers where the contribution (to δBy) from the ionospheric currents can be neglected. It is found that in general, the FAC intensities based on the current sheet model are significantly different from those actually given in the FAC distribution. Specific points to be noted are as follows: (1) On the dusk‐dawn lines passing the central part of the NBZ region the intensity of NBZ under the current sheet approximation is considerably smaller than the actual value, and the intensity ratio between region 1 and NBZ can be overestimated, by >50%, under that approximation. (2) On the dusk‐dawn lines near the edges (but just inside) of the NBZ region, the current sheet model breaks down even qualitatively; the current sheet model cannot infer the right locations of region 1 and NBZ FACs. (3) On the dusk‐dawn lines just outside of the NBZ region the so‐called “W”‐shaped profile in δBy, which can commonly be interpreted as a signature of the presence of NBZ FACs, emerges in the region where actually no NBZ FAC exists.
Mesospheric gravity wave imaging at a subauroral site: First results from Millstone Hill
Authors: Smith Steven M. , Mendillo Michael , Baumgardner Jeffrey , Clark Ronald R.
Published: February 2004

Optical detections of short‐period quasi‐monochromatic gravity waves in the mesospheric nightglow emissions of OH (695–950 nm), O (557.7 nm), and Na (589.3 nm) have been obtained for the first time from Millstone Hill, Massachusetts (42.6°N, 71.5°W). Using a new all‐sky bare charge‐coupled device (CCD) imaging system at this subauroral site, we obtained 12 nights of observations during the period February 1 to July 21, 1998. Wave structure was observed during ∼55% of the total observing time, and 35 events were identified and analyzed. Two types of wave structure were observed: extensive, long‐lasting (∼1–5 hours) waves known as bands and small‐scale, short‐lived (∼5–40 min) features called ripples. The band events are believed to be due to freely propagating or ducted internal gravity waves. The mean measured parameter values of the band events were horizontal wavelength (λh) = 21±7 km, phase speed (cob) = 47±20 m s−1, and observed period (τob) = 8.5±4.6 min. The intrinsic wave parameters (cin and τin) and the vertical wavelength (λz) of the band events were calculated using available meteor radar winds for nine of the events. Of the deduced λz values, five were evanescent, and the remaining four ranged from 12 to 21 km, with a mean of 17±4 km. Calculated energy and momentum fluxes for two case study events yielded 4–14 × 10−3 W m−2 and 5–30 m2 s−2, respectively. Possible sources of the waves were investigated using additional data obtained during 1999. The majority of the events exhibited poleward propagation, even during periods of visible auroral activity. This indicates that although the thermosphere above Millstone Hill exhibits subauroral behavior during enhanced levels of geomagnetic activity (Kp>3), the propagation characteristics and frequency of occurrence of mesospheric gravity waves at this location differ very little from other middle‐ and low‐latitude locations.
Energetic proton observations at 1 and 5 AU: 1. January–September 1997
Authors: Lario D. , Marsden R. G. , Sanderson T. R. , Maksimovic M. , Sanahuja B. , Balogh A. , Forsyth R. J. , Lin R. P. , Gosling J. T.
Published: February 2004

We present energetic particle observations by the Ulysses and Wind spacecraft during the years 1997–1998. During this period, Ulysses moved from +19° to −19° in heliographic latitude with heliocentric distances ranging from 4.71 to 5.41 AU. Wind was located near the Earth at 1 AU from the Sun in the ecliptic plane. The proximity of Ulysses to the ecliptic plane allows us to compare proton fluxes at different heliospheric distances and heliolongitudes but at similar latitudes. Enhancements in the energetic (approximately MeV) MeV proton fluxes were observed by both spacecraft in a close temporal association. We quantify this temporal coincidence and we distinguish two time intervals based on the energy range of the proton flux increases and on the solar wind streams observed by the Ulysses spacecraft. Each one of these two periods (period 1, January–September 1997 and period 2, October 1997 to December 1998) corresponds also to a different level of solar activity. We establish a direct correspondence between individual particle flux enhancements observed by both spacecraft throughout period 1. At 1 AU the proton flux enhancements are associated with the occurrence of coronal mass ejections (CMEs) at the Sun. At 5 AU the presence of high‐speed solar wind streams, the contribution of energetic particles from CMEs, and the evolution of the magnetic field structures along which energetic particles propagate determine the final shape of the proton flux enhancements and their time delays with respect to 1 AU. When a solar energetic particle (SEP) event is observed at 1 AU, particle flux enhancements associated with recurrent high‐speed solar wind streams at ∼5 AU show a higher particle flux intensity. We suggest that SEPs accelerated by CME‐driven shocks act as a background seed particle population available to be reaccelerated by shocks associated with corotating high‐speed streams.
Sources of geomagnetic activity over the solar cycle: Relative importance of coronal mass ejections, high‐speed streams, and slow solar wind
Authors: Richardson I. G. , Cliver E. W. , Cane H. V.
Published: February 2004

We assess the contribution of various types of solar wind structures (coronal mass ejections (CMEs), high‐speed streams, and slow solar wind) to averages of the aa geomagnetic activity index (

) during the solar cycle. We used solar wind plasma, magnetic field, and energetic particle data to identify the flow types present in the near‐Earth solar wind during 1972–1986 (encompassing the decline of solar cycle 20 and all of cycle 21). Corotating high‐speed streams contribute ∼ 70% of
outside of solar maximum and ∼ 30% at solar maximum (1978–1982). CME‐related structures (shocks/postshock flows/ejecta) account for ∼ 50% of
at solar maximum and <10% outside of maximum. Slow solar wind contributes ∼ 20% throughout the solar cycle. Our analysis provides insight into the cause of the so‐called “Gnevyshev Gap” in geomagnetic activity, characterized by a decrease in
near the peak of the sunspot cycle. An example of this phenomenon occurred in 1980 at the maximum of cycle 21 when
registered a value lower than that observed at the preceding solar minimum. We attribute the 1980 depression in
to a temporary reduction in average solar wind speed, evident in both CME and corotating stream related components, and a reduction in mean magnetic fields in all types of solar wind structure. This involvement of all solar wind structures is indicative of a global solar phenomenon, apparently related to an observed depression in the solar open magnetic flux at the time of solar magnetic field polarity reversal. Both CMEs and streams contribute to geomagnetic activity on either side of this minimum. Thus, at least for cycle 21, the Gnevyshev Gap does not reflect a transition between a period of enhanced geomagnetic activity levels due to CMEs just prior to solar maximum and a second enhancement, due to corotating streams, during the descending phase. Beyond the post Gnevyshev Gap peak, high‐speed streams will eventually dominate geomagnetic activity on the decline of the cycle and may, on occasion (as in solar cycle 20), produce a late peak in average geomagnetic activity with relatively little contribution from CMEs.
Electromagnetics of substorm onsets in the near‐geosynchronous plasma sheet
Authors: Erickson G. M. , Maynard N. C. , Burke W. J. , Wilson G. R. , Heinemann M. A.
Published: February 2004

A search of the CRRES database identified 20 events in which the satellite was located within the local‐time sector spanned by the substorm current wedge (SCW) as it formed. Poynting vectors for low‐frequency waves are derived from the electric and magnetic field measurements. In 19 of the events, data are inconsistent with the notion that the SCW initiates from the braking of earthward bulk flows emanating from a near‐Earth X line. Rather, the data support drift‐Alfvén ballooning in the near‐geosynchronous plasma sheet as being responsible for initiation of the SCW and substorm onset. Dipolarization at CRRES is preceded by eastward excursions of the electric field (trigger waves), at which time the first significant electromagnetic energy is observed flowing toward the ionosphere. Dipolarization and the SCW appear before ground onset, following one or more of these trigger waves. The so‐called “explosive growth phase” occurs in association with explosive growth of the trigger waves soon after onset. Seven characteristic features of substorm onsets and expansions observed at CRRES are described. Among these are two stages of expansion. The first expansion stage is initiated by the trigger waves (ballooning) in the near‐geosynchronous plasma sheet. Approximately 10 minutes later a second stage begins consistent with the arrival of earthward bulk flows emanating from a near‐Earth X line. Near‐geosynchronous substorm onsets can explain the observed increase in the occurrence rate of fast bulk flows earthward of its minimum value near X = −12 RE. Drift‐Alfvén ballooning also provides a possible causal link between observed reductions of the solar wind driver and substorm onsets.
Geospace Environment Modeling (GEM) magnetic reconnection challenge: MHD and Hall MHD—constant and current dependent resistivity models
Authors: Otto A.
Published: February 2004

The work is part of several papers investigating two‐dimensional magnetic reconnection in the same initial configuration with different plasma approximations. The present work compares the results of magnetic reconnection in this configuration using constant and current dependent resistivity models in the framework of traditional MHD and Hall MHD. The results can be summarized as follows. For constant resistivity the effects of diffusion or the formation of a long thin current layer limit the reconnection rate. Current dependent resistivity models result in enhanced reconnection rates in all considered cases. In these cases, reconnection is faster by a factor of 2 in the Hall MHD approximation compared to the traditional MHD. The maximum reconnection rate for the Hall MHD for all current dependent resistivities is ∼0.2 and appears largely independent of the model specifics and the initial perturbation.
A model of the Lyman‐α line profile in the proton aurora
Authors: Gérard Jean‐Claude , Hubert Benoît , Bisikalo Dimitry V. , Shematovich Valery I.
Published: February 2004

The Lyman‐α auroral emission is characterized by a broad line profile whose shape depends on the energy and pitch angle distributions of the initial proton beam, whereas its total brightness reflects the proton energy flux precipitated into the auroral upper atmosphere. Global remote sensing of the proton aurora through its ultraviolet signature makes it is increasingly important to relate the characteristics of the Lyman‐α emission to the physical properties of the precipitated proton flux. We present a numerical model of proton and hydrogen flux transport and kinetics based on the direct simulation Monte Carlo method. In this approach, all elastic and inelastic processes are stochastically simulated as well as is the production of Lyman‐α photons with the associated Doppler velocity component. The model also includes collisional, geomagnetic, and geometric spreading of the proton‐hydrogen beam. We show that consideration of the stochastic character of the H atom velocity redistribution after collisions produces line profiles different from those obtained in the strictly forward or mean scattering angle approximations previously used in proton transport codes. In particular, the predicted fraction of photons due to backscattered particles is considerably larger when stochastic collision scattering is considered than in the strictly forward or mean scattering angle approximations. In contrast to the median wavelength, the position of the peak in the line profile shows a weak inverse dependence on the proton energy. The efficiency of the Lyman‐α photon production per unit incident energy flux significantly drops as the mean proton energy increases. The line profile and the amount of blue‐shifted (for downward viewing) emission depends in a complex way on the initial energy and pitch angle distribution of the protons. The line profiles expected for the noon cusp and midnight proton aurora are shown to be significantly different.
Configuration of high‐latitude and high‐altitude boundary layers
Authors: Eastman T. E. , Boardsen S. A. , Chen S.‐H. , Fung S. F. , Kessel R. L.
Published: February 2004

We report comprehensive statistical results for 4 years of Hawkeye observations totaling 1757 boundary crossings. Our objective is to use the full set of Hawkeye plasma, magnetic field, and plasma wave data to identify every cusp‐associated data interval (entry layer, cusp, plasma mantle), to spatially map these regions, and to isolate the primary variables affecting their occurrence frequency and location. We find that SM coordinates best order the angular position of cusp region data intervals and that GSM coordinates are better for ordering in radial distance, especially for the plasma mantle. Dipole tilt and external pressure are the primary variables affecting high‐latitude and high‐altitude boundary configuration. Compared to these, the effects of IMF parameters are minor although discernable when adequate corrections are made for dipole tilt and pressure. New results on cusp flaring and indentation of the high‐latitude boundary are obtained by limiting this data set in pressure, varying dipole tilt ranges, and examining changes in boundary configuration in both SM and GSM coordinates. We find that as the dipole tilts more toward the oncoming magnetosheath plasma flow, indentation becomes enlarged and the cusp outflow region, the plasma mantle, becomes more flared out relative to the Earth‐Sun line. In contrast, as the dipole tilts away from the Sun direction, cusp indentation is reduced but the cusp outflow region remains flared out compared to boundary shapes inferred from low‐latitude observations. A semiempirical magnetopause model by Boardsen et al. [this issue] compares very well with the high‐latitude boundary layer observations reported here including a test for hemispheric symmetry, which is assumed by the model.
Geospace Environmental Modeling (GEM) Magnetic Reconnection Challenge
Authors: Birn J. , Drake J. F. , Shay M. A. , Rogers B. N. , Denton R. E. , Hesse M. , Kuznetsova M. , Ma Z. W. , Bhattacharjee A. , Otto A. , Pritchett P. L.
Published: February 2004

The Geospace Environmental Modeling (GEM) Reconnection Challenge project is presented and the important results, which are presented in a series of companion papers, are summarized. Magnetic reconnection is studied in a simple Harris sheet configuration with a specified set of initial conditions, including a finite amplitude, magnetic island perturbation to trigger the dynamics. The evolution of the system is explored with a broad variety of codes, ranging from fully electromagnetic particle in cell (PIC) codes to conventional resistive magnetohydrodynamic (MHD) codes, and the results are compared. The goal is to identify the essential physics which is required to model collisionless magnetic reconnection. All models that include the Hall effect in the generalized Ohm's law produce essentially indistinguishable rates of reconnection, corresponding to nearly Alfvénic inflow velocities. Thus the rate of reconnection is insensitive to the specific mechanism which breaks the frozen‐in condition, whether resistivity, electron inertia, or electron thermal motion. The reconnection rate in the conventional resistive MHD model, in contrast, is dramatically smaller unless a large localized or current dependent resistivity is used. The Hall term brings the dynamics of whistler waves into the system. The quadratic dispersion property of whistlers (higher phase speed at smaller spatial scales) is the key to understanding these results. The implications of these results for trying to model the global dynamics of the magnetosphere are discussed.
Hydrography, nutrients, and carbon pools in the Pacific sector of the Southern Ocean: Implications for carbon flux
Authors: Daly Kendra L. , Smith Walker O. , Johnson Gregory C. , DiTullio Giacomo R. , Jones David R. , Mordy Calvin W. , Feely Richard A. , Hansell Dennis A. , Zhang Jia‐Zhong
Published: February 2004

We investigated the hydrography, nutrients, and dissolved and particulate carbon pools in the western Pacific sector of the Antarctic Circumpolar Current (ACC) during austral summer 1996 to assess the region's role in the carbon cycle. Low fCO2 values along two transects indicated that much of the study area was a sink for atmospheric CO2. The fCO2 values were lowest near the Polar Front (PF) and the Subtropical Front (STF), concomitant with maxima of chlorophyll a and particulate and dissolved organic carbon. The largest biomass accumulations did not occur at fronts, which had high surface geostrophic velocities (20–51 cm s−1), but in relatively low velocity regions near fronts or in an eddy. Thus vertical motion and horizontal advection associated with fronts may have replenished nutrients in surface waters but also dispersed phytoplankton. Although surface waters north of the PF have been characterized as a “high nutrient‐low chlorophyll” region, low silicic acid (Si) concentrations (2–4 μM) may limit production of large diatoms and therefore the potential carbon flux. Low concentrations (4–10 μM Si) at depths of winter mixing constrain the level of Si replenishment to surface waters. It has been suggested that an increase in aeolian iron north of the PF may increase primary productivity and carbon export. Our results, however, indicate that while diatom growth and carbon export may be enhanced, the extent ultimately would be limited by the vertical supply of Si. South of the PF, the primary mechanism by which carbon is exported to deep water appears to be through diatom flux. We suggest that north of the PF, particulate and dissolved carbon may be exported primarily to intermediate depths through subduction and diapycnal mixing associated with Subantarctic Mode Water and Antarctic Intermediate Water formation. These physical‐biological interactions and Si dynamics should be included in future biogeochemical models to provide a more accurate prediction of carbon flux.
Modeling the thermal surface signature of breaking waves
Authors: Eifler W. , Donlon C. J.
Published: February 2004

A coupled one‐dimensional air‐sea interface transfer (INTRA) model has been developed to investigate atmosphere‐ocean heat transfer processes characterized by periodic wave breaking. Breaking wave and intact surface conditions are incorporated into the model by attributing different transport properties to near‐interface layers. The INTRA model is forced by time‐variable heat fluxes at the air‐sea interface and with wind speed and temperature at 10‐m height. The model is validated by using ocean basin scale and high‐resolution local observations that capture fine‐scale thermal processes at the air‐sea interface. Small differences are found when comparing model output to extensive observations that include a broad range of atmospheric and oceanic conditions collected during a meridional transect of the Atlantic Ocean. Model results simulating the local thermal surface signature of breaking waves show very good agreement with observations made by using a thermal infrared camera. The INTRA model will be of particular use for reconciling the differences between sea surface temperatures observed by using conventional in situ observations and those derived from satellite infrared remote sensing techniques.
Simulating the ice‐thickness distribution in a coupled climate model
Authors: Bitz C. M. , Holland M. M. , Weaver A. J. , Eby M.
Published: February 2004

Climate simulations in a global coupled model are investigated using a dynamic‐thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses. In addition to the sea ice component, the model includes a full primitive‐equation ocean and a simple energy‐moisture balance atmosphere. We introduce a formulation of the ice thickness distribution that is Lagrangian in thickness‐space. The method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth Eulerian distributions. Experiments demonstrate that the model does reasonably well in simulating the mean Arctic climate. We find the climate of the Arctic and northern North Atlantic is sensitive to resolving the ice‐thickness distribution when comparing the model results to a simulation with a two‐level sea ice model. The ice‐thickness distribution causes ice export through Fram Strait to be more variable and more strongly linked to meridional overturning in the North Atlantic Ocean.

The Lagrangian formulation of the ice‐thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an Eulerian method. We find ice growth rates and ocean surface salinity differ in our model with a well‐resolved vertical temperature profile in the ice and snow and an explicit brine‐pocket parameterization compared to a simulation with Semtner zero‐layer thermodynamics. Although these differences are important for the climate of the Arctic, the effects of an ice thickness distribution are more dramatic and extend into the northern North Atlantic. Sensitivity experiments indicate that five ice‐thickness categories with ∼50‐cm vertical temperature resolution capture the effects of the ice‐thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations.
Estimation of wave phase speed and nearshore bathymetry from video imagery
Authors: Stockdon Hilary F. , Holman Rob A.
Published: February 2004

A new remote sensing technique based on video image processing has been developed for the estimation of nearshore bathymetry. The shoreward propagation of waves is measured using pixel intensity time series collected at a cross‐shore array of locations using remotely operated video cameras. The incident band is identified, and the cross‐spectral matrix is calculated for this band. The cross‐shore component of wavenumber is found as the gradient in phase of the first complex empirical orthogonal function of this matrix. Water depth is then inferred from linear wave theory's dispersion relationship. Full bathymetry maps may be measured by collecting data in a large array composed of both cross‐shore and longshore lines. Data are collected hourly throughout the day, and a stable, daily estimate of bathymetry is calculated from the median of the hourly estimates. The technique was tested using 30 days of hourly data collected at the SandyDuck experiment in Duck, North Carolina, in October 1997. Errors calculated as the difference between estimated depth and ground truth data show a mean bias of −35 cm (rms error = 91 cm). Expressed as a fraction of the true water depth, the mean percent error was 13% (rms error = 34%). Excluding the region of known wave nonlinearities over the bar crest, the accuracy of the technique improved, and the mean (rms) error was −20 cm (75 cm). Additionally, under low‐amplitude swells (wave height H ≤ 1 m), the performance of the technique across the entire profile improved to 6% (29%) of the true water depth with a mean (rms) error of −12 cm (71 cm).
Variable swash motions associated with foreshore profile change
Authors: Holland K. T. , Puleo J. A.
Published: February 2004

Variations in swash motions over a temporally changing foreshore surface are examined over the first tidal cycle following the onset of a storm using high‐resolution video observations obtained at Duck, North Carolina. A dramatic example of profile adjustment was observed where nearly 1 m of vertical change occurred over a 4 hour time period. Swash edge excursion measurements during this study compare favorably with predictions from standard equations describing ballistic motions of an object on a plane slope under quadratic friction and showed no strong asymmetries between uprush and backwash that might explain the profile adjustment. Instead, these unique observations showed a tendency toward a predictable equilibrium between swash motions and profile response where the stability condition relates foreshore slope to incident wave period and initial uprush velocity using the ballistic equations. Under these conditions the foreshore adjusts to minimize the difference between swash duration and incident wave period. On the basis of this finding a simple morphodynamic model for changes in foreshore slope as a function of swash and surf conditions is presented and allows prediction of the transition from an erosive to stable condition.
Field observations of the wave bottom boundary layer
Authors: Foster D. L. , Beach R. A. , Holman R. A.
Published: February 2004

This paper presents a comprehensive set of velocity and suspended sediment observations in the nearshore wave bottom boundary layer, collected during the Duck94 field experiment on the Outer Banks of the North Carolina coast. Cross‐shore velocity measurements in the wave bottom boundary layer were made using five hot film anemometers, nominally spaced from 1 to 5 cm above the bed in 2 m of water depth. The time‐varying location of the seabed was estimated to roughly 1 cm with a stacked set of bed‐penetrating fiber‐optic backscatter sensors. The instrument array was intermittently located in the surf zone on the crest of a bar. The location of the bottom varied several centimeters over a 34 min data run. Even over 4 min segments of quasi‐steady statistics, occasional large waves caused short erosion and redeposition events, complicating the definition of bottom location and causing the root‐mean‐square velocity statistics to be nonzero below the mean bed location. This leads to obvious difficulties in comparisons with two, one‐dimensional time‐dependent, eddy viscosity wave bottom boundary layer models. For example, bed shears based on rms amplitude decay were lower than predicted. The observations show some evidence for a velocity overshoot region within the wave bottom boundary layer. The observations were compared with two linear eddy viscosity models. Larger estimates of a constant eddy viscosity and smaller than predicted phase leads are indicative of more rapid mixing of momentum than predicted by the models. The phase and amplitude frequency response estimated with frequency domain empirical orthogonal functions shows a nonlinear response of the wave bottom boundary layer over the incident band. These observations are among the first coherent looks at the wave bottom boundary layer under conditions of significant sediment response. They highlight the added complexity of the dynamics in natural environments.
Sea level variations and their dependency on meteorological and hydrological forcing: Analysis of altimeter and surface data for the Black Sea
Authors: Stanev Emil V. , Le Traon Pierre‐Yves , Peneva Elissaveta L.
Published: February 2004

TOPEX/Poseidon (T/P) altimeter data in the Black Sea are analyzed for almost 5 years in parallel with available hydrological and meteorological data with the aim of studying the water balance and the dependency of sea level oscillations on meteorological and hydrological forcing. This forcing induces seasonal variations of mean sea level with oscillations of ∼10–15 cm. The consistency between satellite and tidal gauge data is demonstrated in several coastal locations, and a mean ascending trend of ∼3 cm yr−1 is found in the two data sets. The variability in all components of water balance, including the Bosphorus outflow calculated as the difference between the fresh water flux and the time rate of sea level change estimated from altimeter data, is analyzed. The T/P data give very clear signals in the patterns of amplitudes of oscillations at intraannual, seasonal, and interannual timescales that help in understanding the variability of circulation. The intraannual variations are well pronounced on the continental slope and shelf and reach highest amplitudes in the areas of Sevastopol and Batumi quasi‐permanent eddies. The clearest representation of oscillations with seasonal periodicity exists in the area of Batumi Eddy. This variability is associated with the transition between states with intense cyclonic circulation in winter and weaker (sometimes anticyclonic) circulation in summer‐fall period. The Sevastopol Eddy is not clearly resolved in the seasonal variability. The interannual variability has the strongest signature in the area of western gyre and southeastern Black Sea. The analysis of satellite data supports some earlier studies on the circulation based on dynamic computations and numerical modeling. They make it possible to estimate the amount of water exchanged between coastal and open ocean areas caused by the time variability in the Ekman drift. The good quality of altimeter data and the high level of signals could ensure more accurate numerical simulations by means of data assimilation.