bluuebunny/crossref_metadata_2025 huggingface dataset:
Shear velocity profiles associated with auroral curls
Authors: Vogt J. , Frey H. U. , Haerendel G. , Höfner H. , Semeter J. L.
Published: August 2003

Optical observations using high‐resolution television cameras frequently show that auroral curls are associated with shear velocities in the apparent optical flow. The present study examines in detail one particular curl system event which happened to yield sufficient resolution to determine the fine structure of velocity and vorticity profiles by means of a new analysis technique. Those observations of curl system evolution are contrasted with large velocity shear events where small‐scale quasiperiodic distortions were subject to sudden decay rather than development into vortices. The results are discussed in light of an electrostatic picture of auroral acceleration and the Kelvin‐Helmholtz instability model. We suggest that the latter cannot fully explain the nonlinear phase of the observed curl system event and that curl models should take auroral acceleration processes into account.
Modeling the magnetosphere for northward interplanetary magnetic field: Effects of electrical resistivity
Authors: Raeder Joachim
Published: August 2003

We develop a simple analytic model and use global simulations of Earth's magnetosphere to investigate the effects of electrical resistivity on the topology of the magnetosphere for northward interplanetary magnetic field (IMF). We find that for low resistivity values (≲104 Ω m) the magnetosphere remains open after 6 hours of northward IMF. For larger values (≳2×105 Ω m) the magnetic flux of the tail lobes decreases rapidly on the timescale of ∼1 hour. In this case the tail becomes closed, tadpole‐shaped, steady state, and of finite length. The tail length decreases with increasing resistivity and becomes as short as about 50 RE for a resistivity value of 106 Ω m. Reconnection between IMF and lobe field lines occurs in all cases and is not significantly affected by the resistivity. However, large values of the resistivity annihilate lobe flux and break the frozen‐in condition for closed tail flux tubes, leading to a decoupling of the flux tube motion from plasma convection. These effects make the development of a steady, closed tail of finite length possible. Because resistivity values larger than 102 Ω m are unrealistic for the quiet time tail, we conclude that the magnetosphere is unlikely to ever close and that models which predict the rapid closure and a steady, finite length tail are possibly in error due to numerical resistivity.
Internal acceleration of relativistic electrons by large‐amplitude ULF pulsations
Authors: Liu W. W. , Rostoker G. , Baker D. N.
Published: August 2003

The flux of relativistic electrons in geostationary orbit exhibits a variability closely regulated by the solar wind, but the acceleration mechanism of relativistic electrons remains poorly understood. Recent observational evidence has shown that the intensification of relativistic electrons often takes place in a matter of several hours. The rapidity is difficult to reconcile with traditional diffusion‐based models which often take days to produce appropriate high‐energy electron fluxes and motivates us to search for alternative mechanisms of internal acceleration. Elaborating on the observation in an earlier paper of Rostoker et al. [1998], we propose that global oscillation of magnetosphere in the Pc4–5 range is capable of accelerating electrons under the catalysis of random pitch angle scattering. This view is developed theoretically and computationally in this paper. The most noteworthy result of the investigation is the demonstration that magnetic pumping by ULF waves can lead to the observed high relativistic electron flux in a time as short as a few hours under parameters appropriate for major magnetic storms. Further development and test of this theory are discussed.
CRRES satellite observations associated with low‐latitude Pi2 pulsations
Authors: Takahashi K. , Hughes W. J. , Anderson R. R. , Solovyev S. I.
Published: August 2003

We studied the electric and magnetic field variations and their relation to the ambient plasma density observed from the Combined Release and Radiation Effects Satellite (CRRES) during two Pi2 events observed on the ground at the low‐latitude (L = 1.2) station Kakioka. At the time of the Pi2s, CRRES was moving outward at L ∼ 5, magnetic local time (MLT) of ∼2200, and magnetic latitude of ∼4°. The satellite was in an apparently detached dense plasmaspheric plasma for the first Pi2 but in a low‐density region for the second Pi2. The first Pi2 had a period of 120 s at Kakioka (MLT ∼ 2000), and the satellite observed a nearly identical oscillation in the (approximately) azimuthal component of the electric field and in the radial and compressional components of the magnetic field. At CRRES the compressional magnetic field and the azimuthal electric field oscillated nearly in quadrature in the decaying phase of the pulsation, which suggests a radially trapped fast mode wave. However, comparison of this observation with numerical models of the plasmaspheric cavity mode is difficult because the plasma density did not have a simple plasmapause structure. The second Pi2 observed at Kakioka exhibited a period of 180 s and was similar to the azimuthal electric field oscillation seen at CRRES but quite different from the compressional magnetic perturbation at the satellite. For this event it is not clear whether the electric field oscillation represents a fast mode wave that was directly related to the ground Pi2 or a local shear Alfvén wave that was not directly related to the Pi2. If the first interpretation is the case, the midlatitude Pi2 is not necessarily confined within the plasmasphere by fast mode trapping or cavity resonance. These examples indicate that electric field oscillations measured by equatorial satellites are a sensitive and possibly better indicator of the onset of substorms and that if the plasma density measurements are also available, the electric field data can be useful for identifying the wave mode of Pi2 pulsations.
Shear flow instability in the dipolar magnetosphere
Authors: Voronkov I. , Rankin R. , Samson J. C. , Tikhonchuk V. T.
Published: August 2003

The three‐dimensional, nonlinear evolution of a shear flow (or Kelvin‐Helmholtz (KH)) instability driven by a large‐amplitude shear Alfvén wave (SAW) in the Earth's magnetosphere is studied by using numerical solutions to the complete set of ideal magnetohydrodynamic equations. An initial setup is chosen to simulate a standing SAW associated with field line resonances (FLRs) in a dipolar magnetosphere. It is shown that KH vortices grow most rapidly in the equatorial plane. In this region, the growth rate is reduced by the ratio of the KH and SAW frequencies when compared to the growth rate predicted by a two‐dimensional theory for transient magnetic field lines. For typical parameters of FLRs, this ratio is small. Field‐aligned gradients of the KH mode vorticity and azimuthal phase velocity initiate Alfvén waves, which carry energy toward the ionosphere. This results in partial restructuring of field‐aligned currents with scale size of ∼10 km above the ionosphere. After one period of the SAW, energy in the KH mode returns to the SAW flow. This suggests that vortex formation might be largely periodic in evolution, reconfiguring after each period of the FLR. Finally, we show that this restructuring of field‐aligned currents does not depend on the initial phase of the SAW. For example, the model predicts that a ground‐based observer in the Northern Hemisphere (looking antiparallel to the Earth's magnetic field) will see that the downward current wraps clockwise and the upward current wraps counterclockwise, though the positions of the currents change latitudes for different phases.
Contribution of intermittent temperature peaks to the generation of the solar wind flow
Authors: Grappin R. , Mangeney A. , Schwartz S. J. , Feldman W. C.
Published: August 2003

Observations of frequent, intermittent, density, velocity, and temperature variations, called jets, in the solar corona have led some authors to propose these jets as possible acceleration mechanisms for the fast solar wind seen at large distances. In the search of possible dynamical effects, we look here at the implications of intermittent temperature fluctuations at the coronal level on the subsonic and supersonic solar wind properties, in a spherically symmetric (single fluid) wind with polytropic index close to unity and no magnetic field. Sudden temperature pulses are applied periodically at the coronal level, with no pressure variation, the velocity being free. One finds that (1) the advected perturbations take the form of a mixture of upward propagating shock waves and advected pressure equilibrium structures and (2) the mean temperature increases due to the larger expansion rate of the fluid with peak temperature. As a result, a main part of the wind flow at large distance appears to be generated by intermittent coronal events with peak temperature. We propose thus to reduce the discrepancy between the fast wind speed observed at 1 AU and the observed coronal temperature by taking into account not the average temperature, but the peak coronal temperature, still to be determined.
Coupling between field‐aligned current impulses and Pi1 noise bursts
Authors: Pilipenko V. A. , Shalimov S. L. , Fedorov E. N. , Engebretson M. J. , Hughes W. J.
Published: August 2003

The estimated densities of local field‐aligned currents related to nighttime substorm onset or magnetic impulse events at cusp latitudes may exceed the threshold for the excitation of high‐frequency turbulence in the topside ionosphere. The evolution of an ion‐acoustic instability is shown to lead to quasi‐oscillations around the saturation level. Consequent variations in anomalous conductivity will result in pulsed electron precipitation and noise generation in the Pi1 band. This proposed mechanism gives a natural interpretation to the experimentally observed coupling between localized magnetic disturbances, electron precipitation/acceleration, and bursts of high‐frequency ULF noise. The alternative interpretations based on mechanisms of ion cyclotron instability stimulation and ionospheric Alfven resonator excitation can be applied only under specific plasma conditions.
Mirror‐mode structures at the Galileo‐Io flyby: Observations
Authors: Russell C. T. , Huddleston D. E. , Strangeway R. J. , Blanco‐Cano X. , Kivelson M. G. , Khurana K. K. , Frank L. A. , Paterson W. , Gurnett D. A. , Kurth W. S.
Published: August 2003

As Galileo passed through the wake of Io it encountered a number of magnetic depressions that have been interpreted to be the result of the mirror‐mode instability. Herein we examine the magnetic signatures of these structures and simultaneous measurements of the electron density and temperature. These structures have phase fronts that propagate at large angles to the magnetic field and scale sizes of several ion gyroradii. The inferred density enhancements that accompany the magnetic field depressions range up to 200% of the background density. The spread in normal directions suggests that the depressions are cylindrical and not sheet‐like. A companion paper [Huddleston et al., this issue] discusses the theoretical aspects of these waves.
A possible role of ion demagnetization in substorm generation
Authors: Lyatsky W.
Published: August 2003

A new model for substorm generation based on a stimulated ion diffusion across the magnetic field lines in the magnetotail plasma sheet is studied. The essence of the model is as follows: A partial ion demagnetization in the plasma sheet produces outward ion diffusion, which leads to charge separation and to the formation of field‐aligned currents removing these charges. The magnitude of field‐aligned currents is controlled by the, ionospheric conductivity. The effect of field‐aligned currents on the magnitude of the ionospheric conductivity can lead to the instability, consisting of an increase in these currents, a sharp increase in the ion diffusion, the dipolarization of the magnetotail magnetic field, and the substorm onset. The model includes the following issues: (1) Before the substorm onset the magnetotail plasma sheet approaches the Earth and magnetic field lines are stretched from the Earth. (2) Partially demagnetized (because of their large Larmor radius) ions in the magnetotail plasma sheet move from the Earth. This produces a radially directed electric field which restricts the ion escape and produces a system of field‐aligned currents, with upward current at the boundary of ion demagnetization and downward current poleward of this boundary. (3) The magnitude of field‐aligned currents is controlled by the ionospheric conductivity. For quiet conditions the ionospheric conductivity is small and field‐aligned currents are weak. An increase in the ion diffusion leads to an increase of field‐aligned currents. This stimulates the growth of the ionospheric conductivity, which leads to a new increase in the ion diffusion and to the substorm onset.
Proton temperature anisotropy in the fast solar wind: A 16‐moment bi‐Maxwellian model
Authors: Li Xing
Published: August 2003

A 16‐moment bi‐Maxwellian model to describe the proton temperature anisotropy and heat flux density in the fast solar wind is presented. Although the proton total heat flux density in this model is found to be significantly smaller than the classical Coulomb collision‐dominated Spitzer‐Härm heat flux density, it still plays a significant role in shaping the proton temperature anisotropy. The proton total heat flux density matches the value observed between 0.3 and 1 AU when the proton temperature is also close to the observed value. A large temperature anisotropy in the inner corona, with a proton perpendicular temperature higher than the parallel temperature, as indicated by recent ultraviolet observations, leads to a higher perpendicular heat flux. Since the perpendicular heat flux conducts energy from the perpendicular to the parallel degree of freedom, an unrealistically high parallel temperature develops in interplanetary space if no cooling mechanism for protons in the direction parallel to the magnetic field is introduced. This study suggests that with a bi‐Maxwellian‐based 16‐moment description of the solar wind protons the high proton perpendicular temperature implied by the Ultraviolet Coronagraph Spectrometer on board Solar and Heliospheric Observatory in the inner corona and by in situ measurements from Helios place strong constraints on the proton heating mechanism: not only must the protons be heated in the direction perpendicular to the magnetic field, but they must also be cooled in the parallel direction.
Stability analysis of the plasma sheet using Hall magnetohydrodynamics
Authors: Lee D.‐Y.
Published: August 2003

Linear stability analysis of the plasma sheet configuration is performed using Hall magnetohydrodynamics, which is more appropriate than the strict ideal MHD for the stressed current sheet during the substorm growth phase. By adding the Hall term in Ohm's law we study the impact of the error involved in assuming perfect conductivity on the stability. The ballooning‐like mode with large perpendicular wavenumber is considered, and its basic eigenmode equations are derived. The ballooning instability is currently one of the strong candidates for causing the substorm onset. Numerical computations of the eigenmode equations are carried out for some model equilibria. It is found that the HaIl‐MHD effect is not so significant in determining the ballooning stability, as the result is not much different from that of ideal MHD: (1) The ballooning instability is rather easily triggered in the model where the field lines are not too much stretched but the plasma beta still exceeds some critical value, which depends on the situation; (2) The ballooning mode, however, seems to be stabilized in the very stretched field models and is not destabilized by adding the HaIl‐MHD effect in such models. The result implies that the ballooning stability in the plasma sheet seems to be much more dependent on equilibrium properties such as the field shape than on the physical formulation. It is further suggested that extensive field modeling and subsequent tests for the ballooning mode are a high priority in future in order to establish a firm connection between ballooning instability and the substorm onset.
Formation of magnetospheric plasma population regimes coupled with the dynamo process in the convection system
Authors: Tanaka T.
Published: August 2003

Based on the magnetosphere‐ionosphere (M‐I) coupling scheme, convection as a compound system is considered including the generation of plasma population regimes in the magnetosphere. In these considerations, primary elements that must be set to a self‐consistent configuration are convection flows in the magnetosphere and the ionosphere, field‐aligned current (FAC) systems, ionospheric currents, energy conversion processes, and plasma population regimes. The convection in the M‐I coupling system is inextricably associated with the FACs. In the present results, the region‐1 and region‐2 FACs are driven by ∇P current inside the magnetosphere through plasma internal energy accumulated in the cusp and plasma sheet, respectively. In this process, mechanisms to drive the region‐1 and region‐2 FACs are the same two‐step process; tangential Maxwell stress on the magnetopause pumps up plasma internal energy inside the magnetosphere, then plasma internal energy drives the FACs. This dynamo can be driven by a steady convection flow which is suitable to project down to the low‐β regions. Thus from the magnetohydrodynamic (MHD) force balance controlling the convection, plasma population regimes appear through a requirement to form dynamo in the magnetosphere, showing that plasma population regimes are indispensable to fulfill the self‐consistency in the convection system. In the model that the convection is driven directly by the line‐tying current, the shoulder of the magnetosphere behind the cusp, where the line‐tying current is mixed with the pure Chapman‐Ferraro current connected to dayside, constructs the dynamo (J•E < 0) for the region‐1 FAC. In the present model with negative IMF Bz, on the contrary, the Chapman‐Ferraro current in this area is not directly connected with the region‐1 FAC but connected with the neutral sheet current in the dayside merging region to increase plasma internal energy (J•E > 0) around the cusp. Similarly, tail theta current system acts to increase plasma internal energy in the plasma sheet through the convection. The magnetospheric model derived from this consideration enables a continuous switch over from the confinement state of geomagnetic field in the Chapman‐Ferraro model to the convection of Dungey model for nonzero IMF Bz. In the present convection model, nearly force‐free open field lines are extending from the polar cap into the lobes. Based on the convection model proposed in this paper, a suggestion is given for the substorm models in the next decade that they must develop from a modular model to a globally self‐consistent model.
Scattering of interplanetary radio waves at kilometric wavelengths
Authors: Hess Roger A. , MacDowall Robert J.
Published: August 2003

We report on measurements of the angular size of Jovian radio sources measured by the URAP instrument on the Ulysses spacecraft. The angular size is found to be substantially larger than that expected from the geometric size of the source, which is essentially a point source when viewed from Ulysses. This increase in size is due to scattering of the radio waves caused by fluctuations in the electron density along the path of the radiation. The angular size varies with wavelength as expected for such scattering, and the magnitude of the scattering is in rough agreement with, though less than, results of previous investigations in the slow solar wind. The magnitude of the scattering is found to vary substantially for different radio events, most likely due to changes in the density and/or fluctuation level along the path of the radiation. These measurements are especially suited to determining scattering parameters as the source is point‐like and precisely located. Our results confirm that interplanetary scattering imposes important constraints on low‐frequency radio observations by new spacecraft missions.
Analytical approach for anisotropic permeability through a single rough rock joint under shear deformation
Authors: Kim H. M. , Inoue J.
Published: August 2003

In this study, anisotropic permeability of a single rock joint with rough surfaces and its change due to shear displacement are investigated using the latest analytical approximation for permeability. The permeability approximation is a function of the spatial correlation of the aperture as well as the statistical parameters (mean and standard deviation) of the aperture distribution. The present approach could well explain the significant increase of permeability due to shear displacement and its gradual approach to an asymptotic upper bound of the permeability. The asymptotic permeability with increasing shear displacement is dependent on the standard deviation of surface roughness. The anisotropy in the permeability was also induced by the shear displacement. Far from the expectation, the degree of anisotropy in rough rock joints with random surface model was more or less negligible, compared with the remarkable increase due to the shear dilation. It was also noticable that the shear‐induced anisotropic permeability became more isotropic as the shear displacement exceeded the characteristic correlation length of surface asperities. All these results were compared and verified by the numerical shear flow experiments using the randomly generated rock surfaces. However, it should be noted that the understanding in the study was based on initially isotropic surfaces, and under absence of normal load.
Radical chemistry at a forested continental site: Results from the PROPHET 1997 campaign
Authors: Mihele C. M. , Hastie D. R.
Published: August 2003

Radical chemistry at a forested site in northern Michigan has been examined using measurements made by a radical amplifier system in the summer of 1997. The radicals show a diurnal variation with the maximum concentration being measured several hours after solar noon. Low but observable concentrations were present at night, but these levels are inconsistent with the previously postulated active nighttime chemistry driven by high concentrations of highly reactive hydrocarbons. A box model, constrained by measured concentrations of CO, O3, NO, NO2, isoprene, and peroxyacetylnitrate, was found to simulate both the maximum concentrations and their diurnal variation. Model sensitivity studies indicate that 54% of the radical production comes from sources other than ozone photolysis, and the presence of isoprene has an impact on the radical concentration through impacts on both radical production and loss.
Aerosol distributions and radiative forcing over the Asian Pacific region simulated by Spectral Radiation‐Transport Model for Aerosol Species (SPRINTARS)
Authors: Takemura Toshihiko , Nakajima Teruyuki , Higurashi Akiko , Ohta Sachio , Sugimoto Nobuo
Published: August 2003

A three‐dimensional aerosol transport‐radiation model coupled with a general circulation model, Spectral Radiation‐Transport Model for Aerosol Species (SPRINTARS), simulates atmospheric aerosol distributions and optical properties. The simulated results are compared with aerosol sampling and optical observations from ground, aircraft, and satellite acquired by intensive observation campaigns over east Asia in spring 2001. Temporal variations of the aerosol concentrations, optical thickness, and Ångström exponent are in good agreement between the simulation and observations. The midrange values of the Ångström exponent, even at the Asian dust storm events over the outflow regions, suggest that the contribution of the anthropogenic aerosol, such as carbonaceous and sulfate, to the total optical thickness is of an order comparable to that of the Asian dust. The radiative forcing by the aerosol direct and indirect effects is also calculated. The negative direct radiative forcing is simulated to be over −10 W m−2 at the tropopause in the air mass during the large‐scale dust storm, to which both anthropogenic aerosols and Asian dust contribute almost equivalently. The direct radiative forcing, however, largely depends on the cloud water content and the vertical profiles of aerosol and cloud. The simulation shows that not only sulfate and sea salt aerosols but also black carbon and soil dust aerosols, which absorb solar and thermal radiation, make strong negative radiative forcing by the direct effect at the surface, which may exceed the positive forcing by anthropogenic greenhouse gases over the east Asian region.
Variations and climatology of ClO in the polar lower stratosphere from UARS Microwave Limb Sounder measurements
Authors: Santee M. L. , Manney G. L. , Waters J. W. , Livesey N. J.
Published: August 2003

The Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite (UARS) measured the global distribution of stratospheric ClO over annual cycles for much of the 1990s, albeit with reduced sampling frequency in the latter half of the decade. Here we present an overview of the interannual and interhemispheric variations in the distribution of ClO derived from UARS MLS measurements, with a particular emphasis on enhancements in the winter polar lower stratosphere. Although ClO enhancement within the Arctic vortex is comparable in both magnitude and spatial extent to that in the Antarctic at 465 K (∼19 km), a significant interhemispheric disparity is seen at higher altitudes, where maximum ClO abundances, and their spatial extent, are considerably larger in the Antarctic than in the Arctic. The Arctic exhibits much more interannual variability in the magnitude, timing, and distribution of ClO enhancement than does the Antarctic. Nevertheless, during the mid‐1990s, when the Arctic lower stratosphere was atypically cold, MLS observed the Arctic vortex to be almost completely filled with enhanced ClO in midwinter to late winter. The peak in the ClO profile is at a higher altitude, and the vertical extent of chlorine activation is larger, in the Antarctic than in the Arctic. The Arctic winter of 1995/1996, however, stands out as having a much more Antarctic‐like ClO distribution, with larger maximum ClO abundances, a higher altitude for the profile peak, and greater horizontal and vertical extent of activation than the other winters observed by UARS MLS. In the Southern Hemisphere, ClO becomes enhanced in the sunlit portions of the vortex by at least late May/early June every year, whereas in the Northern Hemisphere, ClO becomes enhanced in mid to late December in some years but not until January in others. Elevated levels of reactive chlorine persist for 4–5 months in the south but only 2–3 months in the north.
Colonization, succession, and extinction of marine floras during a glacial cycle: A case study from the Windmill Islands (east Antarctica) using biomarkers
Authors: Hodgson Dominic A. , McMinn Andrew , Kirkup Helen , Cremer Holger , Gore Damian , Melles Martin , Roberts Donna , Montiel Pedro
Published: August 2003

With the exception of the diatoms, little is known of the extinction, colonization, and succession of marine floras during glacial cycles. Here we study both morphological and biochemical fossils in two sediment cores from the Antarctic to unravel the sequence of events over a single glacial cycle. The cores, from the nearshore continental shelf off the Windmill Islands (66°S, 110°E), east Antarctica, span the period from Marine Isotope Stage 3 or earlier to the present. New high‐performance liquid chromatography and mass spectrometry methods were used to study fossil pigments with additional data from siliceous microfossils, lithological analyses, and radiocarbon dates. Results show two response processes. First, there is the large‐scale impact of the expanding ice sheet in removing the flora from the inner shelf, primarily through the denial of light, destabilization of the substratum, and elimination of habitats. Second, there are a number of glacial climate interactions that have a surprisingly strong influence on recolonization and succession. These include sea ice extent and the proximity of the ice edge, the annual duration of open water, the stabilization of the substratum first by benthic diatoms and later by macrophyte algae, and relative sea level. A period of warmer climate in the mid‐Holocene had a considerable influence on the composition and species diversity of the marine flora. These are the first data on the timing of colonization and succession of marine floras over a glacial cycle based on both morphological and biochemical fossils.
Uncertainty of quantile estimators using the population index flood method
Authors: Sveinsson O. G. B. , Salas J. D. , Boes D. C.
Published: August 2003

The population index flood (PIF) method is an analytical model that has been recently suggested for regional frequency analysis. In this paper, explicit equations based on Fisher's information are derived for estimating the standard error of at‐site quantile estimators for two regional PIF methods utilizing the generalized extreme value distribution with maximum likelihood estimation. These explicit equations are used to calculate the asymptotic gain in using regional frequency analysis as opposed to single site frequency analysis. Simulation experiments for different sized regions and different values of the shape parameter show that the suggested methods for estimating the standard error of at‐site quantile estimators give values close to the actual or true values. In addition, similar simulation experiments are also used to test the accuracy of a newly suggested procedure for estimating the standard errors of at‐site quantile estimators for the Hosking and Walls regional index flood method. The results of the simulations indicate that these estimated standard errors can in some cases give unreliable results. In general, this study shows that the PIF models are a useful addition to existing regional frequency analysis models. Their analytic structure, which is not present in other regional models, has important theoretical and practical implications.
Comment to “Twentieth century secular decrease in the atmospheric potential gradient” by Giles Harrison
Authors: Williams E. R.
Published: August 2003

Harrison [2002] has attributed the decline in surface potential gradient in the United Kingdom (UK) over the 20th century to the decline in cosmic radiation and the global electrical circuit. This paper addresses the supporting evidence for Harrison's explanation, and considers an alternative hypothesis for the observations based on local changes in aerosol concentration. This hypothesis is supported by the concurrent historical record of black carbon emission in the UK.
Arctic Ocean sea ice response to Northern Annular Mode‐like wind forcing
Authors: Krahmann Gerd , Visbeck Martin
Published: August 2003

The response of the Arctic Ocean sea ice system to Northern Annular Mode‐like wind forcing has been investigated using an ocean/sea ice general circulation model coupled to an atmospheric boundary layer model. A series of idealized experiments was performed to investigate the Arctic Ocean's response to idealized winter wind anomalies on interannual to multi‐decadal time scales. The sea ice response of the model consists of a rapid change of ice movements leading to widespread variation in sea ice thickness and concentration. In most areas the response is largely independent of the forcing frequency with only a slight increase towards longer periods. Only the Greenland Sea exhibited a change in sign of sea ice concentration anomalies at about 20 years period which appears to be caused by slow adjustment of the oceanic circulation.
Reply to Comment by E. R. Williams on “Twentieth century secular in the atmospheric gradient”
Authors: Harrison Giles
Published: August 2003

A substantial long‐term increase in solar activity, with an associated decrease in cosmic rays, is generally accepted to have occurred during the twentieth century [Lockwood et al., 1999]. Cosmic rays are known to modulate the global atmospheric electric circuit through changes in the ionospheric potential, and a decrease in the global atmospheric electric circuit is therefore expected in response to the solar activity increase [Harrison, 2002]. Whether this has been observed in the long series [Harrison, 2003] of surface Potential Gradient (PG) observations at Eskdalemuir, Scotland is questioned by Earle Williams because of: (1) the likely overestimate of stratospheric conductivity changes inferred from a cosmic ray proxy, (2) twentieth century air pollution changes in the UK, (3) the absolute magnitude and (4) absence of solar modulation in the PG at Eskdalemuir. These points are addressed in turn.
Modulation of Jovian electrons at 1 AU during solar cycles 22–23
Authors: Kanekal S. G. , Baker D. N. , Blake J. B. , Looper M. D. , Mewaldt R. A. , Lopate C. A.
Published: August 2003

We report here, on the observation of Jovian electrons during the time period 1992 to 2002, using instruments on board SAMPEX and IMP8 at 1 AU. The Jovian electron flux diminished greatly from early 1996 to the end of 1997 and recovered subsequently and was observed till the end of 2001. The decrease in the Jovian flux was seen in three distinct instruments lasting for about two Jovian synodic periods. Such a dramatic and persistent decrease has not been observed before. The observed decrease could be due to changes at the source or variations in interplanetary conditions affecting transport of these particles. The latter may be solar cycle dependent as in the heliospheric modulation of cosmic rays. Long‐term measurements from IMP8 suggest that solar cycle related propagation effects may not be responsible for the observed decrease. We suggest that either a change in the Jovian source strength or a softening of the Jovian electron energy spectrum produced the observed attenuation.
Monte Carlo uncertainty analysis of a regional‐scale transport chemistry model constrained by measurements from the Atmospheric Pollution Over the Paris Area (ESQUIF) campaign
Authors: Beekmann Matthias , Derognat Claude
Published: August 2003

A Bayesian Monte Carlo uncertainty analysis constrained by measurements is applied to emission scenario calculations with the chemistry transport model CHIMERE within the Ile‐de‐France region. The overall uncertainty with respect to the following model input parameters is evaluated: anthropogenic and biogenic emissions, meteorological parameters such as wind speed and mixing layer height, actinic fluxes, quantum yields, and chemical rate coefficients. Airborne and ground‐based ozone and nitrogen species, volatile organic compounds (VOCs), and wind measurements from the Atmospheric Pollution Over the Paris Area (ESQUIF) campaign are used to construct an agreement function that assigns a larger weight to Monte Carlo simulations closer to observations. The observational constraint reduces the uncertainty in the simulations of daily surface ozone maxima (O3max) and the differential sensitivity of ozone formation (DSO) to NOx and VOC emissions reductions for 3 polluted days in the Ile‐de‐France region by a factor of between 1.5 and 3. Constrained uncertainties in O3max (expressed as relative differences between the 50th and the 10th or 90th percentiles) range from 15 to 30%, both for a baseline and for a 50% reduced emission scenario. Uncertainty in the DSO averaged over the plume ranges from 4 to 10 ppb. Including the observational constraint in the Monte Carlo analysis shifts the DSO in different directions for different days. Sensitivity tests with different input parameter distributions and agreement functions indicate the robustness of the above results.
Chemical data assimilation: A case study of solar occultation data from the ATLAS 1 mission of the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS)
Authors: Lary D. J. , Khattatov B. , Mussa H. Y.
Published: August 2003

A key advantage of using data assimilation is the propagation of information from data‐rich regions to data‐poor regions, which is particularly relevant to the use of solar occultation data such as from the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS). For the first time, an in‐depth uncertainty analysis is included in a photochemical model‐data intercomparison including observation, representativeness, and theoretical uncertainty. Chemical data assimilation of solar occultation measurements can be used to reconstruct full diurnal cycles and to evaluate their chemical self‐consistency. This paper considers as an example the measurements made by the ATMOS instrument ATLAS 1 during March 1992 for a vertical profile in flow‐tracking coordinates at an equivalent potential vorticity (PV) latitude of 38°S. ATMOS was chosen because it simultaneously observes several species. This equivalent PV latitude was chosen as it was where ATMOS observed the atmosphere's composition over the largest range of altitudes. A single vertical profile was used so that the detailed diurnal information that the assimilation utilizes could be highlighted. There is generally good self‐consistency between the ATMOS ATLAS 1 observations of O3, NO, NO2, N2O5, HNO3, HO2NO2, HCN, ClONO2, HCl, H2O, CO, CO2, CH4, and N2O and between the observations and photochemical theory.
Standing Alfven waves in the magnetosphere from a localized monochromatic source
Authors: Leonovich A. S. , Mazur V. A.
Published: August 2003

We have constructed a theory for standing Alfven waves driven in the magnetosphere by a monochromatic source localized in the ionosphere. It is shown that a dominant role in such oscillations is played by harmonics with large azimuthal wave numbers with m ≫ 1. We explore the possibility of such oscillations being excited during active experiments on periodic (with the period of Alfven eigenmodes of the magnetosphere) ionospheric modifications. Our study has made it apparent that the measured distance between local maxima of the amplitude of oscillations excited in such an experiment can be used to infer the value of the polarization splitting of the spectrum between poloidal and toroidal eigenmodes of the magnetosphere.
Transport properties of phosphorus-doped ZnO thin films
Authors: Heo Y. W. , Park S. J. , Ip K. , Pearton S. J. , Norton D. P.
Published: August 2003

The doping behavior of phosphorus in ZnO thin films grown by pulsed laser deposition is examined. The transport properties of epitaxial ZnO films doped with 1–5 at. % P were characterized via room temperature Hall measurements. As-deposited films doped with phosphorus are highly conductive and n type. The origin of the shallow donor level appears to be either substitution of P on the Zn site or formation of a donor complex. Annealing these phosphorus-doped films significantly reduces the carrier density, transforming the transport from highly conducting to semi-insulating. These results indicate that the phosphorus-related donor defect is relatively unstable, and suggests the formation of a deep level upon annealing. The latter is consistent with phosphorus substitution on the O site yielding a deep level in the gap.
Current-induced change in the character of the conduction in La0.775Sr0.225MnO3−δ films
Authors: Pogorily A. N. , Tovstolytkin A. I. , Lezhnenko I. V. , Matviyenko A. I. , Kravchik V. P.
Published: August 2003

A study is made of the electrical properties of thin films of La0.775Sr0.225MnO3−δ prepared on single-crystal substrates of SrTiO3 by magnetron sputtering. A substantially nonlinear character of the current–voltage characteristic of the film samples is observed at temperatures below 270 K. It is shown that increasing the current density leads to a transition from a semiconducting to a metallic character of the conduction. An explanation of the results is proposed, based on the hypothesis of phase separation of the samples into conducting and insulating layers, stimulated by the mechanical stresses arising near the film–substrate boundary.
Quantum spin liquid and antiferromagnetism
Authors: Kuz’min E. V.
Published: August 2003

A spin liquid concept for the Heisenberg Hamiltonian (spin s=1/2) with antiferromagnetic exchange interactions between nearest neighbors is developed. The spin liquid is described by the Green’s function method in the framework of a second-order theory. Equations are presented for the self-consistent calculation of the parameters of the system and its thermodynamic properties at all temperatures. A description of the spin system in the sc and bcc lattices is proposed wherein it is treated as a spatially homogeneous spin liquid with a condensate and with a singlet ground state. It is shown that the modulus of the “staggered” magnetization is expressed uniquely in terms of a condensate at a boundary point of the Brillouin zone and is the long-range order parameter. The existence region in temprature of the ordered state of the spin liquid with a condensate (T<T0) is wider than the existence region of the two-sublattice antiferromagnetism (T0T0 the system passes into an ordinary spin liquid state.
Static skin effect in organic metals
Authors: Kirichenko O. V. , Peschansky V. G. , Savel’eva S. N.
Published: August 2003

Galvanomagnetic phenomena in layered organic conductors with a multisheet Fermi surface in the form of a weakly corrugated cylinder and weakly corrugated planes are studied. It is shown that in a strong magnetic field H unrestricted growth of the resistivity of such conductors with increasing H is accompanied by the current lines being forced out to the surface of the specimen. The main dissipation mechanism of electron current is charge scattering by the boundaries of the sample, even in bulk conductors whose thickness is greater than the free path length l of the conduction electrons. For specular reflection at the surface the resistivity increases linearly with the magnetic field.
Magnetoresistance of tetrathiafulvalene-based organic conductors
Authors: Atalla H. R.
Published: August 2003

It is shown that by studying the angular oscillations of the magnetoresistance of layered conductors, one can determine the character of the falloff of the harmonics as a function of the charge carrier energy from the momentum projection on the normal to the layers.
Intrasubband plasmons in a weakly disordered array of quantum wires
Authors: Bludov Y. V.
Published: August 2003

A theoretical investigation is carried out for plasmons in a weakly disordered array of quantum wires, consisting of a finite number of quantum wires arranged at an equal distance from each other. The array of quantum wires is characterized by the fact that the density of electrons of one “defect” quantum wire was different from that of the other quantum wires. It is assumed that the defect quantum wire can be arranged at an arbitrary position in the array. The existence of a local plasmon mode, whose properties differ from those of usual modes, is found. It is pointed out that the local plasmon mode spectrum is slightly sensitive to the position of the defect quantum wire in the array. At the same time the spectrum of usual plasmon modes is shown to be very sensitive to the position of the defect quantum wire.
Interferometric inscription of surface relief gratings on optical fiber using azo polymer film
Authors: Choi S. , Kim K. R. , Oh K. , Chun C. M. , Kim M. J. , Yoo S. J. , Kim D. Y.
Published: August 2003

We report the fabrication and characteristics of surface relief grating on the end surface of silica optical fiber with a diameter of 125 μm. One- and two-dimensional gratings were inscribed on the fiber surface covered with azo polymer thin-film layer using interferometric methods. Diffraction beam patterns of the zeroth and the first order due to surface relief gratings were observed using a 635 nm laser, and the relation between the measured diffraction beam pattern and the grating period was also investigated.
Growth of a-plane InN on r-plane sapphire with a GaN buffer by molecular-beam epitaxy
Authors: Lu Hai , Schaff William J. , Eastman Lester F. , Wu J. , Walukiewicz Wladek , Cimalla Volker , Ambacher Oliver
Published: August 2003

We report heteroepitaxial growth of InN on r-plane sapphire substrates with an AlN nucleation layer and GaN buffer using plasma-assisted molecular-beam epitaxy. The InN film was identified to be nonpolar (112̄0) a-plane which follows the a-plane GaN buffer. Optical absorption and photoluminescence measurements of this material show that InN has a fundamental band gap of about 0.7 eV, which is also seen for growth on c-plane sapphire. The room-temperature Hall mobility of undoped a-plane InN is around 250 cm2/V s with a carrier concentration around 6×1018 cm−3. We also studied the electrical properties of the a-plane InN as a function of film thickness. In contrast to c-plane InN grown on c-plane sapphire, we did not observe apparent improvement of electrical properties of a-plane InN by growing thicker films.
Electronic structure of Li(Co0.7−xAl0.3)MgxO2 studied by electron energy-loss spectroscopy
Authors: Chen G. , Li C. , Xu X. , Li J. , Kolb U.
Published: August 2003

Electronic structure of Li(Co0.7−xAl0.3)MgxO2 (x=0.01, 0.03, and 0.05) is studied via electron energy-loss spectroscopy. Oxygen K edge and Co L2,3 edge were used to investigate the effect of Mg substitution on both the valence state of Co ion and the density of unoccupied states of O ion. A change in the ratio of the white lines of Co ion, L3/L2, is used to identify the change in the valence state in Co ion, which reveals that Mg substitution gives rise to an increase of the average valence of Co ion. This is a mixed valence state of Co3+ and Co4+ in Mg substitution materials. Relative lowering of the integrated intensity of prepeak in oxygen K edge with the Mg concentration connects with a lower covalency of the Co–O bond, which indicates a significant electron feeding back from Co 3d to O 2p. This makes the oxygen ions closer to the feature of closed shell, which helps electron hopping between Co3+ and Co4+ based on the double-exchange process.
Nanoscale observation of room-temperature ferromagnetism on ultrathin (La,Ba)MnO3 films
Authors: Kanki Teruo , Li Run-Wei , Naitoh Yasuhisa , Tanaka Hidekazu , Matsumoto Takuya , Kawai Tomoji
Published: August 2003

We have fabricated La0.8Ba0.2MnO3 ultrathin films with an atomically flat surface and have systematically investigated the magnetism for film thickness dependence. The 20-nm-thick film showed a maximum peak of TC (310 K). It was found that even the 5-nm-thick film showed a TC of 290 K near room temperature, which opens up the possibility of spin devices working at room temperature. Furthermore, we have adopted noncontact magnetic force microscopy to evaluate local magnetization in ultrathin (La,Ba)MnO3 films, and confirmed that several tens of nanocale ferromagnetic domains appear at room temperature.
Recombination-enhanced formation of the metastable boron–oxygen complex in crystalline silicon
Authors: Bothe Karsten , Hezel Rudolf , Schmidt Jan
Published: August 2003

The formation process of the boron- and oxygen-related defect complex in crystalline silicon, responsible for the performance degradation of solar cells made on boron-doped Czochralski silicon (Cz–Si), is investigated on Cz–Si solar cells as a function of the applied voltage in the dark at temperatures ranging from 298 to 373 K. We show that the defect formation is not only a consequence of illumination or the application of a forward bias voltage but also occurs under equilibrium conditions at elevated temperatures in the dark. It can be partly suppressed by applying a reverse voltage. Our findings provide clear experimental evidence that a recombination-enhanced mechanism correlated with the total recombination rate is the driving force of the formation of the metastable defect.