bluuebunny/crossref_metadata_2025 huggingface dataset:
Compressive fluctuations in the solar wind and their polytropic index
Authors: Bavassano B. , Bruno R. , Rosenbauer H.
Published: July 2005

Abstract. Magnetohydrodynamic compressive fluctuations of the interplanetary plasma in the region from 0.3 to 1 AU have been characterized in terms of their polytropic index. Following Chandrasekhar's approach to polytropic fluids, this index has been determined through a fit of the observed variations of density and temperature. At least three different classes of fluctuations have been identified: (1) variations at constant thermal pressure, in low-speed solar wind and without a significant dependence on distance, (2) adiabatic variations, mainly close to 1 AU and without a relevant dependence on wind speed, and (3) variations at nearly constant density, in fast wind close to 0.3 AU. Variations at constant thermal pressure are probably a subset of the ensemble of total-pressure balanced structures, corresponding to cases in which the magnetic field magnitude does not vary appreciably throughout the structure. In this case the pressure equilibrium has to be assured by its thermal component only. The variations may be related to small flow-tubes with approximately the same magnetic-field intensity, convected by the wind in conditions of pressure equilibrium. This feature is mainly observed in low-velocity solar wind, in agreement with the magnetic topology (small open flow-tubes emerging through an ensemble of closed structures) expected for the source region of slow wind. Variations of adiabatic type may be related to magnetosonic waves excited by pressure imbalances between contiguous flow-tubes. Such imbalances are probably built up by interactions between wind flows with different speeds in the spiral geometry induced by the solar rotation. This may account for the fact that they are mainly found at a large distance from the sun. Temperature variations at almost constant density are mostly found in fast flows close to the sun. These are the solar wind regions with the best examples of incompressible behaviour. They are characterized by very stable values for particle density and magnetic intensity, and by fluctuations of Alfvénic type. It is likely that temperature fluctuations in these regions are a remnant of thermal features in the low solar atmosphere. In conclusion, the polytropic index appears to be a useful tool to understand the nature of the compressive turbulence in the interplanetary plasma, as far as the frozen-in magnetic field does not play a crucial role.
The high latitude convection response to an interval of substorm activity
Authors: Yeoman T. K. , Pinnock M.
Published: July 2005

Abstract. On 17 March 1991, five clear substorm onsets/intensifications took place within a three hour interval. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were available, in addition to data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation. This interval of substorm activity has been interpreted as being in support of a near-Earth current disruption model of substorm onset. In the present study the ionospheric convection response, observed some four hours to the west in MLT by the Halley HF radar in Antarctica, is related to the growth, expansion and recovery phases of two of the substorm onsets/expansions observed in the Northern Hemisphere. Bursts of ionospheric flow and motion of the convection reversal boundary (CRB) are observed at Halley in response to the substorm activity and changes in the IMF. The delay between the substorm expansion phase onset and the response in the CRB location is dependent on the local time separation from, and latitude of, the initial substorm onset region. These results are interpreted in terms of a synthesis of the very near-Earth current disruption model and the near-Earth neutral line model of substorm onset.
Diurnal and seasonal occurrence of polar patches
Authors: Rodger A. S. , Graham A. C.
Published: July 2005

Abstract. Analysis of the diurnal and seasonal variation of polar patches, as identified in two years of HF-radar data from Halley, Antarctica during a period near sunspot maximum, shows that there is a broad maximum in occurrence centred about magnetic noon, not local noon. There are minima in occurrence near midsummer and midwinter, with maxima in occurrence between equinox and winter. There are no significant correlations between the occurrence of polar patches and the corresponding hourly averages of the solar wind and IMF parameters, except that patches usually occur when the interplanetary magnetic field has a southward component. The results can be understood in terms of UT and seasonal differences in the plasma concentration being convected from the dayside ionosphere into the polar cap. In summer and winter the electron concentrations in the polar cap are high and low, respectively, but relatively unstructured. About equinox, a tongue of enhanced ionisation is convected into the polar cap; this tongue is then structured by the effects of the interplanetary magnetic field, but these Halley data cannot be used to separate the various competing mechanisms for patch formation. The observed diurnal and seasonal variation in the occurrence of polar patches are largely consistent with predictions of Sojka et al. (1994) when their results are translated into the southern hemisphere. However, the ionospheric effects of flux transfer events are still considered essential in their formation, a feature not yet included in the Sojka et al. model.
Magnetospheric contributions to geomagnetic daily variations
Authors: Olsen N.
Published: July 2005

Abstract. The contribution of magnetospheric current systems to geomagnetic daily variations is analyzed by means of a spherical harmonic analysis (SHA) using elementary models as well as the Tsyganenko model of the magnetosphere. It is discovered that the magnetospheric contribution to some SHA coefficients is much higher than the known average value of about 20%, especially when considering non-local time terms and solstitial conditions.
Penetration to the Earth's surface of standing Alfvén waves excited by external currents in the ionosphere
Authors: Leonovich A. S. , Mazur V. A.
Published: July 2005

Abstract. The problem of boundary conditions for monochromatic Alfvén waves, excited in the magnetosphere by external currents in the ionospheric E-layer, is solved analytically. Waves with large azimuthal wave numbers m»1 are considered. In our calculations, we used a model for the horizontally homogeneous ionosphere with an arbitrary inclination of geomagnetic field lines and a realistic height disribution of Alfvén velocity and conductivity tensor components. A relationship between such Alfvén waves on the upper ionospheric boundary with electromagnetic oscillations on the ground was detected, and the spatial structure of these oscillations determined.
Gravity wave exclusion circles in background flows modulated by the semidiurnal tide
Authors: Zhong L. , Manson A. H. , Sonmor L. J. , Meek C. E.
Published: July 2005

Abstract. In this short paper the exclusion circles and vertical phase locities for gravity waves launched from the ground into a time-varying wind are studied using a ray-tracing technique. It is shown that waves with initial observed phase speeds that should place them within the local temporally varying exclusion circle, are often Doppler shifted outside of the circle. This, and the finite lifetime of some critical levels, allow waves to survive the critical layer and reach higher altitudes. Also, for slower phase-speed waves, the temporally varying wind can shift the observed frequency to negative values, so that the observed phase motions will be opposite (i.e. horizontally reversed and vertically upward), even though the energy still propagates upward. This effect can also cause the phase velocity to move inside the local exclusion circle. Due to the directional filtering of wave sources by the stratospheric wind, the percentage of such reverse-propagating waves will change systematically with local time and height in our simplified but realistic model. These results are related to ground-based systems, optical and radar, which sample the wind field and gravity waves in the middle atmosphere.
Comparison of surface meteorological measurements in TRACT database 4
Authors: Barthelmie R. J. , Jensen N. O.
Published: July 2005

Abstract. The observational systems utilised during the TRACT experimental campaign (September 1992) can roughly be divided into: existing climate stations and towers: background chemical monitoring stations; aerological measurements; instrumented aircraft; and special micrometeorological stations operated only during the experimental period. Database 4, which contains the latter surface measurements, includes station descriptions and data from 21 sites operated by nine different groups during the campaign period. These data will be described briefly. There are a number of advantages in using a relational database for analysis of this data. Without creating an unnecessarily large database which is awkward to view and slow to process, specific measurements can be selected easily since data from each site have been standardized using a common time index. This allows comparison of the same or different variables from one or more sites for investigating data quality or the effects of site location. Data can readily be combined into hourly or daily averages or time series for comparison with other data sets (e.g. model or aircraft data). Spatial analysis is also straightforward, although the clustering of the sites in the centre of the investigation area means that care must be taken. Some preliminary comparisons are made here in order to demonstrate the availability and reliability of the data.
Variations in the altitude of the F2 peak associated with trough-formation processes
Authors: Crickmore R. I. , Jenkins B. , Bailey G. J.
Published: July 2005

Abstract. A novel approach is described which can help to determine, from ground-based data, which of the possible production mechanisms for the mid-latitude F-region ionospheric trough is dominant during a particular event. This approach involves numerically modelling the possible causal mechanisms of the mid-latitude trough to see how each will affect the altitude of the F2-layer electron-concentration peak (hmF2), and then comparing these predictions with the observed variation of hmF2 during trough formation. The modelling work predicts that, if the neutral-wind velocity does not vary, hmF2 will remain almost constant if the trough is formed via stagnation, but will rise if it is formed as a result of high ion velocities or neutral upwelling. Observations made at Halley (76°S, 27°W, L=4.2), Antarctica, show that most frequently the only changes in hmF2 during trough formation are those expected due to variations in the neutral wind, which suggests that stagnation is the most common production mechanism. During the most geomagnetically active night studied, on which Ap varied between 18 and 32, there was a rise in hmF2 that cannot be explained by changes in the neutral wind. On this night the plasma also decayed faster, and the poleward edge of the trough was seen earlier than on other nights. These differences, together with the fact that the ion velocities remained relatively low, suggest the trough was caused by a change in neutral composition, possibly advected into the observing area.
The O(1S) dayglow emission as observed by the WIND imaging interferometer on the UARS
Authors: Singh V. , McDade I. C. , Shepherd G. G. , Solheim B. H. , Ward W. E.
Published: July 2005

Abstract. Volume emission rate profiles of the O(1D-1S) 5577 Å dayglow measured by the WIND imaging interferometer on the Upper Atmosphere Research Satellite are analyzed to examine the O(1S) excitation mechanisms in the sunlit lower thermosphere and upper mesosphere. The observed emission profiles are compared with theoretical profiles calculated using a model which takes into account all of the known daytime sources of O(1S). These include photoelectron impact on atomic oxygen, dissociative recombination of O+2, photodissociation of molecular oxygen, energy transfer from metastable N2(A3Σ+u) and three body recombination of atomic oxygen. Throughout most of the thermosphere the measured and modelled emission rates are in reasonably good agreement, given the limitations of the model, but in the region below 100 km, where the oxygen atom recombination source is likely to dominate, the measured emission rates are considerably larger than those modelled using the MSIS-90 oxygen atom densities. This discrepancy is discussed in terms of possible inadequacies in the MSIS-90 model atmosphere and/or additional sources of O(1S) at low altitude.
A determination of the hydromagnetic waves polarization from their perturbations on the terminator
Authors: Alperovich L. , Fidel B. , Saka O.
Published: July 2005

Abstract. The influence of the homogeneous and inhomogeneous ionosphere on the orientation angle of the horizontal magnetic vectors of the long-time geomagnetic pulsations is under consideration in this study. It was realized that this angle is small in the case of the homogeneous ionosphere for both the Alfvén  and magnetosonic types of oscillations. An increase in the ionospheric electric field was discovered as the ionospheric conductivity changes during the switch from day to night conditions. It is valid only for the initial Alfvén wave. The ionospheric equivalent current systems excited by the initial magnetospheric waves of Alfvén  and magnetosonic types as well as their behavior near the terminator were studied for different seasons. For the Alfvén source, seasonal variations of the orientation angle close to sunrise at the equator depend on the type of source: odd or even modes of Alfvén oscillations excite observable pulsations. It was found that the ionospheric two-vortex equivalent current system of the long-period pulsations arising in high-latitudes in the equatorial region alters not only its direction, but its intensity too. The largest anomaly (~25% of the source value) would be expected near the terminator. A new experimental method was suggested to recognize the type of incident magnetospheric waves by implementing observations either at a single observatory or at a couple of observatories. In the case of a single observatory it is proposed to study the frequency dependence of the orientation angle of their magnetic components close to sunrise. If the initial wave is magnetosonic, this angle must not be changed as a function of the local time within the wide frequency range of pulsations. When pulsations have an orientation angle sensitive to the presence of the terminator, they may be classified as both Alfvén and magnetosonic. For the Alfvén waves no frequency dependence of the orientational angle is peculiar. On the contrary, magnetosonic waves should be determined as oscillations with an orientational angle proportional to the frequency. These oscillations may be revealed at observatories located on the high-resistance cross sections. The example of the spectral-temporal analysis of pulsation at the equatorial observatory in Huancayo was demonstrated to confirm the proposed experimental technique. A weak dependence of the orientation angle anomaly on the frequency near the terminator was found. The latter is evidence for the dominant contribution of the Alfvén waves to low-latitude and equatorial oscillations.
On I(5577 Å) and I (7620 Å) auroral emissions and atomic oxygen densities
Authors: Gattinger R. L. , Llewellyn E. J. , Vallance Jones A.
Published: July 2005

Abstract. A model of auroral electron deposition processes has been developed using Monte Carlo techniques to simulate electron transport and energy loss. The computed differential electron flux and pitch angle were compared with in situ auroral observations to provide a check on the accuracy of the model. As part of the energy loss process, a tally was kept of electronic excitation and ionization of the important atomic and molecular states. The optical emission rates from these excited states were computed and compared with auroral observations of η(3914 Å), η(5577 Å), η(7620 Å) and η(N2VK). In particular, the roles played by energy transfer from N2(A3Σ+u) and by other processes in the excitation of O(1S) and O2(b1Σ+g) were investigated in detail. It is concluded that the N2(A3Σ+u) mechanism is dominant for the production of OI(5577 Å) in the peak emission region of normal aurora, although the production efficiency is much smaller than the measured laboratory value; above 150 km electron impact on atomic oxygen is dominant. Atomic oxygen densities in the range of 0.75±0.25 MSIS-86 [O] were derived from the optical comparisons for auroral latitudes in mid-winter for various levels of solar and magnetic activity.
Spatial features of mid-latitude field-line resonances from simultaneous ground-satellite measurements
Authors: Prikner K.
Published: July 2005

Abstract. Three series of simultaneous pulsation measurements ( f<0.06 Hz) on the Freja satellite and at the Budkov Observatory have been spectrally processed (FFT) in 6-min intervals of Freja's transits near the local Budkov field line. Doppler-shifted, weighted spectral-peak frequencies, determined in both transverse magnetic components in the mean field-aligned coordinate system on Freja, allowed the estimation, by comparison with the stable frequency at Budkov, of fundamental frequencies of the local magnetic-field-line resonance ranged from 13 to 17 mHz in two pulsation events analyzed, with Kp=2+ to 0+. The ratio of total amplitudes of the spectral-pulsation components on the ground and on Freja at an altitude of ~1700 km (values <0.7) characterizes the transmissivity of the ionosphere. In the Pc3 frequency range this correlates well with simulation computations using models of the ionosphere under low solar activity.
Quasi-periodic precipitation with periods between 40 and 60 minutes
Authors: Rinnert K.
Published: July 2005

Abstract. Intervals of periodic enhancements of E-region electron density have been found in EISCAT (European Incoherent SCATter) data. The periods are typically between 40 and 60 min. The phenomenon is observed during relatively quiet times, though after geomagnetic disturbances; it may last up to 6 h. The events can occur at all times of day with a maximum probability in the MLT morning sector. Using the EISCAT database from recent years, the statistical characteristics of these events, and their relation to magnetospheric conditions defined by the Dst index and the d.c. electric field perpendicular to B\\= have been derived. The latitudinal extent is found to be several degrees, but the longitudinal extent is not known. It is concluded that these events are due to the periodically modulated flux of electron precipitation controlled by oscillations in the magnetospheric tail.
Analysis of laminated structure in ozone vertical profiles in central Europe
Authors: Mlch P. , Lasutovicuka J.
Published: July 2005

Abstract. Using statistical techniques, we study the relationship between the long-term changes in the laminar structure of the ozone vertical profile at two central-European stations - Hohenpeissenberg and Lindenberg - and other quantities potentially affecting the state of the lower stratosphere, and total-ozone content. We consider only positive laminae greater than 30 nbar. Laminae contribute non-negligibly to total ozone, and this contribution varies strongly with season. The maximum laminae-occurrence frequency in late winter/early spring is five-times higher than the minimum in early autumn. The main result of the paper is the discovery of a strong negative trend in the frequency of laminae occurrence, about –15% per decade, and even a slightly stronger negative trend in ozone content in laminae. Strong negative trends in laminae occurrence imply negative changes in total ozone as well. No pronounced effect of the quasi-biennial oscillation and solar cycle on laminae was found, whereas the 100-hPa temperature had a clear effect, and there was an indication of substantial effects of volcanic eruptions and El Niño southern oscillation events. Long-term changes in individual time series of meteorological parameters measured over Hohenpeissenberg do not indicate their significant role in the observed trend in laminae occurrence. On the other hand, there is some increase in the occurrence of very zonal circulation patterns, as well as slight decrease in very meridional circulation patterns. Together with other indications this allows us to say that dynamical effects are expected to be a principal contributor. Thus changes in laminae occurrence will probably be able to serve as an indicator/tracer of long-term changes in lower-stratospheric dynamics.
Calculated wind climatology of the South-Saxonian/North-Czech mountain topography including improved resolution of mountains
Authors: Hinneburg D. , Tetzlaff G.
Published: July 2005

Abstract. A mesoscale model has been applied to calculate climatological means of the surface wind. A reliable average requires more than 40 model runs, which are differentiated by the direction and speed of the geostrophic wind under the assumption of neutral stratification. The frequency distributions of the geostrophic wind have been taken from observations of the 850-hPa winds at the radiosonde station in Prague for a 10-year period. The simulation results have been averaged over all sectors and speed classes of the geostrophic wind according to their frequencies. A comparison of the calculated mean wind speeds with observed ones shows deviations of about 0.4 ms–1 outside the mountains. The representation of steep topography and isolated mountains on the basis of a 3-km horizontal resolution of the simulations needs special treatment in order to reduce the gap of up to 4 ms–1 between observed and simulated mean wind speeds over mountains. Therefore, an empiric speed-up formula has been applied to the isolated mountains that otherwise would fall through the 3-km meshes. The corresponding deviations have been reduced to 1.5 ms–1.
Cancellation exponents and multifractal scaling laws in the solar wind magnetohydrodynamic turbulence
Authors: Carbone V. , Bruno R.
Published: July 2005

Abstract. Some signed measures in turbulence are found to be sign-singular, that is their sign reverses continuously on arbitrary finer scales with a reduction of the cancellation between positive and negative contributions. The strength of the singularity is characterized by a scaling exponent κ, the cancellation exponent. In the present study by using some turbulent samples of the velocity field obtained from spacecraft measurements in the interplanetary medium, we show that sign-singularity is present everywhere in low-frequency turbulent samples. The cancellation exponent can be related to the characteristic scaling laws of turbulence. Differences in the values of κ, calculated in both high- and low-speed streams, allow us to outline some physical differences in the samples with different velocities.
The relationship between VHF radar auroral backscatter amplitude and Doppler velocity: a statistical study
Authors: Shand B. A. , Lester M. , Yeoman T. K.
Published: July 2005

Abstract. A statistical investigation of the relationship between VHF radar auroral backscatter intensity and Doppler velocity has been undertaken with data collected from 8 years operation of the Wick site of the Sweden And Britain Radar-auroral Experiment (SABRE). The results indicate three different regimes within the statistical data set; firstly, for Doppler velocities <200 m s–1, the backscatter intensity (measured in decibels) remains relatively constant. Secondly, a linear relationship is observed between the backscatter intensity (in decibels) and Doppler velocity for velocities between 200 m s–1 and 700 m s–1. At velocities greater than 700 m s–1 the backscatter intensity saturates at a maximum value as the Doppler velocity increases. There are three possible geophysical mechanisms for the saturation in the backscatter intensity at high phase speeds: a saturation in the irregularity turbulence level, a maximisation of the scattering volume, and a modification of the local ambient electron density. There is also a difference in the dependence of the backscatter intensity on Doppler velocity for the flow towards and away from the radar. The results for flow towards the radar exhibit a consistent relationship between backscatter intensity and measured velocities throughout the solar cycle. For flow away from the radar, however, the relationship between backscatter intensity and Doppler velocity varies during the solar cycle. The geometry of the SABRE system ensures that flow towards the radar is predominantly associated with the eastward electrojet, and flow away is associated with the westward electrojet. The difference in the backscatter intensity variation as a function of Doppler velocity is attributed to asymmetries between the eastward and westward electrojets and the geophysical parameters controlling the backscatter amplitude.
The formation of electron-temperature hot spots in the main ionospheric trough by the internal processes
Authors: Mingaleva G. I. , Mingalev V. S.
Published: July 2005

Abstract. A mathematical model of the convecting high-latitude ionosphere is described which produces three-dimensional distributions of electron density, positive-ion velocity and electron and ion temperatures at the F-layer altitudes. The results of simulation of the behaviour of the high-latitude ionosphere, in particular, the heat regime of the F-layer, are presented and analysed. From our study, it was found that electron-temperature hot spots in the main ionospheric trough can arise owing to internal ionospheric processes, and not due to effects of any external causes. Three conditions, to be satisfied simultaneously, are necessary for the formation of the considered electron-temperature hot spots: first, low values of electron density; second, solar illumination of the upper F region and darkness of the lower F region; third, low values of neutral-component densities. These conditions are valid in the main ionospheric trough near the terminator on the nightside when the density of the neutral atmosphere is not high. The physical processes which lead to the formation of the electron-temperature hot spots are the heat transfer from the upper into the lower F region, the reduced heat capacity of electron gas and the weakened cooling of electron gas due to inelastic collisions with neutral atoms and molecules. Also investigated is the influence of seasonal and solar-activity variations on the efficiency of the identified mechanism responsible for the formation of the electron temperature peaks in the main ionospheric trough by the internal processes.
On the longitudinal extent of magnetopause reconnection pulses
Authors: Lockwood M. , Davis C. J.
Published: July 2005

Abstract. The open magnetosphere model of cusp ion injection, acceleration and precipitation is used to predict the dispersion characteristics for fully pulsed magnetic reconnection at a low-latitude magnetopause X-line. The resulting steps, as would be seen by a satellite moving meridionally and normal to the ionospheric projection of the X-line, are compared with those seen by satellites moving longitudinally, along the open/closed boundary. It is shown that two observed cases can be explained by similar magnetosheath and reconnection characteristics, and that the major differences between them are well explained by the different satellite paths through the events. Both cases were observed in association with poleward-moving transient events seen by ground-based radar, as also predicted by the theory. The results show that the reconnection is pulsed but strongly imply it cannot also be spatially patchy, in the sense of isolated X-lines which independently are intermittently active. Furthermore they show that the reconnection pulses responsible for the poleward-moving events and the cusp ion steps, must cover at least 3 h of magnetic local time, although propagation of the active reconnection region may mean that it does not extend this far at any one instant of time.
A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982-1995
Authors: Hocke K. , Schlegel K.
Published: July 2005

Abstract. Recent investigations of atmospheric gravity waves (AGW) and travelling ionospheric disturbances (TID) in the Earth\\'s thermosphere and ionosphere are reviewed. In the past decade, the generation of gravity waves at high latitudes and their subsequent propagation to low latitudes have been studied by several global model simulations and coordinated observation campaigns such as the Worldwide Atmospheric Gravity-wave Study (WAGS), the results are presented in the first part of the review. The second part describes the progress towards understanding the AGW/TID characteristics. It points to the AGW/TID relationship which has been recently revealed with the aid of model-data comparisons and by the application of new inversion techniques. We describe the morphology and climatology of gravity waves and their ionospheric manifestations, TIDs, from numerous new observations.
Simulating the global atmospheric response to aircraft water vapour emissions and contrails: a first approach using a GCM
Authors: Ponater M. , Brinkop S. , Sausen R. , Schumann U.
Published: July 2005

Abstract. The effect of contrails and aircraft water vapour emissions on global climate is studied by means of a general circulation model (GCM). In a first approach water vapour emissions and mean contrail coverage within the main flight routes are prescribed according to current observations in a simplified manner. A hierarchic experiment strategy with gradual increase of the forcing is applied to identify the resulting climate signals. The water vapour increase to be expected from air traffic is too small to force a detectable radiative or climatic response. The sensitivity of the model climate to the occurrence of contrails appears to be higher. For mid-latitude summer conditions, the high cloud increase experiments show a consistent temperature response pattern. However, its magnitude is statistically significant only for a mean contrail coverage exceeding present-day amounts. Moreover, the magnitude of the contrail climate signal is highly sensitive to the details of the experimental setup due to several non-linearities of the cloud-radiative interaction. Hence, the prescription of contrails in the GCM has to be as careful as possible for an optimal treatment of the problem. Respective recommendations are given.
On barotropic and baroclinic tides over an arbitrary sloping topography
Authors: Le Tareau J. Y. , Maze R.
Published: July 2005

Abstract. Some theoretical concepts about the frictionless dynamics of propagation of the barotropic tide over two-dimensional continental slopes of arbitrary shape are developed. A numerical procedure which generalizes the exact solution obtained over a rectilinear sloping topography is given. This technique can be applied to compute the harmonic components of the barotropic tide everywhere over sloping bottom contours of any shape. It permits in particular the avoidance of discontinuities at the boundaries of rectilinear-continental-slope profiles. The barotropic tidal results are used afterwards to calculate the barotropic forcing for the generation of internal tides. Numerical experiments are performed to study the interaction between the tide and some typical sloping topographies. A three-layered model is used for this purpose. Results are compared with those previously obtained over a rectilinear continental slope.
Factors affecting the proportion of sterile soldiers in growing aphid colonies
Authors: Aoki Shigeyuki , Imai Masaru
Published: July 2005

The proportion of sterile soldiers in an aphid colony is positively correlated with colony size. Assuming logistic growth of the aphid colony, Aoki and Kurosu (Insect Soc 50:256–261, 2003) presented an inequality that determines, for any colony size, whether a soldier or a reproductive will be added to the colony. To put it in words, if the marginal defensive efficacy of a soldier, multiplied by the number of reproductives, is larger than the mean productivity of reproductives without defense by that soldier, the soldier will be produced; if not, a reproductive will be produced. Based on Aoki and Kurosu's inequality, we carried out simulations to determine whether the proportion of soldiers increased with colony size. Given a constant level of depredation per aphid and a constant number of predators, proportion of soldiers continued to increase with colony size unless a single soldier was very effective or unless carrying capacity was very large. Given a constant number of nongluttonous predators and a decreasing level of depredation per aphid, proportion of soldiers soon began to decrease after a peak. However, given an increasing number of nongluttonous predators to keep a constant level of depredation per aphid, proportion of soldiers again continued to increase. These results confirmed the argument that the proportion of soldiers can increase with colony size under a wide range of realistic assumptions.
MAKING APARTHEID WORK: AFRICAN TRADE UNIONS AND THE 1953 NATIVE LABOUR (SETTLEMENT OF DISPUTES) ACT IN SOUTH AFRICA
Authors: LICHTENSTEIN ALEX
Published: July 2005

Most analyses of apartheid labor policy focus on the regulation of the labor market rather than the industrial workplace. Instead, this article investigates the administration of South Africa's 1953 Native Labour (Settlement of Disputes) Act to examine shop-floor control rather than influx control. The article argues that in response to the threat of African trade unionism, apartheid policymakers in the Department of Labour addressed the problem of low African wages and expanded the use of ‘works committees’. By shifting the debate about capitalism and apartheid away from influx control and migrant labor, and towards industrial legislation and shop-floor conflict, the article places working-class struggle at the center of an analysis of apartheid.
THE ARCHAEOLOGY OF SOUTHERNMOST AFRICA FROM c. 2000 BP TO THE EARLY 1800s: A REVIEW OF RECENT RESEARCH
Authors: MITCHELL PETER , WHITELAW GAVIN
Published: July 2005

Southernmost Africa (here meaning South Africa, Lesotho and Swaziland) provides an excellent opportunity for investigating the relations between farming, herding and hunting-gathering communities over the past 2,000 years, as well as the development of societies committed to food production and their increasing engagement with the wider world through systems of exchange spanning the Atlantic and Indian Oceans. This paper surveys and evaluates the archaeological research relevant to these communities and issues carried out in the region since the early 1990s. Among other themes discussed are the processes responsible for the emergence and transformation of pastoralist societies (principally in the Cape), the ways in which rock art is increasingly being incorporated with other forms of archaeological data to build a more socially informed view of the past, the analytical strength and potential of ethnographically informed understandings of past farming societies and the important contribution that recent research on the development of complex societies in the Shashe-Limpopo Basin can make to comparative studies of state formation.
Some structural and social correlates of single word intrasentential code-switching in Jersey Norman French
Authors: JONES MARI C.
Published: July 2005

This article investigates single word intrasentential code-switching in obsolescent Jersey Norman French. It considers the relationship between code-switched forms and borrowings and, via an analysis of flagging strategies, reveals that speakers seem to differentiate between these two types of contact form. On the basis of the findings, it is suggested that the presence of self-correction as a flagging device may warrant further investigation as a possible criterion for distinguishing code-switches and borrowings. The switching patterns of individual informants are also examined and it is demonstrated that a speaker's attitude towards the dialect seems to have a bearing on the extent to which they code-switch.
Tense and discourse topic in a corpus of Le Monde political articles
Authors: MACNAMARA MATTHEW
Published: July 2005

The article seeks to account for the communicative values of tense choice in the main clauses of the sentences occurring in a corpus of eighty-two Le Monde articles dealing with French national politics. There are 2,706 such tense choices. A set of three discourse topics, the current situation, its antecedents and its implications, is identified as constituting the subject matter of the articles. All the tense choices are correlated to the evocation of one or other of these discourse topics. The relative frequencies of the three discourse topics are correlated to the context of production and reception of the journalistic texts. An appendix tabulates tense choice in each of eighty-two articles of the corpus.
Synoptic features associated with critical water level rises in the Río de la Plata
Authors: Alessandro A. P.
Published: July 2005

This study aims to describe the synoptic features that caused the water level in the Río de la Plata estuary to rise above critical levels between December 1989 and December 1998. Floods in the estuary can seriously affect the land beside the river from Punta Indio (35.22°S,57.17°W) to the Paraná delta, including the lowlands of Buenos Aires City.

Surface pressure patterns associated with floods in the Río de la Plata estuary were obtained by using Quartimax rotated T‐mode Principal Component Analysis (PCA) of 1000 hPa geopotential heights. The PCA patterns and 1000 hPa composite and anomaly fields show two main causes for overflows in the Río de la Plata estuary. First, the presence of a surface anticyclone, located south of Buenos Aires province and over northern Patagonia; and, second, cyclogenesis over northeastern Argentina or over Uruguay. The two synoptic features are often present simultaneously.

Two representative points were selected in the area under study: one over the continent at the Aeroparque meteorological station (34.34°S,58.25°W) and another over the ocean between 36°S,56°W and 36°S,50°W. Predominant 1000 hPa wind directions associated with overflows were SE at the former location and SSW at the latter.

Based on the analysis of the obtained fields, the relationship between the estuary overflow and blocking situations and/or positive pressure anomalies over southern South America and adjacent seas was studied. The zonal circulation index (I), used to detect blocking actions, was found to be useful for identifying synoptic situations related to the estuary swelling. The probability of water level rises in the Río de la Plata with a blocking or I > 0 at 70°W is 0.48, 0.72, 0.78 and 0.73, for summer, autumn, winter and spring, respectively. When I > 0 is observed over the Atlantic at 40°W the probability of flooding is 0.16 for the whole year, but it decreases to 0.028 in autumn, winter and spring.

These results and weather charts from different numerical prediction models show that alerts of possible Río de la Plata estuary overflow can be released five days in advance. Copyright © 2005 Royal Meteorological Society
Comparison of offshore wind park sites using SAR wind measurement techniques
Authors: Schneiderhan Tobias , Lehner Susanne , Schulz‐Stellenfleth Johannes , Horstmann Jochen
Published: July 2005

Wind farming has grown rapidly in Europe over the last decade. All European countries with shallow coastal waters and strong mean coastal wind speeds are planning or already constructing offshore wind farms. Large parts of the North Sea and Baltic Sea are being investigated to see whether they are suitable for offshore wind parks. In this study we show how satellite images taken by space‐borne radar sensors can be used to determine mesoscale wind fields and thus help in the task of planning offshore wind farms. High‐resolution synthetic aperture radar (SAR) images acquired by the European remote sensing satellite ERS‐2 showing single wind turbines are investigated. The methods for retrieving high‐resolution wind fields from SAR images are explained and statistical comparisons of wind speed and wind direction at the two offshore wind park sites in the North Sea, Horns Rev and Butendiek, are given. Copyright © 2005 Royal Meteorological Society
Introduction to the Special Issue on Constraint Handling Rules
Authors: ABDENNADHER SLIM , FRÜHWIRTH THOM , HOLZBAUR CHRISTIAN
Published: July 2005

During the last decade, Constraint Handling Rules (CHR) have become a major specification and implementation language for logical, constraint-based algorithms and intelligent applications (as witnessed for example by several hundred publications available online that mention CHR). Algorithms are often specified using inference rules, rewrite rules, sequents, proof rules, or logical axioms that can be almost directly written in CHR.
Intelligent search strategies based on adaptive Constraint Handling Rules
Authors: WOLF ARMIN
Published: July 2005

The most advanced implementation of adaptive constraint processing with Constraint Handling Rules (CHR) allows the application of intelligent search strategies to solve Constraint Satisfaction Problems (CSP). This presentation compares an improved version of conflict-directed backjumping and two variants of dynamic backtracking with respect to chronological backtracking on some of the AIM instances which are a benchmark set of random 3-SAT problems. A CHR implementation of a Boolean constraint solver combined with these different search strategies in Java is thus being compared with a CHR implementation of the same Boolean constraint solver combined with chronological backtracking in SICStus Prolog. This comparison shows that the addition of “intelligence” to the search process may reduce the number of search steps dramatically. Furthermore, the runtime of their Java implementations is in most cases faster than the implementations of chronological backtracking. More specifically, conflict-directed backjumping is even faster than the SICStus Prolog implementation of chronological backtracking, although our Java implementation of CHR lacks the optimisations made in the SICStus Prolog system.
Wissenschafts-Praxis-Forum
Authors: Schilling Jan
Published: July 2005

Zusammenfassung. Diese Arbeit untersucht die Frage, welche Vorstellungen Führungsgrundsätze von der Führungsaufgabe und der Beziehung zwischen Vorgesetzten und Mitarbeitern vermitteln. In die vorliegende Studie wurden 29 Führungsgrundsätze von Unternehmen verschiedener Branchen einbezogen, die inhaltsanalytisch ausgewertet wurden. Es zeigte sich, dass die Grundsätze nur wenige und wenig ausgearbeitete Hinweise auf Bedingungen und Wirkungen von Führung geben. Entgegen der verbreiteten Auffassung, dass der Erfolg bestimmten Führungsverhaltens von der spezifischen Situation des Vorgesetzten abhängig ist, finden sich derartige Aspekte in den Leitsätzen kaum. Inhaltlich wird Führung vor allem mit planenden, organisierenden und kontrollierenden Tätigkeiten assoziiert, d. h. die Grundsätze betonen vor allem aufgabenorientierte Führungsaspekte. Besonders auffällig ist schließlich, dass in den Führungsgrundsätzen praktisch ausschließlich Hinweise auf positive, also wünschenswerte Führungsverhaltensweisen gemacht werden. Hinweise auf negative, zu unterlassende Handlungen fehlen. Ausgehend von diesen Ergebnissen wird ein Vorschlag für eine verbesserte inhaltliche Gestaltung von Führungsgrundsätzen entwickelt.
Comparing symmetries and conservation laws of nonlinear telegraph equations
Authors: Bluman G. W. , Temuerchaolu
Published: July 2005

A comparison is made between the symmetries and conservation laws admitted by nonlinear telegraph (NLT) systems. Such systems are not variational. Unlike the situation for variational systems where all conservation laws arise from symmetries, there are many NLT systems that admit more conservation laws than symmetries. The results are summarized in a table which includes the numbers of symmetries and conservation laws for each NLT system. It is also indicated when symmetries map conservation laws to other conservation laws.
Interaction of wide-band-gap single crystals with 248-nm excimer laser irradiation. IX. Photoinduced atomic desorption from cleaved NaCl(100) surfaces
Authors: Nwe K. H. , Langford S. C. , Dickinson J. T.
Published: July 2005

Neutral atomic sodium and chlorine emissions from cleaved, single-crystal NaCl(100) surfaces due to pulsed, 248-nm excimer laser irradiation have been characterized by time-resolved, quadrupole mass spectroscopy. At laser fluences below the threshold for optical breakdown, the resulting time-of-flight signals are consistent with particles emitted in thermal equilibrium with a laser-heated surface. Activation energy measurements made by varying the substrate temperature are consistent with F-H pair formation under UV excitation. By varying the laser fluence and estimating the effective surface temperature from the time-of-flight signals, additional activation energy measurements were made. The corresponding rate-limiting step is attributed to a thermally assisted, photoelectronic process involving atomic steps. Atomic force microscope images of surfaces irradiated at low fluences show monolayer islands that are created by the aggregation of material desorbed from steps. At somewhat higher fluences, monolayer pits due to F-center aggregation are also observed.
Simulating the photoelectron spectra of rare-gas clusters
Authors: Amar François G. , Smaby James , Preston Thomas J.
Published: July 2005

Motivated by the recent experiments of the Swedish group [M. Tchaplyguine, R. R. Marinho, M. Gisselbrecht et al., J. Chem. Phys. 120, 345 (2004)], we simulate the photoelectron spectra of pure xenon and argon clusters. The clusters are modeled using molecular dynamics with Hartree–Fock-dispersion type pair potentials while the spectrum is calculated as the sum of final state energy shifts of the atoms ionized within the cluster relative to the isolated gas phase ion. A self-consistent polarization formalism is used. Since signal electrons must travel through the cluster to reach the detector, we have accounted for the attenuation of the signal intensity by integrating an exponentially decaying scattering expression over the geometry of the cluster. Several different approaches to determining the required electron mean free paths (as a function of electron kinetic energy) are considered. Our simulated spectra are compared to the experimental results.
Surface diffusion during shadow-mask-assisted molecular-beam epitaxy of III-V compounds
Authors: Schallenberg T. , Brunner K. , Borzenko T. , Molenkamp L. W. , Karczewski G.
Published: July 2005

We present a comprehensive discussion of molecular-beam epitaxy of III-V compound semiconductors through shadow masks. Based on model calculations and growth experiments, we examine how the surface diffusion and the incorporation of group-III adatoms depend on the growth configuration, group-III and group-V fluxes, and the crystal orientation. According to a macroscopic diffusion model, gradients of the group-V flux drive the unidirectional migration of group-III adatoms. Although this effect is generally observed in the experiments, the different growth profiles obtained for [11¯0]- and [110]-oriented samples reflect the different roles of A-type and B-type steps in the incorporation of group-III adatoms. We also demonstrate that during the heteroepitaxial growth of InAs, the dissociation of the GaAs substrate is locally enhanced by the incidence of the In beam. This effect can be exploited for shadow-mask-assisted etching on selected areas. In addition, we show how the positions and sizes of III-V nanostructures can be controlled with high precision on a planar substrate by the usage of shadow masks with multiple nanoscale apertures.