Location of type I radio continuum and bursts on Yohkoh soft X-ray maps

A solar type I noise storm was observed on 30 July, 1992 with the radio spectrometer Phoenix of ETH Zürich, the Very Large Array (VLA) and the soft X-ray (SXR) telescope on board theYohkoh satellite. The spectrogram was used to identify the type I noise storm. In the VLA images at 333 MHz a fully left circular polarized (100% LCP) continuum source and several highly polarized (70% to 100% LCP) burst sources have been located. The continuum and the bursts are spatially separated by about 100 and apparently lie on different loops as outlined by the SXR. Continuum and bursts are separated in the perpendicular direction to the magnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also superimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematic motion, whereas the the continuum source shows a small drift of 0.2 min^–1 along the X-ray loop in the long-time evolution. The VLA maps at higher frequency (1446 MHz) show no source corresponding to the type I event. The soft X-ray emission measure and temperature were calculated. The type I continuum source is located (in projection) in a region with enhanced SXR emission, a loop having a mean density of n _e = (1.5 ± 0.4) × 10⁹ cm^–3 and a temperature ofT = (2.1 ± 0.1) × 10⁶ K. The centroid positions of the left and right circularly polarized components of the burst sources are separated by 15–50 and seem to be on different loops. These observations contradict the predictions of existing type I theories.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.     

Decimetric type III radio bursts and associated hard X-ray spikes

A detailed comparison is made between hard X-ray spikes and decimetric type III radio bursts for a relatively weak solar flare on 1981 August 6 at 10: 32 UT. The hard X-ray observations were made at energies above 30 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and with a balloon-born coarse-imaging spectrometer from Frascati, Italy. The radio data were obtained in the frequency range from 100 to 1000 MHz with the analog and digital instruments from Zürich, Switzerland. All the data sets have a time resolution of 0.1 s or better. The dynamic radio spectrum shows many fast drift type III radio bursts with both normal and reverse slope, while the X-ray time profile contains many well resolved short spikes with durations of 1 s. Some of the X-ray spikes appear to be associated in time with reverse-slop bursts suggesting either that the electron beams producing the radio bursts contain two or three orders of magnitude more fast electrons than has previously been assumed or that the electron beams can trigger or occur in coincidence with the acceleration of additional electrons. One case is presented in which a normal slope radio burst at 600 MHz occurs in coincidence with the peak of an X-ray spike to within 0.1 s. If the coincidence is not merely accidental and if it is meaningful to compare peak times, then the short delay would indicate that the radio signal was at the harmonic and that the electrons producing the radio burst were accelerated at an altitude of 4 × 10⁹ cm. Such a short delay is inconsistent with models invoking cross-field drifts to produce the electron beams that generate type III bursts but it supports the model incorporating a MASER proposed by Sprangle and Vlahos (1983).     

Type IV dm bursts: Onset and sudden reductions

The effect of collisions of suprathermal electrons with a thermal background plasma is investigated and is shown to cause flattening of a monotonically descending velocity distribution of fast particles. As a result flare-produced energetic electrons that are trapped in a coronal magnetic arch and that are initially distributed in energy according to a power-law, can give rise to an instability of Langmuir waves in the background plasma and the subsequent emission of continuum radiation as observed in type IV dm bursts.To explain the appearance of sudden reductions observed in type IV dm outbursts the effects both of magnetic compressions of the source region and of renewed injections of fast particles on the continuum source are investigated. It is found that the latter process can explain the observed reductions.     

Capture-zone design in an aquifer influenced by cyclic fluctuations in hydraulic gradients

Design of a groundwater pumping and treatment system for a wood-treatment facility adjacent to the tidally influenced Fraser River estuary required the development of methodologies to account for cyclic variations in hydraulic gradients. Design of such systems must consider the effects of these cyclic fluctuations on the capture of dissolved-phase contaminants. When the period of the cyclic fluctuation is much less than the travel time of the dissolved contaminant from the source to the discharge point, the hydraulic-gradient variations resulting from these cycles can be ignored. Capture zones are then designed based on the average hydraulic gradient determined using filter techniques on continuous groundwater-level measurements. When the period of cyclic fluctuation in hydraulic gradient is near to or greater than the contaminant travel time, the resulting hydraulic-gradient variations cannot be ignored. In these instances, procedures are developed to account for these fluctuations in the capture-zone design. These include proper characterization of the groundwater regime, assessment of the average travel time and period of the cyclic fluctuations, and numerical techniques which allow accounting for the cyclic fluctuations in the design of the capture zone. Electronic Publication     

A discontinuous finite element suspended sediment transport model for water quality assessments in river networks

Suspended sediment plays an important role in the distribution and transport of many pollutants (such as radionuclides) in rivers. Pollutants may adsorb on fine suspended particles (e.g. clay) and spread according to the suspended sediment movement. Hence, the simulation of the suspended sediment mechanism is indispensable for realistic transport modelling. This paper presents and tests a simple mathematical model for predicting the suspended sediment transport in river networks. The model is based on the van Rijn suspended load formula and the advection–diffusion equation with a source or sink term that represents the erosion or deposition fluxes. The transport equation is solved numerically with the discontinuous finite element method. The model evaluation was performed in two steps, first by comparing model simulations with the measured suspended sediment concentrations in the Grote Nete–Molse Nete River in Belgium, and second by a model intercomparison with the sediment transport model NST MIKE 11. The simulations reflect the measurements with a Nash‐Sutcliffe model efficiency of 0.6, while the efficiency between the proposed model and the NST MIKE 11 simulations is 0.96. Both evaluations indicate that the proposed sediment transport model, that is sufficiently simple to be practical, is providing realistic results.     

The Barents Sea Ice Sheet — A model of its growth and decay during the last ice maximum

On the basis of geomorphological and sedimentological data, we believe that the entire Barents Sea was covered by grounded ice during the last glacial maximum. ¹⁴C dates on shells embedded in tills suggest marine conditions in the Barents Sea as late as 22 ka BP; and models of the deglaciation history based on uplift data from the northern Norwegian coast suggest that significant parts of the Barents Sea Ice Sheet calved off as early as 15 ka BP. The growth of the ice sheet is related to glacioeustatic fall and the exposure of shallow banks in the central Barents Sea, where ice caps may develop and expand to finally coalesce with the expanding ice masses from Svalbard and Fennoscandia.The outlined model for growth and decay of the Barents Sea Ice Sheet suggests a system which developed and existed under periods of maximum climatic deterioration, and where its growth and decay were strongly related to the fall and rise of sea level.     

Demonstration of sub-meter GPS orbit determination and 1.5 parts in 108 three-dimensional baseline accuracy

Differential tracking of theGPS satellites in high-earth orbit provides a powerful relative positioning capability, even when a relatively small continental U.S. fiducial tracking network is used with less than one-third of the fullGPS constellation. To demonstrate this capability, we have determined baselines of up to2000 km in North America by estimating high-accuracyGPS orbits and ground receiver positions simultaneously. The2000 km baselines agree with very long baseline interferometry(VLBI) solutions at the level of1.5 parts in10 ⁸ and showrms daily repeatability of0.3–2 parts in10 ⁸. The orbits determined for the most thoroughly trackedGPS satellites are accurate to better than1 m. GPS orbit accuracy was assessed from orbit predictions, comparisons with independent data sets, and the accuracy of the continental baselines determined along with the orbits. The bestGPS orbit strategies included data arcs of at least one week, process noise models for tropospheric fluctuations, estimation ofGPS solar pressure coefficients, and combined processing ofGPS carrier phase and pseudorange data. For data arcs of two weeks, constrained process noise models forGPS dynamic parameters significantly improved the solutions.     

Geophysikalische Einflüsse auf die Länge des Sterntages

Zusammenfassung Die Änderung der Sterntaglänge schwankt im Rhythmus des Luftdruckgefälles zwischen 45 und 65° Süd sowohl im mittleren Jahresgang als auch im Ablauf der sechzig Monate der Jahre 1957–1961. Dieser überzufällige Gleichgang in Phase und Amplitude läßt sich so erklären, daß die Schwankungen der Tageslänge direkt durch den Schub oder die Bremsung der Lithosphäre, auf welche die Atmosphäre mit ihren Monsunen oder Passaten wirkt, erzeugt werden. Die den schwankenden Tropenwinden parallel gehenden außertropischen Westwinde würden voll die schiebende oder bremsende Wirkung der Tropenwinde kompensieren, wenn sie auch direkt die Lithosphäre erfaßten. Da nun aber im Gebiet der braven Westwinde die Hydrosphäre den gesamten Drehimpuls übernimmt und ihn wohl erst mit großer Verzögerung an die Lithosphäre weiterreicht, tritt die Änderung der Tageslänge auf, die sich im wesentlichen harmonisch aus einer halbjährlichen und einer jährlichen Welle zusammensetzt.

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Geophysical effects on the length of the sideral day

Summary The variations in the length of the day are found to be equal in phase to the oscillation of the atmospheric pressure gradient occurring between 45 and 65 degrees south. This rhythm manifests itself in the annual mean as well as in the course of the 60 months of the years 1957 to 1961. The rhythm that seems to be overaccidental may be explained with regard to phase and amplitude in the following way:The variations in the length of the day are produced by the pushing or braking of the lithosphere on which the atmosphere is acting by its monsoons or trade winds. The outertropical westerlies that are blowing parallel to the tropical wind would be able to compensate the pushing and braking effects if they, too, were directly acting on the lithosphere. As, however, in the region of the westerlies the hydrosphere assumes all angular momentum and apparently passes it on to the lithosphere after considerable delay, the variations in the length of the day are caused which essentially consist of the second and first harmonics.

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Effets géophysiques sur la longueur du jour sidéral

Résumé Les variations de la longueur du jour sidéral suivent le rythme du gradient de pression atmosphérique rencontré entre le 45^e et 65^e degré de latitude Sud. Elles se manifestent dans la moyenne annuelle aussi bien que dans la période des soixants mois des années de 1957 à 1961. Cette homogénéité super-aléatoire du rythme qui se montre également dans la phase et dans l'amplitude pourrait être expliquée par le fait que les variations de la longueur du jour sidéral sont directement produites par la poussée et le freinage de la lithosphère sur lequel agit l'atmosphère par ses moussons et ses vents alizés.Les vents extra-tropicaux d'ouest qui soufflent parallèlement aux vents tropicaux seraient à même de compenser les effets de la poussée et du freinage des vents tropicaux pourvu qu'ils agissent de même immédiatement sur la lithosphère. Comme, cependant, dans la région des braves vents d'ouest l'hydrosphère attire tout le moment angulaire et le passe, probablement après un long délai, au lithosphère, il se produit les variations de longueur du jour sidéral, qui se composent essentiellement d'une oscillation harmonique semestrielle et annuelle.

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Nach einem Vortrag Über Erddrehung und atmosphärische Globalzirkulation vor dem Geophysikalischen Kolloquium der Universität Hamburg am 8. Juni 1961, erweitert um die neuen Daten der Tageslänge und des Luftdruckgefälles zwischen 45° und 65° S.