Formation Of Trough Research Articles

Ionospheric disturbances observed by DMSP at middle to low latitudes during the magnetic storm of June 4–6, 1991

This paper extends a recent study of electric field penetration into the inner magnetosphere observed by the Combined Release and Radiation Effects (CRRES) satellite and the Defense Meteorological Satellite Program (DMSP) satellite F8 during the magnetic storm of June 4–6, 1991, to consider its ionospheric consequences. Effects include the development of > 1 km/s subauroral ion drift (SAID) structures, the formation of midlatitude density troughs, and the vertical transport of equatorial plasma, bubbles. Nearly simultaneous auroral electron and plasma drift measurements were acquired by three DMSP satellites with F8 and F9 in one hemisphere and FlO in the other. Moderate to strong SAID structures were consistently detected for ∼10 hours during the early main phase of the storm. Weak SAIDs were encountered during ∼8 hours of the early recovery phase. DMSP data show that SAIDs with similar characteristics developed at magnetically conjugate locations and extended for at least 3 hours in local time. Simultaneous measurements show that the SAIDs spanned temporally grooving but latitudinally narrow plasma density troughs. These observations suggest that the magnetospheric sources of SAIDs act more like voltage than current generators. Energetic electron fluxes, electric fields, and plasma waves measured by CRRES indicate that during this storm the ring current shielding charges and SAID sources were located in regions of high plasma density characteristic of the plasmasphere. The sequence in which DMSP detected equatorial plasma density irregularities is consistent with model predictions that stormtime electrodynamics at low latitudes operate on distinctive fast and slow timescales [Fejer and Schcrliess, 1997].

C 3/C 4 vegetation evolution over the last 7.0 Myr in the Chinese Loess Plateau: evidence from pedogenic carbonate δ 13C

The stable carbon and oxygen isotopic compositions of soil carbonate were measured on an eolian loess and red clay sequence at Lingtai, the Chinese Loess Plateau. This sequence is composed of 130 m of Tertiary red clay deposits with a basal age of 7.05 Ma overlain by 175 m of Pleistocene loess. In the field we identified ca. 110 carbonate nodule horizons in the red clay and 27 nodule horizons in the loess. These carbonate nodule horizons are formed by leaching and re-precipitation of carbonate from the eolian material. The δ 13C record of soil carbonate indicates a major expansion of C 4 plants at ca. 4.0 Myr in the Loess Plateau. This event is comparable in timing with the expansion of C 4 plants in northern North America ( Cerling et al., 1997. Nature 389, 153–158) but is ca. 3 million years later than the C 4 biomass expansion in Pakistan ( Quade et al., 1989. Nature 342, 163–166). The pedogenic characteristics of the soils and the δ 18O record in the red clay suggest that the C 4 plant expansion in the Loess Plateau was not driven by local climatic changes, which may support Cerling et al.'s (1997) assertion that the decline of atmospheric CO 2 levels in the Neogene is responsible for this global vegetation change. Our record also implies that the Tibetan Plateau could have been uplifted to a critical height in the late Miocene, thus resulting in the formation of the atmospheric Great East-Asia Trough.

Submarine slide scars and mass movements in Karmsundet and Skudenesfjorden, southwestern Norway: morphology and evolution

Shallow seismic sections, multibeam bathymetric images and geotechnical investigations of the seafloor in Karmsundet and Skudenesfjorden, SW Norway, have revealed the occurrence of large slide scars and associated mass-movement deposits. The slide escarpments are up to 30–40 m high and 8 km long, with up to 20×10 6 m 3 of sediment released during a single event of retrogressive sliding. The slide scars show a range of associated seafloor topography, reflecting various modes of sediment displacement. The variation in the escarpment morphology and sediment deformation style can be attributed to the varied intensity of liquefaction. Sliding involved mud deposits of Allerød–Younger Dryas to early Holocene age, but partly also deposits older than ca. 12,000 14 C years bp . The sediment failures were probably triggered by seismic reactivation of a local fault by postglacial regional isostatic rebound. Prior to failure, the seafloor deposits were undercompacted and metastable due to high pore pressure, the presence of shallow gas and the relatively steep local slope created by the formation of a major scour trough by sea currents. Minor gravitational sliding may still occur along some of the escarpments, although engineering slope-stability analysis indicates that the deposits can be regarded as stable in the present-day conditions of static load and the anticipated weak sporadic earthquakes with an occurrence likelihood of 10 −4 /year and a peak acceleration of 0.25 g.

Determining parameters of large-scale traveling ionospheric disturbances of auroral origin using GPS-arrays

The intention in this paper is to investigate the form and dynamics of large-scale traveling ionospheric disturbances (LS TIDs) of auroral origin. We have devised a technique for determining LS TID parameters using GPS-arrays whose elements can be selected from a large set of GPS stations forming part of the International GPS Service network. The method was used to determine LS TID parameters during a strong magnetic storm of September 25, 1998. The North-American sector where many GPS stations are available, and also the time interval 00:00–06:00 UT characterized by a maximum value of the derivative Dst were used in the analysis. The study revealed that this period of time was concurrent with the formation of the main ionospheric trough with a conspicuous southward wall in the range of geographic latitudes 50–60° and the front width of no less than 7500 km. The auroral disturbance-induced large-scale solitary wave with a duration of about 1 h and the front width of at least 3700 km propagated in the equatorward direction to a distance of no less than 2000–3000 km with the mean velocity of about 300 m/s. The wave front behaved as if it ‘curled’ to the west in longitude where the local time was around afternoon. Going toward the local nighttime, the propagation direction progressively approximated an equatorward direction.

Physical explanation of the formation and evolution of inversion zones and marginal troughs

Inversion zones are elongate structures, some tens of kilometers wide and up to hundreds of kilometers long, that have deformed in response to compression and produced topography. Inversion zones in the Alpine foreland are mainly associated with Mesozoic grabens and troughs, and although very important in the geologic picture, the conditions of their formation and evolution and their regional geologic significance are not entirely understood. The internal structure of inversion zones is variable and depends on details in the pre-inversion setting, the inversion-inducing stress field, and the sedimentary fill. However, on a larger scale, most inversion zones share certain principal observational features, which sample the physical structure and the rheologic properties of the lithosphere and thereby provide an opportunity to test hypotheses of lithospheric rheology and dynamics. The quantitative model presented in this paper explains how inversion zones and the associated marginal troughs are related to lithospheric zones of differential shortening and regional isostatic compensation of the induced topography.

Europa: Morphological characteristics of ridges and triple bands from Galileo data (E4 and E6) and assessment of a linear diapirism model

Galileo solid‐state imaging (SSI) images of Europa provide high‐resolution data on the morphological characteristics of ridges and permit the development of nomenclatural schemes for their description and classification. Key observations are that ridges (1) are remarkably consistent in their along‐strike linearity, width, and height, (2) form long linear features in which preexisting structures can sometimes be traced up the outer slopes of the ridges and in other cases appear to be buried, (3) contain narrow apical zones of small‐scale, ridge‐parallel faulting, (4) are sometimes flanked by narrow troughs and ridge‐parallel fractures, and (5) often display associated color variations. On the basis of the characteristics and associated features of ridges, we find that a process in which initial fracturing (most plausibly related to tidal deformation) of a brittle layer overlying a buoyant ductile substrate leading to linear diapiric upwelling provides a consistent explanation for the observed features. In this process the upwelling linear diapir causes flexure (bending and faulting) of the region marginal to the fracture, the deformation and uplift of adjacent plains material and its preexisting structures to form the apical part of the ridge, the exposure of the inner walls of the crack, and the mass wasting of the inner and outer walls of the ridge to modify, but often not completely destroy, the preexisting structure of the adjacent plains. Specifically, this mechanism can account for many characteristics of the ridges, including their linearity, their consistent and regular morphology over their great lateral extent, their positive topography, the presence of preexisting structure on the outer ridges (caused by upbowing of background ridged plains), the formation of marginal troughs (as diapiric rim synclines), the detailed nature of their outer and inner slopes (caused largely by faulting and mass‐wasting processes), and their sequential formation with multiple orientations (related to tidal deformation processes). Linear diapirism also provides a possible explanation for color and albedo characteristics, related to thermal effects of the upwelling warm ice (e.g., inducing volatile migration and grain‐size variations). As the vast majority of deformation is vertical in this scenario, this mechanism minimizes the necessity for complementary compressional deformation required by some other models.

Effects of Critical Levels on Two-Dimensional Back-Sheared Flow over an Isolated Mountain Ridge on anfPlane

It is well known that there exist three singular points, U 2 c 56 f/k and U 5 c, where the corresponding levels will be called inertia critical levels (ICLs) and the classic critical level (CCL), in the equation governing a two-dimensional, rotating, continuously stratified, hydrostatic, back-sheared Boussinesq flow. Here U and c are basic wind and phase speed, respectively; f is the Coriolis force; and k is the wavenumber. The effects of these critical levels on flows over an isolated mountain ridge are investigated both analytically and numerically, based on a broad range of Rossby numbers (Ro) and Richardson numbers (Ri). Each wave mode generated from the isolated mountain with a continuous spectrum has its own ICL. To indicate the net effects of all ICLs, the authors define the effective ICL as the height above which the amplitude of the inertia-gravity wave mode is very small. The findings for linear flows are summarized as follows. Regime I is inertia-gravity waves. The flow behaves like unsheared inertia-gravity waves and the effective lower ICL plays a similar role as the CCL does in a nonrotating flow. Regime II is combined inertia-gravity waves and baroclinic lee waves. These waves behave like those in regime I below the lower effective ICL, and like baroclinic lee waves near the CCL. In this regime, the horizontal warm advection by the baroclinic lee wave plays an important role in the formation of the lee pressure trough. On the other hand, near the downslope of the mountain, both the warm advection by the inertia gravity and the adiabatic warming also contribute significantly to the lee trough. Therefore, Smith’s quasigeostrophic theory of lee cyclogenesis is extended to a nongeostrophic regime. Regime III is combined evanescent and baroclinic lee waves. These waves still behave like baroclinic lee waves near the CCL, but they are trapped near the surface. Regime IV is transient waves. Nongeostrophic baroclinic instability exists, as evidenced by the positive domain-averaged north‐south heat flux. There exists no steady state. At earlier times, the flow behaves like trapped baroclinic lee waves. For a relatively large Ri (e.g., Ri . 25), the flow falls into regime I when Ro is relatively large (e.g., Ro $ 2). It then shifts to regime II, and finally to regime III as Ro decreases. For a relatively small Ri (e.g., Ri , 25), the flow shifts from regime I to II, and then finally to regime IV when both Ro and Ri decrease.

The Role of Tropical Cyclones in the Formation of Tropical Upper-Tropospheric Troughs

Tropical upper-tropospheric troughs (TUTTs), also known as midoceanic troughs, are elongated troughs that appear in summer monthly averaged maps of the upper-tropospheric flow over the oceans. The transient part of these climatological features is composed of TUTT cells and their origin is the subject of this study. TUTT cells often occur to the east of tropical cyclones. A nonlinear shallow water model on the sphere was used in a simplified study of the interactions between tropical cyclones and the circumpolar vortex. Based on the results of these simulations and keeping in mind their limitations, it is proposed that dispersion of short Rossby wave energy is a possible mechanism to explain the formation of TUTT cells to the east of tropical cyclones. The model simulations suggest that two types of TUTT cells may form to the east of tropical cyclones. When embedded in cyclonic or weak anticyclonic shear, the trough to the east of the tropical cyclone may broaden, resulting in the formation of an intense TUTT cell that has a strong signature in the wind and mass fields. In the presence of stronger anticyclonic shear, the trough to the east of the tropical cyclone may become a thin and elongated TUTT cell that has a comparatively negligible signature in the mass and flow fields. Moreover, the model simulations indicate that the mode of evolution of TUTT cells that form to the east of a tropical cyclone is strongly dependent on the intensity and relative location of midlatitude waves. Wave–mean flow interaction calculations indicated that tropical cyclones produced a westerly acceleration of the mean zonal flow in the latitudinal band through which they move and an easterly acceleration elsewhere. These calculations also indicated that broadening TUTT cells may cause an easterly acceleration of the zonal mean flow.

Formation of large summit troughs along the East Pacific Rise as collapse calderas: An evolutionary model

Summit troughs wider than 500 m and 30–110 m deep are present along 15–20% of the fast spreading East Pacific Rise (EPR). They occur only along ridge segments with large cross‐sectional areas, indicative of a time‐averaged robust magma supply. Where available, seismic data confirm that these troughs are underlain by an axial magma chamber (AMC) 1.2–1.6 km below the seafloor. Furthermore, detailed investigation of the large summit troughs which notch the EPR between 17°56′ and 18°35′S indicates that the vertical relief of the troughs tends to be maximum where the AMC is shallowest. Both of these observations are inconsistent with the predictions from a model in which large summit troughs form by rifting of the brittle upper crust during phases of amagmatic extension. Rather, we propose that they represent elongated collapsed calderas that form when the melt supply to formerly inflated AMCs wanes or nearly ceases. Because seismic studies constrain the melt lens along the EPR to be only 30–80 m thick, the proposed existence of collapsed calderas 40–110 m deep implies that the entire magma reservoir comprising the melt lens and the underlying crystal mush zone deforms and compacts during periods of waning magma supply. In particular, we suggest that a voluminous crystal mush zone will stretch in response to steady state seafloor spreading when the magma supply temporarily decreases. The resulting caldera will further widen with each subsequent dike intrusion. When an abundant melt supply finally resumes, the associated tumescence of the neovolcanic zone and profuse lava flows will combine to smooth out the caldera.

The treatment of inveterate laryngo-tracheal stenosis

With completion of our society, the original factors of laryngo-tracheal stenosis such as trauma and respiratory stenosis due to surgery or anesthesiology have been remarkably increasing, however, it is not much to say that present condition of its treatment is far from satisfaction. When we consider the methods of treatment for laryngeal stenosis in accordance with the site of lesion, we can manage the anterior type of stenosis with endoscopic surgery using stent, as well as, the posterior type with laryngof issure using graft. On the other hand, considering the methods for tracheal stenosis in accordance with the degree of impairment of tracheal cartrige, the following combination of management can be possible ; endoscopic surgery with stent (or graft) for remained frame, trough formation with stent (or graft) for partially remained frame, and end-to-end anastomosis for unremained frame. Toward future development of endoscopic surgery, the concurrent development of new material and new form of stent is expected.

Nickel ore troughs in Archaean volcanic rocks, Kambalda, Western Australia: indicators of early extension

Abstract The Kambalda nickel sulphide deposits are located in the 2700 Ma Eastern Goldfields Greenstone Belt, Yilgarn Craton, Western Australia. The main lithologies are basalts and komatiites. Nickel sulphide ore occurs within the komatiite at the contact with the underlying basalt. This contact is structurally complex, the result of several phases of compressive deformation that post-date ore formation. Ore is confined to trough structures at the basalt-komatiite contact, these may be tens to hundreds of metres wide, several kilometres in length and tens of metres deep. Troughs are subparallel to each other and to the regional structural trend, ore bodies have a characteristic ribbon-like geometry. Various models have been proposed to explain trough formation but none account for the variety of features seen in the area. A new model is presented explaining the Kambalda structures by analogy with present-day graben structures associated with Icelandic-style fissure swarms. It is proposed that the initial geometries of the Kambalda trough structures, prior to compressive deformation, were similar to the present-day structures seen in Iceland. Komatiitic lavas subsequently exploit this graben topography, resulting in distinctive orebody geometries. Thus, it is suggested that the Kambalda troughs reflect an early phase of extension in the region.

One type of low-latitude ionization trough in the Southern hemisphere

It is deduced from the Intercosmos-19 satellite topside sounding data that at solar maximum at low latitudes of the Southern hemisphere at night time there can occur a peculiar type of ionization trough which seems not to be described in the literature yet. This trough occurs usually in the interval from the second half of November to the beginning of February in the region of the Southern crest of the equatorial anomaly. Its occurrence probability is quite high and at postmidnight hours at longitudes 75° to 300° is about 50%. In other seasons as well as at the anomaly Northern crest this trough was not practically observed. It is suggested that the cause of this trough formation is the thermospheric wind from the summer (Southern) hemisphere to the winter one which at latitudes under consideration lifts the ionization along the geomagnetic field lines and can thereby reduce its density at the hmF2 level. According to the most widely used HWM90 model of neutral winds, at night the wind from the Southern hemisphere to the Northern one in December is somewhat stronger than from the Northern hemisphere to the Southern one in June. But this difference is too little to explain the absence of a trough similar to the one described herein at the anomaly Northern crest in June solstice. This suggests that the asymmetry of the hemispheres is really stronger than represented in the HWM90 model.

The Palaeozoic evolution in the Alps: from Gondwana to Pangea

More than 50% of the Alps expose fragments of Palaeozoic basement which were assembled during the Alpine orogeny. Although the tectonic and metamorphic history of the basement units can be compared to that of the Variscan crust in the Alpine foreland, most of the basement pieces of the Alps do not represent the direct southern continuation of Variscan structural elements evident in the Massif Central, the Vosges–Black Forest or the Bohemian massif. The basement units of the Alps all originated at the Gondwana margin. They were derived from a Precambrian volcanic arc suture fringing the northern margin of Gondwana, from which they were rifted during the Cambrian–Ordovician and Silurian. A short-lived Ordovician orogenic event interrupted the general rifting tendency at the Gondwana active margin. After the Ordovician, the different blocks drifted from the Gondwana margin to their Pangea position, colliding either parallel to Armorica with Laurussia or with originally peri-Gondwanan blocks assembled presently in Armorica. From the Devonian onwards, many basement subunits underwent the complex evolution of apparently oblique collision and nappe stacking. Docking started in the External massifs, the Penninic and Lower and middle Austroalpine units in approximately Devonian/early Carboniferous times, followed by the Upper Austroalpine and the South Alpine domains, in the Visean and the Namurian times, respectively. Wrenching is probably the best mechanism to explain all syn and post-collisional phenomena since the Visean followed by post-orogenic collapse and extension. It explains the occurrence of strike-slip faults at different crustal levels, the formation of sedimentary troughs as well as the extrusion and intrusion of crustal and mantle-derived magmas, and allows for contemporaneous rapid uplift of lower crustal levels and their erosion. From the Stephanian onwards, all regions were deeply eroded by large river systems.

Using Tropopause Maps to Diagnose Midlatitude Weather Systems

The use of potential vorticity (PV) allows the efficient description of the dynamics of nearly balanced atmospheric flow phenomena, but the distribution of PV must be simply represented for ease in interpretation. Representations of PV on isentropic or isobaric surfaces can be cumbersome, as analyses of several surfaces spanning the troposphere must be constructed to fully apprehend the complete PV distribution. Following a brief review of the relationship between PV and nearly balanced flows, it is demonstrated that the tropospheric PV has a simple distribution, and as a consequence, an analysis of potential temperature along the dynamic tropopause (here defined as a surface of constant PV) allows for a simple representation of the upper-tropospheric and lower-stratospheric PV. The construction and interpretation of these tropopause maps, which may be termed “isertelic” analyses of potential temperature, are described. In addition, techniques to construct dynamical representations of the lower-tropospheric PV and near-surface potential temperature, which complement these isertelic analyses, are also suggested. Case studies are presented to illustrate the utility of these techniques in diagnosing phenomena such as cyclogenesis, tropopause folds, the formation of an upper trough, and the effects of latent heat release on the upper and lower troposphere.

Le volcanisme fissural néoprotérozoïque des séries du Dja inférieur, de Yokadouma (Cameroun) et de Nola (RCA) — Signification géotectonique

The basic intrusions in the lower Dja, Yokadouma and Nola Neoproterozoic Séries, around 1 Ga, display a continental tholeiitic composition. The magmas are generated from a spinel lherzolite source sharing lithospheric and asthenospheric components, suggesting a lithospheric thinning. This magmatism has to be related to an extensional phase which favored the pre-Pan-African trough formation in the northern part of the Congo Craton.

Epithelial Cell Wedging and Neural Trough Formation Are Induced Planarly inXenopus,without Persistent Vertical Interactions with Mesoderm

In this study we investigate the induction of the cell behaviors underlying neurulation in the frog,Xenopus laevis.Although planar signals from the organizer can induce convergent extension movements of the posterior neural tissue in explants, the remaining morphogenic processes of neurulation do not appear to occur in absence of vertical interactions with the organizer (R. Kelleret al.,1992,Dev. Dyn.193, 218–234). These processes include: (1) cell elongation perpendicular to the plane of the epithelium, forming the neural plate; (2) cell wedging, which rolls the neural plate into a trough; (3) intercalation of two layers of neural plate cells to form one layer; and (4) fusion of the neural folds. To allow planar signaling between all the inducing tissues of the involuting marginal zone and the responding prospective ectoderm, we have designed a “giant sandwich” explant. In these explants, cell elongation and wedging are induced in the superficial neural layer by planar signals without persistent vertical interactions with underlying, involuted mesoderm. A neural trough forms, and neural folds form and approach one another. However, the neural folds do not fuse with one another, and the deep cells of these explants do not undergo their normal behaviors of elongation, wedging, and intercalation between the superficial neural cells, even when planar signals are supplemented with vertical signaling until the late midgastrula (stage 11.5). Vertical interactions with mesoderm during and beyond the late gastrula stage were required for expression of these deep cell behaviors and for neural fold fusion. These explants offer a way to regulate deep and superficial cell behaviors and thus make possible the analysis of the relative roles of these behaviors in closing the neural tube.

Characterization of the Induced Plastic Zone in a Single Crystal TiN(001) Film by Nanoindentation and Transmission Electron Microscopy

The slip system of TiN at room temperature has been determined to be {110} 〈110〉 by Burgers vector analysis using transmission electron microscopy and slip trace analysis of indents made on a TiN(001) film deposited on a MgO(001) substrate. Both small indents (0.4 mN maximum load) and large indents (40 mN maximum load) were used to study the dislocation structure in TiN. The nucleation of dislocations was investigated using small indents. Further development of the plastic zone was studied using large indents and microhardness indents (1.6 N). The critical resolved shear stress evaluated at the load when pop-in occurs was estimated to be 3.7 GPa, assuming a Hertzian elastic contact. Indents made with a 0.4 mN maximum load show a complex dislocation pattern with loops and straight segments that belong to the same slip system. Dislocations of mixed screw and edge type are dominant. The cascade of dislocations generated during pop-in is likely to nucleate from loops. For larger indents, the plastic zone extends more than three times the diameter of the imprint. The straight dislocations outside the large imprint are arranged in arrays along the 〈100〉 and 〈110〉 directions. A scanning force microscopy study of the surface outside a microhardness indent revealed a raised surface along 〈110〉 and formation of troughs along 〈100〉.

Plate convergence, crustal delamination, extrusion tectonics and minimization of shortening work as main controlling factors of the recent Mediterranean deformation pattern

It is argued that the time-space distribution of major post middle Miocene deformation events in the Central-Eastern Mediterranean region, deduced from the relevant literature, can be coherently explained as a consequence of the convergence between the Africa/Arabia and Eurasia blocks. This plate convergence has mainly been accommodated by the consumption of the thinnest parts of the Northern African (Ionian and Levantine basins) and peri-Adriatic margins. During each evolutionary phase the space distribution of trench zones is controlled by the basic physical requirement of minimizing the work of horizontal forces, induced by plate convergence, against the resisting forces, i.e., the cohesion of the upper brittle crustal layer and the buoyancy forces at the consuming boundaries. The significant changes of tectonic styles which determined the transition from one phase to the next, like those which occurred around the Messinian and the late Pliocene-early Pleistocene, were determined by the suture of consuming boundaries. When such an event occurs, the system must activate alternative consuming processes to accommodate the convergence of the major confining blocks. The observed deformations in the study area suggest that this tectonic reorganization mostly developed by the lateral extrusion of crustal wedges away from the sutured borders. This mechanism allowed the translation of maximum horizontal stresses from the locked collisional fronts to the zones where consumable lithosphere was still present, in order to activate the next consuming processes. The extensional episodes which led to the formation of basins and troughs in the Tyrrhenian and Aegean zones are interpreted as secondary effects of the outward escape of crustal wedges, like those which occurred in response to longitudinal compressional regimes in the Apennines and Aegean regions.

Formation of density troughs embedded in the outer plasmasphere by subauroral ion drift events

A dynamic global core plasma model (DGCPM) is used to investigate the effects of subauroral ion drift (SAID) events on the formation of trough density profiles in the outer plasmasphere during periods of high magnetic activity. The DGCPM includes the influences of convection on the changing flux tube volumes, as well as daytime refilling and nighttime draining of plasma, to calculate the plasma tube contents and equatorial plasma density distribution versus time throughout the magnetosphere. SAIDs are regions of latitudinally narrow westward flow of plasma equatorward of the auroral zone. We present DGCPM results for various presumed SAID locations and durations relative to enhanced substorm convection onset and decay, to parametrically elicit the formation of plasmaspheric density trough structures resulting from SAID effects. It is found that imposing a SAID event in the dusk‐evening sector for 30 min leads to the formation of a narrow (less than 1 RE near the equatorial plane) embedded plasma density trough in the dusk bulge region. The modeled plasmasphere density profiles with troughs generally resemble plasmasphere density profiles observed from DE 1 measurements.

Ground movements over the coal mines of southern Limburg, the Netherlands, and their relation to rising mine waters : R.F. Bekendam & J.J. Pottgens, in: Land subsidence. Proc. international symposium, The Hague, 1995, ed F.B.J. Barends & others, (IAHS: Publication, 234), 1995, pp 3–12

In southern Limburg coal mining has been undertaken for more than 500 years at depths ranging from 0 to more than 800 m. Extensive subsidence, locally exceeding 10 m, resulted in considerable damage. This damage was generally caused by longwall mining at deeper mining levels and can be referred to as sag or through subsidence. After the abandonment of the mines in the 1970s most mine water pumps were switched off and the deeper mines became flooded. Due to the rising mine waters a small vertical lift occurred at the surface of up to 25 cm, which did not bring about additional damage. At the beginning of 1994 pumping ceased completely and the mine waters will reach the shallow mines in the near future. The presence of water in the shallow mines, which are still open, and its overburden will adversely affect the stability of roof, pillars and shafts. This may result in the formation of sinkholes or subsidence troughs threatening structures at the surface. Also the water-supply might be impeded. This article gives an overview of the consequences of the mining activities which arose in the past and deals with the effects of flooding of the shallow mines and eventual saturation of its overburden which can be expected in the future.