Possible ion-acoustic soliton formation in the ionospheric perturbations observed on DEMETER before the 2007 Pu’er earthquake

The data of ionospheric perturbations observed on DEMETER before the 2007 Pu’er earthquake are analyzed. The three-component plasma (ions, electrons and heavy ions) is studied in the fluid concept. The linear dispersion relation for ion-acoustic wave is found in the presence of heavy ions. The nonlinear dynamics is studied for arbitrary amplitude of the wave. The Sagdeev potential is calculated, which shows that solitary structure exists for Mach number within a range defined by the presence of heavy ions. ...     

Geomagnetic storm effects at low latitudes

The geomagnetic horizontal (H) field from the chain of nine observatories in India are used to study the storm-time and disturbance daily variations. The peak decrease in storm-time variation in H showed significant enhancements at the equatorial electrojet stations over and above the normally expected decrease due to the ring current effects corrected for geomagnetic latitudes. The disturbance daily variation of H at equatorial stations showed a large decrease around midday hours over and above the usual dawn-maximum and dusk-minimum seen at any mid-latitude stations around the world. These slow and persistent additional decreases of H of disturbance daily variation at equatorial latitudes could be the effect of a westward electric field due to the Disturbance Ionospheric dynamo coupled with abnormally large electrical conductivities in the E region over the equator.     

Effect of urbanization on runoff characteristics of the On-Cheon Stream watershed in Pusan,Korea

This study investigated the effect of urbanization on runoff from the On-Cheon Stream watershed in Pusan, Korea. This watershed has been experiencing considerable urbanization since the 1960s. There are two gauging stations in the watershed. For one of the stations there are recent flow data and for the other flow data were observed in the past. A linear reservoir model was chosen and runoff was analysed for several flood events. The linear reservoir model has been found to generate flood hydrographs accurately for both gauging stations, and its applicability to the study area has also been established. Using two methods of computing effective rainfall or rainfall excess (ϕ-index and constant percentage method), the results of runoff analyses were investigated. The ϕ-index method yielded better results than the constant percentage method. A comparison of hydrographs observed in the past with the simulation results at the Ie-Sup bridge site revealed that the peak discharge increased and the mean lag time of the study area decreased owing to urbanization over the past two decades. It is also possible to evaluate the effect of urbanization quantitatively. © 1998 John Wiley & Sons, Ltd.     

Simulation of the direct runoff hydrograph at basin outlet

A simple model describing the transformation of effective rainfall to direct runoff through the overland flow mechanism is presented. The model is based on the classical representation of a watershed by a combination of planes and channels. The dynamics of overland flow in each plane is simulated by the non-linear kinematic wave, but the outflow from a given plane is concentrated in the middle of the corresponding drainage channel. The water routing in the channels is carried out by a piece-wise linearized formulation in space of the kinematic wave approximation. Using synthetic events on 10 watersheds, the model was tested by comparing it with results obtained by applying the non-linear kinematic wave to all the elements of the watershed. The model was found to be adequate, even in a form that simplifies the geometric features of the planes through an averaging procedure based on the Horton–Strahler ordering scheme of the watershed. © 1998 John Wiley & Sons, Ltd.     

The composition of nutrient fluxes from contrasting UK river basins

Accurate estimates of N and P loads were obtained for four contrasting UK river basins over a complete annual cycle. The fractionation of these loads into dissolved and particulate, and inorganic and organic components allowed a detailed examination of the nutrient load composition and of the factors influencing both the relative and absolute magnitude of these components. The particulate phosphorus (TPP) loads account for 26–75% of the annual total phosphorus (TP) transport and are predominantly inorganic. The inorganic (PIP) and organic (POP) fractions of the TPP loads represent 20–47% and 6–28% of the annual TP transport, respectively. In contrast, the particulate nitrogen loads (TPN) represent 8% or less of the annual total nitrogen (TN) loads and are predominately organic. For dissolved P transport, the dissolved inorganic fraction (DIP) is more important, representing 15–70% of the TP loads, whereas the dissolved organic fraction (DOP) represents only 3–9% of the TP loads. The TN loads are dominated by the dissolved component and more particularly the total oxidized fraction (TON), which is composed of nitrate and nitrite and represents 76–82% of the annual TN transport. The remaining dissolved N species, ammonium (NH₄-N) and organic N (DON) account for 0·3–1·2% and 13–16% of the annual TN transport, respectively. The TPN and TPP fluxes closely reflect the suspended sediment dynamics of the study basins, which are in turn controlled by basin size and morphology. The dissolved inorganic nutrient fluxes are influenced by point source inputs to the study basins, especially for P, although the TON flux is primarily influenced by diffuse source contributions and the hydrological connectivity between the river and its catchment area. The dissolved organic fractions are closely related to the dissolved organic carbon (DOC) dynamics, which are in turn influenced by land use and basin size. The magnitude of the NH₄-N fraction was dependent on the proximity of the monitoring station to point source discharges, because of rapid nitrification within the water column. However, during storm events, desorption from suspended sediment may be temporarily important. Both the magnitude and relative contribution of the different nutrient fractions exhibit significant seasonal variability in response to the hydrological regime, sediment mobilization, the degree of dilution of point source inputs and biological processes. © 1998 John Wiley & Sons, Ltd.     

Precise Relative Location of 25-ton Chemical Explosions at Balapan Using IMS Stations

—?We test how well low-magnitude (m _bLg 1.8 to 2.6), 25-ton chemical explosions at Balapan, Kazakhstan, can be located using IMS stations and standard earth models, relying on precisely determined relative arrival times of nearly similar, regional and teleseismic waveforms. Three 1997 Balapan explosions were recorded by a number of currently reporting and surrogate IMS stations. Three regional stations and two teleseismic arrays yielded consistent waveforms appropriate for relative picking. Master-event locations based on the AK135 model and ground-truth information from the first, shallowest and best-recorded explosion, fell under 1 km from known locations, for depths constrained to that of the master event. The resulting 90% confidence ellipses covered 12–13?km² and contained the true locations; however, results for depth constrained to true depth were slightly less satisf actory. From predictions based on ground truth, we found a P _g -coda phase at Makanchi, Kazakhstan to be misidentified and poorly modeled. After accounting for this, 90% ellipses shrank to 2–3?km² and true-depth mislocation vectors became more consistent with confidence-ellipse orientations. These results suggest that a high level of precision could be provided by a tripartite array of calibration shots in cases where models are poorly known. We hope that the successful relocation of these small Balapan shots will support the role of calibration explosions in verification monitoring and special event studies, including on-site inspection.     

Distribution functions of spring discharges according to their lithologies and the influence of lower limit to flow: an example from Spain

Specific functions of distribution of the number of springs and of their contributions according to flow for each of nine lithological groups are established. These functions confirm the suitability of a general type of distribution (Sanz 1996), which is a borderline case of the lognormal distribution. The statistical methods proposed for the lithological types presented can be applied to any region if data on flow and lithology of the aquifers drained by springs are available. These methods have been applied to Spain, a representative region with varied geology, climate and topography; 71.2% of spring flow is supplied by limestones, 19.17% by alluvial sediments and marls, 6.7% by conglomerates and sandstones, and 3% by slates, plutonic rocks, quartzites, and other groups. Springs with discharge rates exceeding 2000 L/s exist only in limestones. The majority of springs with low flow occur in marls. If we consider springs with flow greater than 0.5 L/s, alluvial sediments, sandstones, marls, and limestones have the greatest density of springs per surface area, although the average flow varies greatly from one lithology to the next. The cumulative estimated discharge and the estimated number of springs depend upon the definition of the lower limit of flow. For example, total discharge is reduced by 30% if we eliminate all springs with flow lower than 0.5 L/min.     

Transport of three herbicides in ground water at Twin Lake test site,Chalk River,Ontario, Canada

A field tracer test performed under natural flow conditions at the Twin Lake test site, Chalk River Laboratories of the Atomic Energy of Canada Ltd. in Chalk River, Ontario, Canada, using tritium and three herbicides (Chlortoluron, Terbuthylazine, and Pendimethalin) was interpreted using the dispersion equation with a combined reaction model. The reaction model couples an instantaneous equilibrium reaction governed by a linear adsorption isotherm with a reversible or irreversible kinetic reaction of the first order, and decay. An improved interpretation method consists of a simultaneous fitting of theoretical concentration and mass-recovery curves to the experimental data, which leads to a more reliable determining of reaction models and improves the accuracy of fitting. Tritium served as the reference tracer to determine the flow velocity, dispersivity, and the recovery of the herbicides. Chlortoluron was slightly delayed by equilibrium exchange with strongly reduced concentration due to an irreversible kinetic reaction and/or decay. Terbuthilazine was slightly delayed by equilibrium exchange, with strongly reduced concentration due to a reversible kinetic reaction with some influence of decay. A strong equilibrium reaction and a strong reversible kinetic reaction without degradation governed the transport of Pendimethalin, reducing considerably its concentration. The results obtained show that simulations based only on Kd and decay constant, especially if these parameters are found in the laboratory, may considerably differ from those performed with reaction parameters determined in properly performed field tests. The dominant reaction types, and the values of parameters found in the study, supply useful information on the transport of the investigated herbicides in sandy aquifers under natural flow conditions.     

EISCAT雷达观测到的极区电离层等离子体反常对流

综合分析EISCAT雷达与卫星当地测量数据,并利用磁层磁场模式对磁力线进行追踪,研究了发生在极光椭圆朝极盖边界附近电离层中,一例反常的背离太阳流动的强等离子体对流事件,及相关的太阳风-磁层-电离层耦合过程.结果表明,磁暴期间IMFBz指向南时观测到这一反常高速对流,及其相应的等离子体性态特征,很可能是向阳侧磁层顶磁重联过程在电离层中的印记.