Trace elements in groundwater as indicators of anthropogenic impact

The distribution of several minor and trace elements mainly in fresh (dominating TDS 160–400 mg/l) groundwater of Latvia have been investigated by the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) technique. An evaluation of results of about 700 analyses leads to the conclusion that concentrations of these elements is influenced by: pH–Eh conditions, groundwater residence time and diffuse contamination, whereas the role of water-bearing sediments is of secondary importance. Most trace elements are characterised by low mobility under alkaline and reducing conditions; concentrations in confined aquifers are much smaller than the Maximum Permissible Values for drinking water. The strongest anomalies of REE, Al and P were found in shallow groundwater around the former agrochemical storehouses.     

A multiple shooting approach for the numerical treatment of stellar structure and evolution

We present a new numerical method for solving the system of partial differential equations describing the structure and evolution of a spherically symmetric star. As usual, we employ the transversal method of lines in order to split the equations into a coupled spatial and temporal part. The novel features of the algorithm are the following: (a) Instead of using the Lagrangian picture we formulate the system of partial differential equations in the Eulerian picture. (b) We reformulate the equations of stellar structure as a multipoint boundary-value problem. By means of this reformulation the rather clumsy iterative matching procedure of stellar atmosphere and interior is avoided. (c) The multipoint boundary-value problem is solved by the multiple shooting method. This approach not only ensures a high accuracy of the stellar models calculated at each time step but also allows the free boundaries inside the star due to different energy transport mechanisms to be located exactly. (d) The time derivatives involved in the stellar-structure equations are discretized implicitly to second order accuracy. Moreover, at each time step, the chemical abundances are determined by using a sophisticated update procedure. In this way, a high accuracy is achieved with respect to the integration in time. The algorithm has turned out to be exceedingly reliable and numerically accurate. This is shown by the evolution of a 1 M_⊙ star up to the hydrogen-shell burning phase. In this example, the virial theorem, the law of mass conservation, and the law of energy conservation is fulfilled to a hitherto unattainable degree of accuracy. Since the multiple shooting method, which is at the heart of our approach, is a perfect example of a parallel algorithm, the computational speed of the algorithm might be substantially improved provided easy-to-program, high-performance parallel computers with sufficiently many processors become available in the near future.     

Analytic solutions to long's model: A comparison of nonhydrostatic and hydrostatic cases

Summary In this paper, analytic solutions of the nonhydrostatic and hydrostatic forms of Long's model were obtained under two different sets of vertical boundary conditions: The first uses a sumusoidal obstacle at the lower boundary and a rigid-lid top for the upper boundary. The second set applies an isolated obstacle of the Witch of Agnesi type at the lower boundary, while still using a rigid lid at the top. Following the solution evaluations, comparisons between the nonhydrostatic and hydrostatic solutions were processed in order to describe several influences introduced by using the hydrostatic assumption in this model.Through comparisons we have found that, in the case of a sinusoidal lower boundary condition, the hydrostatic solution is obtained as the zero mode of the nonhydrostatic solution. The influence of the hydrostatic assumption on the model solution is trivial in this case. When an isolated lower boundary condition is applied, however, the solutions illustrate dramatic differences, showing the significance of the effect of hydrostatic assumption on this model's solutions. These effects vary considerably with the model parameters as well. The comparison results also reveal that the realization of the hydrostatic assumption in this model's solutions is accomplished through the vertical boundary conditions used in the model evaluations.With 5 Figures     

Modeling heavy precipitation in complex terrain

Summary A numerical prediction model is described which uses the full set of prognostic equations on a domain roughly the size of the United States with a 96 km horizontal grid resolution and six sigma-coordinate levels. Within this grid resides a nested domain of approximately 1000×1000 km with 24 km horizontal resolution. In this nested grid only modifications to the wind field by the better resolved terrain are considered on the lowest two sigma levels. The terrain effects necessitate adjustments in the location of these two sigma levels. Adjusted wind fields cause modifications in the mass and moisture divergence fields, hence in precipitation. These modifications are averaged into the appropriate meteorological fields on the larger grid.The algorithms used by our model allow continuous interaction between both grids with high computational efficiency.The relative importance of synoptic forcing and terrain is demonstrated for the cases of the Big Thompson, Colorado, flood of 1976 and the Cheyenne, Wyoming, flood of 1985.With 15 Figures     

The atmospheric heat budget over the western part of the Tibetan plateau during Monex, 1979

The atmospheric heat source strength over western Tibet has been computed for the period beginning with the last ten days in May, 1979 and extending through August, 1979. Our results show a significantly smaller heat source than that obtained by other authors. The discrepancy is mainly due to adjustments in the dray, coefficient suggested by observations and numerical modeling experiments. We subdivided western Tibet into northern and southern parts. In the north sensible heating, SH, provides the dominant input into the atmospheric heat source, whereas in the southern part latent heat, LP, offers a significant contribution after the start of the rainy season.Detailed heat budget calculations were also carried out over limited regions of southwestern Tibet which hau good station coverage. During periods with area-averaged rainfall ≤1 mm/day an atmospheric heat source maximum was located over southwestern Tibet near the 500 hPa level, while a heat sink dominated the upper troposphere in a layer of subsidence. When rainfall exceeded 4 mm/day, ascending motions and heal sources prevailed throughout the troposphere with maxima near 400 hPa. Time series analyses of the heat sourcs components show that the total atmospheric heat source is strongly modulated by the release of latent heat. Atmospheric radiational cooling reveals a phase shift in its relation with precipitation. During the first part of the observation period a correlation of that cooling exists mainly with the net radiation at the top of the atmosphere, during the last part with the net radiation at the ground.