Variability of parameters of the <Emphasis Type="Italic">F</Emphasis>2-layer maximum in the quiet midlatitude ionosphere under low solar activity: 1. Statistical properties

Results of statistical analysis of the properties of variability of F2-layer maximum parameters (critical frequency foF2 and the height hmF2) in quiet midlatitude ionosphere under low solar activity in the daytime (1000–1500 LT) and nighttime (2200–0300 LT) hours are presented on the basis of Irkutsk station data for 2007–2008. It is found that the distribution density of δfoF2 could be presented as consisting of two distinctly different normal laws of this distribution, one of which corresponds to weak (|δfoF2| < 10%) fluctuations in foF2 and the other corresponds to strong (30% > |δfoF2| > 10%) fluctuations. Weak fluctuations in foF2 to a substantial degree are related to ionospheric variability at times less of than 1–3 h and determine the δfoF2 variability in the daytime hours. Strong fluctuations in foF2 are mainly related to day-to-day variability of the ionosphere at a fixed local time, the variability increasing by approximately a factor of 3 during the transition from day to night and determining the δfoF2 variability in the nighttime hours. The distribution density of ΔhmF2 is close to the normal distribution law. An interpretation of the different character of the distribution densities of δfoF2 and ΔhmF2 is given.     

An Analytical Model For Threshold Crossing Rates Of Concentration Fluctuations In Dispersing Plumes

A simple analytical model is developed for the meanupcrossing rate of plume concentration fluctuations assuming that thisprocess can be well approximated by a lognormal process. The resultingexpression requires only the specification of the in-plume fluctuationintensity and in-plume Taylor micro-time scale and, hence, does notexplicitly involve the joint probability density function of theconcentration and its derivative. The analytical model provides agood fit to some field measurements of the mean upcrossing rate ina dispersing plume.     

On the possible hazard on the major cities caused by asteroid impact in the Pacific ocean

Semi-quantitative investigation is made of hazard expected from an asteroidal impact in the Pacific. An impact ofd (diameter) = 200 m asteroid has a probability of hitting somewhere in the Pacific once in 15000 y. By carrying out a Monte Carlo simulation, such an impact, on average, is shown to create a tsunami as high as 16, 14, 15, and 21 m at Japan, Taiwan, Shanghai and Hawaii, respectively. Wooden houses, stone and brick houses, and reinforced concrete buildings are likely to be demolished by tsunamis of height 2, 7 and 20 m respectively. Thus, there is a probability of 1% or so that most of the artificial constructions on the coast lines of the Pacific be destroyed in the next century by an asteroidal impact.     

Study on uncertainty of inversion and resolution limit in the presence of noise

This study analyzed the uncertainty of inversion and the resolution limit in the presence of noise by means of statistical experiments. The exhaustive method is adopted to obtain the global optimal solution in each experiment. We found that even with small level of noise, solutions fluctuate in a large range for the thin bed. The distribution of solutions in the presence of noise is closely related to the spread of the cost function in the absence of noise. As a result, the area of a certain neighborhood around the true solution on the spread of the cost function in the absence of noise is used to evaluate the uncertainty of inversion and the resolution limit in the presence of noise. In the case that the SNR (signal-to-noise ratio) is 5 in this study, solutions focus around the true solution with a very small uncertainty only when the bed thickness is greater than the reciprocal of the double predominant frequency of the convoluting wavelet.     

An inter-comparison of tidal solutions computed with a range of unstructured grid models of the Irish and Celtic Sea Regions

Three finite element codes, namely TELEMAC, ADCIRC and QUODDY, are used to compute the spatial distributions of the M₂, M₄ and M₆ components of the tide in the sea region off the west coast of Britain. This region is chosen because there is an accurate topographic dataset in the area and detailed open boundary M₂ tidal forcing for driving the model. In addition, accurate solutions (based upon comparisons with extensive observations) using uniform grid finite difference models forced with these open boundary data exist for comparison purposes. By using boundary forcing, bottom topography and bottom drag coefficients identical to those used in an earlier finite difference model, there is no danger of comparing finite element solutions for “untuned unoptimised solutions” with those from a “tuned optimised solution”. In addition, by placing the open boundary in all finite element calculations at the same location as that used in a previous finite difference model and using the same M₂ tidal boundary forcing and water depths, a like with like comparison of solutions derived with the various finite element models was possible. In addition, this open boundary was well removed from the shallow water region, namely the eastern Irish Sea where the higher harmonics were generated. Since these are not included in the open boundary, forcing their generation was determined by physical processes within the models. Consequently, an inter-comparison of these higher harmonics generated by the various finite element codes gives some indication of the degree of variability in the solution particularly in coastal regions from one finite element model to another. Initial calculations using high-resolution near-shore topography in the eastern Irish Sea and including “wetting and drying” showed that M₂ tidal amplitudes and phases in the region computed with TELEMAC were in good agreement with observations. The ADCIRC code gave amplitudes about 30 cm lower and phases about 8° higher. For the M₄ tide, in the eastern Irish Sea amplitudes computed with TELEMAC were about 4 cm higher than ADCIRC on average, with phase differences of order 5°. For the M₆ component, amplitudes and phases showed significant small-scale variability in the eastern Irish Sea, and no clear bias between the models could be found. Although setting a minimum water depth of 5 m in the near-shore region, hence removing wetting and drying, reduced the small-scale variability in the models, the differences in M₂ and M₄ tide between models remained. For M₆, a significant reduction in variability occurred in the eastern Irish Sea when a minimum 5-m water depth was specified. In this case, TELEMAC gave amplitudes that were 1 cm higher and phases 30° lower than ADCIRC on average. For QUODDY in the eastern Irish Sea, average M₂ tidal amplitudes were about 10 cm higher and phase 8° higher than those computed with TELEMAC. For M₄, amplitudes were approximately 2 cm higher with phases of order 15° higher in the northern part of the region and 15° lower in the southern part. For M₆ in the north of the region, amplitudes were 2 cm higher and about 2 cm lower in the south. Very rapid M₆ tidal-phase changes occurred in the near-shore regions. The lessons learned from this model inter-comparison study are summarised in the final section of the paper. In addition, the problems of performing a detailed model–model inter-comparison are discussed, as are the enormous difficulties of conducting a true model skill assessment that would require detailed measurements of tidal boundary forcing, near-shore topography and precise knowledge of bed types and bed forms. Such data are at present not available.     

Retrospective Assessment of Bottom Deposits in Kondopoga Bay,Lake Onega

Long-term observations of the chemical composition of bottom sediments in Kondopoga Bay, Lake Onega, are considered. The present-day state of bottom sediments is characterized, and regularities of variations in the composition and properties of sediments occurring in the zone of influence of wastewaters from a pulp and paper plant (PPP).     

THE STUDY OF THE GENESIS OF SURFACE WATERS BY OBSERVING THEIR ELECTRICAL RESISTIVITIES*

Specific electrical resistivity of natural waters contains information on their genesis. The authors propose to conduct mass and regime observations of this parameter in river and stream beds. The electrical resistivities in streams flowing from under a glacier reveal details formed at the same time as the glacier. Observations in the beds of big rivers show a gradual increase in water salinity overlain by reductions by inflowing glacial waters. The diurnal and annual trend of changes in the electrical conductivity of water associated with the change in the balance of glacial and ground waters has been established near to glaciers. Resistivity observations help to locate discharge sites of sub-permafrost waters, for water.