Stochastic evaluation of simple pairing approaches to reconstruct incomplete rainfall time series

Two-station pairing approaches are routinely used to infill missing information in incomplete rainfall databases. We evaluated the performance of three simple methodologies to reconstruct incomplete time series in presence of variable nonlinear correlation between data pairs. Nonlinearity stems from the statistics describing the marginal peak-over-threshold (POT) values of rainfall events. A Monte Carlo analysis was developed to quantitatively assess expected errors from the use of chronological pairing (CP) with linear and nonlinear regression and frequency pairing (FP). CP is based on a priori selection of regression functions, while FP is based on matching the probability of non-exceedance of an event from one time series with the probability of non-exceedance of a similar event from another time series. We adopted a generalized Pareto (GP) model to describe POT events, and a t-copula algorithm to generate reference nonlinearly correlated pairs of random temporal distributions distributed according with the GP model. The results suggest that the optimal methodology strongly depends on GP statistics. In general, CP seems to provide the lowest errors when GP statistics were similar and correlation became linear; we found that a power-2 function performs well for the selected statistics when the number of missing points is limited. FP outperforms the other methods when POT statistics are different and variables are markedly nonlinearly correlated. Ensemble-based results seem to be supported by the analysis of observed precipitation at two real-world gauge stations.     

Application of SASHA to seismic hazard assessment for Portugal mainland

In the frame of the UPStrat-MAFA “Urban Disaster Prevention Strategies Using MAcroseismic Fields and FAult Sources” project, seismic hazard has been assessed in Portugal in terms of macroseismic intensity. Assessment has been performed by using a probabilistic approach based on the statistical analysis of local seismic histories (i.e., the record of seismic effects at each locality) performed by a new version of the SASHA code (D’Amico and Albarello in Res Lett 79(5):663–671, 2008) on purpose modified to account for this specific area of study. Local seismic histories are reconstructed by considering documented effects or indirect estimates deduced from epicentral information or numerical simulations. All these pieces of evidence are combined taking into account relevant uncertainty and statistical completeness of information locally available. Distribution of expected maximum intensity (i.e., the maximum intensity characterized by a fixed exceedance probability for a exposure time of 50 years) has been obtained and compared with the one deduced from alternative approaches.     

Distribution and composition of suspended matter in water and snow cover in Kaliningrad Bay

Field data, collected by the authors during winter expedition studies in Kaliningrad Bay, are analyzed. Notwithstanding the presence of ice cover, considerable advective processes are shown to be taking place in the bay. Seawater enters the bay, spreading in the bottom horizon all over the water area. Suspended sediment concentration in under-ice period is on the average three times less than that in the ice-free period. The space and time variations of its quantitative and qualitative composition under ice are mostly governed by two factors—the effect of the sea and river runoff. The values of vertical fluxed of eolian material to the bay surface in winter vary from 0.5 to 2.9 with the average of 1.7 mg m^–2 day^–1.     

Problem of transient turbulent convection and a semiempirical profile of turbulent heat exchange coefficient in freshwater bodies

A problem of convective cooling of both freshwater and saltwater lake is formulated. A transient one-dimensional turbulent model with variable layer depth is proposed to describe the process of freezing. The dependence of layer depth on time is determined by a universal equation describing the propagation of Deardorff convective layer. A combination of the main form of equations of Kolmogorov–Obukhov theory and available experimental data is shown to allow the construction of a universal profile of turbulent exchange coefficient, depending on the height.     

Relative dispersion in the Liguro-Provençal basin: From sub-mesoscale to mesoscale

Relative dispersion in the Liguro-Provençal basin (a subregion of the Mediterranean Sea) is investigated using clusters of surface drifters deployed during two Marine Rapid Environment Assessment (MREA) experiments covering different months in 2007 and 2008, respectively. The clusters have initial radii of less than 1 km, or an order of magnitude below a typical deformation radius (approximately 10-20 km). The data set consists of 45 original pairs and more than 50 total pairs (including chance ones) in the spatial range between 1 and 200 km. Relative dispersion is estimated using the mean square separation of particle pairs and the Finite Scale Lyapunov Exponents (FSLEs). The two metrics show broadly consistent results, indicating in particular a clear exponential behaviour with an e-folding time scale between 0.5 and 1 days, or Lyapunov exponent ?? in the range of 0.7-1 days⁻¹. The exponential phase extends for 4-7 days in time and between 1 and 10-20 km in separation space. To our knowledge, this is only the third time that an exponential regime is observed in the world ocean from drifter data. This result suggests that relative dispersion in the Liguro-Provençal basin is nonlocal, namely controlled mainly by mesoscale dynamics, and that the effects of the sub-mesoscale motions are negligible in comparison. NCOM model results are used to complement the data and to quantify errors arising from the sparse sampling in the observations.     

The role of gametes of the macroalgae <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> (L.) Le Jolis and <Emphasis Type="Italic">Fucus vesiculosus</Emphasis> L. (Fucales,Phaeophyceae) in summer nanoplankton of the White Sea coastal waters

Studies of macrophytes in the coastal zone of the Artic Seas, including the White Sea, have shown the essential role of these algae in the activity of the coastal half-latitude ecosystems. In summer, during the macrophyte reproduction period, a great number of reproduction products are released into the water. For a short time, this considerably affects the ratio of the nanoplankton in the populations that inhibit the vast and shallow coastal areas. At different coastal sites in Chernorechenskaya Inlet, Kadalaksha Bay, during the period of intensive reproduction of Ascophyllum nodosum and Fucus vesiculosus, 42 plankton samples were collected in 2005. During this period the concentration of antherozoids in the water reached 55000 cells/ml (216 mg C/m³). The number of eggs was within the range of 0.05–0.7 cells/ml. The proportion of antherozoids in the total biomass of nanoplankton varied at different coastal sites from 0.37 to 99%, with a mean of 46% for the reproduction period of A. nodosum, and only 7% for the reproduction period of F. vesiculosus. As was shown by counts of F. vesiculosus female gametes in sedimentation traps, 1 m² of the macrophyte bed (assuming 100% coverage) produces 18000–108000 eggs per day (0.33–2 mg C). The calculated flux of the reproductive material from the brown algae beds to the coastal water shows good agreement with the sample counts.     

On the global solution of the N-body problem

In connection with the publication (Wang Qiu-Dong, 1991) the Poincaré type methods of obtaining the maximal solution of differential equations are discussed. In particular, it is shown that the Wang Qiu-Dong'sglobal solution of the N-body problem has been obtained in Babadzanjanz (1979). First the more general results on differential equations have been published in Babadzanjanz (1978).     

Pulsar magnetic field for an infinitely conductive accretion disk

The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk.     

Challenging a Paradigm: Do We Need Active and Inactive Areas to Account for Near-Nuclear Jet Activity?

We briefly describe an advanced 3D gas dynamical model developed for the simulation of theenvironment of active cometary nuclei. The model canhandle realistic nucleus shapes and alternative physical models for the gas and dust production mechanism.The inner gas coma structure is computed by solving self-consistently(a) near to the surface the Boltzman Equation(b) outside of it, Euler or Navier-Stokes equations.The dust distribution is computed from multifluid ``zero-temperature' Euler equations,extrapolated with the help of a Keplerian fountain model.The evolution of the coma during the nucleus orbital and spin motion,is computed as a succession of quasi-steady solutions. Earlier versions of the model using simple,``paedagogic' nuclei have demonstrated that the surface orographyand the surface inhomogeneity contribute similarly to structuring the near-nucleusgas and dust coma,casting a shadow on the automatic attribution of such structures to ``active areas'.The model was recently applied to comet P/Halley, for whichthe nucleus shape is available. In the companion paper of this volume,we show that most near-nucleus dust structuresobserved during the 1986 Halley flybys are reproduced, assuming that the nucleus is strictly homogeneous. Here, we investigate the effect of shape perturbations and homogeneityperturbations. We show that the near nucleus gas coma structure is robust vis-a-vissuch effects. In particular, a random distribution of active and inactive areaswould not affect considerably this structure, suggesting that such areas,even if present, could not be easily identified on images of the coma.