Basis Of Available Observations Research Articles

Thermal regime of the Vistula River mouth and the Gdańsk Bay

Surface water temperature characteristics of the Vistula River mouth and the Gdańsk Bay were determined on the basis of available observations, remote sensing and hydrodynamic models. The water temperature in the Vistula River and the Gdańsk Bay was found to be much higher than the air temperature. In recent decades, the water temperature in the Vistula River mouth and the Gdańsk Bay has increased significantly. It hasbeen determined that water temperature in the bay is affected not only by air temperature, but also by water discharge of the Vistula River and wind.

Influence of an inner core on the long-period forced librations of Mercury

The planetary perturbations on Mercury’s orbit lead to long-period forced librations of Mercury’s mantle. These librations have previously been studied for a planet with two layers: a mantle and a liquid core. Here, we calculate how the presence of a solid inner core in the liquid outer core influences the long-period forced librations. Mantle–inner core coupling affects the long-period libration dynamics mainly by changing the free libration: first, it lengthens the period of the free libration of the mantle, and second, it adds a second free libration, closely related to the free gravitational oscillation between the mantle and inner core. The two free librations have periods between 2.5 and 18y depending on the internal structure. We show that large amplitude long-period librations of a few tens of arcsec are generated when the period of a planetary forcing approaches one of the two free libration periods. These amplitudes are sufficiently large to be detectable by spacecraft measurements of the libration of Mercury. The amplitudes of the angular velocity of Mercury’s mantle at planetary forcing periods are also amplified by the resonances, but remain much smaller than the current precision of Earth-based radar observations unless the period is very close to a free libration period. The inclusion of mantle–inner core coupling in the rotation model does not significantly improve the fit to the radar observations. This implies that it is not yet possible to determine the size of the inner core of Mercury on the basis of available observations of Mercury’s rotation rate. Future observations of the long-period librations may be used to constrain the interior structure of Mercury, including the size of its inner core.

A universal procedure for aggregating estimators

In this paper we study the aggregation problem that can be formulated as follows. Assume that we have a family of estimators $\mathcal{F}$ built on the basis of available observations. The goal is to construct a new estimator whose risk is as close as possible to that of the best estimator in the family. We propose a general aggregation scheme that is universal in the following sense: it applies for families of arbitrary estimators and a wide variety of models and global risk measures. The procedure is based on comparison of empirical estimates of certain linear functionals with estimates induced by the family $\mathcal{F}$. We derive oracle inequalities and show that they are unimprovable in some sense. Numerical results demonstrate good practical behavior of the procedure.

Modelling the Transfer and Retention of Nutrients in the Drainage Network of the Danube River

The Danube catchment basin (817 000 km 2, 76×10 6 inhabitants) is the major freshwater contributor to the Black Sea (6300 m 3 s −1, 80% of the annual river discharge into the north-western Black Sea). The aim of the modelling approach developed for the Danube River, is to establish how land use and management of the whole watershed are linked to nutrient (N, P, Si) delivery and retention by the river. The approach uses an adaptation of the RIVERSTRAHLER model, which is based on a schematic representation of the drainage network deduced from geomorphological analysis by stream orders. The whole catchment was divided into 10 sub-basins and one branch, to provide a description satisfying both the need to take into account the heterogeneity of the system and the availability of constraints and validation data. On the basis of this description, a hydrological model was developed, which adequately simulated the seasonal variations of the discharge measured at the outlet of the basin. The model itself resulted from the coupling of the hydrological model with a biogeochemical model (RIVE), which takes into account the main ecological processes. It established a link between microscopic processes, their controlling factors and their macroscopic manifestations in terms of nutrient cycling and ecological functioning at the scale of the whole drainage network. The model was validated for the period from 1988 to 1991 on the basis of available observations of the major water-quality variables involved in the eutrophication processes (inorganic nutrients, phytoplankton biomass, dissolved oxygen, etc.). A reasonable agreement was found between the simulations of the model and the observations. Nutrient fluxes to the Black Sea, calculated for our reference period, are in the same range as those obtained via other approaches. Si/P and N/P ratios suggest silicon, rather than phosphorus, limitation for diatoms and phosphorus, rather than nitrogen, limitation for overall phytoplankton in the coastal zone of the Black Sea. The sharp drop in N and P delivery to the Black Sea, observed since 1991, was simulated with a scenario constructed to reproduce new constraints based on documented modifications of human activity in the watershed. Due to the scarcity of data, there is a need for further validation of the model. Nevertheless, the structure of the model allows the specificity of each sub-basin to be taken into account in future management plans.

Localization of unknown sources for parabolic systems on the basis of available observations

The paper considers two problems. Firstly the nonlinear localization problem; on the basis of available observations on the diffusion process, recover the location of an unknown single source generating this process. In general, the solution of this problem is set-valued and disconnected. Secondly, the identifiability problem; what types of observations (finite-dimensional at every moment of time, as generally occurs in physical situations) are able to provide enough information to restore the location point? A new approach is given, based on the introduction of a space of test-functions: in order to determine the unknown location, one needs to analyse a relevant system of algebraic equations. The latter can be determined in advance (‘off-line’). Sufficient conditions of identifiability are derived and the duality relations between the above nonlinear localization problems and the associated adjoint linear control problems are established. The above problems are motivated by environmental monitoring.

Baroclinic Flow and Transient-Tracer Fields in the Canary–Cape Verde Basin

Simulated transient-tracer distributions (tritium, 3H3, freons) on the isopycnal horizons σ0=26.5 and 26.8 kg m−3 are presented for the East Atlantic, 10° −40°N. Tracer transport is modeled by employing a baroclinic flow field based on empirical data in a kinematic isopycnal advection-diffusion numerical model, in which winter convection is taken as the mechanism of communication with the ocean surface layer, and the isopycnal diffusivity is a free parameter. Diapucnic transport is ignored. The simulations employ time-dependent tracer boundary conditions, which are constructed on the basis of available observations. Simulations are compared to data obtained on a meridional section in 1981 (F/S Meteor, cruise 56/5). Best simulations were obtained by means of a subjective optimization procedure. On both levels, the observed distributions and the best simulated distributions agree well. The fact that the surface boundary conditions and interior distributions of the tracers are distinctly different leads us to the conclusion that our model provides a consistent description of upper main-thermocline ventilation and interior transport Surface-water densities in February are found to represent adequately the winter outcrop boundaries with an uncertainty of about ±300 km across. The required isopycnal diffusivity south of 29°N is 1700 m2 s−1, and 2900 m2 s−1 further north (+70/−40%). Interior transport is found to be predominantly advective. Advective ventilation across 30.5°N east of 33°W amounts to only 12% and 40% for the 26.5 and 26.8 horizons of the total ventilation rates reported by Sarmiento. The North Atlantic/South Atlantic Central Water boundary near 15°N is found to be predominantly determined by advection.

The Nonlinear Filtering Problem for A Multistage System with Statistical Uncertainty

This paper deals with the problem of state and parameter estimation [1,2] on the basis of available observations for a discrete-time nonlinear system when the distributions of the disturbances or the transitional distributions of the corresponding Markov processes are not specified precisely [3-8]. An approach proposed here is based on the investigation of the set of all conditional means or the set of all conditional distributions consistent with the available information for the process. The knowledge of the above sets allows to obtain minmax estimates for the unknown actual state of the system. The approach was first suggested in [8] for the linear-gaussian case. In the given work we attempt to present a rather general scheme for the investigation of the evolution of the "informational sets" mentioned above and perhaps for the specification of the best minmax estimate for the state of the system.

The rates of tritium input to the world oceans

Mean annual rates of tritium input into the ocean averaged over 5° latitude bands are presented for the major oceans, for the period 1952–1975. The rates are obtained by converting tritium concentrations in marine precipitation into net oceanic tritium input, by means of a hydrological model. The tropospheric tritium pattern is specified on the basis of available observations, and climatological means from the literature are used for the rates of evaporation and precipitation and for the relative humidity in ship's height, that enter the model. Tritium input by water vapor exchange exceeds that by precipitation about three-fold. Tritium input by river runoff and by net tropospheric tritium outflow from the continents is also accounted for. This contribution is small except for the northern Indian Ocean and the North Atlantic. The inputs have hemispheric maxima near 50° latitude. The northern hemisphere inputs were strongly peaked in 1963–1964, whereas temporal changes in the southern hemisphere were much more gradual. By 1972, about 75% of the total oceanic input had been received by the northern ocean. For the Pacific, the computed total input agrees with the actual tritium inventory within the limits of uncertainty (about ±20%). The global tritium inventory is estimated at 1.9 GCi in 1972, which corresponds to an average tritium yield of 0.9 kg tritium per megaton TNT equivalent of nuclear fusion.

Synthetic light curves of two eclipsing binary systems, U Sge and AW UMa

Photometric curve fits have been investigated by means of numerical quadratures to develop theoretical light curves appropriate to stars built up in accordance with the Roche model. The method has been applied previously to β Per (Al-Naimiy and Budding, 1977) on the basis of available observations in red and infrared, while presently applied to two systems with contact components.