Prediction of hydrological phenomena using self-organizing mathematical models

The paper considers the application of self-organizing models, specifically, the method of grouped arguments consideration (MGAC), to forecast short and non-stationary time series of observations in the ocean. A sequence of operations for the treatment of observational series is suggested. To assess its efficiency, we have used mean monthly oxygen concentration data collected in the surface and near-bottom layers of the Taganrog Bay. It is shown that the application of the MGAC model allows one to reduce by two times the root-mean-square error of that of the series prediction by five points, in comparison with the Jenkins-Box regressional model. It has been concluded that the predictors' non-linear functions may be effectively used in the treatment of short samplings. Translated by Vladimir A. Puchkin.     

Numerical modelling of the Sea of Azov's dynamics resulting from narrowing of the mouth of Taganrog Bay

The currents and surface level oscillations in the Sea of Azov ensuing from contraction of the mouth of Taganrog Bay are computed using the grid technique on the basis of a numerical solution to the system of quasi-linear, degenerate, parabolic, partial derivative equations (shallow-water equations). It is demonstrated what changes are to be expected in the dynamics of the Sea of Azov should this project be realized. The computations were carried out for typical wind directions.Translated by Vladimir A. Puchkin.     

Experimental research on the hydrophysical characteristics and dynamics of waters in the north-west Black Sea in the region of the main Black Sea current

The results of measurements of hydrophysical parameters in the upper layer of the sea at an observation site located south-west of the Crimea are reported. The current pattern, the distribution of the upwelling and downwelling zones at the observation site, and the location of the mesoscale fronts are discussed.Translated by Mikhail M. Trufanov.     

The choice of a dynamico-stochastic model for ocean monitoring — A compromise between the accuracy and cost of computations

In this paper we compare, two dynamico-stochastic models (DSMs) with different hydrodynamic parts, designed to study a large-scale North Atlantic region. As a performance criterion, RMS errors (over the horizon) in density and velocity field reconstruction are used. It has been shown that in some cases it seems rational to use DSMs with simplified hydrodynamic parts. This helps to expedite the computations and to reduce the related costs without much detriment to the quality of hydrophysical field simulation.UDK 551.465.001.573(261.1).Translated by Vladimir A. Puchkin.     

Preservation conditions and the use of sediment pigments as a tool for recent ecological reconstruction in four Northern European estuaries

Down-core sediment pigment concentrations from four Northern European estuaries were measured using high-performance liquid chromatography (HPLC) to investigate phytoplankton community structure and preservation conditions over the last ca. 100 years where all sites have experienced different levels of eutrophication. Phytoplankton pigments have been shown to be useful biomarkers for phytoplankton community structure and abundance due to their taxonomic specificity. The pigment concentrations and sediment pigment inventory showed large variation between the four sites. Concentrations ranged from more than 6000 nmol/g OC to less than 100 nmol/g OC and the inventory integrated over the top 10 cm from more than 300 nmol/cm² to less than 30 nmol/cm² for total identified pigments. Good pigment preservation in Mariager Fjord (Denmark) reflected the almost permanently anoxic conditions. Pigments in Laajalahti (Finland) showed peak concentrations around the time of highest nitrogen loading events known from historical and modelled records over the past 100 years. In contrast, poor down-core preservation of pigments (especially carotenoids) was observed in the Ems-Dollard (The Netherlands) and Himmerfjärden (Sweden) estuaries. The Ems-Dollard site is an intertidal mudflat that experiences daily exposure to light and air, which enhances pigment degradation. In Himmerfjärden, resuspension is an important process affecting both the sedimentation rate and degradation properties. The different preservation conditions at the four sites were supported by the differences in two degradation indicators; the ratio of pheopigment-a to chlorophyll-a and total carotenoids to total pigments. Class-specific carotenoid pigments represented the dominant algal groups reported from each site, however, no distinct down-core changes in the pigment composition were observed at any of the four sites. This indicated that changes in plankton community structure on the group level have been limited over this time period or masked by low preservation of pigments.     

Storminess and vulnerability along the Atlantic coastlines of Europe: analysis of storm records and of a greenhouse gases induced climate scenario

Identification of the distinctive circulation patterns of storminess on the Atlantic margin of Europe forms the main objective of this study; dealing with storm frequency, intensity and tracking. The climatology of the extratropical cyclones that affect this region has been examined for the period 1940–1998. Coastal meteorological data from Ireland to Spain have been linked to the cyclone history for the North Atlantic in the analysis of storm records for European coasts. The study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the North Atlantic Oscillation (NAO). Results indicate a seasonal shift in the wind climate, with regionally more severe winters and calmer summers established. This pattern appears to be linked to a northward displacement in the main North Atlantic cyclone track.

An experiment with the ECHAM4 A-GCM at high resolution (T106) has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region. The experiment consists of (1), a 30-year control time-slice representing present-day equivalent CO₂ concentrations and (2), a 30-year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent CO₂ concentrations. The boundary conditions have been obtained from an atmosphere-ocean coupled OA-GCM simulation at low horizontal resolution. An algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones. For most of the northern part of the study region, covering Ireland and Scotland, results describe the establishment by ca. 2060 of a tendency for fewer but more intense storms.

The impacts of these changes in storminess for the vulnerability of European Atlantic coasts are considered. For low-lying, exposed and ‘soft’ sedimentary coasts, as in Ireland, these changes in storminess are likely to result in significant localised increases in coastal erosion.     

An Ecosystem Model Coupled with Nitrogen-Silicon-Carbon Cycles Applied to Station A7 in the Northwestern Pacific

A model based on that of Kishi et al. (2001) has been extended to 15 compartments including silicon and carbon cycles. This model was applied to Station A7 off Hokkaido, Japan, in the Northwestern Pacific. The model successfully simulated the observations of: 1. a spring bloom of diatoms; 2. large seasonal variations of nitrate and silicate concentrations in the surface water; and 3. large inter-annual variations in chlorophyll-a. It also reproduced the observed features of the seasonal variations of carbon dioxide partial pressure (pCO₂)—a peak in pCO₂ in winter resulting from deep winter convection, a rapid decrease in pCO₂ as a result of the spring bloom, and an almost constant pCO₂ from summer through fall (when the effect of increasing temperature cancels the effect of biological production). A comparison of cases with and without silicate limitation shows that including silicate limitation in the model results in: 1. decreased production by diatoms during summer; and 2. a transition in the dominant phytoplankton species, from diatoms to other species that do not take up silicate. Both of these phenomena are observed at Station A7, and our results support the hypothesis that they are caused by silicate limitation of diatom growth. This revised version was published online in July 2006 with corrections to the Cover Date.     

Monitoring the Kuroshio Extension with Dynamically Constrained Synthesis of the Acoustic Tomography, Satellite Altimeter and in situ Data

A finite-difference quasigeostrophic (QG) model of an open ocean region has been employed to produce a dynamically constrained synthesis of acoustic tomography and satellite altimetry data with in situ observations. The assimilation algorithm is based upon the 4D variational data interpolation scheme controlled by the model's initial and boundary conditions. The data sets analyzed include direct and differential travel times measured at the array of five acoustic transceivers deployed by JAMSTEC in the region of the Kuroshio Extension in 1997, Topex/Poseidon altimetry, CTD soundings, and ADCP velocity profiles. The region monitored is located within the area 27.5°–36.5°N, 143°–155°. The results of assimilation show that mesoscale variability can be effectively reconstructed by five transceivers measuring direct and reciprocal travel times supported by relatively sparse in situ measurements. The misfits between model and data lie within the observational error bars for all the data types used in assimilation. We have compared the results of assimilation with the statistical inversion of travel time data and analyzed energy balances of the optimized model solution. Energy exchange between the depth-averaged and shear components of the observed currents reveals a weak decay of the barotropic mode at the rate of 0.2 ± 0.7⋅10⁻⁵ cm²/s³ due to topographic interaction. Mean currents in the region are unstable with an estimate of the available potential energy flux from the mean current to the eddies of 4.7 ± 2.3⋅10⁻⁵ cm²/s³. Kinetic energy transition has the same sign and is estimated as 2.8 ± 2.5⋅10⁻⁵ cm²/s³. Potential enstrophy is transferred to the mesoscale at a rate of 5.5 ± 2.7⋅10⁻¹⁸ s⁻³. These figures provide observational evidence of the properties of free geostrophic turbulence which were predicted by theory and observed in numerical experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal variation of pteropods from the Western Arabian Sea sediment trap

Sediment trap samples collected from the Western Arabian Sea yielded a rich assemblage of intact and non-living (opaque white) pteropod tests from a water depth of 919 m during January to September 1993. Nine species of pteropods were recorded, all (except one) displaying distinct seasonality in abundance, suggesting their response to changing hydrographical conditions influenced by the summer/winter monsoon cycle. Pteropod fluxes increased during the April–May peak of the intermonsoon, and reached maximum levels in the late phase of the southwest summer monsoon, probably due to the shallowing of the mixed layer depth. This shallowing, coupled with enhanced nutrient availability, provides ideal conditions for pteropod growth, also reflected in corresponding fluctuations in the flux of the foraminifer Globigerina bulloides. Pteropod/planktic foraminifer ratios displayed marked seasonal variations, the values increasing during the warmer months of April and May when planktic foraminiferal fluxes declined. The variation in fluxes of calcium carbonate, organic carbon and biogenic opal show positive correlations with fluxes of pteropods and planktic foraminifers. Calcium carbonate was the main contributor to the total particulate flux, especially during the SW monsoon. In the study area, pteropod flux variations are similar to the other flux patterns, indicating that they, too could be used as a potential tool for palaeoclimatic reconstruction of the recent past.