Application of periodic autoregressive process to the modeling of the Garonne river flows

Accurate forecasting of river flows is one of the most important applications in hydrology, especially for the management of reservoir systems. To capture the seasonal variations in river flow statistics, this paper develops a robust modeling approach to identify and to estimate periodic autoregressive (PAR) model in the presence of additive outliers. Since the least squares estimators are not robust in the presence of outliers, we suggest a robust estimation based on residual autocovariances. A genetic algorithm with Bayes information criterion is used to identify the optimal PAR model. The method is applied to average monthly and quarter-monthly flow data (1959–2010) for the Garonne river in the southwest of France. Results show that the accuracy of forecasts is improved in the robust model with respect to the unrobust model for the quarter-monthly flows. By reducing the number of parameters to be estimated, the principle of parsimony favors the choice of the robust approach.     

Estimation of effect of unequal secular variation on geomagnetic data reduction

The geomagnetic field components are periodically measured at repeat stations. The main objective of the repeat stations is to provide data for tracing the secular variation of the geomagnetic field components. Secular variation at the repeat station is generally different from that at geomagnetic observatory used in the data reduction. The effect of the secular variation differences on geomagnetic data reduction was estimated for the regions of Europe, North America (below 60°N) and Australia, respectively, during the period of 2000-2010. These estimations were obtained by using the monthly mean values of north, east and vertical components of geomagnetic field, recorded at geomagnetic observatories. The effects were calculated by using observatories pairs, with distances from 350 km (in Europe) to 3100 km (in North America and Australia). The maximal effects were found to be the smallest in east component in Europe and North America, and vertical component in Australia; the effects increase with time from a central reduction epoch and they are not constant during mentioned eleven years; they were less than 1 nT only in Europe, for distances between the observatories up to 1000 km in all three components and for periods spanning ±1 month from a central epoch. It was found that their year to year variability is mostly due to the non-eliminated external field residuals in the observatories monthly means; their effect is up to 3 nT for ±3 months from a central epoch. Further, the real effects were compared to those modeled by IGRF-12 model. The maximal differences between the real and the modeled values are below 4.5 nT in all three components, for ±3 months from a central epoch.     

Recent Efforts Toward the Establishment of the Lonjsko Polje Geomagnetic Observatory

More than ten years ago, the Geophysical Institute initiated the installation of a geomagnetic observatory in Croatia. Over the past decade, extensive surveys and studies have been conducted in order to determine the proper location for the observatory. Finally, in 2012, the observatory was established in Lonjsko Polje. This paper presents the first data recorded in the period 2012.5-2015.0. Also presented are the technical aspects and data processing techniques of this remotely operated observatory. Analysis of data quality and comparison with data from the surrounding INTERMAGNET observatories is discussed in detail. Although remote observatories cannot provide the ideal environment for magnetometers, the obtained results accentuate the potential of the new observatory to provide high-quality data. The establishment of this observatory paves the way for scientific and professional development of geomagnetism in Croatia.     

Spherical Elementary Current Systems Method Applied to Geomagnetic Field Modeling for the Adriatic

The aim of this work was to derive an accurate regional model of geomagnetic components on the Adriatic. Data of north, east and vertical geomagnetic components at repeat stations and ground survey sites enclosing the Adriatic Sea were used to obtain a geomagnetic model at 2010.5 epoch. The core field was estimated by use of the global Enhanced Magnetic Model, while the crustal field by a mathematical technique for expanding vector systems on a sphere into basis functions, known as spherical elementary current systems method. The results of this method were presented and compared to the crustal field estimations by the Enhanced Magnetic Model. The maps of isolines of the regional model are also presented.     

Multiple phase transitions of leonite-type compounds: optical, calorimetric, and X-ray data

Summary Low-temperature phase transitions of leonite-type compounds, K₂Me²⁺(SO₄)₂ · 4H₂O (Me = Mg, Mn, Fe), are investigated by temperature dependent measurements of single-crystal X-ray reflection intensities and lattice parameters. The transition temperatures and the progress of the transitions are determined by birefringence data and differential scanning calorimetry. The cause for the phase transitions of leonite-type compounds is a dynamic disorder of sulphate groups at room temperature (C2/m), that freezes in to an ordered structure (I2/a) at −4(1) °C in leonite, K₂Mg(SO₄)₂ · 4H₂O. At −153(1) °C the crystal structure switches to another ordered phase (P2₁/a). The Mn analogue shows the same succession with transition temperatures at −68(1) °C and −104(1) °C. The disordered room temperature structure of the isotypic mineral mereiterite, K₂Fe(SO₄)₂ · 4H₂O, transforms directly to the ordered P2₁/a structure at 3(2) °C. Analysis of X-ray intensities and of excess birefringence reveals that the displacive I2/a ⇔ P2₁/a phase transition of leonite and Mn-leonite is first order. According to Landau theory the C2/m ⇔ I2/a (leonite, Mn-leonite) and C2/m ⇔ P2₁/a (mereiterite) order-disorder transitions are almost tricritical. Received March 7, 2001; revised version accepted June 27, 2001     

Nebenmeere im humiden und ariden Klimabereich

Zusammenfassung Nebenmeere im humiden und ariden Klimabereich unterscheiden sich in ihrer Wasserzirkulation. Sie wirkt sich auch auf Organismen und Sedimente aus. Dabei ergeben sich die folgenden beiden Modelle:Schon bei rezenten Fällen kommen Abweichungen vor, etwa durch intensive winterliche Abkühlung, durch die Witterungsverhältnisse an den entscheidenden Verbindungsstraßen zum offenen Ozean, durch klimatische Unterschiede zwischen Einzugsgebiet und Nebenmeer oder in den Lagunen desselben Beckens. Deshalb dürfen diese Modelle nicht schematisch auf fossile Verhältnisse übertragen werden. Die Analyse der einzelnen Faktoren und der Versuch, daraus ein Gesamtbild zu gewinnen, sind wichtiger als das Modell selbst.

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Adjacent seas in humid and arid climates differ in their water circulation patterns. This difference effects both the organisms and the sediment. The following table compares the two ideal models:Even recent examples do, however, show divergences from the ideal model. These discrepancies can develop through severe cooling during winter, anomalous weather condition in the straits leading to the open oceans or through differences in climate between the surrounding land area and the adjacent sea or the lagoons of the same basin. Therefore, one should not attempt to apply this model scheme as a whole to fossil conditions. The analysis of the individual factors, and the attempt to reconstruct a complete picture from them is more important than the model itself.

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Résumé Les mers intérieurs situées sous climat humide se différencient de celles soumises au climat aride par le mode de circulation de leurs eaux. De cette différence découle le parallélisme entre les deux modèles suivants.Des circonstances récentes ont cependant déjà apporté des modifications à cette généralisation schématique: modifications dues, soit à un refroidissement hivernal intensif, soit aux conditions météorologiques des détroits déterminant la communication avec l'océan, soit encore aux différences climatiques existant entre le continent et la mer interieure, ou entre cette dernière et ses lagunes.On ne doit donc pas transposer hâtivement le schéma de ces modèles à celui des paléobassins du même type.L'analyse des différents facteurs, l'essai de déduction d'un schéma d'ensemble sont en fait plus importants que le modèle lui-même.

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Ein Stoss-Kolbenlot für Flachwasser

Zusammenfassung Es wird ein leichtes Gerät beschrieben, das durch das Kolbenlot-Prinzip und die Verwendung von Kunststoff-Folien die Entnahme ungestörter SedimentKerne aus Wassertiefen bis 35 m erlaubt.     

Jahreslagen in Sedimenten der mittleren Adria

Zusammenfassung In einer abgeschnürten Meeresbucht von Mljet herrschen euxinische Verhältnisse, weshalb das Sediment in deren tiefstem Teil feinstgeschichtet ist. An der Hell-Dunkel-Wechsellagerung eines Kerns wird gezeigt, daß die durchschnittlich 0,25 mm mächtigen Doppellagen Jahres schichten sind. Zum Beweis werden sich im Sediment abbildende historische Ereignisse wie auch jahreszeitliche Veränderungen herangezogen. Danach werden im Sommer die hellen, kalzitführenden Schichten, im Herbst-Winter-Frühling die dunklen, organische Substanz, Eisensulfid und Quarz enthaltenden Lagen abgesetzt.