Das Kuriosum eines scheinbaren “Tidewindes” im Revier Außenelbe

Zusammenfassung Bei einer Auswertung der Windmessungen deutscher Feuerschiffe für die Sturmflut-Periode Mitte Februar 1962 fiel es auf, daß die Differenzen der Windgeschwindigkeit zwischen den Feuerschiffen Elbe 1 und Elbe 2 offenbar einem bestimmten Rhythmus unterlagen. Da der Abstand der meisten Maxima der Winddifferenz (Elbe 1 minus Elbe 2) etwa 12 Std. betrug, tauchte die Vermutung auf, daß dieser Rhythmus gezeitenbedingt war. Die Mittelbildung über 13 nach den Gezeiten geordnete Fälle ergab denn auch den Tidewind in ausgeprägter Form, wobei das relative Windmaximum von Elbe 1 bei Mitte Ebbstromzeit lag^** und der mittlere Schwankungsbetrag (Maximum — Minimum) 3.6 kn betrug. Eine auf die Gezeiten bezogenen Auswertung von Fällen quasikonstanter Windrichtung ergab noch größere Schwankungsbeträge und vor allem eine gegenläufige Schwingung des Tidewindes bei westlichen und östlichen Winden. Da dies Verhalten des Windes — nach Vorzeichen und Betrag — recht genau den differentiellen Schwankungen des Gezeitenstromes bei Elbe 1 und Elbe 2 entsprach, so hätte man an einen Mitführungseffekt des strömenden Wassers auf die Luft denken können, wäre nicht die ungeschwächte Übertragung von Bewegungsgröße bis in Anemometerhöhe von 18 m allzu unwahrscheinlich gewesen. Tatsächlich erlischt, wie E. R. Reiter [1955] zeigen konnte, der Mitführungseffekt bei einem Flusse ähnlicher Geschwindigkeit wie die Außenelbe in etwa 3 m Höhe über Wasser.Des Rätsels Lösung liegt in der kombinierten Wirkung des Gezeitenstroms und des Windes auf die Lage (Kielrichtung) der vor Anker schwojenden Feuerschiffe. Damit verändert sich im Verlauf einer Tide — bei konstanter Windrichtung — die Anblasrichtung der Schiffe, und diese Änderungen des Anströmungswinkels ergeben systematische Änderungen der gemessenen. Windgeschwindigkeit in Abhängigkeit von der Strömmungsstörung am Schiffshindernis. Die mit dem Gezeitenstrom schwojenden Feuerschiffe erscheinen so als ein geeignetes Versuchsobjekt zur besseren Feststellung des quantitativen störenden Schiffseinflusses auf den Wind.

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The strange phenomenon of an apparent tidal wind in the Estuary of the Outer Elbe (Außenelbe)

Summary When the wind measured by the German lightvessels for the storm surge period mid February 1962 was studied, it became obvious that the differences of wind velocities observed on the lightvessels Elbe 1 and Elbe 2 showed a certain rhythm. As most maxima of these wind differences (Elbe 1 minus Elbe 2) followed one another within about 12 hours, it was supposed that this rhythm was connected with the tide. The average of a series of 13 tides showed very remarkably the tidal wind, the maxima of the wind differences being at the centre of the ebbstream interval at Elbe 1 and the mean range of maximum-minimum being 3.6 kn. Cases of wind with quasi-constant directions showed even greater values of deviation when referred to the tide and, above all, deviations in opposite directions at easterly and westerly winds. As this phenomenon, in sign and quantity, very nearly corresponded to the differences of the tidal currents at Elbe 1 and Elbe 2, one could have thought of an effect by which air is carried along by the streaming water, if not, up to the height of the anemometer of 18 m, the unweakened transfer of momentum would have been too unlikely. In fact, as E. R. Reiter [1955] demonstrated, the effect of air being carried along by the streaming water fades out at about 3 m above the water level of a river at similar velocities as the Outer Elbe.The explanation of this phenomenon is the combined effect of the tidal current and the wind on the course of the lightvessels swinging round their anchors. At a constant direction of the wind, during one tide, the angle between wind and course varies and this variation of the angle leads to a systematic variation of the measured wind speed according to the disturbance caused by the ship as an obstacle. Therefore, lightvessels swinging round with the tidal current seem to be a suitable test to study how much the ship herself disturbs the wind.

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Aspect curieux d'un «vent de marée» apparent dans la zone de l'Elbe extérieure

Résumé A l'occasion d'une étude des vitesses du vent mesurées aux bateaux-feu au cours des ondes de tempête de mi-février 1962, on fit la remarque que les différences de vitesse du vent entre les bateaux-feu «Elbe 1» et «Elbe 2» paraissaient obéir à un certain rythme. Comme l'écart de la plupart des maxima de différence («Elbe 1» moins «Elbe 2») était d'environ 12 heures, il vint d'abord à l'esprit, que ce rythme était subordonné à la marée. La moyenne obtenue dans 13 cas pris dans l'ordre suivant la marée, faisait d'ailleurs apparaître nettement le «vent de marée» pour lequel le maximum relatif de «Elbe 1» correspondait au «milieu de la période de jusant» et la variation moyenne (maximum-minimum) se chiffrait à 3.6 noeuds. Une étude, rapportée à la marée, de cas de direction de vent quasi-constante, fit apparaître des variations encore plus grandes et surtout une oscillation en sens contraire du «vent de marée» par vents d'Ouest-d'Est. Comme ce comportement du vent-selon prévision et grandeur correspondait très exactement aux variations différentielles du courant de marée à «Elbe 1» et «Elbe 2», on aurait pu penser à un effet d'entraînement exercé sur l'air par le courant d'eau, si cet entraînement n'avait gardé la même force jusqu'à la hauteur de 18 m de l'anémomètre, ce qui était invraisemblable. En fait, comme l'a montré E. R. Reiter [1955] l'effet d'entraînement pour un fleuve d'une vitesse analogue à l'Elbe extérieure, cesse de se faire sentir à environ 3 m au-dessus de l'eau.Cette énigme trouve son explication dans l'action combinée du courant de marée et du vent sur la situation (direction de la quille) des bateaux-feu évitant sur leur ancre. C'est ainsi qu'au cours d'une marée-le vent gardant la même direction-le navire reçoit le vent sous des angles variables. Il en résulte des modifications systématiques de la vitesse de vent mesurée qui dépend de l'obstacle que le navire présente au courant d'air. Ainsi les bateaux-feu s'évitant au courant de marée semblent fournir un élément d'expérience approprié pour une meilleure détermination quantitative de l'influence perturbatrice du navire sur le vent.

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Herrn Prof. Dr. H. U. Roll zum 60. Geburtstag gewidmet.     

U.S. Mussel Watch: 1977–1978 results on trace metals and radionuclides

The results of the U.S. Mussel Watch Monitoring Program for the period 1976–1978 for trace metals and artificial radionuclides in bivalves are presented. The substances analysed included Ag, Cu, Zn, Cd, Ni, Pb, ²³⁸Pu, ^239+240Pu and ²⁴¹Am. The analyses of organic substances will be presented elsewhere. The concentrations of these substances in the bivalves may reflect upwelling processes, anthropogenic inputs or natural levels. Off the California coast, mussels show markedly elevated Pu and Cd concentrations in coastal areas adjacent to the most intensive upwelling zones. Elevated levels of Pb, for example, are found in organisms living adjacent to highly urbanized places. The general patterns of distribution repeat themselves year after year at a given site. Thus, it is concluded that annual monitoring activities may not be necessary and that a frequency of sampling of several or so years may be more appropriate to identify pollution problems. Finally, national or regional baselines for metal concentrations in bivalves from unpolluted waters are proposed. National baselines for Pb in the west coast mussels of 1·0 parts 10^?6 and for Ag in east coast mussels of 0·05 parts 10^?6 are suggested.     

Anisotropy of magnetic susceptibility variations in a single icelandic columnar basalt

Measurements of the anosotropy of magnetic susceptibility in 34 specimens drilled from a single Icelandic columnar basalt segment reveal a preferred, long-axis alignment of magnetic minerals normal to the long axis of the column and well grouped. Maximum elongation of these minerals occurs in regions which crystallized late, as independently indicated by relative samarium concentrations. We propose that the variations in magnetic mineral elongation are controlled by variations in thermal stress in the cooling column, before complete solidification. An upper limit of 75–100 bars is suggested for these stresses.     

Robotic telescopes for high energy astrophysics in Ondřejov

We report on two small aperture robotic telescopes called BART and D50 operated in Ondřejov. Both telescopes are capable of automatic observation of gamma ray burst (GRB) optical afterglows. Coordinates of GRBs are taken from alerts distributed via Internet. Telescopes observe other interesting high energy sources when there is not any alert. The smaller telescope BART has aperture D = 254 mm. The bigger telescope D50 has a primary mirror of diameter D = 500 mm. Both telescopes are controlled by free software package RTS2 and are accessible through Internet. We describe the two telescopes and related software and show some results such as our first observed optical counterpart of GRB.     

A unique Galactic planetary nebula with a [WN] central star

We report the discovery of the first probable Galactic [WN] central star of a planetary nebula (CSPN). The planetary nebula candidate was found during our systematic scans of the AAO/UKST Hα Survey of the Milky Way. Subsequent confirmatory spectroscopy of the nebula and central star reveals the remarkable nature of this object. The nebular spectrum shows emission lines with large expansion velocities exceeding 150 km s⁻¹, suggesting that perhaps the object is not a conventional planetary nebula. The central star itself is very red and is identified as being of the [WN] class, which makes it unique in the Galaxy. A large body of supplementary observational data supports the hypothesis that this object is indeed a planetary nebula and not a Population I Wolf–Rayet star with a ring nebula.     

Ultra-Deep Optical Spectroscopy with PMAS. Using the Nod-and-Shuffle Technique

PMAS, the Potsdam Multi-Aperture Spectrophotometer, is a new integral field spectrograph in the optical, which is optimized for good transmission and high image quality from 350 nm to 1 μm. We present our plan to implement a CCD charge-shuffle mode to allow for beam switching with a very high degree of sky subtraction accuracy for faint object 3-D spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of a “flickering” Geminid fireball

Abstract— In the early morning hours of December 13, 2002, a bright Geminid fireball with an absolute magnitude of ?9.2 ± 0.5 was observed from Southern Saskatchewan, Canada. The fireball displayed distinct small‐scale oscillations in brightness, or flickering, indicative of the parent meteoroid being both non‐spherical and rotating. Using the light curve derived from a calibrated radiometer, we determine a photometric mass of 0.429 ± 0.15 kg for the meteoroid, and we estimate from its initial rotation rate of some 6 Hz that the meteoroid was ejected from the parent body (3200) Phaethon some 2500 ± 500 years ago. We find that 70% of Geminid fireballs brighter than magnitude ?3 display distinct flickering effects, a value that is in stark contrast to the 18% flickering rate exhibited by sporadic fireballs. The high coincidence of flickering and the deep atmospheric penetration of Geminid fireballs are suggestive of Geminid meteoroids having a highly resilient structure, a consequence, we suggest, of their having suffered a high degree of thermal processing. The possibility of Gemind material surviving atmospheric ablation and being sampled is briefly discussed, but the likelihood of collecting and identifying any such material is admittedly very small.