A SOLAR α - ω DYNAMO STUDY AND ITS TRANSITION TO CHAOS

In this contribution we present a nonlinear dynamo model, described by an infinite dimensional system of differential equations, whose solutions depend on the essential parameter D, the dynamo number. The solutions and the bifurcation points of the system are determined with the help of a new developed computer code. We show that, depending on D, stationary, oscillatory and chaotic solutions, which are characterized by Lyapunov exponents, result. We find that the solar dynamo may operate either in the chaotic or in the stable limit cycle domain, depending on the characteristic value of the dynamo number or the motion of the convection zone.     

Neptune: Limb brightening within the 7300-Angstrom methane band

Narrow-waveband (100 Å) photoelectric slit-scan photometry of the Neptune disk is reported. Observations were concentrated within the strong CH₄ band at λ7300 Å. For comparison, measurements were also made within a continuum waveband at λ6800 Å. Point spread function data were obtained in both colors. Qualitative estimates of the true intensity distribution over the Neptune disk were made. Within the λ6800-Å continuum band, Neptune appears as an essentially uniform disk. Within the λ7300 Å CH₄ band, the planet exhibits strong limb brightening. Our results appear to require the presence of an optically thin layer of brightly scattering aerosol particles high in the Neptune atmosphere.     

Contents of Volume 24

Table of Contents

Contents of Volume 24     

The Makassar Strait Tsunamigenic Region,Indonesia

The Makassar Strait region has had the highest frequency of historical tsunamievents for Indonesia. The strait has a seismic activity due to the convergenceof four tectonic plates that produces a complex mixture of structures. The maintsunamigenic features in the Makassar Strait are the Palu-Koro and Pasternostertransform fault zones, which form the boundaries of the Makassar trough.Analysis of the seismicity, tectonics and historic tsunami events indicatesthat the two fault zones have different tsunami generating characteristics.The Palu-Koro fault zone involves shallow thrust earthquakes that generatetsunami that have magnitudes that are consistent with the earthquakemagnitudes. The Pasternoster fault zone involves shallower strike-slipearthquakes that produce tsunami magnitudes larger than would normallybe expected for the earthquake magnitude. The most likely cause for theincreased tsunami energy is considered to be submarine landslidesassociated with the earthquakes. Earthquakes from both fault zonesappear to cause subsidence of the west coast of Sulawesi Island.The available data were used to construct a tsunami hazard map whichidentifies the highest risk along the west coast of Sulawesi Island.The opposite side of the Makassar Strait has a lower risk because it isfurther from the historic tsunami source regions along the Sulawesicoast, and because the continental shelf dissipates tsunami wave energy.The greatest tsunami risk for the Makassar Strait is attributed tolocally generated tsunami due to the very short travel times.     

Tsunami Hazard for the Auckland Region and Hauraki Gulf,New Zealand

The Hauraki Gulf is a semi-enclosed sea next to the largest population centre in New Zealand, the Auckland metropolitan region. The potential tsunami hazard is of concern to regional and local planners around the Hauraki Gulf. The Hauraki Gulf has recorded 11 tsunamis and one meteorological tsunami (rissaga) since 1840.The historical tsunami data are relatively sparse, particularly for the largest events in 1868 and 1883. Moreover, local sources may produce damaging tsunamis but none has occurred during recorded history. Therefore numerical modelling of potential tsunami events provides a powerful tool to obtain data for planning purposes. Three main scenarios have been identified for numerical modelling:1. A teletsunami event from an earthquake off the West Coast of South America. Historically this region has produced the largest teletsunamis in the Hauraki Gulf.2. A tsunami generated by a local earthquake along the Kerepehi Fault. This fault bisects the Gulf, has been active during the last century at the southern inland end, and is overlain by a considerable thickness of soft sediment that may amplify the seismic waves.3. A tsunami generated by a volcanic eruption within the Auckland Volcanic Field. This field has involved a series of mainly monogenetic basaltic eruptions over the last 140,000 years. Many of these eruptions have involved phreatomagmatic eruptions around the coastal margins, or within the shallow waters close to Auckland.     

The periodicity of storm surges in the Bering Sea from 1898 to 1993, based on newspaper accounts

Spectral analysis of 96 yr of Bering Sea storm records reported in the Nome News (1899–1903) and Nome Nugget (1901–1993) newspapers indicate regularities in the 11-, 5–7- and 3-yr periods. Statistical tests on the 11-yr period found no statistically significant correlation with sunspot cyclicity despite a tendency toward maximum storminess during low sunspot periods. The 3- and 5–7-yr cycles may correlate with variability in the El Niño Southern Oscillation and easterly shifts in the mean position of North Pacific low pressure anomalies. Storm surges were infrequent from 1916 to 1928 and 1947 to 1959, while the most frequent and intense storms hit during 1900–1913, 1936–1946, 1974–1976 and in 1992.     

Single-zircon Pb-evaporation and 40Ar/39Ar dating of the metamorphic and granitic rocks in north-west Spitsbergen

North-west Spitsbergen consists of a complex of Caledonian and Grenvillian crystalline rocks, situated at the north-west corner of the Barents Shelf. The aim of this study is to understand the extent of pre-Caledonian basement rocks and their protoliths. Micas and zircon grains from six rocks from north-west Spitsbergen have been dated by the ⁴⁰Ar/³⁹Ar and single-zircon Pb-evaporation methods. Two grey granites yielded Late Caledonian mica ⁴⁰Ar/³⁹Ar and zircon ages of ca. 420-430 My, with inherited zircon grains as old as 1725 My. Zircon grains from a gneissose granite xenolith in a grey granites gave crystallization ages of ca. 960 My; some grains from a migmatite neosome show similar ages. Zircon grains yielding Archean and late Palaeoproterozoic ages (1600-1800 My) are interpreted as xenocrysts of detrital origin. The youngest ages obtained from detrital zircon grains from a greenschist facies quartzite of the Signehamna unit are ca. 1800 My. Similar schists are included as xenoliths in the 960 My old gneissose granite; therefore, the sedimentary protoliths of the unit are Mesoproterozoic. The dating results suggest a significant tectonothermal event during Grenvillian time; subsequent Caledonian events had less extensive thermal effects. However, it is still a matter of debate whether Grenvillian or Caledonian metamorphism produced the majority of the migmatites. A large population of zircon grains with Late Palaeoproterozoic ages suggests a wide surface exposure of rocks of this age in the source area, with some Archean zircons.     

Simultaneous measurements of turbulence over land and water

Turbulence and mean flow variables under unstable conditions are examined with special emphasis on the consequences of roughness and surface elevation change. An interpolation formula for _w ², between neutral and free convection, is shown to bring order to the data. The spectral distribution of vertical wind variance is found to be in good agreement with results over horizontal homogeneous terrain, both with respect to form and position. In particular, the length scale _m corresponding to the maximum of nS _w(n) is unchanged. Another turbulent length scale, (k/)z, is found to be substantially reduced in the disturbed zone of the internal boundary layer. To a first approximation, the flow-acceleration effect on the non-dimensional wind shear can be separated from the diabatic effect.     

Die Calina-der Staubdunst des spanischen Sommers

Zusammenfassung Nach einleitenden Bemerkungen zu früheren Arbeiten über die Calina werden die Voraussetzungen ihres Entstehens besprochen. Eine kritische Auswahl der Calinameldungen aus den Resumenes de los observaciones meteorologicas wird der Ableitung einer räumlichen Verteilung dieses Phänomens zugrunde gelegt. Schließlich wird der Jahresgang der Calinahäufigkeit untersucht.

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Summary After introductory remarks about former papers on the calina the conditions for the development are discussed. A critical selection of calina data from the Resumenes de los observaciones meteorologicas is used for the design of the space distribution of this phenomenon. Finally the annual variation of the frequency of calina is studied.

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Résumé Après quelques allusions à d'anciennes recherches sur la calina, l'auteur expose les conditions de sa formation et fonde sur un choix critique des messages de los observaciones meteorologicas la répartition géographique de ce phénomène. Enfin, la variation annuelle de la fréquence d'apparition est etudié.

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