Structure and oscillations in quiescent filaments from observations in He i λ10830 å

Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i 10830 Å line.The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures.     

Distribution of lunar impacts by objects in parabolic low inclination orbits

This paper presents a computer investigation extending to the case of parabolic orbits, an earlier investigation conducted by Barricelli and Metcalfe (1969) on lunar impacts by external low eccentricity satellites as a means to interpret the asymmetric distribution of lunar maria. Parabolic orbits can be approximated by two kinds of objects:

1. High eccentricity external satellites may, near periapsis, approach the Moon with orbital velocity and other characteristics closely resembling those of a parabolic orbit.
2. Asteroids and meteoroids approaching the Earth-Moon system with a low velocity may have moved in a nearly parabolic orbit when they reached the lunar distance from the Earth at the time when the impacts which carved the lunar maria took place.

The investigation gives, therefore, not only additional information relevant to the interpretation of the distribution of lunar maria by the satellite impacts hypothesis (in this case high eccentricity ones), but also information about the alternative hypothesis (Wood, 1973) that asteroid impacts rather than satellite impacts were involved.     

Noble gases in the Allende and Abee meteorites and a gas-rich mineral fraction: investigation by stepwise heating

Noble gases in three meteoritic samples were examined by stepwise heating, in an attempt to relate peaks in the outgassing curves to specific minerals: NeKrXe in Allende (C3V) and an Allende residue insoluble in HF-HCl, and Xe in Abee (E4). In Allende, chromite and carbon contain most of the trapped Ne (²⁰Ne/²²Ne ≈ 8.7) and anomalous Xe enriched in light and heavy isotopes, and release it at ~850°C (bulk meteorite) or 1000°C (residue). Mineral Q, containing most of the trapped Ar, Kr, Xe as well as some Ne (²⁰Ne/²²Ne ≈ 10.4), releases its gases mainly between 1200 and 1600°C, well above the release temperatures of organic polymers (300–500°) or amorphous carbon (800–1000°). The high noble-gas release temperature, ready solubility in oxidizing acids, and correlation with acid-soluble Fe and Cr all point to an inorganic rather than carbonaceous nature of Q.All the radiogenic ¹²⁹Xe is contained in HCl, HF-soluble minerals, and is distributed as follows over the peaks in the release curve: Attend 1000° (75%), 1300° (25%); Abee (data of Hohenberg and Reynolds, 1969) ~850° (15%), 1100° (60%), 1300° (25%). No conclusive identifications of host phases can yet be given; possible candidates are troilite and silicates for Allende, and djerfisherite, troilite and silicates for Abee.Mineral Q strongly absorbs air xenon, and releases some of it only at 800–1000°C. Dilution by air Xe from Q and other minerals may explain why temperature fractions from bulk meteorites often contain less ^124–130Xe for a given enrichment in heavy isotopes than does xenon from etched chromitecarbon samples, although chromite-carbon is the source of the anomalous xenon in either case. Air xenon contamination thus is an important source of error in the derivation of fission xenon spectra.     

The fine structure of prominences

The fine structure of nonspot prominences are studied from H filtergrams. The size of the smallest prominence structures increases with height above the chromosphere. Some prominences contain structures close to 1/2 arc second, which is the spatial resolution in the present data. The effective thickness of many nonspot prominences ranges between 4 × 10⁷ cm and 1.5 × 10⁸ cm. An apparent downward directed motion is observed in the majority of the prominences. No preferred direction of the motion is seen in regions composed of comparatively large diffuse structures. Some bright threads are visible for 1 hr and longer. Bright knots have an average observed lifetime of about 8 min. The process of condensation and subsequent destruction of prominence fine structure appears to take place on a very short time scale compared to the life time of the regions where prominences may exist. The observed H brightness of the prominences in the present data may be accounted for as scattered chromospheric radiation.     

Single frequency processing of Ørsted GPS radio occultation measurements

The Global Positioning System (GPS) radio occultation measurements obtained using the TurboRogue GPS receiver on the Danish satellite Ørsted have been processed using the single frequency method. Atmospheric profiles of refractivity and temperature are derived and validated against numerical weather prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF). Results from the Ørsted GPS measurement campaign in February 2000 indicate that the single frequency method can provide retrievals with accuracy comparable to that of using two frequencies. From comparisons between measured dry temperature profiles and corresponding dry temperature profiles derived from ECMWF analysis fields, we find a mean difference of less than 0.5 K and a standard deviation of 2–4 K between 500 and 30 hPa in height. Above 30 hPa the impact of the ionosphere becomes more dominant and more difficult to eliminate using the single frequency method, and the results show degraded accuracy when compared to previous analysis results of occultation data from other missions using the dual frequency method. At latitudes less than 40° (denoted low latitudes), the standard deviation is generally smaller than at latitudes higher than 40° (denoted high latitudes). A small temperature bias is observed centered at 200 hPa for low latitudes and at 300 hPa for high latitudes. This indicates that the ECMWF analyses do not adequately resolve the tropopause temperature minimum. In the lowest part of the troposphere an observed warm bias is thought to be due to erroneous tracking of the GPS signal in cases of atmospheric multipath propagation.     

Daily Air Temperature and Pressure Series for Stockholm (1756–1998)

Daily meteorological observations have been made at the old astronomical observatory in Stockholm since 1754. Complete daily mean series of air temperature and sea level pressure are reconstructed from the observational data for 1756–1998. The temperature and pressure series arereconstructed and homogenized with the aid of metadata, statistical tests and comparisons with data from other stations. Comparisons with independently reconstructed daily series for nearby Uppsala (1722–1998) show that the quality of thedaily Stockholm data is good, although the reliability is lower before the mid-19th century. The daily temperature data show that the colder winter mean temperatures of the late 18th to early 19th centuries were connected with a particularly high frequency of very cold winter days. The warmer summers of the same period are more connected with a general shift of the temperature distribution towards higher temperatures than in the late 20th century.     

The fall and rise of metropolitan government in Copenhagen

In this paper it is argued that the re-establishment of a metropolitan government in the Greater Copenhagen Area in 2000 (Greater Copenhagen Authority) is not to be seen as a return to the kind of regional, coordinative authority (Greater Copenhagen Council) that was abolished in the Thatcherite climate of the 1980s. Throughout the 1980s and 1990s new forms of urban governance, entrepreneurialism and a higher national priority to the capital region were introduced, which changed the conditions under which the new metropolitan government is operating. This `contextualization' of the analysis of the two generations of metropolitan government points to the fact that typologies of metropolitan government, such as the one put forward by Sharpe (1995), often lacks analytical cogency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrons in feldspar II: a consideration of the influence of conduction band-tail states on luminescence processes

 Most natural feldspars contain many charged impurities, and display a range of bond angles, distributed about the ideal. These effects can lead to complications in the structure of the conduction band, giving rise to a tail of energy states (below the high-mobility conduction band) through which electrons can travel, but with reduced mobility: transport through these states is expected to be thermally activated. The purpose of this article is twofold. Firstly, we consider what kind of lattice perturbations could give rise to both localized and extended conduction band-tail states. Secondly, we consider what influence the band tails have on the luminescence properties of feldspar, where electrons travel through the sample prior to recombination. The work highlights the dominant role that 0.04–0.05-eV phonons play in both the luminescence excitation and emission processes of these materials. It also has relevance in the dating of feldspar sediments at elevated temperatures. Received: 11 May 2001 / Accepted: 6 September 2001     

Phytoplankton, nutrients, and transparency in Danish coastal waters

We present a comparative analysis of 1400 data series of water chemistry (particularly nitrogen and phosphorus concentrations), phytoplankton biomass as chlorophylla (chla) concentrations, concentrations of suspended matter and Secchi depth transparency collected from the mid-1980s to the mid-1990s from 162 stations in 27 Danish fjords and coastal waters. The results demonstrate that Danish coastal waters were heavily eutrophied and had high particle concentrations and turbid waters. Median values were 5.1 μg chla 1⁻¹, 10.0 mg DW 1⁻¹ of suspended particles, and Secchi depth of 3.6 m. Chlorophyll concentration was strongly linked to the total-nitrogen concentration. The strength of this relationship increased from spring to summer as the concentration of total nitrogen declined. During summer, total nitrogen concentrations accounted for about 60% of the variability in chlorophyll concentrations among the different coastal systems. The relationship between chlorophyll and total phosphorus was more consistant over the year and correlations were much weaker than encountered for total nitrogen. Secchi depth could be predicted with good precision from measurements of chlorophyll and suspended matter. In a multiple stepwise regression model with In-transformed values the two variables accounted for most of the variability in water transparency for the different seasons and the period March–October as a whole (c. 80%). We were able to demonstrate a significant relationship between total nitrogen and Secchi depth, with important implications for management purposes.