The non-independence of rainfall erosivity and soil erodibility

Three high erosivity conditions (50 mm hr^?1, 100 mm hr^?1, and 200 mm hr^?1) were generated in a laboratory using a rainfall simulator and coherent soil block samples from fourteen different soil erodibility conditions. The data acquired supports the theoretical contention that soil loss should not increase as a simple linear function of storm intensity. Rather, a variable relationship is caused by the rupturing of surface seals and the changing relative significance of splash, wash and rainwash processes. Slope angle appears to influence soil loss at the higher erosivity conditions of 100 mm hr^?1 and 200 mm hr^?1 on slopes that were either very steep (> 20°) or very shallow (< 3°), but on moderate slopes the relationship is unclear. Examination of the variation of soil loss with erosivity when soil loss for a specific high erosivity condition is known revealed that conversion and power factors are of doubtful value and little generality. A satisfactory predictive equation, a power curve, is seen to be of value only when comparing rainwash soil loss between the higher erosivity conditions. The relationship is most safely considered as soil and site specific. Where the influence of slope and soil erodibility are disregarded, a strong association between soil loss and rainfall intensity is found. That soil loss, and hence, soil erodibility varies non-uniformly with erosivity is clear. The findings indicate caution is required when comparing conclusions drawn from studies based upon different erosivity conditions.     

A Framework and Software Tool to Support Collaborative Landscape Analysis: Fitting Square Pegs into Square Holes

For landscape models to be applied successfully in management situations, models must address appropriate questions, include relevant processes and interactions, be perceived as credible and involve people affected by decisions. We propose a framework for collaborative model building that can address these issues, and has its roots in adaptive management, computer‐supported collaborative work and landscape ecology. Models built through this framework integrate a variety of information sources, address relevant questions, and are customized for the particular landscape and policy environment under study. Participants are involved in the process from the start, and because their input is incorporated, they feel ownership of the resulting models, increasing the chance of model acceptance and application. There are two requirements for success: a tool that supports rapid model prototyping and modification, that makes a clear link between a conceptual and implemented model, and that has the ability to implement a wide range of model types; and a core team with skills in communication, research and analysis, and knowledge of ecology and forestry in addition to modelling. SELES (Spatially Explicit Landscape Event Simulator) is a tool for building and running models of landscape dynamics. It combines discrete event simulation with a spatial database and a relatively simple modelling language to allow rapid development of landscape simulations, and provides a high‐level means of specifying complex model behaviours ranging from management actions to natural disturbance and succession. We have applied our framework in several forest modelling projects in British Columbia, Canada. We have found that this framework increases the interest by local experts and decision‐makers to participate actively in the model building process. The workshop process and resulting models have efficiently provided insight into the dynamics of large landscapes over long time frames. The use of SELES has facilitated this process by providing a flexible, transparent environment in which models can be rapidly implemented and refined. As a result, model findings may be more readily incorporated into decision‐support systems designed to assist resource managers in making informed decisions.     

The relation between the concentration of atmospheric condensation nuclei and other meteorological elements at valentia observatory

Summary Measurements of the concentration of condensation nuclei made twice daily (0h and 12h GMT) with aNolan-Pollak photo-electric counter at Valentia Observatory, in the extreme Southwest of Ireland, over the 4 years 1951–1954, are analysed to show relation with other meteorological elements. It is found that concentration at 12h is generally higher than at (h and that precipitation at the time of observation or in the preceding hour reduces concentration by between 40% and 50%. From measurements made when there was no precipitation at the time or in the previous hour it is found that concentration decreases with increasing wind speed but does not vary appreciably with wind direction apart from a sector from which pollution could be expected. High concentrations are found with visibility below 7 miles, with inversion of temperature, when free from the effects of pollution, follows fairly closely that of duration of bright sunshine.

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Zusammenfassung Es werden Messungen der Konzentration von Kondensationskernen, welche zweimal täglich (um 0 ^h und 12 ^h G.M.T.) mit einem photo-elektrischen Kernzähler nachNolan undPollak am Observatorium in Valentia (im äussersten Südwesten von Irland) in den Jahren 1951 bis 1954 durchgeführt wurden, auf Beziehungen zu anderen meteorologischen Elementen hin untersucht. Die Resultate zeigen, dass die Konzentration um 12 Uhr im allgemeinen grösser ist als um 0 Uhr und, dass die Niederschlag zur Zeit der Beobachtung oder in der der Beobachtung vorausgehenden Stunde die Konzentration um 40 bis 50% herabsetzt. Wenn kein Niederschlag zur Zeit der Messung oder in der vorangehenden Stunde verzeichnet wurde, nimmt die Konzentration mit zunehmender Windgeschwindigkeit ab; sie ändert sich jedoch nicht nennenswert mit der Windrichtung, abgesehen von einem Sektor, aus welchem Verunreinigung zu erwarten war. Hohe Konzentration wurde bei Sichtweiten unterhalb 7 Meilen gefunden, ferner bei Temperaturinversion, und, um 12 Uhr, bei geringer Bewölkung. Der jährliche Gang der Konzentration der Kerne folgt ziemlich genau jenem der Sonnenscheindauer, wenn die Fälle, wo Verunreinigung der Luft stattfindet, ausgeschlossen werden.

     

Absence of whistlers at the equator reaffirmed

Synoptic observations made on magnetic recording tape at Huancayo, Peru, at the magnetic dip equator, during the International Geophysical Year 1957–1958, were aurally reviewed at that time and no whistlers, hiss, or other emissions were heard. In view of the more recent observation of whistlers at geomagnetic latitudes as low as 12°, and in conjunction with a study of equatorial hiss observed in the topside ionosphere, these recordings have recently been reassessed by reducing them with modern real-time, digital spectrographic equipment. Although the observations were found to be of high quality, and to show the classical features of ground-wave and sky-wave propagation of sferics and VLF transmissions, again no evidence whatsoever of whistlers, hiss, or other emissions is found. Thus it is concluded that the whistlers observed at very low latitudes do not propagate subionospherically to the equator and it is confirmed that “hybrid” whistlers must be due to subionospheric propagation across the equator of the causative sferic rather than of the short whistler.     

Circulating subbeam systemsand the physics of pulsar emission

The purpose of this paper is to suggest how detailed single-pulse observations of slow radio pulsars may be utilized to construct an empirical model for their emission. It links the observational synthesis developed in a series of papers by Rankin in the 1980s and 90s to the more recent empirical feedback model of Wright (2003a) by regarding the entire pulsar magnetosphere as a non-steady, non-linear interactive system with a natural built-in delay. It is argued that the enhanced role of the outer gap in such a system indicates an evolutionary link to younger pulsars, in which this region is thought to be highly active, and that pulsar magnetospheres should no longer be seen as being driven by events on the neutron stars polar cap, but as having more in common with planetary magnetospheres and auroral phenomena.Received: 8 May 2003, Published online: 14 November 2003 Correspondence to: Joanna M. Rankin. On leave from: Physics Department, University of Vermont, Burlington, VT 05405, USA     

First Results from Viper: Detection of Small-scale Anisotropy at 40 GHz

Using all available major samples of Seyfert galaxies and their corresponding closely matched control samples of nonactive galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in nonactive galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., "thin" or "strong" bars) in Seyfert galaxies compared to nonactive galaxies. Accompanied with a large dispersion due to small number statistics, this effect is strictly speaking at the 2 sigma level. To obtain this result, the active galaxy samples of near-infrared surface photometry were matched to those of normal galaxies in type, host galaxy ellipticity, absolute magnitude, and, to some extent, redshift. We discuss possible theoretical explanations of this phenomenon within the framework of galactic evolution, and, in particular, of radial gas redistribution in barred galaxies. Our conclusions provide further evidence that Seyfert hosts differ systematically from their nonactive counterparts on scales of a few kiloparsecs.