Ball lightning as a radiation bubble

Summary A model for ball lightning is presented and its properties discussed. The model is that of a microwave radiation field contained within a plasma dielectric sphere, resonant at a frequency much greater than the electron-molecule collision frequency. Calculations are made of the energy stored in the microwave field, the electron temperature, the rate of energy loss due to ionization, and the effects of recombination. It is concluded (a) that a self-consistent set of conditions can be obtained only when the neutral density within the sphere is much lower than atmospheric, and (b) that the microwave field strength required is of the order of 10⁹V/m. Under these conditions the radiation pressure becomes comparable to that of the atmosphere; the second case investigated is when these two become equal. It is then found that this radiation bubble appears to satisfy the requirements imposed on energy storage and dissipation, recombination and resonant frequency. The electron density in such a bubble is found to be typically 10¹¹ cm^–3 and the stored energy typically 10³ Joules. A discussion is given of some of the problems associated with the model-formation, stability, neutral number density, and the problem of hydrostatic equilibrium.     

The structure and evolution of coronal holes

When observed at soft X-ray wavelengths coronal holes are seen as open features, devoid of X-ray emission and bounded by apparently divergent coronal loop structures. Inspection of the topology of the photospheric magnetic fields associated with these features suggests that holes are formed when the remnants of active region fields, emerging in both hemispheres over a period of several solar rotations, combine to form a large area of essentially unipolar field. Remnants of opposite polarity fields surround these features resulting in a divergent magnetic configuration at the hole boundaries. Holes are seen to form and evolve while the large scale divergent field pattern is reinforced and to close when large scale remnants occur which disrupt the general field pattern. Two types of holes are observed in the early Skylab observations. The first are elongated features which are aligned approximately north-south extending from one solar pole to a polar filament channel in the opposite hemisphere. The polar holes and somewhat lower latitude holes appear to lie in unipolar areas which are completely confined by opposite polarity fields. Studies of the rotation properties of an elongated hole, which extended from the north pole to a latitude of approximately 20° S, showed it to rotate with a synodic rate of (13.25±0.03)?(0.4±0.1 sin²φdeg day^?1. Possible explanations for the almost rigid rotational characteristics of this feature are discussed.     

An Estimate of Eros's Porosity and Implications for Internal Structure

Earth-based spectral measurements and NEAR Shoemaker magnetometer, X-ray, and near-infrared spectrometer data are all consistent with Eros having a bulk composition and mineralogy similar to ordinary chondrite meteorites (OC). By comparing the bulk density of 433 Eros (2.67±0.03 g/cm³) with that of OCs (3.40 g/cm³), we estimate the total porosity of the asteroid to be 21-33%. Macro (or structural) porosity, best estimated to be ∼20%, is constrained to be between 6 and 33%. We conclude that Eros is a heavily fractured body, but we find no evidence that it was ever catastrophically disrupted and reaccumulated into a rubble pile.     

Photogrammetric and laser altimetric reconstruction of water levels for extreme flood event analysis

This paper assesses the feasibility of estimating water levels using digital photogrammetry. A common problem during an extreme flood event is that automated water level recorders do not record the highest water levels, as a result of instrument malfunctioning. This paper explores two possible solutions to this problem based upon data acquired using synoptic remote sensing methods. The first method requires: (a) high-resolution elevation data (for example, in the form of a digital elevation model for the floodplain); and (b) information on the planimetric position of the maximum flood extent, such as from debris lines (known as wrack lines) visible on aerial imagery flown after the event. The planimetric data can then be used to segment the topographic data in order to identify water level elevations. The second method uses a digitial photogrammetric approach and is suitable where no topographic data are available, but aerial imagery is available, flown after the event. Provided this imagery is of the right scale, digital photogrammetric analysis may be used to identify the elevations of wrack lines visible on the imagery. In this paper, the second of these options is compared with the first. The research shows that desktop photogrammetric methods, using 1:4500 scale imagery, can yield water level estimates that are precise to ±0·147 m, on the basis of check data obtained from lidar data. This is a worst possible estimate of the acquired precision given uncertainties in the lidar data. When compared with the first option, based upon segmenting lidar data using flood outlines, the photogrammetric approach was found to be preferable given both the quality of the lidar and uncertainties over how to segment it.     

A chlorine-36 study of regional groundwater flow and vertical transport in southern Nevada

Chlorine-36 data for groundwater from the Death Valley regional flow system is interpreted in the context of existing conceptual models for regional groundwater flow in southern Nevada. Chlorine-36 end member compositions are defined for both recharge and chemically evolved groundwater components. The geochemical evolution of ³⁶Cl is strongly controlled by water-rock interaction with Paleozoic carbonate rocks that comprise the regional aquifer system, resulting in chemically evolved groundwater that is characteristically low in ³⁶Cl/Cl and high in Cl. Groundwater from alluvial and volcanic aquifers that overlie the regional carbonate aquifer are generally characterized by high ³⁶Cl/Cl and low Cl signatures, and are chemically distinct from water in the regional carbonate aquifer. This difference provides a means of examining vertical transport and groundwater mixing processes. In combination with other geochemical and hydrogeologic data, the end members defined here provide constraints on aquifer residence times and mixing ratios.     

Mathematical Geology in Perspective: Has Objective Hypothesis Testing Become Overlooked?

The meaning of the term Mathematical Geology was contentious at the founding meeting of IAMG in 1968 and has remained so ever since. In North American usage, it has primarily meant statistical applications in geology, and thus is an extension of inventory that has been traditional in geology. To the Leningrad school (originally led by A. B. Vistelius), it is the discipline of testing geological hypotheses mathematically. Although mathematical hypothesis testing has considerable potential for the earth sciences, unfortunately, by comparison with inventory-type studies, it has received very little attention. Reference is drawn to recent papers in which geological hypotheses have been tested mathematically.     

Testing spatial patterns and growth spillover effects in clusters of cities

 This paper analyzes the spatial patterns of households' distribution in clusters of cities and the effects on regional growth using spatial exploratory techniques and a model of growth that incorporates spatial location. Our empirical analysis shows that, over the 1980–1990 period, in Southern New England, patterns of spatial clustering of households did create heterogeneous growth rates in the region. Also, there is evidence that clusters of cities and isolated cities created spillover growth effects in bordering towns. Received: 5 September 2001 / Accepted: 2 August 2002     

Incipient tunnel channels

Glaciated terrains in east-central Alberta and south-central Michigan contain channels that have hummocks and transverse ridges separating depressions along their floors. This association imparts a linked pothole appearance. Similar channels are often interpreted as tunnel channels or subaerial channels, partly filled with sediment from a subsequent glacial advance, a stagnating ice roof, or slumped sediment from the channel margins. However, the truncation of sedimentary packages in the channel walls and intrachannel hummocks indicates that they are erosional landforms, cut into glacial sediments (till), bedrock, or gravel. Eskers overlie and are found within a few channels, indicating that these channels formed before the final stagnation that produced the eskers. These two characteristics, combined with the observation that many channels have convex-up long profiles, indicate that the channels were eroded by pressurized, subglacial water. Because the formative mechanisms for this type of channel are not clear, and modern environments that could produce this type of landform are inaccessible, we draw on several morphologic analogues to propose mechanisms for channel erosion. We conclude that the erosion of these linked pothole channels (incipient tunnel channels) was the product of the complex interaction between complex turbulent flow structures and various scales of roughness elements.     

Geophysical modeling of the northern Appalachian Brompton-Cameron, Central Maine, and Avalon terranes under the New Jersey Coastal Plain

A regional terrane map of the New Jersey Coastal Plain basement was constructed using seismic, drilling, gravity and magnetic data. The Brompton-Cameron and Central Maine terranes were coalesced as one volcanic island arc terrane before obducting onto Laurentian, Grenville age, continental crust in the Taconian orogeny [Rankin, D.W., 1994. Continental margin of the eastern United States: past and present. In: Speed, R.C., (Ed.), Phanerozoic Evolution of North American Continent-Ocean Transitions. DNAG Continent-Ocean Transect Volume. Geological Society of America, Boulder, Colorado, pp. 129–218]. Volcanic island-arc rocks of the Avalon terrane are in contact with Central Maine terrane rocks in southern Connecticut where the latter are overthrust onto the Brompton-Cameron terrane, which is thrust over Laurentian basement. Similarities of these allochthonous island arc terranes (Brompton-Cameron, Central Maine, Avalon) in lithology, fauna and age suggest that they are faulted segments of the margin of one major late Precambrian to early Paleozoic, high latitude peri-Gondwana island arc designated as “Avalonia”, which collided with Laurentia in the early to middle Paleozoic. The Brompton Cameron, Central Maine, and Avalon terranes are projected as the basement under the eastern New Jersey Coastal Plain based on drill core samples of metamorphic rocks of active margin/magmatic arc origin. A seismic reflection profile across the New York Bight traces the gentle dipping (approximately 20 degrees) Cameron's Line Taconian suture southeast beneath allochthonous Avalon and other terranes to a 4 sec TWTT depth (approximately 9 km) where the Avalonian rocks are over Laurentian crust. Gentle up-plunge (approximately 5 degrees) projections to the southwest bring the Laurentian Grenville age basement and the drift-stage early Paleozoic cover rocks to windows in Burlington Co. at approximately 1 km depth and Cape May Co. at approximately 2 km depths. The antiformal Shellburne Falls and Chester domes and Chain Lakes-Pelham dome-Bronson Hill structural trends, and the synformal Connecticut Valley-Gaspe structural trend can be traced southwest into the New Jersey Coastal Plain basement. A Mesozoic rift basin, the “Sandy Hook basin”, and associated eastern boundary fault is identified, based upon gravity modeling, in the vicinity of Sandy Hook, New Jersey. The thickness of the rift-basin sedimentary rocks contained within the “Sandy Hook basin” is approximately 4.7 km, with the basin extending offshore to the east of the New Jersey coast. Gravity modeling indicates a deep rift basin and the magnetic data indicates a shallow magnetic basement caused by magnetic diabase sills and/or basalt flows contained within the rift-basin sedimentary rocks. The igneous sills and/or flows may be the eastward continuation of the Watchung and Palisades bodies.