The reversal of the solar polar magnetic fields

Some theoretical difficulties confronting the current model of the polar magnetic reversal by cancellation with the flux remnants of decaying active regions are discussed. It is shown that the flux transport equation does not adequately describe the essential physical consequences of the transport of large-scale fields, linked to deep subsurface toroids, over distances comparable with the solar radius. The possibility that subsurface reconnections may release these fields to form U-loops is discussed but it is shown that, in this event, the loops will quickly rise to the surface. Mechanisms whereby the flux may escape through the surface are considered.     

Orbit of the Murchison meteorite

Abstract— Because the path of the Murchison meteorite fortuitously intersected the Earth's path at an angle of only a few degrees, the visual observations establish the entry velocity to be within 2 km/s of 13 km/s and determine the nature of its orbit with a precision quite unusual for visually sighted falls.     

The reversal of the solar polar magnetic fields

Observations of the first large-scale patterns of magnetic fields near the sunspot minimum of 1986 (the start of cycle 22) are presented using synoptic magnetic data provided by the National Solar Observatory and contour maps constructed from data provided by the Mount Wilson Solar Observatory. The latter are compared with simulated contour maps derived from numerical solutions of the flux transport equation using data from particular Carrington rotations as initial conditions.The simulated evolutions of the large-scale magnetic fields are qualitatively consistent with observed evolutions, but differ in several significant respects. Some of the differences can be removed by varying the diffusivity and the parameters of the large-scale velocity fields. The remaining differences include: (i) the complexity of fine structure, (ii) the response to differential rotation, (iii) the evolution of decaying active regions, and (iv) the emergence of new elements in the weak, large-scale fields independent of the evolution of the observed active regions.It is concluded that the patterns of weak magnetic fields which comprise the large-scale features cannot be formed entirely by the diffusive decay of active regions. There must be a significant contribution to these patterns by non-random flux eruptions within the network structure, independent of active regions.     

Three-dimensional strain produced by >50 My of episodic extension, Horse Prairie basin area, SW Montana, U.S.A.

The Horse Prairie basin of southwestern Montana is a complex, east-dipping half-graben that contains three angular unconformity-bounded sequences of Tertiary sedimentary rocks overlying middle Eocene volcanic rocks. New mapping of the basin and its hanging wall indicate that five temporally and geometrically distinct phases of normal faulting and at least three generations of fault-related extensional folding affected the area during the late Mesozoic (?) to Cenozoic. All of these phases of extension are evident over regional or cordilleran-scale domains. The extension direction has rotated 90° four times in the Horse Prairie area resulting in a complex three-dimensional strain field with 60% east–west and >25% north–south bulk extension. Extensional folds with axes at high angles to the associated normal fault record most of the three-dimensional strain during individual phases of extension (phases 3a, 3b, and 4). Cross-cutting relationships between normal faults and Tertiary volcanic and sedimentary rocks constrain the ages of each distinct phase of deformation and show that extension continued episodically for more than 50 My. Gravitational collapse of the Sevier fold and thrust belt was the ultimate cause of most of the extension.     

Comment on “superrotation of the upper atmosphere by global deposition of meteoroids”

The hypothesis that superrotation of the Earth's atmosphere results from meteoroid influx is untenable. Meteor observations are not of sufficient precision to substantiate direct rotation when the meteoroid influx is treated macroscopically. Detailed dynamic studies argue against any possible direct rotation.     

Partial analysis of the flare-prominence of 30 April 1974

A portion of an east limb flare-prominence observed in Hα by NOAA/Boulder and NASA/ MSFC patrol facilities on 30 April 1974 is analyzed. Following a rapid (～2 min) achievement of a maximum mass ejection velocity of about 375 km s^?1, the ascending prominence reached a height of, at least, 2 × 10⁵ km. We use a one-dimensional, time-dependent hydrodynamic theory (Nakagawa et al., 1975) to compute the total mass (～2 × 10¹¹ g) and energy (～4 × 10²⁶erg) ejected during this part of this event. Theoretical aspects of the coronal response are discussed. We conclude that a moderate temperature and density pulse (factors of ten and two, respectively), for a duration of only 3 min, is sufficient for an acceptable simulation of the Hα observations and the likely coronal response to the ascending prominence and flare-related ejections. No attempt was made to simulate the additionally-important spray and surge features which probably contributed a higher level of mass and energy efflux.     

A piston-driven shock in the solar corona

A solar flare that occurred on the west limb at 1981, March 25, 2038 UT generated a massive, rapidly-expanding optical coronal transient, which moved outward with an approximately constant velocity of 800 km s^–1. An associated magnetohydrodynamic shock travelled out ahead of the transient with a velocity estimated to be approximately 1000 km s^–1. The optical and radio data on the transient and shock fit well with general theories concerning piston-driven shocks and with current MHD models for propagation of such shocks through the solar corona.     

Evaluation of the importance of clay confining units on groundwater flow in alluvial basins using solute and isotope tracers: the case of Middle San Pedro Basin in southeastern Arizona (USA)

As groundwater becomes an increasingly important water resource worldwide, it is essential to understand how local geology affects groundwater quality, flowpaths and residence times. This study utilized multiple tracers to improve conceptual and numerical models of groundwater flow in the Middle San Pedro Basin in southeastern Arizona (USA) by determining recharge areas, compartmentalization of water sources, flowpaths and residence times. Ninety-five groundwater and surface-water samples were analyzed for major ion chemistry (water type and Ca/Sr ratios) and stable (¹⁸O, ²H, ¹³C) and radiogenic (³H, ¹⁴C) isotopes, and resulting data were used in conjunction with hydrogeologic information (e.g. hydraulic head and hydrostratigraphy). Results show that recent recharge (<60 years) has occurred within mountain systems along the basin margins and in shallow floodplain aquifers adjacent to the San Pedro River. Groundwater in the lower basin fill aquifer (semi confined) was recharged at high elevation in the fractured bedrock and has been extensively modified by water-rock reactions (increasing F and Sr, decreasing ¹⁴C) over long timescales (up to 35,000 years BP). Distinct solute and isotope geochemistries between the lower and upper basin fill aquifers show the importance of a clay confining unit on groundwater flow in the basin, which minimizes vertical groundwater movement.     

A comparative synoptic climatology of cool-season rainfall in major grain-growing regions of southern Australia

Two distinct synoptic weather systems, cut-off lows and fronts, deliver most of the cool-season rainfall to the cropping regions of southern Australia. A comparative synoptic climatology of daily rainfall events over approximately five decades reveals both spatial and temporal variations of the dominant synoptic types. The rainfall characteristics and associated large-scale drivers differ between the two synoptic types. Understanding regional rainfall depends on understanding these differences. Cut-off lows contribute one half of growing season rainfall in southeast Australia, while frontal systems associated with Southern Ocean depressions contribute about a third. The proportions are reversed in the Central Wheat Belt (CWB) of Western Australia where Southern Ocean fronts are the dominant source of growing season rainfall. In the southern island state of Tasmania, topography strongly influences the outcome with cut-off lows contributing about half the rainfall near the east coast and fronts dominating a short distance to the west. Cut-off lows generally contribute their highest proportion of rainfall in the austral autumn and spring while frontal rainfall is at its maximum in late winter. Cut-off low rainfall contributes more strongly in percentage terms to the recent decline in rainfall. The distribution of synoptic types is explained by the dominant long-wave structure in the winter half of the year. The major trough near Western Australia favours frontogenesis to the southwest of the CWB but fronts moving out of the region encounter a persistent meridional ridge in the Tasman Sea where there is a high frequency of blocking events.