The stability of a velocity shear in the presence of an inhomogeneous magnetic field

The stability of a velocity shear in the presence of a parallel but non-uniform magnetic field is considered in general terms. Two special cases are then investigated; (i) the well known case of a plane interface at which a discontinuity in the magnetic field coincides with the velocity shear; (ii) an axially symmetric flow in which discontinuities in the magnetic and velocity fields occur at a cylindrical surface whose axis is parallel to the flow. In the first case the flow is stabilized if the rms Alfvén velocity of the magnetic field exceeds the shear velocity; a result consistent with that obtained by other writers. In the second case it is shown that the discontinuity in the magnetic field increases the stability of the system. The significance of this result for the stability of the flux ropes associated with sunspots in the solar convection zone is considered.     

A new model for flux emergence and the evolution of sunspots and the large-scale fields

Existing models for the evolution of sunspots and sunspot groups, describing the subsurface structure of the magnetic fields and their interactions with the convective motions, are briefly reviewed. It is shown that they are generally unable to account for the most recent data concerning the relationship between the large-scale solar magnetic field structures and the magnetic fields of active regions. In particular, it is shown that the former do not arise directly from the decay of the latter, as required by the Babcock model and all other models based on it. Other observations which are not adequately explained by current models are also cited.A new model is put forward based on the expulsion of toroidal magnetic flux by the dominant (i.e. giant) cells of the convection zone. The flux expelled above these cells forms the large-scale field and thus the configuration of this field provides a clue to the structure of the giant cell patterns. The flux expelled below the cells becomes twisted into a rope as in the Babcock model but a loop or stitch forms only in the region of upflow of the giant cells. The interaction of this loop with intermediate-sized cells as it rises to the surface determines the configuration and extent of the active region which appears at the surface. The compatibility of the model with other observations is discussed and its implications for theories of the solar cycle are noted.     

On the prospect of using butterfly diagrams to predict cycle minimum

On the basis of butterfly diagrams for the period 1874-present (covering late cycle 11 through late cycle 21), features are identified that may be useful for predicting the beginning and the length of a solar cycle, as well as the discernment of turning points in the period-growth dichotomy. For example, the first occurrence of high latitude new cycle spots during the decline of an old cycle usually occurs in the northern hemisphere, regardless of bimodal class, about 1.4 yr before new cycle minimum or about 5.4 yr after old cycle maximum, being true for 7 out of the 10 data-available cycles. Also, the last occurrence of high latitude old cycle spots tends to occur in the southern hemisphere when the old cycle is of long period (4 out of 4 cycles) and to occur in the northern hemisphere when the old cycle is of short period (4 out of 5 cycles). Application of these sorting features to the butterfly diagram for late cycle 21 yields candidate dates for the last occurrence of high latitude old cycle spots which in every case predict that cycle 21 will be a long-period cycle, ending after July 1987. Taking April 1985 to be the first occurrence of high latitude new cycle (cycle 22) spots during the decline of cycle 21 (the old cycle), one deduces that the last occurrence of high latitude old cycle spots was September 1983 (occurring in the southern hemisphere) and predicts that minimum for cycle 22 will be about 1986.7 ± 1.1 yr, or that it should occur before the end of 1987.     

Classification of five new ordinary chondrites (RC 073, 074, 076–078) from Roosevelt County,New Mexico

Abstract— Five new ordinary chondrites from Roosevelt County, New Mexico, USA, have been assigned to a chemical group, petrologic type and shock stage. All five are moderately to heavily weathered. They are: RC 073, H5(S2); RC 074, L5(S3); RC 076, L4(S3); RC 077 , L4(S2); RC 078, L4(S2).     

The extent and significance of mass-movements in Eastern Africa: case studies of some major landslides in Uganda and Kenya

The East African region has experienced major landslides in recent years. These landslides have caused many fatalities and injuries, loss of many hectares of productive farmlands and destruction to infrastructure such as roads, railways and bridges. The warm and wet climate of the landslide-prone regions causes rapid weathering and produces a regolith weaker than the underlying rock with an interface between the two layers. This interface serves as the most common plane along which landslides are initiated once it becomes saturated. Landslides in the region are associated with steep topography, human activities such as deforestation, overgrazing, and unplanned farming on steep slopes and are induced by earthquakes and high intensity of rainfall. The landslide-prone areas are agriculturally very productive and the inhabitants depend on agriculture for their livelihood. The areas also contribute substantially to the national food reserve. The landslides are therefore a burden to the economies of the individual farmers and national governments of the region.     

Geophysical monitoring and evaluation of coastal plain aquifers

We use time domain electromagnetic (TDEM) soundings to monitor ground water conditions beneath the coastal plain in eastern North Carolina. The TDEM method measures the earth's response to an induced electromagnetic field. The resulting signal is converted, through a complex inversion process, to apparent resistivity values, which can be directly correlated to borehole resistivity logs. TDEM soundings are used to map the interface between fresh and salt water within coastal aquifers, and estimate depth to basement when siting new monitoring wells. Focused TDEM surveys have identified areas of salt water encroachment caused by high volumes of discharge from local supply wells. Electromagnetic sounding, when used in tandem with the state's network of monitoring wells, is an accurate and inexpensive tool for evaluating fresh water/salt water relationships on both local and regional scales within coastal plain aquifers.     

Facular models and the sunspot energy deficit

The problem of the energy deficit in a sunspot is shown to be critically related to the depth of a given sunspot model. Recent facular models are discussed and a new model is derived from recent data using a two-dimensional radiative transfer analysis. The excess non-radiative energy required by this and other models is evaluated and it is shown that in some models this may account for a considerable fraction of the sunspot energy deficit. For these models the Alfvén energy travelling along the closed flux loops from the sunspot is insufficient to supply the requirements of the faculae and it is suggested that excess energy flux from below the faculae is also required. These results provide further support for deep as opposed to shallow sunspot models.