The British Government, Ernest Shackleton, and the rescue of the Imperial Trans-Antarctic Expedition

The remarkable rescue of Shackleton's men from Elephant Island, after the sinking of Endurance, and from Ross Island, has been recounted many times by both participants and historians. There has been little critical examination of the part played by governments, nor assessment of some of Shackleton's own actions. In this paper we explore more fully from official British archival sources the extent to which the British Government was prepared to underwrite the rescue efforts; the importance of the plea made by Emily Shackleton directly to the Prime Minister; the role and actions of the Relief Advisory Committee (especially in respect of limiting Shackleton's actions); the significance of the media rights to the debt-laden expedition, and how such preoccupation could have influenced Shackleton's endeavour to rescue his marooned parties

Solar-cycle modifications of the effects of thermospheric winds on the height of the F2-layer over Antarctica

Results of analysis of the diurnal variations of hmF2 for Argentine Islands (65°15'S, 64°16'W) and Halley Bay (75°30'S, 26°40'W) are presented. It is shown that, for summer months, the diurnal variations can be approximated by simple sinusoidal functions, the phases of which vary smoothly with solar activity. This behaviour can be explained in terms of the effects of thermospheric winds; it results partly from a change in the relative importance of ‘ion drag’ and Coriolis force, and partly from changes in the chemistry which controls the characteristic time required for the layer to respond to the wind. A comparison of observations and theory suggests that the local solar time at which the thermospheric pressure maximum occurs does not vary with solar activity

An improved model of the variation of electron concentration with height in the ionosphere

An empirical model of the variation of electron concentration with height is described which overcomes some limitations found in practice with a previous widely used model (Bradley and Dudeney, 1973). In particular, the new model will generate more realistic variations of electron concentration with real height and virtual height, both including and excluding an F1-ledge. The model has no gradient discontinuities and will reproduce cases in which the F1-ledge does not have a true turning point. The model should prove very valuable for a wide range of propagation problems and for certain aeronomical applications

The accuracy of simple methods for determining the height of the maximum electron concentration of the F2-layer from scaled ionospheric characteristics

The techniques for estimating hmF2 from M(3000)F2 are reviewed with particular stress put upon those in which the effects of underlying ionization are accounted for by a correction (ΔM) to M(3000)F2, formulated in terms of the ratio foF2/foE(=xE). The simplifying assumptions involved in the three practical implementations (Bradley and Dudeney, 1973; Dudeney, 1974; Bilitza et al., 1979) are emphasised and their consequences investigated quantitatively using a numerical simulation. The factors considered are the dependence upon ymF2, the importance of the underlying layer shape (in particular the significance of the F1-ledge), and the influence of the geomagnetic field. It is demonstrated that the correction technique relies upon ymF2 being a direct polynomial function of hmF2. Analysis of observational data suggests that this relationship holds in practice. Fluctuations in ymF2 about this mean variation are shown to produce only small effects which decrease in magnitude as the amount of underlying ionization increases. The results indicate that underlying layer shape becomes very important when a large amount of underlying ionization is present (xE<2.5). However, the global morphology of the occurrence of the F1-ledge is such that it is invariably present in such circumstances (ignoring the polar regions). Hence, the ionosphere tends to assume a specific profile form for low xE cases. The three implementations are shown all to fortuitously incorporate this behaviour. It is demonstrated that exclusion of the geomagnetic field introduces a very small extra uncertainty dependent upon gyrofrequency and geomagnetic latitude, which decreases as the amount of underlying ionization increases. The three implementations are compared and it is concluded that the Dudeney (1974) scheme gives the best overall performance. The more modern and complex Bilitza et al. (1979) scheme appears to have no performance advantages, whilst containing a sunspot number dependent geomagnetic term whose behaviour is irreconcilible with the numerical simulation. The Dudeney (1974) equation is shown to be accurate to between 4 and 5% at magnetic mid-latitudes. The scope for further refinement is considered but rejected as being unlikely to produce an increase in accuracy commensurate with the effort required