Monthly mean winds in the mesosphere at 44S and 78S

A medium frequency partial-reflection spaced-antenna wind radar was installed at Scott Base (78S) on Ross Island, Antarctica, in November 1982. Results from this radar for the period December 1982 to October 1984 inclusive are compared with simultaneous measurements made with a similar radar at Christchurch (44S), N. Z. Monthly mean zonal winds measured at 80 km are compared with recent models for the Southern Hemisphere middle atmosphere. There is a general agreement with the models but there is evidence that the Christchurch winter flow was atypical in 1983.     

K/Ar dates of hydrothermal clays from core hole VC-2B, Valles caldera, New Mexico and their relation to alteration in a large hydrothermal system

Seventeen K/Ar dates were obtained on illitic clays within Valles caldera (1.13 Ma) to investigate the impact of hydrothermal alteration on Quaternary to Precambrian intracaldera and pre-caldera rocks in a large, long-lived hydrothermal system ( 1.0 Ma to present). Clay samples came from scientific core hole VC-2B (295°C at 1762 m) which was spudded in the Sulphur Springs thermal area and drilled into the boundary between the central resurgent dome and the western ring-fracture zone. Six illitic clays within Quaternary caldera-fill debris flow, tuffaceous sediment, and ash-flow tuff (48 to 587 m depth) yield ages from 0.35 to 1.09 Ma. Illite from Miocene pre-caldera sandstone (765 m) gives an age of 6.74 Ma. Two dates on illite from sandstones in Permian red beds (1008 and 1187 m) are 4.33 and 4.07 Ma, respectively. Surprisingly, three dates on illites from altered andesite pebbles within the red beds (1010–1014 m) are 0.95 to 1.06 Ma. Four illite dates on variably altered Precambrian quartz monzonite (1615–1762 m) range from 2.90 to 276 Ma.Post-Valles age illite is not correlated with alteration style (argillic to propylitic). Rather, post-Valles ages are uniformly obtained from illites in highly fractured, intensely altered, caldera-fill rocks and the Permian volcanic clasts. Generally, finer clay fractions from identical samples yield younger ages. Plots of ⁴⁰Ar/³⁶Ar versus ⁴⁰K/³⁶Ar and ⁴⁰Ar* versus ⁴⁰K for the illites in caldera-fill rocks lie close to a 1-Ma isochron. Most illite dates older than Valles caldera are difficult to interpret because they correspond to the ages of pre-Valles volcanic and hydrothermal episodes in the Jemez volcanic field ( 13 Ma). In addition, older dates may be caused by co-mingling of different illites during sample preparation, or by inherited argon or lost argon in illites from rocks with potentially complex hydrothermal histories. However, the range of ages obtained from illites in Permian sands and pebbles and from Precambrian crystalline rocks indicates that Valles hydrothermal activity is overwhelming illite produced by earlier geologic events.     

Carbon tetrachloride lifetimes and emissions determined from daily global measurements during 1978–1985

Seven years of daily gas chromatographic measurements of CCl₄ at the five globally distributed ALE/GAGE surface sites are reported. It is determined that CCl₄ has been accumulating in the atmosphere at a rate of 1.3±0.1%/yr over the period 1978–1985 and that the releases of CCl₄ into the atmosphere have remained fairly constant, with the smallest releases in 1981–1982. Using an inversion scheme based on a nine box model of the atmosphere, we infer a CCl₄ lifetime of approximately 40 yr, an inventory on 1 July 1978 of (2.08±0.07)×10⁹ kg and an average rate of release over the period 1978–1985 of (0.9±0.9)×10⁷ kg/yr. These results produce excellent agreement with a release scenario derived from global production estimates for CCl₄ and the major CCl₄ byproduct, the chlorofluorocarbons. However, to obtain this consistency, it is necessary that our current ALE/GAGE absolute calibration standard be reduced approximately 25% thus bringing it into agreement with measurements by Yokohata et al. (1985) and Hanst et al. (1975).     

Propagation of Pc 1 pulsations in off-meridian directions

Experimental investigations on the horizontal propagation of Pc 1 pulsations in directions out of the geomagnetic meridian have been carried out using data recorded over a three-year period at four widely-separated middle and low latitude stations. The results obtained show that Pc 1 signals propagate in off-meridian directions, and that horizontal propagation characteristics in the early morning hours have small directional changes.     

Ionospheric dispersion and Pc 1 pulsations

Dispersion measurements were performed on geomagnetic pulsation data recorded over an Australasian network in a search for evidence of ionospheric dispersion of Pc 1 signals. A method of analysis was adopted in which the slope of emission elements of a selected Pc 1 event are examined individually. It has been found that there are no significant ionospheric dispersion effects for propagation between middle and low latitudes. Magnetospheric propagation paths calculated from dispersion measurements show large variations and are not considered generally reliable.     

Theoretical Love wave dispersion in a single layer model

Summary From a study of the Love wave dispersion in a single layer model it is shown that the shape of the dispersion curves is very insensitive to the changes in the density ratio. The bilogarithmic grids giving dispersion curves for different shear velocity ratios and a mean density ratio of 1.20 should be sufficient for interpretation by the method of curve matching. Such grids and the numerical data are given both for the phase velocity and the group velocity. An example is given illustrating the use of these grids.     

Peripherality in the global container shipping network: the case of the Southern African container port system

Regional trade co-operation, economic growth and greater political stability have enabled increased container throughput and container port capacity development. Earlier academic work has indicated that the functional position of this port region in the global maritime network might be shifting from a remote region in the periphery of the network to a more intermediate position. This paper aims to analyze the changing level of peripherality and remoteness of the Southern African container port system as part of the global container shipping network. The central hypothesis is that Southern Africa has moved from a remote shipping region to a more central shipping region in the global network. The methodology consists of the calculation of network measures for Southern African ports. The changing geographical distribution of flows among the main container ports in South Africa, Namibia, Mozambique, Mauritius and Madagascar will also be explored in terms of their respective shipping services, port calling patterns, market structure (in terms of the number of active carriers) and the up-scaling of vessel and port capacity. The overall result is a mapped port hierarchical structure with a clear indication of the shifted maritime centrality of Southern African ports from 1996 to the present decade.     

Measurements of trace gases emitted by Australian savanna fires during the 1990 dry season

During 18–23 July 1990, 31 smoke samples were collected from an aircraft flying at low altitudes through the plumes of tropical savanna fires in the Northern Territory, Australia. The excess (above background) mixing ratios of 17 different trace gases including CO₂, CO, CH₄, several non-methane hydrocarbons (NMHC), CH₃CHO, NO _x (– NO + NO₂), NH₃, N₂O, HCN and total unspeciated NMHC and sulphur were measured. Emissionratios relative to excess CO₂ and CO, and emissionfactors relative to the fuel carbon, nitrogen or sulphur content are determined for each measured species. The emission ratios and factors determined here for carbon-based gases, NO _x , and N₂O are in good agreement with those reported from other biomass burning studies. The ammonia data represent the first such measurements from savanna fires, and indicate that NH₃ emissions are more than half the strength of NO _x emissions. The emissions of NO _x , NH₃, N₂O and HCN together represent only 27% of the volatilised fuel N, and are primarily NO _x (16%) and NH₃ (9%). Similarly, only 56% of the volatilised fuel S is accounted for by our measurements of total unspeciated sulphur.