The pattern of surface wind flow in Antarctica

Summary The main characteristics of surface winds are tabulated for 34 Antarctic stations. Using these data, supplemented by traverse records, the average wind flow is interpolated for each region and presented as a map showing the pattern of surface wind flow for the whole continent. Attention is focused on the flow in relation to surface contours. Statistics are presented for surface slope, wind speed, temperature, seasonal variations of speed and temperature, diurnal variation (including power spectra) of the wind speed and times of maximum and minimum speed at coastal and inland stations, wind frequency versus direction, the occurrence of calms, the deviation of the plateau wind from the downslope direction, the wind direction near the front of ice shelves, the proportion of cloud cover, and wind chill factors. In all cases data are grouped according to the environs of the stations in an attempt to isolate systematic differences depending on location: coastal stations near the foot of the ice slope and fully exposed to katabatic flow, coastal stations on offshore islands, coastal stations on peninsulas, coastal stations on extensive rock areas, ice shelf stations and inland stations.     

On the evaluation of stationary sea surface topography using geodetic techniques

One of the principal problems in separating the non-tidal Newtonian gravitational effects from other forces acting on the ocean surface with a resolution approaching the 10 cm level arises as a consequence ofall measurements of a geodetic nature being taken eitherat orto the ocean surface. The latter could be displaced by as much as ±2 m from the equipotential surface of the Earth’s gravity field corresponding to the mean level of the oceans at the epoch of observation— i.e., the geoid. A secondary problem of no less importance is the likelihood of all datums for geodetic levelling in different parts of the world not coinciding with the geoid as defined above. It is likely that conditions will be favourable for the resolution of this problem in the next decade as part of the activities of NASA’s Earth and Ocean Physics Applications Program (EOPAP). It is planned to launch a series of spacecraft fitted with altimeters for ranging to the ocean surface as part of this program. Possible techniques for overcoming the problems mentioned above are outlined within the framework of a solution of the geodetic boundary value problem to ±5 cm in the height anomaly. The latter is referred to a “higher” reference surface obtained by incorporating the gravity field model used in the orbital analysis with that afforded by the conventional equipotential ellipsoidal model (Mather 1974 b). The input data for the solution outlined are ocean surface heights as estimated from satellite altimetry and gravity anomalies on land and continental shelf areas. The solution calls for a quadratures evaluation in the first instance. The probability of success will be enhanced if care were paid to the elimination of sources of systematic error of long wavelength in both types of data as detailed in (Mather 1973 a; Mather 1974 b) prior to its collection and assembly for quadratures evaluations.     

The harmonic representation of the disturbing potential

Summary The alternative harmonic representations of the disturbing potential, correct to the order of the flattening, are examined and an example is given where the incorrect use of a spherical harmonic expansion can give rise to fallacious results. The correct usage of the spherical harmonic expansion for the disturbing potential is given in the solution of the general surface integral to define the indirect effect in the case of the non-regularised geoid.     

Four dimensional studies in Earth space

Summary A system of reference which is directly related to observations, is proposed for four dimensional studies in Earth space. The requisite data is used to define both global control network and also polar wandering. The determination of variations of the Earth’s gravitational field with time also forms part of such a system. Techniques are outlined for the unique definition of the motion of the geocenter, and the changes in the location of the axis of rotation of an instantaneous Earth model, in relation to values at some epoch of reference. The instantaneous system referred to is directly related to a fundamental equation in geodynamics. The reference system defined would provide an unambiguous frame for long period studies in Earth space, provided the scale of the space were specified. Presented at the I.A.G./A.G.U. Symposium on Earth Gravity Models related problems, St Louis, Missouri, U.S.A., 16–18 August 1972.     

The forest transition: a theoretical basis

Summary A theoretical basis for the forest transition (the change from contraction to expansion of national forest area) is suggested in terms of increasing agricultural adjustment to land quality. This adjustment, operating through a process of learning by farmers, results in the concentration of agricultural production in smaller areas of better land, and the agricultural abandonment of larger areas of poorer land, which are then available for reforestation through natural regeneration or planting.     

The influence of great earthquakes on volcanic eruption rate along the Chilean subduction zone

Seismic activity has been postulated as a trigger of volcanic eruption on a range of timescales, but demonstrating the occurrence of triggered eruptions on timescales beyond a few days has proven difficult using global datasets. Here, we use the historic earthquake and eruption records of Chile and the Andean southern volcanic zone to investigate eruption rates following large earthquakes. We show a significant increase in eruption rate following earthquakes of M_W > 8, notably in 1906 and 1960, with similar occurrences further back in the record. Eruption rates are enhanced above background levels for ~ 12 months following the 1906 and 1960 earthquakes, with the onset of 3–4 eruptions estimated to have been seismically influenced in each instance. Eruption locations suggest that these effects occur from the near-field to distances of ~ 500 km or more beyond the limits of the earthquake rupture zone. This suggests that both dynamic and static stresses associated with large earthquakes are important in eruption-triggering processes and have the potential to initiate volcanic eruption in arc settings over timescales of several months.