Some observations at Halley Bay in seismology, glaciology and meteorology

Abstract

1. Seismology Considerable microseismic activity was observed at Halley Bay during the summer season from December to February, particularly during on-shore winds. Examples of microseismic and wind observations are shown to illustrate the nature of the relation between these two observations. The short-period three-component Willmore seismograph used on the floating ice-shelf was found to record P earth waves from earthquakes at most epicentral distances but S waves were badly recorded. 2. Glaciology The results of elevation, temperature and accumulation studies on the ice-shelf are presented and discussed. These indicate that the ice-shelf was floating with its flat upper surface maintained at 28.6 m above sea level by the yearly addition of about 1 m of snow with a mean density of 0.36 g cm -3 . The results of daily accumulation studies are examined ; these show that during winter considerable ablation occurred during 24 h and therefore the net accumulation of longer periods may be due to precipitation greatly in excess of the net accumulation. Geomagnetic survey measurements over a small area around the base showed that the coastal features of the ice-front were defined by geological structure beneath the ice-shelf. 3. Meteorology ( a ) The seasonal features of the behaviour of the atmosphere over Halley Bay up to a height of about 20 km are shown and discussed with special reference to wind and tempera­ture changes. A notable feature is the small annual range of monthly mean air temperatures through the troposphere, where extremes are about 10 °C apart, and the increase in the range of mean air temperatures through the stratosphere culminating, at the top of the ascents, in extremes 59.3 °C apart at the 30 mb surface. ( b ) The variation of total and diffuse solar radiation received at Halley Bay on a horizontal surface is examined for dependence on solar elevation, cloud, and drifting snow. With a solar elevation of between 5 and 35°, total solar radiation is within 5 % of 75 % of the estimated extra-terrestrial radiation in the band from about 0.3 to 3.0 μ. Diffuse radiation accounts for a greater proportion of total radiation as the solar elevation falls from 14 % at 35° elevation to 30% at 5° elevation. The effect of low and medium cloud of all types was found to be similar, and depended on cloud cover and solar elevation. The seasonal and diurnal variation of the net flux of short- and long-wave radiation is examined. Over the year 1958 the net flux of radiation was an outward flow of 590 cal cm -2 , to an estimated accuracy of about 50 %, despite the exceptionally sunny weather of November and December when the mean radiation income amounted to 62 cal cm -2 day -1 . ( c ) The results of sixteen ozone soundings made in 1958 are described and discussed. A clear relation was observed between the first tropopause and the beginning of the ozone layer, even in winter when the determination of the tropopause from temperature lapse changes was more difficult. The results of the soundings describe the seasonal changes in the form of the lower part of the ozone layer and confirm the lateness of the seasonal rise in the total quantity of ozone in the atmosphere as measured by a spectrophotometer. ( d ) The seasonal and diurnal variation of tropospheric ozone, sampled at the surface, is described and discussed. A possible relation between the diurnal movement of the tropo­pause and the amount of surface ozone is examined; no marked relation is found between surface ozone and other meteorological measurements. ( e ) The difference between the two hemispheres in the seasonal change of the total quantity of atmospheric ozone is notable at Halley Bay. Total ozone results from sixteen other I. G. Y. stations are examined to show the seasonal variation of ozone from pole to pole. The relation between fluctuations in the total quantity of ozone and upper-air measure­ments of temperature and pressure is investigated at Halley Bay and south-east England for short (3-day means) and long (10-day running means) periods. At Halley Bay only the short-period fluctuations of total ozone are related to upper-air measurements, but in south-east England both the long- and short-period variations are related.