Modification of Stratospheric Properties by Trace Constituent Changes

Abstract

IT has been suggested that large quantities of water vapour and other pollutants introduced into the stratosphere by supersonic transporters may change the basic properties of the stratosphere¹. But what happens when large changes in trace constituent concentrations occur naturally, for example, after a volcanic eruption ? The stratospheric temperature seems to increase by about 5° C and it remains higher than normal for several years. Some of the evidence for this is given in. Figs. 1 and 2. which are based on daily upper air data from Australia and New Zealand. Monthly temperature means were formed for each month, then mean monthly values computed from data for the period 1958–62 inclusive. Deviations from these long term values were noted, and a three-month running average obtained. Fig. 1 gives the time variations of these deviations at selected stations. A major eruption of Mt Agung, Bali (8° S, 115° E), occurred on March 17, 1963, and there have been reports of other eruptions that year. Temperature at the low latitude stations increased almost immediately and remained higher than normal for over two years. Fig. 2 contains meridional cross-sections of the temperature deviations for particular months based on station data for the longitude region 110° E to 180° E. At the beginning of 1963, temperature was below the five year normal and the time variations had been following the characteristic southern hemisphere biennial pattern². The eruption interrupted this pattern. The cross-sections bear some resemblance to those for the products of nuclear weapons tests (for example, see the isolines of tungsten 185 radioactivity in ref. 3), as might be expected. The deviation pattern exhibits a maximum at low latitudes in the lower stratosphere and slopes downwards towards the pole, in some cases at a slope greater than that of the potential temperature surfaces. It is difficult to detect the changes, if any, below 300 mbar. While negative values predominate in the examples shown, it was not possible to draw in a −2° C contour. Similarly, at higher latitudes in the stratosphere the effect is uncertain; large deviations from average are more common there. It has been reported² that the Australian Weather Bureau changed its thermistor mounting at the end of 1962. Maps of temperature for January 1963 and 1964 show that the temperature change is present at other longitudes.