The isothermal layer of the atmosphere and atmospheric radiation

Abstract

The investigation of the upper air by means of balloons carrying self-recording instruments, which have furnished values for the atmospheric temperature up to heights between 15 and 20 kilometres, has revealed the existence of an abnormal change in the vertical temperature gradient. After a fairly uniform fall, with increasing altitude, of about 6° C. per kilometre, a height is reached above which the temperature changes very little, sometimes increasing, sometimes diminishing slowly. The phenomenon was first noticed by M. Teisserenc de Bort in a communication to the Société de Physique in June, 1899. He improved his apparatus and made further investigations, in many cases sending up the balloons by night to eliminate any possible insolation effects. He found the average height, at which the change began, to be about 11 kilometres. He discovered also that the height was greater near the centre of high pressure areas than in low pressure areas, the average heights for the two cases being 12-5 and 10 kilometres respectively. More recently he found that the height increased with approach towards the equator and that near the equator, ballons-sondes , ascending to 15 kilometres, had failed to reach this layer if it existed there. He proposed to call this layer, in which little temperature change occurred, the “Isothermal Layer of the Atmosphere,” and the name has been generally accepted.