A strange atmospheric anomaly was identified 100 years ago today. It was the time of the early upper air experiments, when recording instruments were regularly sent aloft by meteorologists to measure pressure and temperature in the upper reaches of the atmosphere. When the balloon burst, the instruments would parachute to Earth, allowing the readings to be analysed at leisure. And it was as a result of such a venture on June 8th, 1898, that a Frenchman called Leon Teisserenc De Bort made what has been called "the most striking discovery in the whole history of meteorology".
For many years it had been a matter of common observation that temperature decreased with height at a rate of about 2 Celsius for every 1,000 feet. Moreover, there was no reason to suppose that this decline did not go on indefinitely; indeed, the leading scientists of the day could think of many convincing reasons why it should.
Teisserenc De Bort's famous balloon was launched at 3 a.m. on the morning of June 8th from his observatory at Trappes, just outside Paris. It ascended to a height of 13 km above the ground, probably a record for the time, and when the readings came to be examined, they showed that the temperature had decreased in the normal way to a height of 11.8 km. But above that level, it remained more or less constant at . minus 59.
So strongly held was the assumption that temperature must decrease with height indefinitely, that Teisserenc De Bort at first assumed his instruments to be in error, or else that the thermometer had been affected by increasing radiation from the sun. But subsequent ascents produced the same results, and that "most striking discovery" was made.
This unexpected and quite astounding turn of events had the effect of dividing the atmosphere into two parts. Confined in the lower portion, where temperature falls rapidly with increasing height, were all the weather phenomena with which we are familiar; this nether region is forever agitated by vertical movements of the air which result in clouds and rain, in snow and hail and every kind of storm. Teisserenc De Bort called it troposphere - the "sphere of change".
Above this turbulent lower layer there lies a quieter place - a zone of frozen peace where the air is clear and thin, and where the temperature is more or less constant in the vertical. Since this thermal structure stifles any vertical movement, masses of air forced into the upper region from below spread out in horizontal strata - and thus it came to be called the stratosphere, the "sphere of layers".