The stratosphere
Overview
The atmosphere can be divided into several distinct layers. In the Met Office only the bottom three are currently studied:
- the troposphere
- the stratosphere
- the mesosphere
The troposphere extends from the Earth's surface to the tropopause (about 10-16 km in altitude). It contains about 90% of the mass of the atmosphere and supports weather systems and strong vertical motions.
The stratosphere is a relatively stable region, characterised by an overall increase of temperature with height and approximately horizontal motion.
The mesosphere lies above the stratopause, at roughly 50 km in altitude. This is where rapid fluctuations, gravity waves and tides, play a predominant role.
The stratosphere and mesosphere form the middle atmosphere.
Traditionally, meteorologists have focused on the troposphere, as this is where we live and where weather systems occur.
Initially interest in the stratosphere arose from concerns over the ozone layer. However, over the last 20 years it has become clear that the middle atmosphere, in general, and the stratosphere, in particular, influence tropospheric weather and climate.
Stratospheric research at the Met Office
The Met Office has been involved in stratospheric research since the 1940s. In the early years the focus was on the structure and composition of the stratosphere. Subsequently there has been increasing recognition of the stratosphere’s importance (see key dates).
The discovery of the Antarctic ozone hole, arguably the most spectacular example of human impact on the environment, drew unprecedented attention to the stratosphere.
Since the signing of the Montreal Protocol, invited Met Office researchers have joined an international group of scientists in the preparation of the WMO/UNEP four-yearly ozone assessment reports, which have been an important resources for governments and policymakers.
The advent of global satellite observations and high-resolution numerical models revolutionised our understanding of the stratosphere. In turn, our increased understanding of the stratosphere has led to developments in modelling and analysis.
- The Unified Model, which is used for all Met Office forecasts and climate predictions, now includes a stratosphere.
- The Met Office's assimilation system has been extended to allow for the assimilation of stratospheric observations — leading to better weather forecasts in the troposphere and a better description of ozone and other chemical constituents.
Our activities have demonstrated the importance of the stratosphere to weather forecasts and ozone predictions. However, there is a need for improved representations of the stratosphere, and further research into the impacts on surface climate and weather.
Specialist information
For more specialist information on the stratosphere, please visit our password-protected area.
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Some key dates in the history of stratospheric research at the Met Office
1937: Meteorologist Alan Brewer joins the Met Office. He performs important work on aeroplane contrails and makes ozone measurements at different latitudes. These studies lead to the realisation that the stratosphere is very dry, and contributes to the discovery of the stratospheric meridional circulation, the so-called Brewer-Dobson circulation, which becomes fundamental to our understanding of the stratosphere.
1961: Met Office scientists Murgatroyd and Singleton publish an analysis of the heat budget (the balance of heat gain and loss) of the stratosphere. Their work puts the Met Office at the forefront of research on ozone depletion due to supersonic transport. In 1982 Murgatroyd gave evidence that it would take 1,000 Concordes, flying continuously, to produce a variation equal to the natural variations in stratospheric ozone concentration. This caused attention to turn instead to CFCs (which were then used widely in things like aerosol spray cans).
1970s: Beginning of the satellite era. The Met Office designs the Stratospheric Sounding Unit (SSU) and uses data from this instrument to produce the first three-dimensional analyses of stratospheric data.
1985: A team of British Antarctic Survey scientists discovers the Antarctic Ozone Hole.
1987: The Met Office provides forecast support for a NASA-led aircraft campaign to Antarctica and contributes to the analysis of the data, leading to an understanding of the mechanism by which the ozone hole forms.
1992: Met Office modelling studies, published in Nature, demonstrate that doubling the concentration of CO2 in the atmosphere would lead to the formation of an Arctic ozone hole comparable to that observed over Antarctica, with nearly 100% local depletion of lower-stratospheric ozone (if chlorine levels remained high). This underscores the importance of curbing CO2 emissions.
2000: The Met Office achieves the first realistic simulation of the dynamical quasi-biennial oscillation in a standard climate model. The QBO is an important component of the atmospheric variability in the tropics.
2006: The Met Office's operational numerical weather prediction system is extended to include the entire stratosphere.
