Long-term temperature trends in the middle stratosphere of the Northern Hemisphere

Abstract

Analysis of Northern Hemisphere mid-latitude temperature data at the 30-mbar level over the last 20 years, based on daily hemispheric analyses of radiosonde data, suggests a long-term negative trend of about −0.6 K/decade (between 50 and 60 N), and a negative trend of about −0.24 K/decade when all observations between 10N and 90N are considered, until April 1980. This stratospheric cooling which has been tentatively attributed to the increase of the carbon dioxide amount in the stratosphere is in qualitative agreement at 30 mbar with model calculations of the historical evolution of temperature and chemical composition in the middle atmosphere. The temperature increase detected after April 1980 which is attributed to the increased aerosol load after the volcanic eruptions of Mount St.Helens and E1 Chichon is discussed briefly. A comparison with another trend analysis based on monthly mean values of selected stations is also discussed, and it is shown that this data set is incomplete before the year 1970, because of missing data over the USSR. In summary, the use of carefully analyzed radiosonde data for monitoring temperature trends in the middle stratosphere is strongly advocated.