An 18-year time series of OH rotational temperatures and middle atmosphere decadal variations

Rotational temperatures are derived from measurements of the (3-1) transitions of the OH Meinel bands. They are found to be a reasonable proxy for atmospheric kinetic temperatures at an altitude of 3 x 10(-3) hPa (87 kin). Measurements were taken in Wuppertal (51degreesN/7degreesE) from 1980 to 1998. A second (shorter) data set (1980-1991) is available for Northern Scandinavia (Andoya, 69degreesN/16degreesE, and Kiruna, 68degreesN/21degreesE). Data are analyzed for seasonal variations (annual, semi-annual, terannual) and for long-term changes of the temperature. Furthermore atmospheric wave activity is studied by means of measured short-tens temperature fluctuations. Amplitudes and phases of the seasonal components do not change much during the measurement period. On the contrary annual mean temperatures and wave activity show strong long-term and even decadal variations. Similar decadal "episodes" are found in data from the Stratospheric Sounding Units (SSU) and from radiosondes at lower altitudes (1 hPa/47 km and 10 hPa/31 km, respectively). Temperature variations during these episodes are rather large (10 K) and need to be taken into account when using reference or standard atmospheres. Episodic variations of temperature and wave activity are found to be correlated. They appear to be consistent with the "downward control principle" (Rev. Geophys. 33 (1995) 403). (C) 2002 Elsevier Science Ltd. All rights reserved.