On long-term ozone trends at Hohenpeissenberg

More than 2000 ozone soundings and a large number of Dobson observations have been performed since 1967 in a unique procedure. The achieved very homogeneous data sets were used to evaluate significant long-term trends both in the troposphere and the stratosphere. The trend amounts to about plus 2 percent per year in the troposphere and to about minus 0.5 percent per year in the stratosphere. Extremely low ozone records obtained during winter 1991/92 are discussed in the light of the long term series. The winter mean of the ozone column is the lowest one of the series. The ozone deficit occurred mainly in the lower stratosphere. One cause may be the Pinatubo cloud. Even compared with the extreme winter mean following the El Chichon eruption the ozone content was lower. Additionally ozone was reduced by dynamical effects due to unusual weather situations

Spectral and integral observations of UV-B-radiation and ozone measurements

Initial investigations of the properties and capabilities of the Brewer spectrophotometer as a UV-measuring instrument were done at Hohenpeissenberg before 1990. In this BayFORKLIM-project, however, a more exact and comprehensive analysis was carried out. Possible sources of errors, namely, wavelength instability, temperature and humidity dependence, non-linearity of the detector, straylight effects, cosine error and quality of the calibration lamps have been investigated and most of them could be quantified. Systematic errors can now be corrected in the evaluation procedure. Although the Brewer is only a single monochromator, it proved to be a relatively precise and very reliable instrument for monitoring purposes. Minor error sources (maximum error <#+-#1%) are concerning wavelength setting and temperature dependence of the entire system. Errors up to #+-#5% may occur due to non-linearity and straylight (below 300 nm) if no correction is applied. The main causes of measurement errors are uncertainties in the calibration lamps and the non-ideal cosine response of the entire spectrometer. Errors of more than 10% are possible and a correction requires a large amount of effort but is absolutely necessary. Relocation of the instrument and changes in the local geography can be important for the homogeneity of long time series. The Hohenpeissenberg Brewer 010 was moved in May 1993 in order to be able to see the entire horizon. This relocation has lead to systematic changes in the measured UV-B of about +10%, for clear sky and high sun, up to +20% at low sun and enhanced turbidity. Corrections have been applied to the first period of the entire UV time series in order to remove the bias resulting from the relocation. (orig.)SIGLEAvailable from TIB Hannover: ZA 368/1(204) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman