HR: 0800h
AN: A21B-0436    [Abstracts]
TI: Temperature And Bandwidth Effect in Brewer and Dobson Direct Sun Observations
AU: * Scarnato, B
EM: barbara.scarnato@env.ethz.ch
AF: ETH, Universitaetstrasse 16, Zurich, 8092, Switzerland
AU: Staehelin, J
EM: johannes.staehelin@env.ethz.ch
AF: ETH, Universitaetstrasse 16, Zurich, 8092, Switzerland
AU: Stuebi, R
EM: Rene.Stuebi@meteoswiss.ch
AF: MeteoSwiss, Aerological Station, Yves-Alain, Roulet 317, Payerne, 1530, Switzerland
AB: Dobson and Brewer spectrophotometer are the main instruments to monitor the ozone shield by ground based observations, and they have an important role for validation of ozone satellite data. Ground based total ozone observations from Brewer and Dobson spectrophotometers, operated at mid-latitudes stations, typically show a seasonal bias in the residual with a amplitude of a few percent. Mid-latitude total ozone trends caused by ozone depleting substances are on the order of few percents per decade. Therefore, only a maximum instrumental shift of 1% over the measured period can be tolerated for measurements to derive reliable trends. At Arosa two Dobson and three Brewers instruments have been co-located since 1992, producing a unique data set of quasi-simultaneous observations that is valuable for the study of systematic differences within the measurements. The differences can be at least partially attributed to the different sensitivities of the wavelengths used in the retrieval algorithms. This might explain different column ozone as a consequence of seasonal variability, mainly, in temperature in the lower stratosphere and in ozone slant path. The temperature dependence has been calculated using three different absorption spectra (Bass and Paur, Daumont and those used in the GOME satellite), weighing of the slit functions for each operational Brewer and for the primary standard Dobson spectrophotometers. The seasonal bias between Dobson and Brewer total ozone measurements is reduced from 3% to 1%, if one takes into account the temperature dependence of the Bass and Paur absorptions spectra and the ozone slant path effect. The accuracy and the resolution step of the experimental data of ozone cross sections have an important role. The ozone cross section must be convoluted for the slits functions that can vary from one instrument to an other, therefore the different spectra yield different results.
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting