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The main objective is to quantify the levels of air pollution in the artctic, and to document any changes in the exposures. It includes the necessary components to address impacts on ecosystems, human health, materials and climate change.
Polar stratospheric clouds play a key-role in polar ozone destruction. Cold temperatures in the vortex allow formation of these clouds. Depending on the PSC-type different formation-temperatures have to be reached. Synoptic temperatures do not always fall to these formation-temperatures, but waves in the atmosphere can lead to additional cooling of several 10 K, which allows PSC-formation. Whereas the wave-activity at the ESRANGE is very high due to hilly surrounding area, the orographic wave-activity at ALOMAR is expected to be rather small. Waves with long wavelengths will be present at both stations simultaneously. Coordinated measurements of temperature and aerosols will show both the large-scale wave-part and also the locally induced wave-part. Such measurements should allow identification of the different wavelngth scales and in addition contribute to a better estimate of the importance of wave-induced clouds for PSC-formation.
During the past years, atmospheric research in high latitudes has been focussed on processes causing ozone loss in the polar winter lower stratosphere1). Recent research efforts also dealt with regions up to the lower mesosphere, and studied the effects of charged particle precipitation on NO and ozone2)-5). However, the measurement techniques and hence the database for studying such processes in this altitude range are very limited. The Airborne SUbmillimeter Radiometer ASUR6),7) of the Institute of Environmental Physics of the University of Bremen has recently been equipped with a high-resolution spectrometer that will enable the retrieval of vertical profiles of ozone up to an altitude of about 65 - 70 km. Its measurement capabilities comprise also several other species of interest, especially NO. This makes the measurement technique particularly suitable for upper stratospheric/lower mesospheric studies. The lidar at ALOMAR is capable of measuring highly resolved vertical profiles of ozone up to an altitude of 60 km, thus giving the rare opportunity for intercomparison and validation studies in an altitude range reaching from the lower stratosphere to the lower mesosphere. Therefore we propose to perform simultaneous ozone measurements of the ASUR instrument with the ALOMAR lidar, supported by launches of ozone sondes.
Noctilucent clouds (NLC) remain a fascinating phenomenon of the upper atmosphere to study. The questions about the typical particle density and particle size distribution within a NLC are very prominent ones, to which a number of answers have been given, though some of the answers contradict each other. The parameters of particle size distributions can be derived from groundbased lidar measurements of the spectral dependence of the volume backscatter coefficient of an NLC. Such studies have been performed during a number of NLC events by e.g. the ALOMAR Rayleigh/Mie/Raman (RMR) lidar (von Cossart et al., GRL, 26, 1513, 1999). A drawback of these experiments is the wavelength limitation of the RMR lidar, the shortest wavelength of which is 355 nm. At this wavelength, the sensitivity of the lidar to particles with sizes smaller than, say, 25 nm is minimal. Because a considerable part of the entire particle population may have sizes below that threshold, a lingering question remains whether or not this drawback matters for typical NLC distributions. Using the ALOMAR ozone lidar, a measurement of the NLC volume backscatter coefficient at 308 nm becomes possible. Due to the l-4 -dependence of the backscatter coefficients, the latter are almost a factor of 2 larger at this wavelength than at 355 nm. For this reason and in order to gain a fourth wavelength to the spectral distribution, we aim at using the ozone lidar for the outlined project.
These investigations confirm the fact that in the stratosphere the ozone is considerably influenced by dynamical processes and it is a good indicator of them. In this context the main objectives of the proposed study are: 1) to investigate the possible relationship between stratospheric ozone perturbations and the temperature enhancement in the upper mesosphere, observed by Shepherd et al. (2001); 2) to examine whether changes in ozone, concomitant with the phenomenon, take place and how and when they would be manifested; and 3) to investigate the stratospheric ozone behaviour during the equinox atmospheric transition in the North Hemisphere, for better understanding of the middle atmosphere dynamics.