AbstractsAstronomy & Space Science

This thesis is devoted to the study of the total ozone column with remote sensing techniques. Total ozone column can be derived through remote sensing techniques from both ground-based and satellite instruments. High quality measurements of the total ozone column from the ground are needed for estimating changes of very small magnitude in the ozone trends and for validating satellite measurements. These changes can be related either with the decreases in the ozone depletion substances, or with factors of dynamical origin, mostly linked with human induced climate changes. Thus, their study can provide valuable information for the processes that affect the ozone layer. The ozone retrieval algorithm of Brewer spectrophotometers was thoroughly examined, for the effect of a possible replacement of the ozone absorption cross-sections that are currently used, with newer, high-resolution spectroscopic datasets. Furthermore, the effect of the temperature dependence of the ozone cross-sections which is currently ignored in the standard Brewer ozone retrieval algorithm was investigated. The aim for this study was to contribute to the higher accuracy total ozone column retrieval from Brewer spectrophotometers. Moreover, the variability, in different time scales, of a thirty-year record of total ozone column measurements over Thessaloniki was examined. The total ozone column cannot be assumed stable throughout the day, since it exhibits different daily patterns of variation. The dominant is the monotonic increase, especially during summer, connected with the evolution of the near surface ozone due to the enhanced photochemical activity. The day-to-day variations are more pronounced during winter, because of the higher dynamical variability and are almost negligible during summer. In the long-term, the TOC over Thessaloniki exhibited a decline in the period 1982-1996, attributable to the increase in the ozone depletion substances, while after 1996 there is a stabilization or a small increase, though not statistical significant. This indicates that the ozone layer over Thessaloniki has started to “respond” to the reduction of the abundance of the ozone depletion substances, following the successful implementation of the Montreal’s protocol. Finally, the year-to-year variability is highly determined from the extreme events in the TOC time series. These can be of chemical origin (i.e. from volcanic eruptions) or dynamical origin (i.e. NAO) and influence the levels of the ultraviolet irradiance reaching the earth’s surface. However, in urban areas such as Thessaloniki, this effect can be masked from the high aerosol load. In this thesis are presented evidences of the important influences by the aerosol optical depth levels, even under conditions of extreme-low ozone events. Η παρούσα διδακτορική διατριβή επικεντρώνεται στη μελέτη της ολικής στήλης του όζοντος με μεθόδους φασματοφωτομετρικής τηλεπισκόπησης. Η ολική στήλη του όζοντος μπορεί να προσδιοριστεί με τηλεσκοπικές τεχνικές, είτε από επίγεια, είτε από δορυφορικά όργανα.…