Georgios T. Amanatidis

Accurate and reliable predictions and an understanding of future changes in the stratosphere are major aspects of the subject of climate change. Simulating the interaction between chemistry and climate is of particular importance, because continued increases in greenhouse gases and a slow decrease in halogen loading are expected. These both influence the abundance of stratospheric ozone. In recent years a number of coupled chemistry–climate models (CCMs) with different levels of complexity have been developed. They produce a wide range of results concerning the timing and extent of ozone-layer recovery. Interest in reducing this range has created a need to address how the main dynamical, chemical, and physical processes that determine the long-term behavior of ozone are represented in the models and to validate these model processes through comparisons with observations and other models. A set of core validation processes structured around four major topics (transport, dynamics, radiation, and stratospheric chemistry and microphysics) has been developed. Each process is associated with one or more model diagnostics and with relevant datasets that can be used for validation. This approach provides a coherent framework for validating CCMs and can be used as a basis for future assessments. Similar efforts may benefit other modeling communities with a focus on earth science research as their models increase in complexity.

Interest in atmospheric ultraviolet radiation (UV) research has increased considerably since the discovery of the Antarctic ozone “hole” and after indications of the existence of a similar kind of potential in northern high latitudes. UV measuring and research activities have grown accordingly, including development of new instruments, improvement in quality assurance/quality control methodologies, as well as development of models. Modeling methodologies have been applied for development of spaceborne techniques for estimating the global distribution of solar UV radiation. The European Conference on Atmospheric UV Radiation (ECUV), which was held on June 28 to July 2, 1998 in Helsinki, Finland, brought together 160 scientists from all parts of the world. The Journal of Geophysical Research (JGR) ECUV special issue summarizes 32 papers presented at the conference. New UV trend analyses based on spectral and broadband measurements and modeled UV data for the most recent decades indicate increases of UV‐B radiation in various parts of Europe. Additional observational and modeled information on the impact of cloudiness, total ozone, ozone profiles, aerosols, and albedo on ground level UV irradiance has been gathered. The regional UV albedo has been studied over snow‐covered surfaces, vegetation, and sea areas by aircraft‐based, ground‐based, and modeled methods. Further instrument development, improved QA/QC practices, and the application of data correction methods have already taken place but are also clearly needed in the future. Different methods for estimating UV irradiance using spaceborne information have been developed. Additional efforts to improve our understanding of the impact of cloudiness, albedo, and aerosol on UV are expected to improve spaceborne UV retrievals in the future. In Europe the European Commission and national funding agencies have been supporting research projects aimed at understanding the UV climatology in Europe through UV instrument development and intercomparisons, UV database establishment, and UV process, trend, and scenario studies.

A statistical evaluation of the air pollution situation in Athens for the year 1982 is presented. This analysis refers to NO₂, NO, O₃ and SO₂ concentration levels measured at the National Observatory of Athens (NOA) with a fully automatic monitoring station. The seasonal, weekly and daily variations of the above pollutants are in agreement with the corresponding activities in the city which are responsible for these emissions. Auto‐ and cross‐correlation techniques are applied to the pollutants for January and July. It is found that all pollutants exhibit a well defined oscillatory behaviour because of their diurnal peaks in both months, except for NO₂ in January whose auto‐correlation function shows no regular shape. For the same reason the January NO‐NO₂ cross‐correlation function behaves in the same way; the pairs NO‐O₃ and NO₂‐O₃ exhibit a clear oscillatory pattern. The spectral estimate method is also employed to the above pollutants for the two months in question. The energy content of O₃, for instance, in July shows to be concentrated around a frequency corresponding to a periodicity of 24 hours.