A Web site questionnaire survey in Finland suggested that maps illustrating projected shifts of Köppen climatic zones are an effective visualization tool for disseminating climate change information. The climate classification is based on seasonal cycles of monthly-mean temperature and precipitation, and it divides Europe and its adjacent land areas into tundra, boreal, temperate, and dry climate types. Projections of future changes in the climatic zones were composed using multimodel mean projections based on simulations performed with 19 global climate models. The projections imply that, depending on the greenhouse gas scenarios, about half or possibly even two-thirds of the study domain will be affected by shifts toward a warmer or drier climate type during this century. The projected changes within the next few decades are chiefly located near regions where shifts in the borders of the zones have already occurred during the period 1950–2006. The questionnaire survey indicated that the information regarding the shifting climatic zones as disseminated by the maps was generally interpreted correctly, with the average percentage of correct answers being 86%. Additional examples of the use of the climatic zones to communicate climate change information to the public are included.

In situ observations of ClO mixing ratios obtained from a balloonborne instrument launched in Kiruna on 27 January 2000 and on 1 March 2000 are presented. ClO mixing ratios and quasi‐simultaneously observed ozone loss are compared to model simulations performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). ClO mixing ratios are simulated initializing the model simulations for early winter conditions. Sensitivity studies are performed to explore the impact of the surface area of the background aerosol, of denitrification, and of the recently reported kinetics of the ClO self‐reaction [Bloss et al., 2001] on simulated ClO. For 27 January 2000, model simulations agree with rate constants reported by Bloss et al. [2001], whereas for 1 March 2000 simulations employing rate constants reported by Bloss et al. [2001] and by Sander et al. [2000] reproduce the ClO measurements. The impact of uncertainties arising from accumulated errors along the calculated backward trajectories and uncertainties within temperatures derived from the UK Met Office are also studied. For both flights, simulated ClO show a good overall agreement with measured ClO within uncertainties arising from accumulated errors along air parcel histories. We find a layer of low ClO mixing ratios < 100 pptv between 600 and 620 K for the flight on 27 January 2000 and between 525 and 550 K on 1 March 2000. For this layer, measured ClO is substantially lower than simulated ClO. Potential causes are discussed, but the discrepancy remains unexplained at present. Furthermore, for 1 March 2000, an overall agreement is found between model simulations and measurements by the HALOE instrument of HCl and NOx (=NO + NO2) for all altitudes considered. We conclude that denitrification occurred up to a potential temperature of ≈550 K (≈24 km altitude) on 1 March 2000. Finally, model simulations show that between late January and 1 March, a significant ozone loss of about 0.8–1.8 ppmv is derived between 425 and 490 K of potential temperature in agreement with measured ozone loss and correlated with the enhanced ClO. For 1 March 2000, 77 ± 10 DU is obtained as an estimate of the loss in column ozone.

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Abstract. Balloon-borne backscattersondes have been used to study the relationship between particle scattering and ambient temperature near the vertical edge of arctic polar stratospheric clouds (PSCs) as well as to delineate the cloud type occurrence probability as a function of temperature. The observed typical threshold temperatures as a function of altitude are about IøK warmer than the temperature Ts•:s expected for rapid growth of supercooled ternary solution aerosols. A more descriptive analysis shows that the threshold temperatures occur over a definable range of temperatures and tend to cluster near, but somewhat warmer than, Ts•:s. Considering the experimental and theoretical uncertainties, this difference may not be significant. The probability of type Ib PSC occurrence shows a dramatic increase at TST s -+-IøK, while for type Ia PSCs the probability is roughly constant at 10% for temperatures below the formation point of nitric acid trihydrate (TNAT). Koop and Carslaw [1996] have described a multiple component system in which frozen and cooling background stratospheric aerosol particles can undergo a sudden melting and dramatic growth over only a IøK temperature range at a welldefined temperature (deliquescent temperature Td). As these authors indicate, such an effect should be observable in existing and future field measurements. This deliquescent effect should not be confused with the deliquescence of the liquid background sulfuric acid aerosol.In this study we use a database of PSC observations obtained from balloon-borne instrumentation employing a backscattersonde to examine what we define as the threshold temperature at which PSCs are just detectable. In addition, a probability of 28,195