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The Etesians are the dominant synoptically driven winds observed in the Eastern Mediterranean, usually from late spring to late summer. Due to the complex topography, the Etesians can be very strong and pose significant environmental hazards, especially over wildfire incidents. This study assesses the impacts of climate change on future Etesians by analyzing the response of the most recent EURO-CORDEX regional climate simulations at the 12-km grid resolution over the twenty-first century. The mean model ensemble projects a significant increase of the Etesians' frequency and intensity under the two emission scenarios RCP4.5 and RCP8.5. This response is connected to an increase in the zonal wind at 200 hPa, a reinforcement of the midlatitude westerly flow, and a decrease in the wave amplitude. These circulation changes accelerate the mid-to-high latitude eastward propagation of the large-scale circulation systems which can favor enhanced ridges over the Balkans. A strengthening and poleward shift of the subtropical jet stream is also projected, connected with stronger subsidence over the Eastern Mediterranean. The projected changes will have profound environmental and societal implications, including the lengthening of the wildfire season and increasing air pollution risk in the region. On the other hand, the current estimate of future wind power potential in the Aegean Sea will be significantly increased by the end of the century, which might have positive impact in the regional economy.

The 10-year (1988–1997) surface ozone record at Jungfraujoch (JFJ; 46°33′N, 07°59′E) in the Swiss Alps is analyzed with regard to changes in the seasonal cycle. For comparison, the surface ozone time series (1988–1996) at Zugspitze (ZUG; 47°25′N, 10°59′E, 2960 m above sea level) on the northern fringe of the Alps in Germany is also examined. The applied structural model in state space form is flexible enough to isolate a statistically significant decrease in the estimated seasonal component for May ozone concentrations over the last 10 years, in both the original JFJ and ZUG ozone records. A negative trend in May is also displayed by ordinary linear regression but is not statistically significant, demonstrating the advantage of the employed methodology over simple regression approaches in the analysis of changing seasonal cycles of tropospheric ozone records. We attempt to isolate potential mechanisms underlying the observed changes in the seasonal ozone cycles at JFJ by analyzing filtered ozone records. Sieving was carried out with wind direction, wind speed, and time windows to exclude the confounding influences from the atmospheric boundary layer and outflow from southern Europe. Taking only nighttime (2400–0500 central European time (CET)) ozone values into account, the seasonal ozone cycle at JFJ is characterized by a broad spring-summer maximum. This filter is believed to represent the lower free troposphere over the Alps and also shows a significant decrease in May ozone concentrations. It is suggested that the results may reflect ozone changes in the free troposphere over continental Europe.

The second Free Tropospheric Experiment (FREETEX ’98) took place at the Jung-fraujoch Observatory (3580 m above sea level), Switzerland, in March/April 1998. A number of trace gases and photolysis parameters were measured, including peroxy radicals (HO2+RO2), the photolysis rate coefficients j(NO2) and j(O1D), O3, NOx, NOy, HCHO, peroxyacetylnitrate (PAN), CO, CN, and hydrocarbons. The average midday concentration of HO2+RO2 observed during the campaign is 13±3 parts per trillion by volume (pptv). The peroxy radical concentrations measured during FREETEX '98 are discussed in terms of the respective NO measurements and box model calculations. By screening out polluted and cloudy conditions during FREETEX ’98, 8 relatively clean days are selected. These 8 days represent near free tropospheric conditions. The average midday concentration of HO2+RO2 observed during these 8 days is 17±5 pptv and the modeled diurnal cycle of [HO2]+[CH3O2] simulated by a photochemical box model shows very good agreement with the mean diurnal cycle of the peroxy radicals over these 8 days. The in situ net ozone production rate is calculated for each day during FREETEX '98 using the peroxy radical, j(O1D), NO, H2O, and O3 measurements. The mean net ozone production rate during the 8 relatively clean selected days is 0.09 ppbv h−1. If more stringent criteria are applied, 3 free tropospheric days can be selected with a mean net ozone production rate of 0.05±0.01 ppbv h−1, indicating the positive role of in situ photochemistry during springtime in the free troposphere over the Alps and supporting the previous results of the first FREETEX campaign in April/May 1996. Using the experimental data, it is estimated that the ozone compensation point, that is, the point where photochemical ozone production equals destruction, occurs at 24±9 pptv of NO in good agreement with theoretical calculations.

Continuous measurements of peroxy radicals (HO2+RO2), the photolysis rate coefficients j(NO2) and j(O1D), and a number of other trace gases including O3, NOx, and CO, were carried out at the alpine site at Jungfraujoch (3580 m asl), Switzerland, in April/May 1996 during the Free Tropospheric Experiment (FREETEX '96). In spring, the Jungfraujoch Observatory is very often located in the lower free troposphere. A mean midday concentration of 17.1±2.2 parts per trillion by volume (pptv) was calculated from continuous measurements of the sum of inorganic and organic peroxy radicals using the chemical amplification technique. The average diurnal cycles for peroxy radicals and the photolysis rate coefficient j)O1D) during FREETEX '96 showed a statistically more significant square root than first-order relationship, indicative of a relatively clean atmosphere at the mountain site, where peroxy radical self- and cross-reactions were the dominant peroxy radical loss processes. The average ozone diurnal cycle during FREETEX '96 displayed an increase of about 2 ppbv during the daytime despite the square root relationship. Similar results were derived from individual days during the campaign. A simple photochemical box model indicated that there is a regime in NO concentration from about 20 pptv to 100 pptv where a better square root (than first-order) correlation between peroxy radicals and j(O1D) is accompanied by net ozone production. Taking into account that median daytime concentrations of NO at Jungfraujoch range from 51 pptv in March to 93 pptv in April, it is suggested that Jungfraujoch, during FREETEX '96, has been in the net ozone production regime in spite of the observed square root dependence of peroxy radicals on j(O1D)

[1] Regional climate-air quality simulations were performed over Europe for two future decades, 2041–2050 and 2091–2100 under IPCC A1B scenario and the control decade 1991–2000. The simulations serve as a theoretical experiment investigating the impact of changing climate on summer surface ozone. Our simulations suggest that changes in summer surface ozone imposed by climate change until the 2040s are below 1 ppbv and more pronounced until the 2090s. The median of summer near surface temperature for whole Europe is 2.7 K higher at the end of the 21st century than to the end of the 20th century with more intense temperature increase simulated for southern Europe. A prominent feature is the decrease of cloudiness mostly over western Europe at the end of the 21st century associated with an anticyclonic anomaly which favors more stagnant conditions and weakening of the westerly winds for the larger part Europe southern of 50°N. Biogenic emissions double in the simulation at the end of the 21st century for latitudes below 50° and together with changes in circulation patterns, temperature, and solar radiation, contribute to the enhanced average ozone concentrations at the end of the 21st century. The change is more intense over southwest Europe, where the median of ozone increases by 6.2 ppbv. Sensitivity simulations suggest that biogenic emissions, temperature and solar radiation have a comparable impact on average surface ozone in the examined range of perturbations. The maximum response of the imposed perturbations was seen over southern Europe.