Cyclones in the Mediterranean region: present and future climate scenarios derived from a general circulation model (HadAM3P)

International audienceIn this paper, an attempt is made to assess and evaluate the skill of the Hadley Center atmospheric General Circulation Model (HadAM3P) in generating successfully the frequency and intensity of severe cyclones (<1000 hPa) in the Mediterranean region. The cyclonic occurrence is studied in three regions of enhanced cyclonic activity: Gulf of Genoa, Southern Italy and Cyprus. It was found that the HadAM3P predicts a future decrease of the frequency of the severe cyclones at the SLP level, but the future cyclones will be more intense (deeper), especially at the 500 hPa level

The influence of Indian summer monsoon on the climatic regime of Eastern Mediterranean

The objective of this study is to further investigate the ISM impact on the temperature and wind regime of the Eastern Mediterranean region, with the aid of multivariate statistics. For this purpose, the standardized Dynamic Indian Monsoon Index by Wang and Fan (1999) was used for a period of 44 years (1958-2001) along with ERA40 Reanalysis data, including monthly means of surface air temperature and wind at 850hPa with a horizontal resolution of 0.25° latitude x 0.25° longitude. Initially, the correlation maps of the seasonal anomalies of the two variables upon ISM index are computed and subsequently Empirical Orthogonal Function Analysis (EOF) is carried out on individual fields. Under this framework, correlation coefficients between the derived EOF amplitudes and ISM index are calculated and in order to validate the results from the first method, the EOF modes that exhibit high correlation coefficients are compared to the aforementioned correlation patterns. Our results verify that there is correlation between Indian monsoon and the etesian pattern over the Aegean Sea

Atmospheric circulation types and daily mortality in Athens, Greece.

We investigated the short-term effects of synoptic and mesoscale atmospheric circulation types on mortality in Athens, Greece. The synoptic patterns in the lower troposphere were classified in 8 a priori defined categories. The mesoscale weather types were classified into 11 categories, using meteorologic parameters from the Athens area surface monitoring network; the daily number of deaths was available for 1987-1991. We applied generalized additive models (GAM), extending Poisson regression, using a LOESS smoother to control for the confounding effects of seasonal patterns. We adjusted for long-term trends, day of the week, ambient particle concentrations, and additional temperature effects. Both classifications, synoptic and mesoscale, explain the daily variation of mortality to a statistically significant degree. The highest daily mortality was observed on days characterized by southeasterly flow [increase 10%; 95% confidence interval (CI), 6.1-13.9% compared to the high-low pressure system), followed by zonal flow (5.8%; 95% CI, 1.8-10%). The high-low pressure system and the northwesterly flow are associated with the lowest mortality. The seasonal patterns are consistent with the annual pattern. For mesoscale categories, in the cold period the highest mortality is observed during days characterized by the easterly flow category (increase 9.4%; 95% CI, 1.0-18.5% compared to flow without the main component). In the warm period, the highest mortality occurs during the strong southerly flow category (8.5% increase; 95% CI, 2.0-15.4% compared again to flow without the main component). Adjusting for ambient particle levels leaves the estimated associations unchanged for the synoptic categories and slightly increases the effects of mesoscale categories. In conclusion, synoptic and mesoscale weather classification is a useful tool for studying the weather-health associations in a warm Mediterranean climate situation

The ability of a barotropic model to simulate sea level extremes of meteorological origin in the Mediterranean Sea, including those caused by explosive cyclones

Storm surges are responsible for great damage to coastal property and loss of life every year. Coastal management and adaptation practices are essential to reduce such damage. Numerical models provide a useful tool for informing these practices as they simulate sea level with high spatial resolution. Here we investigate the ability of a barotropic version of the HAMSOM model to simulate sea level extremes of meteorological origin in the Mediterranean Sea, including those caused by explosive cyclones. For this purpose, the output of the model is compared to hourly sea level observations from six tide gauge records (Valencia, Barcelona, Marseille, Civitavecchia, Trieste, and Antalya). It is found that the model underestimates the positive extremes significantly at all stations, in some cases by up to 65%. At Trieste, the model can also sometimes overestimate the extremes significantly. The differences between the model and the residuals are not constant for extremes of a given height, which limits the applicability of the numerical model for storm surge forecasting because calibration is difficult. The 50 and 10 year return levels are reasonably well captured by the model at all stations except Barcelona and Marseille, where they are underestimated by over 30%. The number of exceedances of the 99.9th and 99.95% percentiles over a period of 25 years is severely underestimated by the model at all stations. The skill of the model for predicting the timing and value of the storm surges seems to be higher for the events associated with explosive cyclones at all stations

A composite approach to produce reference datasets for extratropical cyclone tracks: application to Mediterranean cyclones

Many cyclone detection and tracking methods (CDTMs) have been developed in the past to study the climatology of extratropical cyclones. However, all CDTMs have different approaches in defining and tracking cyclone centers. This naturally leads to cyclone track climatologies with inconsistent physical characteristics. More than that, it is typical for CDTMs to produce a non-negligible number of tracks of weak atmospheric features, which do not correspond to large-scale or mesoscale vortices and can differ significantly between CDTMs. Lack of consensus in CDTM outputs and the inclusion of significant numbers of uncertain tracks therein have long prohibited the production of a commonly accepted reference dataset of extratropical cyclone tracks. Such a dataset could allow comparable results on the analysis of storm track climatologies and could also contribute to the evaluation and improvement of CDTMs. To cover this gap, we present a new methodological approach that combines overlapping tracks from different CDTMs and produces composite tracks that concentrate the agreement of more than one CDTM. In this study we apply this methodology to the outputs of 10 well-established CDTMs which were originally applied to ERA5 reanalysis in the 42-year period of 1979-2020. We tested the sensitivity of our results to the spatiotemporal criteria that identify overlapping cyclone tracks, and for benchmarking reasons, we produced five reference datasets of subjectively tracked cyclones. Results show that climatological numbers of composite tracks are substantially lower than the ones of individual CDTMs, while benchmarking scores remain high (i.e., counting the number of subjectively tracked cyclones captured by the composite tracks). Our results show that composite tracks tend to describe more intense and longer-lasting cyclones with more distinguished early, mature and decay stages than the cyclone tracks produced by individual CDTMs. Ranking the composite tracks according to their confidence level (defined by the number of contributing CDTMs), it is shown that the higher the confidence level, the more intense and long-lasting cyclones are produced. Given the advantage of our methodology in producing cyclone tracks with physically meaningful and distinctive life stages, we propose composite tracks as reference datasets for climatological research in the Mediterranean. The Supplement provides the composite Mediterranean tracks for all confidence levels, and in the conclusion we discuss their adequate use for scientific research and applications

A composite approach to produce reference datasets for extratropical cyclone tracks: application to Mediterranean cyclones

Many cyclone detection and tracking methods (CDTMs) have been developed in the past to study the climatology of extratropical cyclones. However, all CDTMs have different approaches in defining and tracking cyclone centers. This naturally leads to cyclone track climatologies with inconsistent physical characteristics. More than that, it is typical for CDTMs to produce a non-negligible number of tracks of weak atmospheric features, which do not correspond to large-scale or mesoscale vortices and can differ significantly between CDTMs. Lack of consensus in CDTM outputs and the inclusion of significant numbers of uncertain tracks therein have long prohibited the production of a commonly accepted reference dataset of extratropical cyclone tracks. Such a dataset could allow comparable results on the analysis of storm track climatologies and could also contribute to the evaluation and improvement of CDTMs. To cover this gap, we present a new methodological approach that combines overlapping tracks from different CDTMs and produces composite tracks that concentrate the agreement of more than one CDTM. In this study we apply this methodology to the outputs of 10 well-established CDTMs which were originally applied to ERA5 reanalysis in the 42-year period of 1979–2020. We tested the sensitivity of our results to the spatiotemporal criteria that identify overlapping cyclone tracks, and for benchmarking reasons, we produced five reference datasets of subjectively tracked cyclones. Results show that climatological numbers of composite tracks are substantially lower than the ones of individual CDTMs, while benchmarking scores remain high (i.e., counting the number of subjectively tracked cyclones captured by the composite tracks). Our results show that composite tracks tend to describe more intense and longer-lasting cyclones with more distinguished early, mature and decay stages than the cyclone tracks produced by individual CDTMs. Ranking the composite tracks according to their confidence level (defined by the number of contributing CDTMs), it is shown that the higher the confidence level, the more intense and long-lasting cyclones are produced. Given the advantage of our methodology in producing cyclone tracks with physically meaningful and distinctive life stages, we propose composite tracks as reference datasets for climatological research in the Mediterranean. The Supplement provides the composite Mediterranean tracks for all confidence levels, and in the conclusion we discuss their adequate use for scientific research and applications.</p

Developing an index for heavy convective rainfall forecasting over a Mediterranean coastal area

Heavy convective rainfall incidents that occurred over western coastal Greece and led to flash floods are analyzed with respect to mesoscale analysis for the period from January 2006 to June 2011. The synoptic scale circulation is examined throughout the troposphere along with satellite images, lightning data and synoptic observations of weather stations. Well-known instability indices are calculated and tested against synoptic observations. Taking into account the severity of the incidents, the performance of the indices was not as good as expected. Further detailed analysis resulted in the development of a new index that incorporates formalized experience of local weather and modeled knowledge of mechanisms of severe thunderstorms. The proposed index named Local Instability Index (LII), is then evaluated and its performance is found to be quite satisfactory. © 2014 Author(s)

VOC and O3 distributions over the Densely populated area of Greater Athens, Greece

The horizontal and vertical distributions of volatile organic compounds (VOCs) and ozone (O3) concentrations within the lower troposphere over the greater Athens area. Greece, under sea-breeze conditions were studied. Furthermore, an attempt was made to explain the dynamic and chemical mechanisms responsible for the formation of these distributions. Measurements were collected using a specially instrumented Falcon 20-E5 research aircraft, ground-based meteorological instrumentation, and a network of air quality monitoring stations within the context of the Scientific Training and Access to Aircraft for Atmospheric Research Throughout Europe (STAAARTE) 1997 experimental campaign. Relatively high ozone values (55-100 ppbv) were identified within the first 300-400 m above ground, and significantly reduced values were found over the depth of the atmospheric boundary layer. High values of VOC concentrations [150-350 ppbCarbon (C)] were observed near the ground as well as within the first 300 400 m above ground. At higher altitudes, of 1400-1600 m, VOC concentrations remained relatively high (100-200 ppbC). It was demonstrated that the sea-breeze circulation plays a major role in the formation of the above-mentioned concentration levels and that chemical transformations explain specific characteristics