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

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

A Climatological Analysis of Potential Vorticity Over Greater Athens Area for 1979-2014 Time Period

Potential Vorticity (PV) is a conservative parameter of the atmosphere useful for exploring strong atmospheric invasions. In this paper, we explored the Potential Vorticity climatological characteristics over the Greater area of Athens. For this purpose 3 isentropic levels (315, 330 and 350 K) and 3 isobaric levels (300, 350 and 500 hPa) of reanalysis data were examined. Data were derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) website. The results indicate the occurrence of low values of PV in Greater Athens Area. However, there were cases, especially during winter and spring, that very high values of PV were observed

Identifying the Skill of Higher Resolution Precipitation Forecasts with Neighborhood Verification Techniques

As numerical weather prediction models began to increase considerably in resolution, it became clear that traditional grid-point-by-grid-point verification methods did not provide material information about forecast performance. High-resolution numerical weather prediction (NWP) models produce more detailed precipitation structures but the real benefit is the more realistic statistics obtained from the higher resolution rather than the information for the specific grid point. Neighborhood verification rewards closeness by relaxing the requirement for exact matches between forecasts and observations. The advantage of the neighborhood approachis the use of a spatialwindowsurrounding the forecast and/or observedpoints. The size of the neighborhood can be varied to provide verification results at multiple scales, enabling the determination of which scales the forecast has the most useful skill. A strong convective event is used as a test case for forecasting precipitation over the complexterrain of the Alps. Theavailable precipitation data are treated withinwindows using a variety of methods for averaging (upscaling), thresholding, and PDF generation, each of which provides distinctly useful information on model performance

Large scale variability associated with Indian summer monsoon

The objective of this study is the investigation of the large scale variability of the atmospheric circulation over the Mediterranean region in relation to the Indian summer monsoon. For this purpose composite anomalies of selected fields at various isobaric levels are analyzed for strong versus weak monsoon years. Gridded, monthly mean data, such as geopotential height, horizontal wind components, vertical velocity and relative vorticity at 300 hPa were used, as obtained from the ERA-40 Reanalysis Data Base, with 2.5 2.5 resolution for the boreal summer (June-September) and for a 44-year period (1958–2001). The standardized Dynamic Indian Monsoon Index by Wang and Fan (1999) was employed to determine the strong and weak monsoon years in the 44-year period. It was found that there are significant differences between strong and weak composites for all fields, especially in the upper troposphere. The results suggest that these differences may be related to the existence of Rossby wave trains as well as to the intensity and the meridional shift of the upper-level jet streams

Generating a “Typical Air Pollutant Day” in Thriasio Plain, Greece

The Thriasio Plain is the first and main industrial zone of Greece. The scope of this paper is to generate “Typical Air Pollutant Day” in Thriasio Plain. For this purpose we used data for the time period 2001-2014. The data were provided from the Ministry of Environment and are hourly concentration values of Sulfur Dioxide, Nitrogen Monoxide and Dioxide, Ozone and daily values of PM10 at Elefsis central station. The results show an improvement of air quality during the last years, especially for Sulfur Dioxide and Nitrogen Monoxide and Dioxide. The time period considered, concurs with the economic and financial crisis in Greece. For Ozone, the results are unclear. Similar results for Ozone were obtained when we compared measurements from the Ministry of Environment’s data for specific days with measurements from the local municipality’s network

Relationship of extreme dry spells in eastern mediterranean with large-scale circulation

The relationship of prolonged dry spells in Eastern Mediterranean with large-scale surface and upper circulation is investigated on seasonal basis with the aid of the Singular-Value Decomposition Analysis (SVDA) for the period 1958-2000. The study was based on daily precipitation data of 56 stations, evenly distributed over Eastern Mediterranean region. Extreme dry spells are defined using the CDD index (maximum number of consecutive dry days). It was found that teleconnection patterns centered over Northern Atlantic and northern Europe seem to affect the duration of the longest dry spells over the Eastern Mediterranean, while surface synoptic scale systems in Northern Africa play a substantial role. The SVDA results compare well with the corresponding results of Canonical Correlation Analysis (CCA), mainly for the surface circulation during winter and summer