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Mediterranean explosive cyclogenesis is the result of the interaction between upper level baroclinic and low level diabatic processes. This interaction presents significant differences in specific Mediterranean sub-areas and in different cases of rapid deepening, especially regarding the evolution of the diabatic processes. In this study, the regional atmospheric model COSMO-GR is used for the evaluation of the spatial and temporal variations of low level diabatic heating in a case of explosive cyclogenesis in the north Aegean Sea. Model runs were performed for a series of different values of the model parameter sea roughness, which has proved to significantly affect the simulation of the diabatic processes. It was found that smaller values of the above parameter compared to the default parameterization, lead to significant enhancement of the model calculated surface turbulent fluxes and the respective surface deepening rates during the explosive deepening period and thus to lower minimum pressures, which are closer to ERA-Interim reanalysis values. Moreover, the intrusion of the diabatic heating in the middle troposphere due to latent heat release was also examined, demonstrating the necessity for the determination of the most suitable parameterization of the model physics.

A comprehensive climatology of anticyclones affecting the Mediterranean has been assembled employing the objective finding and tracking scheme of the University of Melbourne (MS). The identified anticyclones have been characterized as cold or warm on the basis of their thermal structure at the lower isobaric levels with the aid of an extension module of MS that enables the examination of the vertical thermal extent of synoptic systems. The aim of the present study is to get a perspective of the processes involved in the formation of surface anticyclones. The mean and anomaly fields and the system-centered composites of several atmospheric variables are studied throughout the troposphere, taking under consideration the position of the systems and the season of the year at the time of formation. The present analysis is confined to cold-core systems and focuses on the areas of anticyclogenetic maxima in order to ensure the statistical robustness. The synergy of the low-level cooling and the upper-level dynamics is confirmed for the northern examined areas for both seasons, while anticyclogenesis over central and eastern African areas seems to be mainly governed by thermal processes.

In this study the synoptic environment and thermodynamic mechanisms of two cases of surface cyclogenesis in the south Ionian and Aegean Seas, associated to strong low-level cold surges, are analyzed. The cases are characteristic examples of two different synoptic categories, affecting the weather in the Greek area. The analysis was performed using the ERA-Interim dataset on a 0.5 degrees x 0.5 degrees regular latitude-longitude grid. In the first case, the passage of a frontal depression from North Greece caused the extension of a cold anticyclone from NW Europe towards Greece. Then, the formation of a surface frontal depression is triggered over the south Ionian Sea. In the second case, the eastward movement of a strong frontal depression from North Europe along with a secondary frontogenesis in East Europe favored surface cyclogenesis over the north Aegean Sea. The depression propagated towards the south Aegean Sea, combined with the extension of a cold anticyclone over the Balkans. Although upper-level baroclinic processes significantly affected the formation of the surface depressions in both cases, the two cases are characterized by differences at the low levels, i.e. strengthening of low-level baroclinicity and convergence in the first case and low-level cold advection from the north in the second.

The dynamic and kinematic characteristics of surface explosive cyclones in the Mediterranean are examined and compared to those of ordinary cyclones. The cyclone detection is performed with the tracking algorithm developed in the University of Melbourne, using the 1° × 1° ERA-40 mean sea level pressure dataset for a 40 year period. It is verified that the explosive cyclogenesis in the Mediterranean is mainly a maritime phenomenon, occurring along the northern Mediterranean coast during the cold season. On the contrary, the ordinary cyclogenesis exhibits significant maxima in both continental and maritime environments throughout the year. The explosive cyclones are characterized by longer lifetime and greater propagation speed. They are larger and deeper in the eastern Mediterranean, whereas the ordinary cyclones are deeper in the western and larger in the eastern Mediterranean. The trend analysis revealed that both explosive and ordinary cyclones become less frequent in the Mediterranean basin, while there is a tendency for deeper ordinary cyclones over North Africa and shallower over the Aegean Sea and Cyprus. © 2013, Springer-Verlag Berlin Heidelberg.

An objective climatology of anticyclones over the greater Mediterranean region is presented based on the Interim ECMWF Re-Analysis (ERA-Interim) for a 34-yr period (1979-2012) and the Melbourne University automatic identification and tracking algorithm. The scheme's robustness and reliability for the transient extratropical propagation of anticyclones, with the appropriate choices of parameter settings, has been established and the results obtained here present new research perspectives on anticyclonic activity affecting the Mediterranean. Properties of Mediterranean anticyclones, such as frequency, generation and dissipation, movement, scale, and depth are investigated. The highest frequency of anticyclones is found over continental areas, while the highest maritime frequency occurs over closed basins exhibiting also maxima of anticyclogenesis. There is a significant seasonality in system density and anticyclogenesis maxima, this being associated with the seasonal variations of the larger-scale atmospheric circulation that affect the greater Mediterranean region. © 2014 American Meteorological Society.

The vertical structure of surface cyclonic tracks affecting the eastern Mediterranean region is studied on a climatological basis for the cold period of the year. The dataset used is the 1° × 1° ERA-40 Reanalysis for a 40-year period (1962-2001). The vertical tracking of surface cyclonic tracks was performed with the aid of the Melbourne University Vertical Tracking Algorithm. It was found that about 83 % of the cyclones were extended up to the 500-hPa level and almost 65 % up to 200-hPa level, implying that the cyclones are in general well organized. The surface tracks that originate within the examined area exhibit the smallest vertical extension, intensity, radius, and depth compared to the cyclones originating in the other sectors. Moreover, the 500-hPa counterparts for the said cyclones are mainly located to the north-west or south-west of the surface cyclone position, consistent with the baroclinic character of the Mediterranean cyclones. The zonal (eastward) component of motion predominates both at the surface and at 500 hPa. © 2012 Springer-Verlag.

For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.

An attempt is made to explore the vertical structure of the surface explosive cyclones in the Mediterranean on a climatological basis during the cold period of the year in order to get a better insight in the interaction between the upper and lower levels responsible for the genesis and evolvement of the phenomenon. The vertical profile of the explosive cyclones was examined with the aid of the vertical tracing software of the University of Melbourne Cyclone Tracking Algorithm, using the 1 × 1° spatial resolution of ERA-40 reanalysis data. It was found that about 57 % of the track steps of surface explosive cyclones extend up to 500 hPa. The north-westward tilting of the surface cyclones with height during the stage of explosive cyclogenesis, with a mean distance of 350 km between mean sea and 500 hPa levels, confirms the importance of baroclinicity. About 45 % of the surface explosive cyclones reached their maximum depth before their 500 hPa counterparts, implying the role of surface processes. © 2012 Springer-Verlag.

An objective climatology of explosive cyclones is performed over a 40-year period (1962-2001), for the Mediterranean region with the aid of the Melbourne University automatic cyclone finding and tracking scheme. The major temporal and spatial characteristics of Mediterranean explosive cyclones are investigated, including frequency, movement, generation and dissipation, scale, depth, and intensity. It was verified that the explosive cyclogenesis in the Mediterranean is a rather rare phenomenon that occurs mainly from November to March. Explosive cyclones preferentially form along the northern Mediterranean coast, with maximum density in the Ligurian and Aegean Seas. The cyclogenesis mechanism that predominates in their development is characterized by an interaction of a short and an open long wave in a pre-existing development (referred to as the KF mechanism). There are distinct differences between Western Mediterranean and Eastern Mediterranean explosive cyclones. Although explosive cyclones tend to form in the Western Mediterranean, their scale and depth is greater in the Eastern Mediterranean. Explosive cyclones more likely move from the main cyclogenetic areas in the Western Mediterranean along specific eastward paths over southern Italy and the Ionian Sea where they dissipate or they generate in Eastern Mediterranean and move north-eastwards to the Black Sea or eastwards to Cyprus and Middle East. © 2010 Royal Meteorological Society.

A comparison of two objective climatologies of explosive cyclones in the Mediterranean region is performed. The results are derived from two different mean sea-level pressure reanalysis data resolutions, but from the same assimilation model, in order to quantify the pure impact of higher resolution on the identification and characteristics of explosive cyclones, when the assimilation model is the same. The explosive cyclones were identified with the aid of the Melbourne University automatic cyclone finding and tracking scheme over a 40-year period, using the 6-hourly analyses of ERA-40 mean sea-level pressure (MSLP) on: (a) 2.5 × 2.5 and (b) 1 × 1 latitude-longitude grid. The comparison of the two datasets revealed the significant role of the increase in spatial resolution of MSLP data on the identification and tracking process, and the number of the explosive cyclones in the high-resolution dataset is almost four times greater than the respective one in the lower resolution dataset. However, the comparison of explosive cyclone characteristics, including spatial and temporal variations of explosive deepening, revealed differences in the geographical distribution of the location of the maximum explosive deepening and average explosive cyclone Laplacian of the central pressure. These differences are due to the identification in the higher resolution set of smaller scale and secondary explosives along the strongly baroclinic northern Mediterranean boundaries, south of the Alps and the Pyrenees. Explosive deepening appears a bias to the daytime period from 12 to 18 Coordinated Universal Time (UTC) for both datasets, which is more prominent in the LR dataset. Statistically significant difference of pressure tendency between the two datasets appear for the daytime period from 06 to 12 UTC, accounting for better representation of orographic forcing in the HR dataset. © 2011 Springer-Verlag.

In this study, an updated and extended climatology of cyclonic tracks affecting the eastern Mediterranean region is presented, in order to better understand the Mediterranean climate and its changes. This climatology includes intermonthly variations, classification of tracks according to their origin domain, dynamic and kinematic characteristics, and trend analysis. The dataset used is the 1962-2001, 2.5° × 2.5°, 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). The identification and tracking of the cyclones was performed with the aid of the Melbourne University algorithm. It was verified that considerable intermonthly variations of track density occur in the eastern Mediterranean, consistent with previous studies for the entire Mediterranean, while further interesting new features have been revealed. The classification of the tracks according to their origin domain reveals that the vast majority originate within the examined area itself, mainly in the Cyprus area and the southeastern Aegean Sea, while the tracks that originate elsewhere most frequently enter from the west. Deeper cyclones follow the southwest track originating from the area between Algeria and the Atlas Mountains. A greater size characterizes the westerly tracks (southwest, northwest, and west), while the northwest tracks propagate faster over the study area. A negative trend of the track frequency was found on an annual basis that can be mostly attributed to the winter months, being associated with variations in the baroclinicity. This negative trend is more prominent for the westerly and northeasterly tracks, as well as for those originating in the northern part of the examined area. © 2010 American Meteorological Society.

International audience; The aim of this work is to assess potential future Antarctic surface mass balance changes, the underlying mechanisms, and the impact of these changes on global sea level. To this aim, this paper presents simulations of the Antarctic climate for the end of the 20th and 21st centuries. The simulations were carried out with a stretched-grid atmospheric general circulation model, allowing for high horizontal resolution (60 km) over Antarctica. It is found that the simulated present-day surface mass balance is good on continental scales. Errors on regional scales are moderate when observed sea surface conditions are used; more significant regional biases appear when sea surface conditions from a coupled model run are prescribed. The simulated Antarctic surface mass balance increases by 32 mm water equivalent per year in the next century, corresponding to a sea level decrease of 1.2 mm yr-1 by the end of the 21st century. This surface mass balance increase is largely due to precipitation changes, while changes in snow melt and turbulent latent surface fluxes are weak. The temperature increase leads to an increased moisture transport towards the interior of the continent because of the higher moisture holding capacity of warmer air, but changes in atmospheric dynamics, in particular off the Antarctic coast, regionally modulate this signal.

A mass balance inverse modelling procedure is applied with a time-dependent methane concentration boundary condition and a chemical transport model to relate observed changes in the surface distribution of methane mixing ratios during the 1990s to changes in its surface sources. This work serves as an important starting point for future inverse modelling work examining changes in both the source and sink terms in the methane budget together. The model reproduces essential features of the global methane cycle, such as the latitudinal distribution and seasonal cycle of fluxes, without using a priori knowledge of methane fluxes. A detailed description of the temporal and spatial variability of the fluxes diagnosed by the inverse procedure is presented, and compared with previously hypothesised changes in the methane budget, and previous inverse modelling studies. The sensitivity of the inverse results to the forcing data supplied by surface measurements of methane from the NOAA CMDL cooperative air sampling network is also examined.

The Unified Modeling Language (UML) is a collection of techniques intended to document design decisions about software. This contrasts with systems engineering approaches such as for example Statemate and the Yourdon Systems Method (YSM), in which the design of an entire system consisting of software and hardware can be documented. The difference between the system- and the software level is reflected in differences between execution semantics as well as in methodology. In this paper, I show how the UML can be used as a systemlevel design technique. I give a conceptual framework for engineering design that accommodates the system- as well as the software level and show how techniques from the UML and YSM can be classified within this framework, and how this allows a coherent use of these techniques in a system engineering approach. These ideas are illustrated by a case study in which software for a compact dynamic bus station is designed. Finally, I discuss the consequences of this approach for a semantics of UML constructs that would be appropriate for system-level design.