Assessing characteristics of Mediterranean explosive cyclones for different data resolution

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

Climatological aspects of explosive cyclones in the Mediterranean

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 high-resolution climatological study on the comparison between surface explosive and ordinary cyclones in the Mediterranean

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

On the vertical structure of Mediterranean explosive cyclones

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

Seasonal aspects of an objective climatology of anticyclones affecting the mediterranean

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