Objective Climatology of Cyclones in the Mediterranean Region

Abstract

A B S T R A C T The Mediterranean storm track constitutes a well-defined branch of the North Hemisphere storm track and is characterised by small but intense features and frequent cyclogenesis. The goal of this study is to assess the level of consensus among cyclone detection and tracking methods (CDTMs), to identify robust features and to explore sources of disagreement. A set of 14 CDTMs has been applied for computing the climatology of cyclones crossing the Mediterranean region using the ERA-Interim dataset for the period 1979Á2008 as common testbed. Results show large differences in actual cyclone numbers identified by different methods, but a good level of consensus on the interpretation of results regarding location, annual cycle and trends of cyclone tracks. Cyclogenesis areas such as the north-western Mediterranean, North Africa, north shore of the Levantine basin, as well as the seasonality of their maxima are robust features on which methods show a substantial agreement. Differences among methods are greatly reduced if cyclone numbers are transformed to a dimensionless index, which, in spite of disagreement on mean values and interannual variances of cyclone numbers, reveals a consensus on variability, sign and significance of trends. Further, excluding 'weak' and 'slow' cyclones from the computation of cyclone statistics improves the agreement among CDTMs. Results show significant negative trends of cyclone frequency in spring and positive trends in summer, whose contrasting effects compensate each other at annual scale, so that there is no significant long-term trend in total cyclone numbers in the Mediterranean basin in the 1979Á2008 period.

Coupled atmosphere ocean climate model simulations in the Mediterranean region: effect of a high-resolution marine model on cyclones and precipitation

“…2a on annual basis for the control run) are in agreement with previous findings (Trigo et al, 1999;Maheras et al, 2001;Campins et al, 2011). The main cyclogenetic regions (Gulf of Genoa, Cyprus, Atlas Mountains, Black Sea and Balearic Sea) are correctly represented and also the seasonality of cyclogenesis is realistically reproduced.…”

“…Basically, all tracking algorithms for extratropical cyclones are characterized by two steps: cyclone identification and tracking. Some methods use MSLP (Pettersen, 1956;Gulev et al, 2001;Maheras et al, 2001;Campins et al, 2011) or geopotential height at 1000 hPa (Alpert et al, 1990;Trigo et al, 1999), others use relative vorticity at 850 hPa (Sinclair, 1997;Flocas et al, 2001) or the Laplacian of sea level pressure (Simmonds and Murray, 1999;Simmonds and Key, 2000). In any case, Mediterranean cyclone climatology presents very distinctive features, which arise clearly, independent of the specific algorithm applied.…”

“…cell of the Mediterranean region, following Trigo et al (1999). Differently from Trigo et al (1999), and analogously as Campins et al (2011), we include in our analysis also cyclones lasting less than 24 h. The analysis has been applied to both model results and ERA-Interim.…”

“…This number can be apparently small, being the Mediterranean one of the regions of the world with the highest frequency of extratropical cyclogenesis. On the other hand, a cyclone lasting 5.5 days is a very rare event in the Mediterranean, where cyclones typically last 2-3 days (see e.g., Trigo et al, 1999 andCampins et al, 2011). Maximum deepening rate is shown in Figs.…”

Estudo de caso de ciclone extratropical sobre a América do Sul: sensibilidade das análises

“…Mais recentemente, devido o avanço da tecnologia e utilizando métodos automáticos de detecção dos ciclones, Murray e Simmonds (1991), Sinclair (1994), Blender et al, (1997) e Trigo et al, (1999) criaram climatologias mais amplas dos ciclones extratropicais tanto para o Hemisfério Sul (HS) com para o Hemisfério Norte (HN). Esses autores utilizaram em seus estudos algoritmos, que tendem a procurar e encontrar o mínimo e/ou o máximo da Pressão ao Nível Médio do Mar (PNMM) ou a altura geopotêncial à superfície (e.g.…”