Cyclones that produce high impact weather in the Mediterranean, MEDEX


Dr. Agustí Jansà, Instituto Nacional de Meteorología, Spain

Prof. Pinhas Alpert, Tel Aviv University jointly with Israel Meteorological Service

Dr. Philippe Arbogast, Météo-France

Dr. Andrea Buzzi, CNR, ISAO (Bologna), Italy


Project Summary
1. Background and Motivation
2. Research Proposal
3. Scientific Management
Supporting Documentation

Project Summary

MEDEX (Mediterranean Experiment on Cyclones that produce High Impact Weather in the Mediterranean) is designed to contribute to the better understanding and short-range forecasting of high impact weather events in the Mediterranean, mainly heavy rain and strong winds. Due to the supposed close relationship between high impact weather and cyclones, MEDEX will be focused to Mediterranean cyclones that produce high impact weather.

A dynamically oriented climatology of cyclones and high impact events is the first milestone of MEDEX. A second milestone will be the determination of sensitive areas where an observing effort will provide a more accurate prediction of Mediterranean cyclones, followed by impact analyses of additional data in these areas. From both, recommendations about the observing systems, data assimilation procedures and modelling and refined conceptual models for forecasters will arise.

In parallel, an evaluation of the societal impacts of the phenomena and of the benefits of forecasting accuracy improvements will be done.

The climatology of cyclones and high impact events performance requires a continuous and systematic effort and will require one or two permanent MEDEX Centres.

The establishment of a Data Assimilation Mediterranean-oriented Centre (DAMC), including a data base centre and a data assimilation centre, is intended in order to provide facilities for numerical experiments and sensitive studies.

1. Background and Motivation

In spite of the usually pleasant weather (that makes the region a tourist pole) the Mediterranean area is quite frequently affected by sudden events of extreme adverse weather, often producing high social impacts. The unique geography of the region, with small and steep river basins and highly populated, industrialised and tourist areas, makes the Mediterranean especially sensitive to the impact of weather phenomena, mainly in case of heavy rain. A brief selection of events (in only 10 years) prepared by the Munich Reinsurance Company (see Supporting documentation) collects 166 cases of heavy rainfall and floods and 104 cases of strong wind and storms producing serious damages. The total number of deaths is over 1,900 and the quantified economic losses (only a little part of the total losses) is over 6,000 M Euros. These figures are certainly underestimates. For Spain alone, and only in four years (1996-99), the Programme of Natural Hazards of the Spanish Directorate of Civil Defence has accounted 155 deaths by heavy rain and flood events and 28 deaths by storms and strong winds (in front of 5 and 5 in the Munich Re. listing). See also the Opening address at the INM/WMO International Symposium on Cyclones and Hazardous Weather in the Mediterranean, Palma de Mallorca, Spain, 14 April 1997, by Prof. Obasi, Secretary General of WMO.

The reduction of the dramatic consequences of these extreme weather events is the ultimate motivation of the present proposal. Improving forecasts of such events is a necessary, though not sufficient, condition for the above achievement. In particular, an accurate enough forecast in the short-range would permit an on time warning to the population under risk (for self protection) as well as a proper organisation and deployment of the civil defence forces and means, to provide emergency management.

Direct NWP operational model outputs do not give yet a totally reliable guidance about extreme rainfall or wind speed in the Mediterranean area. Although examples of quite good prediction can be found, in many others values are strongly under- or overestimated and/or badly located. Improving the model behaviour or improving the added value provided by the forecasters to the model outputs are two obvious ways to improve the short-range forecasts of extreme events in the Mediterranean. Both ways require a better understanding of the mechanisms that lead to these extreme events. This better understanding would permit not only improved monitoring of the model behaviour (in order to correct it, if possible) and a refinement of the conceptual models used by the forecasters, but also the formulation of recommendations about how the observing systems could be better matched to the forecasting needs.

Although not all the extreme weather events in the Mediterranean are related to cyclones and most of the cyclones do not produce extreme weather, it is plausible to assume that Mediterranean cyclones influence most of the high impact phenomena, at least in an indirect way. Therefore, in order to focus the project on a tractable near term scientific objective, the main general objective of MEDEX is stated to be the improvement of knowledge and forecasting of cyclones –in the most general sense of the word- that produce high impact weather in the Mediterranean area.

Apart from the direct impact of Mediterranean cyclones downstream, even far from the region of origin, an improved understanding and forecasting of cyclones related to high impact weather in the Mediterranean will positively affect the understanding and forecasting of hazardous weather around the world. The Mediterranean area is a good target region for a project devoted to improving our knowledge of the hazardous weather, owing to the high intensity and frequency of this type of events in it and to the aforementioned additional circumstances.

2. Research Proposal

Science basis of the proposal

As mentioned before, the main general objective of MEDEX is stated to be the improvement of knowledge and forecasting of cyclones –in the most general sense of the word- that produce high impact weather in the Mediterranean area.

Assuming that the basic and practical motivation of MEDEX is to contribute to the improvement of the forecasting of the high impact weather, the above objective will make sense only if it is verified that cyclones do play a determining role in this kind of events.

Our present knowledge about the Mediterranean Meteorology (see Supporting documentation, Summary of knowledge about Mediterranean Hazardous Weather and Cyclones, and References for a summary) does not allow definitive assessments on this point, but gives us some keys and guidance. A priori the following types of situation in which there is an active relationship between cyclone and high impact weather, can be identified:

(a) Shallow (usually orographic) depressions, contributing to sustenance of moist inflow for localised and persistent deep convection (and heavy rain), in unstable environment. (b) Deep extensive baroclinic cyclones (usually associated with a combination of factors, including the presence of upper level PV ‘anomalies’, release of latent heat and low level effects of orography and surface heat exchanges), contributing to extensive strong winds and possible heavy rain. (c) Quasi-tropical small cyclones (mainly sustained by surface heat fluxes and by latent heat release), producing local strong winds and heavy rain. Combined types are also possible.

Recent work (Jansa et al., 2000, see Fig. 1) has established that in most of the cases (around 80%) of heavy rain in the Western Mediterranean there is a cyclone in the vicinity that can play a role in the heavy rain generation or at least in its location. The most frequent type of situation is (a). The location of the heavy rain seems to be closely related with the location of the depression.

In any case, the previous results have to be considered provisional and need more extensive validation and (possible) generalisation. This requires a work of systematic exploration of events.

On the other hand, the correct forecasting of the appearance and evolution of cyclone centres (small or large, shallow or deep, weak or intense) and all their details will become a necessary condition for high impact weather prediction. The scarcity of conventional surface and upper air observations in wide areas of the Mediterranean and its surroundings (as the marine extensions and the southern flank) and the small size of most of the Mediterranean cyclones (at least in its initial stage) makes this forecasting specially difficult. The sensitivity of this forecasting to certain data availability and assimilation is a central topic for MEDEX. The identification of sensitive areas in which additional or enhanced observations (targeted observations) could be convenient (or existing data have to be warranted) is a part of this topic.

Regarding the influence of cyclones on 'downstream' weather (in particular, on heavy rain appearance), the most relevant observations might concern the flow characteristics at low levels (wind and temperature and humidity). The flow convergence and its strength and water content are critical for the release of convection and to determine the intensity of the rainfall. Also information about surface fluxes is very relevant. But to learn about the cyclogenetic processes (and to better forecast them), accurate upper and mid level 'upstream' information becomes necessary. See Fig. 2 for an example in a typical type (a) scenario. Note that in this type of cases the sensitive area (where the target observations would have to be placed) is usually Mediterranean and marine for the shorter-range forecasting and frequently north African for longer-range predictions. Water content and low level winds, as well as information about surface fluxes within the Mediterranean are also critical magnitudes for the shorter-range forecasting of the cyclone evolution in type (b) and type (c) evolutions. Upstream upper air details, frequently out of the Mediterranean basin, are also necessary for longer-range forecasting.

Forecast development path

A logical flow of tasks to implement and develop MEDEX is summarised in Fig. 3.

A dynamically oriented climatology of cyclones and high impact events is the first milestone of MEDEX. This includes the following tasks.

The first step (1) is the identification of types of situation. Although the preliminary study of particular known cases is a valid way to do so, MEDEX considers that a systematic or climatological study (2) is more promising and rich.

Task (2), systematic/climatological study, will consist of detection and description of cyclones based on operational objective analyses and the formation of a calendar of high impact weather events. INM/ CMTIBAL/ Palma is ready to do the first task using the HIRLAM/INM model. Concerning the information/ calendar on high impact events, a network of focal points in contact with CMTIBAL has to be implemented. A provisional list of meteorological services engaged with this task (with the corresponding focal points) is included in the Supporting documentation. The list will have to be completed later. A delay of at least one-year will be needed to extend the same kind of work to the Eastern Mediterranean. The detection and description of cyclones will also be made in Palma, based on ECMWF or other analyses, although the implementation of such a duty in an Eastern Centre is not ruled out.

Task (3), experiments concerning factors, will begin by the second year, on the basis of calendars of selected cases. The participating institutions will prepare and perform numerical simulations and experiments on these cases by using their available models and initial and boundary conditions. When available (see later), a common data base of reanalyses will be used, if derided. The results will be available for all the participating institutions . A provisional list of participating institutions, as well as their available models is also included in the Supporting documentation. The list is expected to grow in the future.

A second milestone will be a climatology of the most sensitive areas. The computation of the sensitivity of some criteria to the state variable of the atmosphere 12, 24 or 36 hour before will be made by adjoint model calculations. Such numerical experiments could indicate the preferred locations where the reduction of the model analysis error has the greatest impact on the forecast of Mediterranean cyclones. This is Task (4). The leadership for this part will be assumed by Météo-France and will begin by the second or third year.

A few selected cases of the defined types of event will be considered for Task (5), targeted additional observations. In general, additional data will mainly be obtained in dynamically sensitive areas and will be focused to determine low level distribution of wind, temperature, humidity and surface fluxes and of upper and mid level dynamic features.

Concerning historical cases, existing complementary observations (if any) will be recovered. The engaged meteorological services and other institutions will be requested to provide this kind of information, if available. An alternative or complementary way would be to get additional data obtained in independent observational campaigns and projects, mainly related to EUCOS (like E-ASAP, E-AMDAR and other). Also data from a joined CNES/METEO-FRANCE subproject embedded within THORPEX (several drifting balloons will be launching dropsondes in the North-Atlantic area) could be used.

Regarding real time cases, a limited number of short field campaigns, in which new observations will be obtained, will be designed to be carried out within the last one or two years. Several groups of additional data for them are considered:

-Additional observations from existing platforms: existing (but not internationally distributed) data will be used (surface weather stations in islands - also in their mountains - would be relevant, although a pre-processing of data could be necessary) and, additionally, some existing platforms (radiosonde and surface stations and other) will be requested to produce additional observations.

-In situ aircraft measurements (AMDAR systems). Note the great density of air-traffic in some parts of the Mediterranean.

-Additional on board ships stations, drifting buoys and ASAP-ships.

-Constant level balloons and research aircraft (if available).

-Liquid water from SSMI.

-New types of observations:

high resolution humidity observations from GPS data, lidars, sodars

high resolution wind data (from fixed or mobile Doppler radar)

Also new products coming from the Meteosat Second Generation – MSG - satellites will become available in a very few years and could be used: high resolution winds, water content, stability, etc.

Furthermore, precipitation, radar or lightning data, among others, will also be requested to the participant meteorological services and institutions for verification purposes.

All the additional data (even the conventional ones) will be stored in a specific data base, located in INM, Meteo-France, or other institutions, or distributed among several of them, that is a part of the DAMC (see later).

Additional data will be used to produce reanalyses for selected cases (or periods), oriented towards a better description of the 3D potential vorticity field and the humidity field. For additional data of the last group aforementioned (new types of observation) and for some satellite data the development of observation operators is required, in order to assimilate them. The advanced data assimilation systems relevant for MEDEX reanalyses either in operation or in development are on one hand 3DVAR schemes with potentially high spatial resolution of the control variable - enough for the description of the mesoscale - and global 4DVAR. The advantages of the former system is the resolution of the control variable whereas the advantages of the latter scheme is the dynamical consistency of the analysis. In particular, a non trivial coupling between dynamics and thermodynamics is provided by the 4DVAR scheme. Global reanalyses will provide coupling field for all the LAM involved in MEDEX. Aladin and Hirlam are serious candidates for a 3DVAR high resolution (i.e. horizontal resolution of about 50 km). ARPEGE/IFS is the best candidate if the 4DVAR is chosen by the MEDEX community, knowing that the system is already in operation in ECMWF for 2 years and has been just implemented at METEO-FRANCE. Of course, the MEDEX community will take benefit from refinements of the system such as the increase of the resolution or the introduction of a stretched control variable.

In order to build an observing strategy in these areas, Observing Systems Simulations Experiments (OSSEs hereafter) will be performed for every group of additional observations aforementioned (Task 6). The contribution of the additive observations will be addressed through assimilation (OSSEs) and using a new technique that is the computation of sensitivities of the assimilation system to additional observations (Doerenbecher A. , Bergot T. and Bouttier F., Proceedings of CGC/WMO Workshop, Toulouse 6-8 march 2000; WMO/WWW Technical Report, to be published; Baker and Daley, QJRMS, 2000, 126, 1431-1454).

These studies, as well as numerical experiments as those mentioned for Task 3, will permit the assessment of some recommendations about the critical role played by existing and additional data. Also, some assessments and recommendations about the behaviour of the models and of the analyses procedures will be formulated (Task 7). The potential use of ensemble forecasting with a variety of models as the elements of the ensemble will also be concerned by these recommendations.

Task 3 (experiments concerning factors) and Task 6 (Observing Systems Simulations Experiments) will permit the formulation of refined conceptual models for forecasters for the most important types of cyclones that produce high impact weather in the Mediterranean. This will be Task 8. As a consequence, Task 8 will help the forecasters in a critical interpretation of the model outputs and to improve their forecasts.

Task 8 (conceptual models) and Task 7 (recommendations) would lead to an improvement of the final forecasting concerning the cyclones that produce high impact weather in the Mediterranean and of the forecasting of the high impact weather events themselves.

One of the first tasks to be undertaken for the MEDEX development is to review the present development path and to prepare a much more detailed program design and an implementation plan. A restricted workshop will be convened with this objective during the first months. On the other hand, Task 7 (recommendations) and 8 (conceptual models) would be supported by the conclusions of an open workshop or seminar to be held by the fourth year of program.

Impact of the proposed program on society

In principle, any forecasting accuracy improvement for the cyclones that produce high impact weather has to produce an improvement of the forecasting of the high impact phenomena themselves. This, in turn, induces increased confidence within the institutions that are responsible for civil defence and marine safety and of the population to the forecasts and warnings concerning high impact weather. The ultimate goal, then, is enhanced protection of human lives and property and a reduction of the negative societal impacts.

The institutions responsible for civil defence and marine safety need to have quantitative information about (a) the impacts that are of concern to MEDEX (susceptible reduction as a result of the program), (b) the possible reduction in those impacts. To do so, the scientific team of MEDEX will collaborate with the institutions that are responsible for civil defence and marine safety, insurance companies, hydrologists, etc., as far as possible.

In parallel to the elaboration of a calendar of cases, as described regarding Task (2), systematic/ climatological study, also the impacts associated to them have to be evaluated. From there, the distribution of the impacts among different situations will be established (as far as possible). This is a necessary step to estimate the potential effect of the project in the impact reduction.

The following step for the estimation of the potential effect of the project in the impact reduction is the measurement of the improvement of the goodness of the final forecasting of extreme events. This can be established by inter-comparison of model outputs, with different models, different data assimilation procedures and/or different sets of data. Special attention will be put on the measurement of the goodness of the probabilistic predictions based on ensemble forecasting with multiple models and/or multiple data assimilation procedures. Also the added value of the forecaster, when using refined conceptual models, has to be evaluated.

Finally, hydrologists, insurance companies and end users like the institutions responsible for civil defence and marine safety will be consulted in order to establish the degree of the impact reduction that could be obtained when using the improved forecasting.

3. Scientific Management

Regarding particular activities, Task (2), systematic/climatological study, requires a permanent working centre. The Meteorological Centre at Palma of the Spanish INM will undertake this role for the Western Mediterranean. By the second year it will be decided if Palma will undertake the task also for the Eastern Basin or a parallel centre will be established (in Israel).

It is intended the implementation of a Data Assimilation Mediterranean-oriented Centre (DAMC), with two components, that can act separately, although in close co-ordination, a data base, collecting all additional data (as well as conventional data), satellite products, model data and SST analyses, and a data assimilation centre, to provide 3DVAR/4DVAR analyses, climatology of sensitive areas, inter-comparison of LAM, to centralise works of ensemble prediction. The data base could be located at INM or Météo-France (to be decided rapidly), being Météo-France the most clear candidate for the data assimilation centre.


Apart from the proposers, the following persons have contributed to the preparation of the MEDEX project, as members of the former MEDEX Interim Steering Committee:

Adrian Broad (Meteorological Office, U.K.), Natalia Chakina (Hydrometeorological Centre, Russian Federation), Charles Doswell (NOAA, NSSL, U.S.A.), James Doyle (Naval Research Lab., U.S.A.), Christo Georgiev (National Institute of Meteorology and Hydrology, Bulgaria), Klaus P. Hoinka (DLR, Germany), Branka Ivançan-Picek (Meteorological and Hydrological Service, Croatia), Mikdat Kadiouglu (Istanbul Technical University, Turkey), Vassiliki Kotroni (National Observatory of Athens, Greece), Nicholas Prezerakos (Technological Education Institute of Pyraeus, Greece), Clemente Ramis (Balearic Islands University, Spain), Evelyne Richard (Laboratoire d'Aerologie, Toulouse, France), Franco Siccardi (Genoa University, Italy) and Antonio Speranza (DSTN-PCM and Camerino Univ., Italy).

Apart from those that are proposing institutions, several other institutions have expressed support to MEDEX and manifested a certain degree of involvement. See Participant institutions in the Supporting documentation.


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Supporting Documentation


I. INM/WMO International Symposium on Cyclones and Hazardous Weather in the Mediterranean. Address by Prof. Obasi.

II. Summary of knowledge about Mediterranean Hazardous Weather and Cyclones.

III. Participant institutions. Available and possible complementary observations. Available models and data assimilation procedures.

IV. MEDEX Interim Steering Committee (MISC) and MEDEX contacts and focal points

V. Summary of events: Munich Reinsurance Company. (Not available in electronic support)

VI. C.V. of the proposers: P. Arbogast, P. Alpert, A. Buzzi, A. Jansa