Western Mediterranean Oscillation (WeMO)


Group of Climatology, University of Barcelona, Catalonia, Spain





    The proposal of a new regional teleconnection pattern, the Western Mediterranean Oscillation (WeMO), is only defined within the synoptic framework of the western Mediterranean basin and its vicinities. The suggested areas are the Po plain, in the north of the Italian peninsula, an area with a relatively high barometric variability due to the different influence of the central European anticyclone and the Liguria low; and the gulf of Cádiz, in the southwest of the Iberian peninsula, often subject to the influence of the Azores anticyclone and, episodically, to the cut off of circumpolar lows or to its own cyclogenesis. The transect linking both areas matches more or less to the coastline of the basin’s northwestern quadrant, that is to say, a large part of the eastern façade of the Iberian peninsula. The main reason of its definition is due to the poor relationship between the eastern Iberian façade rainfall and NAOi. Following the classical methods used to create other variable low- frequency pattern indexes, it was decided to use only two specific observation points, one for each dipole area, with some of the longest barometric series in Europe, Padua (45º24’N-11º47’E) in the north of Italy and San Fernando (Cádiz) (36º17’N-6º07’W) in the southwest of Spain. Both barometric series with a daily resolution were collected within the framework of the European project IMPROVE (Camuffo and Jones, 2002). The series cover jointly and continuously the 1821-2000 period.


    WeMO Positive Phase

    WeMO Negative Phase

    The WeMOi has been applied at daily resolution to the torrential events with very satisfactory results (Martin-Vide and Lopez-Bustins, 2004 and 2006). Actually, the daily WeMOi has been applied to several climatic variables:

- Convective rainfall (López-Bustins and Azorín-Molina, 2004).

- Sea-breeze occurrence (Lopez-Bustins, and Azorin-Molina, 2005; Azorin-Molina and Lopez-Bustins, 2008).

- Urban Heat Island (Lopez-Bustins et al., 2006).

    On the other hand, WeMOi has been already correlated with the sunshine variability (Lopez-Bustins and Sanchez-Lorenzo, 2006) and winter rainfall trends in the Iberian Peninsula (Lopez-Bustins et. al., 2008) . A WeMOi reconstruction from 1500 to 1820 has been also recently carried out in winter season (DJF) using Luterbacher et al. (2002) SLP reconstructed maps (Oliva et al., 2006).

    Currently, the WeMO features are developed in a PhD about the WeMO application to the Catalan Countries rainfall (Eastern Iberian Peninsula) by Lopez-Bustins. PhD supervisor: Martin-Vide.


Download WeMOi:

           > WeMOi updated till January 2010. WeMOi_update.xls

> Instrumental period (1821-2000) (Martin-Vide, J., Lopez-Bustins, J.A., 2006). Microsoft Excel File (.xls)  / Text File (.txt)

 > Pre-instrumental period + instrumental period (winter season, DJF) (1499/1500-1999-2000) (Oliva, M., López-Bustins, J.A., Barriendos, M., Muedra, C., Martín-Vide, J., 2006. Reconstrucción histórica de la Oscilación del Mediterráneo Occidental (WeMO) e inundaciones en el levante peninsular (1500-2000). V Congreso de la Asociación Española de Climatología (AEC), Zaragoza, 18-21 September 2006. Paper and Poster).  Microsoft Excel File (.xls) / Text File (.txt)


(The winter WeMOi instrumental period (1821-2000) values are slightly different in the two databases as it has been standardized by different methods. Anyway, both databases are standardized referring to the 1961-1990 period

Temporal evolution of the WeMOi in winter (December, January, February and March) for the period 1821-2000 with a 3-grade polynomial adjustment.



Winter WeMOi (DJF) with a 11-year running mean and catastrophic floods in Iberian Mediterranean basins 1499/1500-1999/2000



International publications

Martín-Vide, J., Lopez-Bustins, J.A., 2006. The Western Mediterranean Oscillation and rainfall in the Iberian Peninsula. International Journal of Climatology, 26 (11), 1455-1475. (21 times cited in journals included in the SCI)

Azorin-Molina, C., Lopez-Bustins, J.A., 2008. An automated sea breeze selection technique based on regional sea-level pressure difference: WeMOi. International Journal of Climatology. 28(12): 1681-1692.

Lopez-Bustins, J.A., Martin-Vide, J., Sanchez-Lorenzo, A., 2008. Iberia winter rainfall trends based upon changes in teleconnection and circulation patterns. Global and Planetary Change, 63(2-3): 171-176.  

Martin-Vide, J. Sanchez-Lorenzo, A., Lopez-Bustins, J.A.; Cordobilla, M.J., Garcia-Manuel, A. and Raso, J.M., 2008. Torrential Rainfall in Northeast of the Iberian Peninsula: Synoptic patterns and WeMO influence. Advances in Science and Research. 2: 99-105.

González-Hidalgo, J.C., Lopez-Bustins, J.A., Stepanek, P., Martin-Vide, J. and de Luis, M., 2009. Monthly precipitation trends on the Mediterranean fringe of the Iberian Peninsula during the second-half of the twentieth century (1951-2000). International Journal of Climatology. 29(10): 1415-1429.



Lopez-Bustins, J.A., 2007. The Western Mediterranean Oscillation and Rainfall in the Catalan Countries. PhD Thesis, Department of Physical Geography and Regional  Geographical Analysis, University of Barcelona, Catalonia, 184 pp.

Lopez-Bustins, J.A., 2007. L’Oscil•lació de la Mediterrània Occidental i la Precipitació als Països Catalans. Tesi doctoral, Departament de Geografia Física i Anàlisi Geogràfica Regional, Universitat de Barcelona, 400 p.


Book chapters

Martín Vide, J., 2002. Ensayo sobre la Oscilación del Mediterráneo Occidental y su influencia en la pluviometría del este de España. In: Guijarro, J.A. et al. (eds) El Agua y el Clima. AEC, Serie A, 3, Palma de Mallorca, 35-42.

López-Bustins, J.A., Azorín-Molina, C., 2004. Aplicación del índice diario de la Oscilación del Mediterráneo Occidental al estudio de la tipología pluviométrica en Alicante. In: García Codrón et al. (eds) El Clima, entre el Mar y la Montaña. AEC, Serie A, 4, Santander, 333-345.

Oliva, M., López-Bustins, J.A., Barriendos, M., Muedra, C., Martín-Vide, J., 2006. Reconstrucción histórica de la Oscilación del Mediterráneo Occidental (WeMO) e inundaciones en el levante peninsular (1500-2000). V Congreso de la Asociación Española de Climatología (AEC), Zaragoza, 18-21 September 2006. Paper and Poster.



Webmaster: Joan Albert Lopez-Bustins  

Last update: February 2011