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 the North Atlantic Oscillation (NAO). Following the classical methods used to create other variable low-frequency pattern indexes, it was decided to use two specific observation points for the calculation of the WeMO index (WeMOi): one for each dipole area, with some of the longest barometric series in Europe, Padua (45º24’N-11º52’E) in the north of Italy and San Fernando (36º28’N-6º12’W) in the southwest of Spain. Both barometric series were collected at daily time scale within the framework of the European project IMPROVE (Camuffo and Jones, 2002).



Positive WeMO phase                                                  Negative WeMO phase



The WeMOi has been applied at daily time scale to heavy rainfall events with very satisfactory results (Martin-Vide and Lopez-Bustins, 2006; Martin-Vide et al., 2008). Actually, the daily WeMOi has been also applied to other climatic variables:

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

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

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

Moreover, WeMOi has been already correlated with the sunshine variability (Lopez-Bustins and Sanchez-Lorenzo, 2006) and winter rainfall trends in the Iberian Peninsula (Oliva et al., 2006; Lopez-Bustins et. al., 2008). 

The WeMO features were developed in a PhD about the WeMOi application to the Catalan Countries rainfall variability (Eastern Iberian Peninsula) by Joan A. Lopez-Bustins. PhD supervisor: Javier Martin-Vide.


  Monthly WeMOi data (1821-2013): Microsoft Excel File (.xls) / Text File (.txt) 


Temporal evolution of the WeMOi in winter (December, January and February) along the 1821/22-2012/2013 period with a 5-year running mean




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

Camuffo D, Jones P. 2002. Improved Understanding of Past Climatic Variability from Early Daily European Instrumental Sources. Kluwer Academic Publishers, Dordrecht, 392 pp.

Lopez-Bustins JA.  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.

López-Bustins JA, Azorín-Molina C. 2004. Aplicación del índice diario de la Oscilación del Mediterráneo Occidental al estudio de la tipología pluviométrica en Alicante. Actas IV Congreso de la Asociación Española de Climatología (AEC), Santander, 333-345.

Lopez-Bustins JA, Sanchez-Lorenzo A. 2006. The Western Mediterranean Oscillation (WeMO) effect on the sunshine duration variability in Iberian Peninsula. 6th Annual Meeting of the EMS / 6th ECAC, Ljubljana, Slovenia.

Lopez-Bustins JA, Martin-Vide J, Moreno MC, Raso JM. 2006. Urban Heat Island Intensity in Barcelona and the Western Mediterranean Oscillation. Preprints of the 6th International Conference on Urban Climate, Göteborg, 830-833.

Lopez-Bustins JA, 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.  

Martín-Vide J, Lopez-Bustins JA. 2006. The Western Mediterranean Oscillation and rainfall in the Iberian Peninsula. International Journal of Climatology 26(11): 1455-1475. (65 times cited)

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

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). Actas V Congreso de la Asociación Española de Climatología (AEC), Zaragoza, 241-250. 



Webmaster: Joan A. Lopez-Bustins  (jlopezbustins@ub.edu)

Last update: July 2014