Western European water vapour flux - South West England rainfall associations

The relationship between monthly rainfall anomalies over southwest England and vapor flux anomalies at five western European radiosonde stations (Brest, La Coruna, Crawley, Keflavik, Valentia) is analyzed over the period from January 1961 to June 1997. Monthly rainfall anomalies are positively associated with zonal, meridional, and vector flux anomalies over the British Isles, France, and Spain but are inversely related to the flux anomalies of the Icelandic station, Keflavik. An enhanced westerly and/or southerly flux over Iceland is thus more likely to be accompanied by below-average rainfall over southwest England. A six-variable vapor flux anomaly model can account for 69.0% of the intermonthly variance in a regional rainfall anomaly (RRA) index. Independent validation of this equation over the period from July 1997 to May 2000 confirmed the physical robustness of this equation (variance = 61.5%, number of months = 35). Vapor flux rainfall anomaly associations vary not only intraregionally and seasonally but also between drought events. Study results reveal that RRA is more dependent on zonal flux variations during the winter. RRA is also generally more dependent on variations in Brest's 850-hPa zonal flux anomaly during drought events when the controlling anticyclone is positioned to the north and east of Britain rather than to the south and west.