North atlantic teleconnection patterns of low-frequency variability and their links with springtime precipitation in the western Mediterranean

The relationship between springtime (March-May) precipitation in the western Mediterranean area and several North Atlantic teleconnection patterns of low-frequency variability is analysed for the period 1948-89. Singular value decomposition analysis (SVDA) of the springtime monthly mean fields for the three paired combinations of 300 hPa geopotential height-precipitation, 300 hPa zonal wind-precipitation and 300 hPa meridional wind-precipitation has shown that their covariability is dominated by two main large-scale atmospheric circulation patterns. In every SVD combination, the first mode relates precipitation anomalies to the east Atlantic jet pattern. Above-normal rainfall anomalies are linked with a blocking pattern affecting Iberian weather. The second covariability mode for the three SVD As takes into account the response of the precipitation to the North Atlantic oscillation (NAO) pattern. An enhanced spring NAO pattern is related to positive (negative) precipitation anomalies over the southern (northern) western Mediterranean. Through these two modes, the North Atlantic large-scale atmospheric dynamics explains about 50% of the total spring precipitation variability in the western Mediterranean area. A Monte Carlo approach has allowed setting the statistical significance of the modes obtained and to assess the effectiveness of the western Mediterranean precipitation response to the teleconnection patterns. Copyright (C) 2004 Royal Meteorological Society.