On the relationships between daily circulation patterns and precipitation in Portugal

摘要: Daily circulation (sea level pressure) maps over east Atlantic-Europe were classified into six patterns (CPs) by using k-means clustering coupled with principal component analysis. The relationships between winter monthly rainfall in Portugal and the occurrence frequencies of CPs also examined. CP classification scheme is effective not only discriminating regional wet/dry weather conditions, but differentiating various conditions associated different precipitation intensities. For southern Portugal, CP6 CP3 are wettest patterns: under their presence probability rainy day intensity twice as high those dry CPs; about 26.6% two wet together contribute 66.8% total rainfall. northern CP4 turned out to be patterns. They produce 60% 31% chance occurrence. In terms long-term variation intimately related CPs. found good predictors for precipitation. addition, it evident that decrease March throughout country last 3 decades has been a consequence reduction frequency pattern, CP6, which coincides upward trend North Atlantic Oscillation index could northeastward shifting strengthening Azores High.