Key features of cold-air pool episodes in the North-East of the Iberian Peninsula (Cerdanya, Eastern Pyrenees)

Located in the North-East of the Iberian Peninsula, Cerdanya experiences intense Cold-Air Pool (CAP) episodes in which a decoupling between the valley atmosphere and the regional circulation develops, especially in winter. A network of 40 temperature sensors was deployed from 2012 to 2015 along seven elevational transects to collect hourly data of temperature and humidity, enabling the measurement of CAP characteristics and behaviour. Empirical Orthogonal Functions (EOFs) of minimum temperature anomalies were examined to study the spatial distribution of CAP. Days were classified as CAP or no-CAP using EOF analysis. The temporal variation of EOF analysis scores for the first component (PC1) indicates days prone to CAP. A synoptic analysis using Principal Component Analysis (factorization), cluster analysis (classification) and a Discriminant Analysis (reclassification) was performed successively. Results showed CAP days to be associated with high pressure and light winds, whilst no-CAP days were associated with surface northerly or north-easterly flow behind frontal passages.