Study of Europe-ENSO teleconnection in an El Niño index phase analysis framework

El Niño/Southern Oscillation (ENSO) is the most important coupled ocean-atmosphere phenomenon to cause global climate variability on seasonal to interannual time scales. Therefore understanding some of its most important features may help to shed light on the field of climate predictions. Here the focus is put on the seasonal precipitation patterns which respond to persistent thermal forcing happening thousands of kilometers far away. The first objective of this work is to look for and describe the correlation patterns between seasonal rainfall anomalies over Northern Italy and global seasonal Sea Surface Temperature anomalies (SSTA). Tri-monthly means of precipitation and tri-monthly means of SSTA from observational datasets are used in an anomaly correlation study in order to explore this teleconnection. The study is developed in the Nino Index Phase Analysis (NIPA) framework, as presented by Zimmerman et al., which consists in separating the positive and negative ENSO phase years in the computation of the anomaly correlation. The second objective of the work is to check if the correlations found are consistent with the shift of the circulation pattern which is due to a non-weak ENSO state. The anomaly means of the main ocean-atmospheric variables are examined in order to characterise the way in which the circulation works when the system is under El Niño or La Niña conditions and when the precipitation over the basins is higher or lower. Then, a Rossby waves simulation software is used to show that the propagation of a Rossby wave train, in a basic state with zonally varying middle latitude or low latitude jet, may be the cause of the correlations in the area under exam and for the seasons chosen, and how. This is an indication of the fact that the ENSO state and its spatial features can influence the tropospheric pathways through which planetary waves can propagate and this, in turn, could have an effect on midlatitudes large-scale circulation.