Interdecadal changes in the ENSO teleconnection to the Caribbean region and the North Atlantic oscillation

The El Nino-Southern Oscillation (ENSO) phenomenon and variability in the s ubtropical North Atlantic high sea level pressure (SLP) are known to affect rainfall in the Caribbean region. An El Nino event is associated with drie r-than-average conditions during the boreal summer of year (0), and wetter- than-average conditions during the spring of year (+1). Dry conditions duri ng the summer of year (0) of an El Nino are associated with the locally div ergent surface circulation engendered by the eastward shift of deep convect ion in the Pacific Ocean. Wet conditions during the spring of year (+1) of an El Nino are associated with the lagged warming of the tropical North Atl antic Ocean. Variability in the strength of the North Atlantic high is gove rned mainly by the North Atlantic oscillation (NAO) with a positive NAO pha se implying a stronger than normal high and vice versa. The NAO is negative ly correlated with Caribbean rainfall indirectly via anomalous sea surface temperatures (SST) associated with anomalies in the surface wind speed at t ropical latitudes and directly via anomalous subsidence. The combined effec t of the two phenomena is found to be strongest when the two signals interf ere constructively: During the summer following winters characterized by the positive phase of the NAO, the dryness associated with a developing warm ENSO event adds to t he dryness associated with a positive SLP anomaly in the subtropical North Atlantic (7 out of 11 El Ninos between 1949 and 1999 fall in this category) . During the spring following winters characterized by the negative phase of the NAO, the wetness that follows a warm ENSO event is augmented by the wet ness associated with the warmer-than-average tropical North Atlantic SSTs ( 5 out of 11 El Ninos between 1949 and 1999 fall in this category). The coincidence in the recurrence of a positive phase of the NAO during the winters coinciding with peak warm ENSO conditions has increased in the las t 20 years in comparison with the previous few decades. This partially expl ains the noticeable consistent dry signal over the Caribbean during the sum mer of year (0) of a warm ENSO event and the disappearance of the wet signa l during the spring of year (+1) in the recent record.