Interdecadal Pacific Oscillation modulation of ENSO teleconnections in its decaying stages: Relations with Indian Ocean basin-wide mode and South American precipitation

This study examines the Interdecadal Pacific Oscillation (IPO) modulation of the El Nino-Southern Oscillation (ENSO) teleconnections in its decaying stages with the tropical ocean by focusing on the Indian Ocean Basin-Wide (IOBW) mode and the precipitation over South America (SA) in the 1901-2012 period. Composite analyses revealed that the ENSO teleconnections are IPO-modulated due to the differential ENSO decaying speed, which is slower during the positive than negative IPO phase, for both El Nino (EN) and La Nina (LN) cases. Negative precipitation anomalies related to EN persist over northeastern SA until austral winter for the positive IPO phase (POS IPO), while significant opposite sign anomalies occur in this region for the negative IPO phase (NEG IPO). These results are associated with the Walker circulation's reversal during NEG IPO which is, in turn, accompanied by negative IOBW. During the POS IPO, the positive IOBW causes upward movements over there and, by continuity, downward movements over SA. In the NEG IPO, for LN events the wave train originating in the north of Australia propagates toward subtropical SA, which, coupled with the surface circulation, causes dryness in this region. In addition, the rapid decay of LN in the NEG IPO, followed by the emergence of EN, caused changes in the Walker circulation, such that enhanced upward movements occurred over the Pacific and SA region, and downward movements over the Indian Ocean until austral winter. In turn, the slower decay of the LN in the POS IPO maintains strong subsidence over the central Pacific and weak upward motions over western SA. So, the EN (LN) and positive (negative) IOBW during the POS (NEG) IPO prolong the scarcity of precipitation over equatorial (subtropical) SA. Persistent dry periods over these regions during the ENSO decaying stage might have important implications for the seasonal forecasts.