Teleconnections with Tropical Precipitation Surges

Abstract

Precipitation surges in the equatorial Pacific ?dry zone? (as delineated in a study by Doberitz) reveal statistically significant teleconnections with midlatitude tropospheric flow patterns during all seasons. These connections are strongest, however, during winter and agree with linear numerical model results. There is evidence that deep troughs in the central North Pacific antecede precipitation surges in the equatorial dry zone during that season, suggesting the possibility of triggering of such surges by middle latitude planetary-wave perturbations. Nonlinear numerical model results also indicate that the midlatitude planetary-wave response is strongest when North Pacific cold sea-surface temperature anomalies and equatorial East Pacific warm anomalies are present simultaneously. The planetary-wave pattern associated with equatorial Pacific precipitation surges appears to be in phase with orographically generated wave patterns, whereas an anomalous low-latitude heat source over the extreme equatorial west Pacific, the Bay of Bengal and India, corresponding to rainfall during an active phase of the Indian monsoon, tends to be associated with wave perturbations out-of-phase with orographic forcing.