QUANTIFYING SOUTHERN OSCILLATION - PRECIPITATION RELATIONSHIPS

A series of earlier studies has identified regions of the world in whi ch precipitation appears to have a consistent relationship with the So uthern Oscillation (SO). In this paper, the authors attempt to quantif y this relationship based on shifts in the statistical distribution of precipitation amounts with emphasis on shifts in the median, which ar e associated with the warm (low SO index) and cold (high SQ index) pha ses of the SO. This paper is partially an attempt to provide long-rang e forecasters with some guidance in making seasonal and multiseasonal predictions. Observed SO-related shifts in the median precipitation am ounts, expressed as percentiles with respect to ''climatological'' con ditions, can be used as a simple indication of the ''typical'' SO resp onse for a given region. In general, the authors find that for many of the large areas identified in previous studies, median precipitation amounts shift on the order of 20 percentile points, that is, from the median to either the 30th percentile or the 70th percentile. The autho rs also find considerable spatial variations in the typical patterns o f SO-related precipitation percentiles in some regions. This study als o provides empirically based estimates of SO-related precipitation ano malies in terms of precipitation rates for use in numerical model stud ies. For selected areas in the Tropics, the authors find empirically e stimated anomalous precipitation rates ranging from 1 to 3.5 mm/day, t hat is, from 15% to 83% of the climatological median.