Figure 4From: Effects of the El Niño-Southern Oscillation on dengue epidemics in Thailand, 1996-2005 El Niño Southern Oscillation (ENSO) data, 1996-2005. The monthly multivariate ENSO index (MEI) (red line with rectangles) and the anomalies of the sea level pressure index (SLP) (blue line with bars). MEI > 1 (or SLP < -1) defines the occurrence of El Niño. A more positive value of MEI (or a more negative value of SLP) indicates a stronger El Niño.Back to article page