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Tropical Highlights - July 2002

Warm episode (El Niņo) conditions continued during July 2002, with SST anomalies greater than +1°C persisting across the central equatorial Pacific between 170°E and 130°W (Fig. T18). Consistent with this warmth the Niņo 3.4 and Niņo 4 region indices remained near +1.0°C, the largest values since the end of the 1997-98 El Niņo episode (Fig. T5, Table T2).

Accompanying the ongoing El Niņo the oceanic thermocline remained deeper than normal across most of the equatorial Pacific during July (Figs. T15, T16), with sub-surface ocean temperatures at thermocline depth also remaining above average (Fig. T17). The tropical sea-level pressure (SLP) pattern during July featured small positive anomalies over most of the global Tropics (Fig. T19), in association with a negative value of the Tahiti-Darwin Southern Oscillation Index (SOI) (Table T1). The SOI has remained negative since March 2002 (Table T1), with the five-month running mean (March - July) of the SOI reaching -0.8. This is the five-month running mean value of the SOI since the end of the 1997/98 warm episode (Fig. T1).

Tropical intraseasonal oscillations associated with the Madden-Julian Oscillation (MJO) continued to strongly influence the atmospheric variability in the Tropics and subtropics during July, including contributing to a weakening of the low-level easterlies across the equatorial Pacific (Figs. T13, T20). These westerly wind anomalies were associated with the development of an oceanic Kelvin wave in mid-month, which produced additional deepening of the oceanic thermocline in the central equatorial Pacific (not shown).

Tropical convection also continued to be strongly influenced by the MJO during the month (Fig. T11), with suppressed convection dominating much of the region extending from Indonesia eastward to the central tropical Pacific (Fig. T25). Elsewhere, monsoon rainfall over both the Indian peninsula and the African Sahel were also both well-below normal during July (Figs. E3, E4).

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