Tropical Highlights

  Table of Atmospheric Indices  (Table 1)

  Table of Oceanic Indices  (Table 2)

  Time Series

  Time-Longitude Sections

  Mean & Anomaly Fields

  Appendix 1: Outside Contributions

Tropical Highlights

JANUARY 2008

Atmospheric and oceanic indices during January 2008 indicated a further strengthening of mature cold episode (La Ni�a) conditions throughout the tropical Pacific.  This strengthening is highlighted by a decrease in the Ni�o 4 sea surface temperature (SST) index to -1.5 for the first time since February 1999, and in the Ni�o3.4 region, where the index dropped to -1.8, the lowest value since January 2000.  Overall, equatorial sea surface temperatures (SSTs) anomalies were more than 2.0�C below average across parts of the central and east-central equatorial Pacific (Fig. T18). The magnitude of the negative SST anomalies has decreased along the South American coast, as shown by an increase in the negative values in Ni�o 1+2 index region (Table T2, Fig. T5).

Accompanying these surface conditions, the oceanic thermocline during January remained shallower than normal across the equatorial Pacific east of 160�W and continued to deepen in the region west of the International Date Line (Fig. T16).  Consistent with this structure, sub-surface temperature departures remained negative across the eastern equatorial Pacific, with temperatures at thermocline depth -2�C to -5�C below average, while remaining above average west of 170�W (Fig. T17).

Strong low-level easterly anomalies and upper-level westerly anomalies persisted across the central equatorial Pacific during the month (Figs. T20 and T21, Table T1), which is consistent with the shallower-than-average thermocline in the central and eastern equatorial Pacific (Figs. T15, T16). These conditions were associated with enhanced convection (above-average rainfall amounts) over the far western tropical Pacific and a continuation of suppressed convection (below-average rainfall amounts) across the central and eastern equatorial Pacific (Figs. T25, T26, E3). Consistent with these anomalies, the Tahiti � Darwin SOI remained strongly positive for the second month in a row (+1.9) (Table T1, Fig. T1) while the equatorial SOI remained above +2.0 (Fig. T2).

An important player across the global tropics during January 2008 was the continuation of the strongest and longest-lived MJO activity since the Mar-Apr-May period of 2005. Coherent eastward propagation of the MJO is seen in time-longitude sections of anomalous OLR (Fig. T11) and 850-hPa zonal wind (Fig. T13). Although convection was suppressed during the month as a whole across the Indian Ocean and parts of Indonesia, January saw enhanced convection and associated westerly wind anomalies shift from Indonesia to the Date Line (south of the equator) and later re-enter the Indian Ocean. Suppressed conditions shifted from Africa to Indonesia during the month. Weakened easterlies across the western Pacific associated with this MJO activity initiated a strong oceanic Kelvin wave during the middle of the month.

For the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at:

  http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html