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

JULY 2009

Sea surface temperature (SST) anomalies during July 2009 remained above average across the equatorial Pacific Ocean (Fig. T18).  Consequently, all of the Niño-region SST indices were between +0.6°C to +1.0°C throughout the month (Table T2, Fig. T5).

The oceanic thermocline along the equator, measured by the depth of the 20°C isotherm, remained deeper than average across the equatorial Pacific Ocean (Figs. T15, T16). Consistent with these conditions, temperatures were 1^o-4^oC above average at thermocline depth across the equatorial Pacific (Fig. T17).  Also during July, convection was suppressed over Indonesia and enhanced across the western Pacific and near the Date Line (Figs. T25, E3). This coupling of the oceanic and atmospheric anomalies reflects El Niño conditions.

The 200-hPa streamfunction field indicates El Niño was impacting the upper-level circulation during July in both the subtropics and extratropics. The impacts were strongest in the winter (i.e., Southern) hemisphere, where they extended from the subtropical South Pacific well into the higher latitudes (Fig. T22).

 In the SH, the subtropical ridge was stronger than average across the central South Pacific and weaker then average over the Indian Ocean . This circulation reflected an overall eastward extension/ shift of the mean subtropical ridge, and is consistent with the El Niño-related pattern of anomalous tropical convection. These conditions were also associated with an eastward extension of the South Pacific jet stream, and with an eastward shift of the jet core to the date line (Fig. T21).

The 500-height field shows the El Niño impacts extending well into the SH high latitudes, as indicated by an extensive area of negative anomalies across the central South Pacific and positive anomalies over the high latitudes of the eastern South Pacific (Fig. E15). Another El Niño impact seen during July was cyclonic streamfunction anomalies in the extratropics of both hemispheres, as indicated by negative values in the NH and positive values in the SH (Fig. T22). This pattern is opposite to that seen earlier in the year in association with La Niña.

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