Tropical
Highlights - November 2001
ENSO-neutral conditions prevailed across the
tropical Pacific during November 2001, as indicated by near-normal equatorial atmospheric
(Table T1) and sea surface temperature (SST) indices (Table T2). ENSO-neutral conditions have persisted since May
2001, although a non-significant weak dipole pattern of positive SST anomalies (0.5 to
1.0°C) across the western and central Pacific and negative SST anomalies (1.0°C) across
the eastern Pacific has persisted since September 2001 (Fig. T18).
During November, the SST anomalies reflected an expansion of the 30°C isotherm in the
region just west of the date line, and the persistence of anomalously warm SSTs in the
Niño 4 region (Table T2).
The oceanic thermocline (indicated by the 20°C isotherm) remained deeper than normal
across nearly the entire equatorial Pacific, and slightly shallower than normal in the
extreme eastern Pacific (Fig. T15). Consistent with these
conditions, temperatures at thermocline depth were 2-3°C above normal throughout the
western and central equatorial Pacific and 2-3°C below normal in the extreme east (Fig. T17). This overall anomaly pattern has persisted since
August, although the positive anomalies have slowly expanded eastward during the period.
Tropical convection during November was enhanced over the eastern Indian Ocean and
Indonesia and near-normal across the rest of Pacific (Fig. T25).
However, this pattern of anomalous tropical convection was again modulated by
intraseasonal (Madden-Julian Oscillation-MJO) activity during the month, especially over
the Indonesian sector (Fig. T11).
The low-level (850-hPa) westerly winds were slightly weaker than normal across the
western and central equatorial Pacific during November, with 3 ms-1 easterly
anomalies recorded between 175°E and 160°W (Fig. T20).
The 850-hPa indices in the western (0.8) and central (0.9) Pacific are the largest values
recorded in each region since April 2001 (Table T1). At
upper levels (200-hPa) westerly anomalies were observed across most of the equatorial
Pacific in association with cyclonic circulation anomalies straddling the equator in the
central Pacific (Fig. T21, T22).
The sea level pressure (SLP) pattern during November featured negative anomalies
extending from the eastern Indian Ocean across Indonesia to the western Pacific and
positive anomalies across the central and eastern Pacific (Fig.
T19). This pattern was associated with a positive value of the Tahiti - Darwin
Southern Oscillation Index (SOI) (0.7) (Table T1). The
equatorial SOI also remained positive during November (1.2), and has been positive since
the beginning of the 1998-2001 cold episode (Fig. T2). |
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