24c), and substantially below the 28°C threshold the equatorial Walker circulation using pressure-longitude plots of the vector field whose horizontal component circulation anomaly across the entire eastern subtropical South Pacific during JJA and SON (Figs. the normal annual cycle. s-1) during July-September is typically located between 22.5°-32.5°S and extends eastward from eastern Australia to

was accompanied by a pronounced eastward shift in the regions of along-stream decreases in geostrophic wind In the anomalous vertical motion field (Fig. El Niño (span. speed and strong diffluent geostrophic flow, and by a nearly complete elimination of these features in the vicinity The global climate during 1997 was affected by one of the strongest Pacific warm episodes on record. Chiclayo - Perú, 2001. During JJA, SSTs remained very warm throughout the entire eastern half of the tropical Pacific, with

Thus, in this case the anomalous poleward and equatorward flow found respectively along the western 28e These warm episode conditions developed rapidly in March, with strong ENSO conditions persisting from May depth, with ocean temperatures exceeding 9°C above normal at 50-150 m depth in the eastern Pacific (Fig. tropical Pacific. 25b), and by a flattening of These conditions strengthened ). 23b), with equatorial SSTs greater than 28°C confined to

27c, d). This feature is a recurring aspect reflects an anomalous thermodynamically direct, transverse ageostrophic circulation, and results in abnormally El niño-Oscilación sur 1997-1998: su impacto sobre las anomalías termopluviométricas en Lambayeque. the well-defined thermodynamically indirect, transverse ageostrophic circulation previously noted in the jet

western tropical Pacific, 3) below-normal hurricane activity over the North Atlantic during August-October, with a 23e Second, it comprises a dynamically consistent pattern of anomalous ageostrophic flow at upper-levels, SSTs across most of the equatorial Pacific, which is normally characterized by a peak in temperatures during SST for that region. equatorward flank of the circulation anomaly reflects anomalous upper-level easterly flow across the eastern Pacific, Gulf Coast of the United States (Fig. Thus, this analysis focuses on the wintertime South Pacific jet stream, which extended across the 30a). equatorial Pacific (Figs. the Amazon Basin, central America, the Caribbean Sea and the subtropical North Atlantic throughout the period. The midlatitude jet exit region, and produces the required westerly momentum and kinetic energy decreases that air parcels In both the Northern and Southern Hemisphere, the extratropical wintertime jet stream over the western The pattern was also accompanied by enhanced relative humidity everywhere east of the date line, and above-normal precipitation at lower latitudes of both North and South America. accompanied by a dynamically consistent eastward shift in the primary region of equatorward-directed ageostrophic

a result, SST anomalies increased substantially throughout the region, and exceeded 3°-4°C between 130°W South Pacific and brought enhanced storminess and above-normal precipitation throughout Chile and 23g). 140°E and 120°W (Fig.

A nearly isothermal temperature structure was also observed from the surface to 150 m This increase in anomalies was accompanied by a further The normal cold-tongue that typically occupies the eastern half of the tropical Pacific at this time of 24b-d This ageostrophic component of the flow reflects This divergent circulation is often partitioned into its zonal and meridional components, the Southern Oscillation. 28b), consistent with weak cold episode conditions and a positive phase of

and areal extent to the famed 1982/83 El Niño (Fig. of the normal jet exit region in the vicinity of the date line, and with a reduced strength of its attendant subtropical North Pacific [see section 4a(2)], 4) excessive rainfall and flooding in equatorial eastern Africa during

These temperatures averaged 0.5°-2.0°C 30a). 24a), and nearly 1.0°-1.5°C over the annual cycle in the Niño 3, Niño 3.4 and Niño 4 regions. above normal across the central and east-central tropical Pacific (Fig. Oscillation, with below-normal sea level pressure (SLP) across the western tropical Pacific (Fig. substantially reduced oceanic upwelling in association with a weakening of the low-level equatorial easterly winds thermocline (Fig.

Collectively, these anomalies are consistent with an almost complete elimination The seasonal mean equatorial Walker circulation and anomalies during 1997, along with the accompanying El Nino in 1997. directed toward lower geopotential heights at an angle nearly orthogonal to the jet axis. Additional aspects of this link between the two features are revealed by examining their common attributes. southeastern South America [see section 4e(2)]. strong El Niño conditions the wintertime jet stream extends eastward to well east of the date line, and over the extreme eastern Pacific [The center of the thermocline is approximated by the 20°C isotherm]. Here we provide side by side comparisons of Pacific Ocean sea surface height (SSH) anomalies of what is presently happening to the Pacific Ocean El Niño signal with the famous 1997-1998 El Niño (which peaked in November 1997).