Oceanographic variability in the ecuadorian sea associated with the enso event 97-98

At the beginning of April 97, Ecuadorian Ship of Investigation B/I Orión effected an oceanographic cruise in the Ecuadorian sea and in the immediacies of the Galapagos Islands. Analyses showed dramatic results: 15°C isotherm was to 240 m depth, more than 150 meter below the normal.

Anomalies of Sea Surface Temperature (SST) registered until +4.0°C. Simultaneously the shore station of La Libertad registered positive anomalies of +0.7°C. Termohaline analysis determined an anomalous invasion of subtropical waters surface from the Central Pacific. The undercurrent of Cromwell was perceived weakened and fathomed and equatorial upwelling could not be evidenced.

Oceanographic panorama in the Ecuadorian Sea was confused. Initial diagnosis suggested El Niño conditions in progress. For May and June, evolution of conditions confirmed the presence of a warm event. In July of 1997 anomalies of SST reached +3.2°C, the air temperature (AT) +4.1°C and the Mean Sea Level (MSL) in La Libertad +25 cm of positive anomaly. The wet station was prolonged on the Ecuadorian coast, in answer to the intensification of the Intertropical Convergence Zone (ITCZ), which stayed stationary over the country. The seasonal cycle permitted that the considerable thermal anomalies do not have considerable convective effect. The weak influence of Humboldt Current and corresponding activation of the Southeast trade winds kept temperature of ocean below deep convection threshold although they were warmer than the normal. Starting from July and until September, the level of the anomalies of the MSL descended. However to final of September began a consistent ascent that would culminate in December, where the MSL overcame the marks of the EL Niño 82-83, registering +42 cm in La Libertad. Meanwhile the SST and AT during the same period maintained anomalies average of +3.5°C. The isotherm of 15°C for the month of December was been located below the 200 meter. The conjunction of warming typical of seasonal cycle and anomalies favored by the ENSO, caused the terrible wet station supported in Ecuador. It was the second and great maximum of the ENSO event 97-98 respect to the MSL. Since January to May of 1998 SST anomalies of +3.0°C were registered, whose absolute value surpassed deep convection threshold (28.1°C). Anomalies of accumulated precipitation in Guayaquil since January of 1997 to September of 1998 overcame the 5300 mm. For April of 1998, when the fall of the anomalies was expected, a new Kelvin pulse break out again the conditions, configuring the stage of a third maximum in MSL characterizing to this ENSO event, breaking the comparative schemes with their similar (ENSO 82-83). After that Ecuadorian Sea experienced since May of 1998 descent of their anomalies. Magnitude of the anomalies reached in this event as well as their duration ( 19 months) convert it in the most severe ENSO event of the century supported over Ecuadorian territory.