Instituto del Mar del Perú Nro. 8 Mayo 1997 Pacific ENSO update EDITADO POR :

P a c i f i c E N S O u p d a t e

I N F O R M A T I V O C L I M A T I C O

E l N i ñ o S o u t h e r n O s c i l l a t i o n

nformativo de la Oficina de Comunicaciones del

Instituto del Mar del Perú - IMARPE, sobre el Sistema de Observación Climático

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INDICE :

Pag.

1. Presentación

2

2. Diagnostico y Pronóstico al 15 Mayo 1997

- Diagnostic Advisore Climate Prediction Center 9 Mayo 4 - Climate Diagnostics Bulletin - April 1997 CPC 14 Mayo 7 - Prognostic Discussions for long-lead outlooks

NCEP 15 Mayo 12 - Pronóstico Columbia University 15 - Pronóstico Climate Modeling Branch CMB / NCEP 17 - Pronóstico CDC 20

- Pronóstico BMRC 21

- Pronóstico NESDIS 22

3. Anexo

EDITADO POR :

ING. MARIO RAMIREZ ALVITES ( INGENIERO PESQUERO )

OF. COMUNICACIONES

INSTITUTO DEL MAR DEL PERÚ

- National Oceanic Atmospheric Administration NOAA - National Oceanographic Data Center NODC - Australian Oceanographic Data Center AODC - Japan Oceanographic Data Center JODC - British Oceanographic Data Center BODC - Pacific Marine Environmen. Laboratory PMEL - National Climate Data Center NCDC - Center Ocean-Atmos. Prediction Studies COAPS - Tropical Ocean-Global Atmospheric TOGA - World Ocean Circulation Experiment WOCE - Enviromental Modeling Center EMC - National Centers for Environ. Prediction NCEP - Fleet Numerical Meteor. Oceanography Center FNMOC - Forecast System Laboratory FSL - National Environ. Satellite Data Inform. Service NESDIS - Climate Diagnostic Center CDC - Earth Observing System EOS - Geostation. Operational Environ. Satellite GOES

- Global Change Data Service GCDS

entre otras.

World Wide Web INTERNET http://nic.fb4.noaa.gov

Climate Prediction Center / CPC

National Centers for Environmental Prediction / NCEP NOAA/National Weather Service

Washington, D.C. 20233

CLIMATE PREDICTION CENTER / NCEP May 9, 1997

The evolution of the atmospheric and oceanic conditions in the tropical Pacific during the past few months is consistent with the beginning stages of warm episode conditions. Since early 1997 sea surface temperature (SST) anomalies have increased throughout the equatorial Pacific (Fig. 1), with areas centered on the date line and

near the South American coast experiencing anomalies in excess of +1°C during April (Fig. 2).

In addition, the oceanic thermocline has deepened in the central equatorial Pacific and the oceanic heat content has increased throughout the western and central equatorial Pacific.

During the past several months enhanced tropical convection has gradually shifted eastward toward the date line, accompanied by a transition to suppressed convection over the western equatorial Pacific and Indonesia (Fig. 3). Accompanying this evolution has been an overall weakening of the equatorial low-level easterlies across the central and eastern Pacific and a strengthening of low-level equatorial westerlies over the western Pacific. As a result, low-level westerly wind anomalies during March and April extended across the entire tropical Pacific (Fig. 4). In addition, the SOI has switched from positive to strongly negative during the period.

Collectively, this evolution indicates the early stages of a warm (ENSO) episode.

In recent months, the NCEP coupled model and CCA statistical technique have been consistent in indicating the development of warm episode conditions during the first half of 1997. The latest forecasts from these two techniques indicate a continued warming trend through the end of the year.

Based on the recent evolution and the indications given by these forecasts we can expect warm episode conditions to intensify during the next several months.

The Climate Prediction Center will continue to monitor the evolution of oceanic and atmospheric anomalies and additional advisories will be issued as warranted.

Climate Prediction Center / CPC

National Centers for Environmental Prediction / NCEP NOAA/National Weather Service

Washington, D.C. 20233

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CLIMATE PREDICTION CENTER

CLIMATE DIAGNOSTICS BULLETIN - APRIL 1997

Date: May 14, 1997

Tropical Highlights - April 1997

Positive sea surface temperature (SST) anomalies increased throughout the equatorial Pacific during April

as warm episode (ENSO) conditions continued to develop (Fig. 1).

The largest anomalies (greater than +1°C) were observed from 160°E to 160°W and from 90°W to the South American coast (Fig. 1 ). A small region just off the South American coast registered +2°C anomalies. During April, all four Niño SST index regions featured substantial positive anomalies (Table T2, Fig. 2). The most significant of these anomalies is the +1 in the Niño 4 region, where enhanced convection and low-level westerly anomalies have been observed during the last two months (negative OLR and 850-hPa zonal wind indices, Table T1).

Since February, the oceanic thermocline has deepened throughout the equatorial Pacific and the upper ocean heat storage has increased. During April, subsurface equatorial temperature anomalies in the vicinity of the thermocline were positive throughout the Pacific (Fig. 3), with maximum anomalies greater than +6°C near 150 m depth from 150°-180°W.

The SOI was strongly negative (-1.3) for the second consecutive month.

The intraseasonal (30-60 day) oscillation (MJO) that has had a strong impact on atmospheric indices during the last several months, remained active but with a shorter period (30-40 days instead of 50-60 days). With this shorter period the influence of the MJO on the monthly atmospheric indices has been reduced.

Since the beginning of 1997, positive SST anomalies have increased and low-level easterlies have weakened throughout the central and eastern equatorial Pacific. Also, convective activity has weakened over Indonesia and increased over the equatorial Pacific in the vicinity of the date line, and the SOI has switched from positive to strongly negative during the period.

Collectively, this evolution indicates the early stages of a warm (ENSO) episode.

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(Continua en Pag. 11)

Fig. 1 Sea Surface Temperature (°C) and SST anomalies (°C).

Fig. 2. SST anomalies Nino 3 , Nino 4 and Nino 1+2

Fig. 3. Equatorial Depth-Longitude Section Ocean Temperature (°C) and Anomalies.

(Viene de la Pag. 7)

DISCUSION Y PERSPECTIVAS FUTURAS

La evolución de las condiciones oceano-atmosfera en el Pacifico tropical durante los meses pasados es consistente con el inicio gradual de las condiciones de episodio de calentamiento. Desde inicios de 1997, la anomalía de temperatura superficial del mar se ha incrementado a casi todo el Pacifico ecuatorial, con áreas focalizadas sobre la línea de cambio de fecha, y frente a la costa sudamericana experimentando anomalías mayores a +1 °C durante abril.

Además, la termoclina oceánica se ha profundizado en el Pacifico ecuatorial central y la energía calórica contenida se ha incrementado a casi todo el Pacifico ecuatorial central y occidental.

Así mismo, en los meses pasados una marcada actividad convectiva se ha desplazado hacia el este de la línea de cambio de fecha, acompañado por una transición a la disminución de esta actividad convectiva sobre el Pacifico ecuatorial oriental e Indonesia. Acompañando esta evolución ha habido un extenso e intenso desplazamiento hacia el este de vientos anómalos de bajo nivel del oeste y de amplia cobertura desde Indonesia hacia el Pacifico ecuatorial central. Durante marzo y abril, dichos vientos se extendieron por casi todo el Pacifico tropical.

En suma, los índices atmosféricos típicamente utilizados para monitorear las fases del Indice Oscilacion Sur son ahora consistentes con el inicio de las condiciones de episodio de calentamiento.

CLIMATE PREDICTION CENTER

CLIMATE DIAGNOSTICS BULLETIN - APRIL 1997 Date: May 14, 1997

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PROGNOSTIC DISCUSSIONS FOR LONG-LEAD OUTLOOKS CLIMATE PREDICTION CENTER / NCEP

NATIONAL WEATHER SERVICE - WASHINGTON DC

Date: May 15, 1997

PROGNOSTIC DISCUSSION OF SST FORECASTS

THE OFFICIAL SST FORECAST FOR THE EAST-CENTRAL EQUATORIAL PACIFIC (120-170W LONGITUDE - ALSO CALLED NINO 3.4) CALLS FOR SST ANOMALIES TO CONTINUE THE WARMING TREND WHICH HAS BEEN OBSERVED SINCE LATE JANUARY. THE SSTs FROM THE DATE LINE TO THE SOUTH AMERICAN COAST HAVE BEEN MORE THAN 1 DEGREE C ABOVE NORMAL IN THE LAST WEEK - AND HAVE WARMED MOST RAPIDLY IN THE LAST 6 WEEKS.

El pronostico oficial de temperatura superficial del mar (TSM) para el Pacifico ecuatorial oriental-central (120° - 170°W longitud - Niño 3 , 4) sugiere la continuación de la tendencia al calentamiento vía incremento de las anomalías TSM , que han sido observadas desde fines de enero. Las TSMs desde la línea de cambio fecha hasta la costa sudamericana ha estado por arriba de 1°C de lo normal en la semana ultima, y el calentamiento se ha desarrollado mas rápidamente en las pasadas 6 semanas.

THE SST FORECAST IS BASED ON A COMBINATION OF SEVERAL STATISTICAL AND DYNAMIC FORECASTING TOOLS AND THE MOST RECENT OBSERVATIONS INDICATING VERY SUDDEN WARMING. A STATISTICAL MODEL BASED ON A CONSTRUCTED ANALOGUE (CA) AND ONE BASED ON CANONICAL CORRELATION ANALYSIS (CCA - Page 14) INDICATE POSITIVE SST ANOMALIES BY SUMMER AND BECOMING MORE STRONGLY ABOVE NORMAL BY FALL 1997 AND WINTER 97/98. THE DYNAMIC FORECAST FROM THE NCEP MODEL INDICATES A SIMILAR EVOLUTION OF POSITIVE NINO 3.4 SST ANOMALY. ALTHOUGH THESE THREE MODELS AGREE - THEY DO NOT FORECAST THE SUDDENNESS OF THE WARMING AS IT APPEARS TO TAKE PLACE RIGHT NOW. THIS IS IN PART BECAUSE THE LATEST INITIAL CONDITIONS FOR THESE MODELS ARE THE SEASONAL FMA AVERAGE OR SOME OTHER LOW FREQUENCY DESCRIPTION THAT INCLUDES THE COOL CONDITIONS IN THE PAST SEASON AND LAST YEAR. ** THE SUDDEN WARMING OF THE LAST WEEKS IS THUS NOT KNOWN TO ANY OF THESE MODELS. **

OPINIONS DIFFER AS TO WHETHER THE SUDDEN WARMING IS JUST A BLIP OR AN EARLY ONSET OF A WARM EVENT TO STAY. ANOTHER DYNAMIC MODEL - A NEW VERSION OF THE CANE AND ZEBIAK MODEL (LDEO2) INDICATES CONTINUED NEGATIVE ANOMALIES THROUGHOUT 1997. THIS MODEL IS THE ONLY ONE AMONG THE FOUR WHICH CONTINUES TO PREDICT COLD EVENT CONDITIONS. IN VIEW OF THE RECENT UPWARD TREND IN SSTS TO DECIDEDLY ABOVE NORMAL TEMPERATURES IN THE EAST-CENTRAL TROPICAL PACIFIC - TEMPERATURES WOULD HAVE TO DECLINE FROM CURRENT VALUES TO BE IN AGREEMENT WITH LDEO2. HOWEVER - ATMOSPHERIC CONDITIONS FOR SUCH A DROP IN TEMPERATURE CURRENTLY DO NOT EXIST.

IN FACT - LOW LEVEL EQUATORIAL PACIFIC WINDS AND THE SOUTHERN OSCILLATION INDEX ITSELF HAVE BEEN SUGGESTIVE OF A DEVELOPING WARM EPISODE DURING MARCH APRIL AND MAY. FOR THESE REASONS THE CONSENSUS FORECAST AMONG THE THREE MODELS WHICH ARE IN AGREEMENT IS THE SCENARIO CURRENTLY CONSIDERED TO BE THE MOST LIKELY TO OCCUR. THUS - A FORECAST OF POSITIVE SST ANOMALIES AND WARM EVENT CONDITIONS THROUGH AT LEAST WINTER 97/98 IS INDICATED.

Las opiniones actuales difieren en que sea este repentino calentamiento solo una “cresta”, ó sea realmente el principio del inicio de un evento de calentamiento que permanecerá. Otro método de pronostico dinámico, la nueva versión del modelo de Cane y Zebiak (LDEO2) (Pag. 15) indica la continuación de anomalías negativas durante 1997. Este modelo es el único de entre cuatro que continua pronosticando condiciones hacia un enfriamiento. En vista de la fuerte tendencia actual al incremento de la TSM por encima de temperaturas normales en el Pacifico tropical oriental-central, la TSM tendría que declinar de sus valores actuales para concordar con lo pronosticado por este modelo LDEO2. Sin embargo, no existen condiciones atmosféricas para tal descenso de la temperatura. Lo real, es que los vientos del Pacifico ecuatorial de bajo nivel y el Índice de Oscilación Sur (IOS) por si mismo estuvieron y están sugiriendo en el desarrollo del episodio de calentamiento durante marzo, abril y mayo. Por estas razones el consenso de pronostico de los tres modelos concordantes es que el escenario que actualmente se considera y valida, es el que debiera ocurrir.

** Por lo tanto, el pronostico de anomalías positivas de temperatura superficial del mar y condiciones para un evento de calentamiento, hasta por lo menos el invierno 1997- 98, es lo que debiera ocurrir. **

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El modelo CANONICAL CORRELATION ANALYSIS (CCA), indica

incremento de anomalías positivas de TSM hasta marzo 1998, luego

disminuye gradualmente.

Pronostico de la ATSM en el Pacifico Ecuatorial, Abril 1997.

Por: Steve Zebiak

El pronostico relacionado con la Temperatura Superficial del Mar se produce mensualmente utilizando el modelo acoplado océano-atmósfera desarrollado por Zebiak and Cane - 1987.

“Sea Surface Temperature (SST) will be normal across the central and eastern equatorial Pacific through 1997”.

ENSOFORECAST LDEO2 06 Months SSTA toward Oct. 1997

SSTA = Sea Surface Temperature Anomaly

ENSOFORECAST LDEO2 09MON ssta Time is Jan1998 (degC)

ENSOFORECAST LDEO2 12MON ssta Time is Apr1998 (degC)

Predicted SST anomalies at 6, 9 and 12 month lead times. Predictions are based on the ensemble mean individual forecasts initialized from the six consecutive months ending in April 1997. Forecasts for each lead time independent of start month have been corrected for systematic biases using a singular value decomposition analysis, based on the years 1972-1992. The coupled dynamical forecast system is that described in Cane et al (1986, Nature) and Zebiak and Cane, (1987, Mon. Wea. Rev.)

Figure: Nino-3 and Nino3.4 SST forecasts

Time evolution of predicted and observed SST anomalies for the Nino-3 (150W-90W, 5S-5N) and Nino3.4 (170W-120W, 5S-5N) from the NCEP/CMB coupled model (CMP12). The forecasts are for lead times of 1-season (top), 2- seasons (middle) and 3-seasons (bottom). Observed SST anomalies are depicted in solid lines. Forecast SST anomalies are indicated by "+"s. Figure: Nino-3 and Nino3.4 SST forecasts

MODELO INVERSO LINEAL PARA EL PRONOSTICO ENSO (Abril 1997).

climatología estándar COADS 1950-1979, tanto para el período de prueba 1950-1984 y este pronóstico. Los datos de temperatura superficial del mar utilizados en este pronóstico han sido proporcionados por la National Centers for Environmental Prediction, cortesía de R. W. Reynolds. El modelo de pronóstico inverso lineal esta descrito en Penland and Magorian (1993, J. Climate, 6).

“Slower and much weaker transition towards warm episode conditions.”

Pronóstico Experimental

¨El Niño¨

Utilizando el modelo acoplado Océano-Atmósfera

Presentación :

El modelo acoplado océano-atmósfera para el pronóstico de temperaturas del Océano Pacifico Tropical Oriental, ha sido desarrollado por el Dr. Richard Kleeman y colaboradores, en el Bureau of Metereology Research Centre en Melbourne - Australia. El calentamiento asociado a temperaturas por arriba del normal, esta ligado al evento El Niño, mientras que el enfriamiento por debajo de las condiciones normales esta ligado al evento La Niña. El índice NIÑO3 es utilizado para medir estas desviaciones de temperatura. Si el índice es mayor a 1.5, se dice que existen condiciones de un evento El Niño - fuerte.

Contrariamente, valores menores a -1.5 indican que existen condiciones de un evento La Niña - fuerte.

PRONOSTICO ACTUAL :

El pronóstico actual muestra esencialmente, condiciones de El Niño Moderado y fortaleciendose rapidamente.

La línea vertical azul (Feb-97) indica cuando fueron ingresados los últimos datos al modelo.

A Satellite-only climatology has been provided at 36 km resolution by Al Strong and interpolated to 50 km resolution. The maps provided below are the anomalies between the Operational 50 km Day/Night SST Analyzed Field and the Satellite-only cliamtology, and the anomalies between the Experimental 50 km Nighttime SST Analyzed Field and the Satellite-only climatology.

Anomaly charts are available for:

Nighttime 5.17.1997 Nighttime 5.12.1997 Comments on 5.12.1997 Nighttime 5.10.1997 . . .

Notas al chart de Anomalia Temperatura Superficial Mar global (50 Km Resolución) del 12 Mayo 1997

NOTES: 12 MAY 1997

NOAA's Climate Prediction Center has officially stated we appear to be in the beginning stages of the El Nino of 1997 -- ENSO Advisory: 7 May 97.

It is obvious from the referenced SST anomaly chart that all of the eastern equatorial Pacific has risen to above normal levels with the eastward progression of the large Kelvin Wave across the Pacific during March and April.

See WWW Internet : [http://wesley.wwb.noaa.gov/eileen/sealevel.html].

Still noteworthy is the South Atlantic region of negative anomaly from the Equator to 30S. This area appears to have been maintained below climatology for much of 1997 beneath an enhanced surface pressure gradient. A similar situation can been seen NW of Hawaii where below normal SSTs prevail.

AES

El Nino 1997 SST Anomalies and Sea Level Observations (1997)

Satellites have been monitoring the Equatorial Pacific for the predicted 1997 el Niño. During the last few months of Topex/Poseidon data, one can see a Kelvin Wave [10-20cm elevation of sea level] moving eastward from Indonesia[140°E] to South America [280°E or 80°W] along the Equator. This first significant impulse in over two years is now being followed by a second Kelvin Wave with even large magnitudes. The second Kelvin Wave had reached 260°E [100°W] by April 20 [not shown]. NESDIS's satellite-derived sea surface temperature [SST] anomalies [AVHRR] continue to show the eastern tropical Pacific in a warming mode that began late-January 1997.

Three charts are shown in the mosaic-image that depict the surface warming that is accompayhing the Kelvin Wave. Initial warming has become much more robust in the past week -- see April 25. SSTs near the Galapagos Islands are 4-5 deg °C above climatology.

Preliminary predictions from the NOAA Climate Prediction Center are consistent with the beginning stages of warm episode conditons.

A N E X O

Fuente: Bureau of Metereology - Australia

Fig. 1 Sea Surface Temperature Monthly Anomaly April 1997.

Fig. 2. Global SST Anomaly Week ending May 18, 1997 Fig. 3 Ecuatorial Temperature and Anomaly Section Analyses May 1997 Fig. 4 Ocean Analysis Depth 20°C Isotherm May 1997 Fig. 5 CAC + BMRC monthly SST indices May 1997

Fuente: National Oceanic Atmospheric Administration NOAA Climate Modelling Branch - CMB

Fig. 6 Pacific Sea Surface Temperature Anomaly April 30, 1997 Fig. 7 Sea Surface Temperature Anomaly 11 - 17 May, 1997

Fig. 3

Fig. 5

Fig. 7