Inter-El Niño variability and its impact on the LLJ East of the

Andes during Austral Summer

Tércio Ambrizzi and Gyrlene A. M. da Silva

Department of Atmospheric SciencesUniversity of São Paulo – Brazil

VAMOS/MESA Meeting – Mexico City, Mexico7 – 11 March, 2005

Conceptual model of the SALLJ physical environment during the wet season (Marengo et

al. 2004 - JC)

Schematic figures of the Atmosphere Circulation during Canonical El Niño/La Niña

eventos

EL NIÑO

LA NIÑA

Streamfunction Anomaly and Precipitation

AVERAGE FOR 4 EL NIÑOS

Div Q and Omega Anomaly

(Ambrizzi and Magaña, 2005)

I = (Xi - Xi)/i

ENSO episodes and the South American Regional Precipitation

Seasonal Standardized index for the austral summer (DJF) and autumn (MAM)

were calculated for the precipitation over key-areas of South America and the SSTa over the Niño 1.2, 3, 3.4 and 4

(Ambrizzi and Souza, 2003)

El Niño episodes and the South American Regional Precipitation during 1950-1990

(g)

-2,5

-1,5

-0,5

0,5

1,5

2,5

3,5

4,5

Ecuador/P eru

(f)

-2,5-1,5-0,50,51,52,53,54,5

Altiplano

(e)

-2,5-1,5-0,50,51,52,53,54,5

SE South America

(d)

-2,5-1,5-0,50,51,52,53,54,5

SACZ

(c)

-2,5-1,5-0,50,51,52,53,54,5

NE Brazil

(b)

-2,5-1,5-0,50,51,52,53,54,5

E Amazon

(a)

-2

-1

0

1

2

3

4

Niño 1+2 Niño 3 Niño 3+4 Niño 4

Niños SSTa

E Amazon

NE Brazil

SACZ

SE South America

Altiplano

Ecuador Peru

La Niña episodes and the South American Regional Precipitation during 1950-1990

(a)

-2

-1

0

1

2

3

4

Niño 1+2 Niño 3 Niño 3+4 Niño 4

(b)

-2,5-1,5-0,50,51,52,53,54,5

E Amazon

(c)

-2,5-1,5-0,50,51,52,53,54,5

NE Brazil

(d)

-2,5-1,5-0,50,51,52,53,54,5

SACZ

(e)

-2,5-1,5-0,50,51,52,53,54,5

SE South America

(f)

-2,5-1,5-0,50,51,52,53,54,5

Altiplano

(g)

-2,5

-1,5

-0,5

0,5

1,5

2,5

3,5

4,5

Ecuador/P eru

Niñas SSTa

E Amazon

NE Brazil

SACZ

SE South America

Altiplano

Ecuador Peru

SLC – PACIFIC BOXES - DEC - MAY – EL NIÑO

CB

E GSVD

(Coelho, Uvo and Ambrizzi, 2002 – TAC)

SLC – PACIFIC BOXES - DEC - MAY – LA NIÑA

EB

F GSVD

(Coelho, Uvo and Ambrizzi, 2002 – TAC)

OBJETIVE

To study the relationship between different intensities of ENSO events and the South America Low Level Jet East of the Andes during Austral Summer.

METHODOLOGY

Data composites and Baroclinic model experiments.

DATA

Monthly SST ( Wooddruf et al, 1987) OLR from 1975 – 2003 (Liebmann and Smith, 1996) Reanalysis (NCEP/NCAR) (Kalnay et al, 1996) – From

1969-2003)

ENSO Selected Events (CDC/NOAA)

El NiñoEl Niño – 9 Weak, 2 Moderate, 3 Strong

La NiñaLa Niña – 4 Weak; 3 Moderate; 3 Strong

NeutralNeutral – 10 Summers

(a)

(b)

Climatological DJF Wind vector and intensity

for the period 1969 - 2003850 hPa 200 hPa

(m/s)

Number of Jet occurrences = 17± 8

73-74, 88-89, 00-01 Niña

82-83, 91-92, 98-99 Niño

Nu

mb

er o

f Je

ts

DJF composite fields for SST anomalies during strong and weak

ENSO events (°C)Strong El Niño Weak El Niño

Strong La Niña Weak La Niña

Weak El Niño

DJF composite fields for Streamfunction anomalies during

strong and weak ENSO events - 200 hPa (m2/s)

Strong El Niño

Strong La Niña Weak La Niña

Weak El Niño

DJF composite fields for Streamfunction anomalies during

strong and weak ENSO events - 850 hPa (m2/s)

Strong El Niño

Strong La Niña Weak La Niña

Weak E

l N

iño

DJF Composite Fields of Water Vapor Flux and Divergence Anomaly (g/ms)

Str

on

g E

l N

iño

Str

on

g L

a N

iña

Weak L

a N

iña

Day -

1

Day -

2D

ay 0

Day +

1

SLP Anomalies and Wind Vector at 850 hPa

for Strong El Niño Events

Day -

1

Day -

2D

ay 0

Day +

1

SLP Anomalies and Wind Vector at 850 hPa

for Weak El Niño Events

Day -

1

Day -

2D

ay 0

Day +

1

SLP Anomalies and Wind Vector at 850 hPa

for Strong La Niña Events

Day -

1

Day -

2D

ay 0

Day +

1

SLP Anomalies and Wind Vector at 850 hPa

for Weak La Niña Events

Weak E

l N

iño

Conceptual Diagram of the SALLJ average position during ENSO

extreme eventsS

tron

g E

l N

iño

Str

on

g L

a N

iña

Weak L

a N

iña

0°N, 120°W 0°N, 160°W

Wind Vector Anomaly at 850 hPa

Baroclinic Model Experiments for the Heat Source Centered in the Equator -

Streamfunction Anomaly

FINAL COMMENTS

•SALLJ Frequency events: higher during Strong and Weak El Niños and slightly below average during Strong and Weak La Niña events → There is not a clear tendency during ENSO events;

•SALLJ intensity and position during ENSO:

Strong El Niños → higher amplitudes and displacement to the La Plata Basin region – weak SACZ

Weak El Niños and Strong and Weak La Niñas → smaller amplitudes and displacement to the southeast of Brazil – strong SACZ (Liebmann et al, 2004, JC)

•Source of moisture in the corridor along the eastern slope of the Andes: during El Niños → trade winds; During La Niñas it seems that the east Pacific ocean may play some role

•Transients are important to modulate the position of the SALLJ

•Simple numerical experiments suggest that the tropical forcing plays an important part on the intensification of the jet but it is dependent of the synoptic activities to better positioning of it.

Climate Studies GroupClimate Studies Group

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THANKS TO JOSS/UCAR FOR THE TRAVEL SUPPORT TO THIS MEETING