INTRASEASONAL VARIABILITY OF THE MONSOON SYSTEMS IN THE AMERICAS:

ORIGIN AND PREDICTABILITY

Carlos D. Hoyos, Paula A. Agudelo and Judith A. Curry

Peter J. Webster

School of Earth and Atmospheric SciencesGeorgia Institute of Technology

2008

Two sets of studies under CPPA funding:

(1) Instability of the East Pacific ITCZ: Diagnostic, theoretical and diagnostic study of the variability of the ITCZ and the genration of easterly waves:

Toma and Webster 2008a: Oscillations of the ITCZ: (I) Theoryand diagnostic studies (under review)

Toma and Webster 2008b: Oscillations of the ITCZ: (II)Numerical studies (under review)

(2) Intraseasonal variability over the Americas: Hoyos, Webster, Agudelo and Curry

(a) Diagnostic study of the magnitude of ISV in the Americasand its connection to global ISV: Regional versusremote control

(b) Prediction of ISV: Errors and model failures and thedevelopment of hybrid models

Two sets of studies under CPPA funding:

(1) Instability of the East Pacific ITCZ: Diagnostic, theoretical and diagnostic study of the variability of the ITCZ and the generation of easterly waves:

Toma and Webster 2008a: Oscillations of the ITCZ: (I) Theoryand diagnostic studies (under review)

Toma and Webster 2008b: Oscillations of the ITCZ: (II)Numerical studies (under review)

(2) Intraseasonal variability over the Americas: Hoyos, Webster, Agudelo and Curry

(a) Diagnostic study of the magnitude of ISV in the Americasand its connection to global ISV: Regional versusremote control

(b) Prediction of ISV: Errors and model failures and thedevelopment of hybrid models

Introduction: Long-Term Mean Precipitation (CPC retrospective precipitation analyses)

Is there intraseasonal modulation of precipitation in the Americas?

How? Is it predictable? If so, how can we forecast it?

Outline

Americas ISO diagnostic analysis: local variability in connection with large scale ISO/MJO

Extended Predictability: Serial Runs Analysis

First Steps towards Americas ISO forecasting: Hybrid Prediction

Boreal Summer

Austral Summer

Amplitude of Intraseasonal OLR variability

Wm-2

N.H. Summer N.H. Winter

Detail of the Americas Intraseasonal OLR variability

Long-Term mean precipitation from GPCP data.

Regions selected (From North to South):

South West USASouth East USA

Northern Mexico

East PacificEquatorial AmericaCentral-East Brazil

Southern BrazilSouth Atlantic (‘SACZ’)

Regional Analysis

Average wavelet spectra for the selected regions

The thick blue and red lines represent the multi-year average while the thin lines correspond to individual years from 1997 to 2006.

Northern Hemisphere

Boreal Summer Austral Summer

Average wavelet spectra for the selected regions

The thick blue and red lines represent the multi-year average while the thin lines correspond to individual years from 1997 to 2006.

Northern Hemisphere

Boreal Summer Austral Summer

Episodic ISO (specific years with strong ISO)

Boreal Summer Austral SummerSouthern

Hemisphere

Average wavelet spectra for the selected regions

Thick blue and red lines represent the multi-year average while the thin lines correspond to individual years from 1997 to 2006.

Boreal Summer Austral SummerSouthern

Hemisphere

Average wavelet spectra for the selected regions

Thick blue and red lines represent the multi-year average while the thin lines correspond to individual years from 1997 to 2006.

Episodic ISO (specific years with string ISO)

MJO Events: Average Convective Track

38 events

31 events

Composite Analysis

38 winter and 31 summer events are selected for the composite analysis.

The events correspond to eastward propagation ISO events (MJO)

These events are used to study the link between Indian Ocean-West Pacific ISO to the Americas ISO

Evolution of Intraseasonal OLR Anomalies: Boreal Summer

Evolution of Intraseasonal OLR Anomalies: Austral summer

Composites of OLR for the Boreal Summer MJO Is there any connection with the Observed ISV in the Americas?

Intraseasonal OLR anomalies over the Americas occur regularly associated with those over the Indo-West Pacific Basin.Anomalies appear in the west coast of the Americas during summer extending from Mexico to Peru. These anomalies are associated with either directly or indirectly with the activity over the Indian Ocean

Negative (positive) convective anomalies over the Central Equatorial Indian Ocean are associated with positive (negative) convective anomalies in the Tropical Americas.

Composites of OLR for the Austral Summer MJO

Is there any connection with the Observed ISV in the Americas?

Intraseasonal OLR anomalies over the Americas occur regularly associated with those over the Indo-West Pacific Basin.

Lagged convective anomalies in Brazil associated with MJO convection

Maximum positive and negative convective anomalies over Brazil appear about 10 days after convective anomalies of different sign over the Indian Ocean

Difference of cumulative rainfall between two different phases of MJO BOREAL SUMMER

Enhanced precipitation in the Equatorial Americas, East Pacific and South East United States about 10 prior to the maximum convection over the Indian Ocean

Enhanced rainfall tend to occur around Day 0 in Equatorial South America, while less rainfall is seen South East United States. In contrast, enhanced rainfall is seen South East United States around Day 15 while less precipitation fall over Equatorial America and the East Pacific

Day (-13..-17) - (+2…+8) Transition

Day (+12..+18) - (+22..+33) Break

Day (-3..+3) - (+12…+18) Active

Difference of cumulative rainfall between two different phases of MJO AUSTRAL SUMMER

Similar features are observed for austral summer. The bottom line is that there are phases of the summer and winter MJO where there is enhanced rainfall (more accumulation) in the Americas compared to other phases of the same phenomena.

Day (-13..-17) - (+2…+8) Transition

Day (+12..+18) - (+22..+33) Break

Day (-3..+3) - (+12…+18) Active

Composites of 200mb Stream Function for the Austral summer MJO

Due to their elongation, the cyclones/ anticyclones located to the east of the convective anomaly reach the Americas potentially impacting indirectly the atmospheric conditions suggesting the existence of a teleconnection-like pattern.

Successive daily integration throughall phases of ISO life cycle

Use ECMWF climate model run for 30 day forecasts on 45 successive days in ensemble mode (5/day)

Two cases: o Winter: TOGA COARE, 1992/93o Summer: May/June 2002, 2004

OLR variability through summer case

Serial Experiment using coupled Ocean-atmosphere models

Agudelo et al. (2008)

Forecasting Skill and Predictability

200 mb Zonal Winds

OLR

Joint PDF: 200 mb Zonal Winds

Joint PDF: OLR

Zonal Winds

1992/1993

Forecast of the Vertical Structure of the Atmosphere

There are states of the system for which the skill of the forecast is always low

Coincide with convective events.

99% statistical significance threshold

ISO maxconvection

ISO maxconvection

Specific Humidity

1992/1993

Forecasts of specific humidity, associated with the moist convective anomalies during the ISO, have no skill.

Forecasts of zonal winds which correspond mainly to regional circulation anomalies associated with the ISO, are skillful up to about 13 days.

Forecast of the Vertical Structure of the Atmosphere

ISO maxconvection

ISO maxconvection

Where do the errors come from?Day 1 Errors

Where do the errors come from?Day 2 Errors

Where do the errors come from?Day 3 Errors

Where do the errors come from?Day 4 Errors

Where do the errors come from?Day 5 Errors

Modeling Lessons From Previous Work

Approach problem of intraseasonal prediction from the following hypothesis:

• Strong observed ISO eroded in NWP by errors mainly associated with the convective parameterization.

• Utilize findings of physically based empirical scheme that uses wavelet banding to separate significant spectral bands. Linear regression and recombination of the bands provides pentad forecasts at 20 days with correlation coefficients of ~0.8 (Webster and Hoyos 2004).

• Developed integration scheme that applies the philosophy of the banded wavelet empirical scheme to the coupled ocean-atmosphere GCM.

• 30-day forecasts during the Summer of 2004 show an improvement in the forecasts of the evolution of the monsoon ISO.

Goal: Design a hybrid system that combines the idea of spectral separation of different time scales of variability used in the empirical forecasting scheme with the operational 51-ensemble forecasts from the ECMWF in order to provide improved probabilistic forecasts of rainfall and river discharge for the South-East Asian region during the summer monsoon.

Hybrid Approach

1. Separation of different time scales of variability in the data: Use of dominant EOF modes of OLR as spatio-temporal filters. EOFs are estimated from unfiltered daily anomalies (relative to the annual cycle) of OLR for all the summers (May to September) from 1980 to 2005. The goal is to forecast each of the significant principal components in terms of variance.

2. Physically based predictors for each PC: Predictors should be selected from the 3D circulation structure since the ECMWF model is more skillful forecasting their anomalies.

3. Forecast Each OLR PC: Use of statistical relationships between all predictors and OLR principal components together with operationalforecasts of the predictors to produce a hybrid forecast.

OLR EOF’s (Summer)

EOF#1 EOF#2

PC#1

PC#2

Modes 1 and 2 account for most of the ISO summer variability

2002

OLR Anomalies

Reconstructed using PC1 and PC2

First two EOFs and the Fourier spectra of their corresponding PC’s for unfiltered daily anomalies (relative to the annual cycle) of OLR for all the summers (May to September) from 1980 to 2005

Example: Using a single predictor

In this example we use a single predictor for each mode defined as the projection of 850mb relative vorticity onto the corresponding EOF.

OLR Anomalies

Relative Vorticity Anomalies

OLR

Ano

mal

ies

Correlations and scatter plot between relative vorticity and OLR

Predictor (Relative Vorticity) and Predictand (OLR)

ECMWF OLR PC#1 Forecasts

Black Line: Observations (EC Analysis)

51-Ensemble ECMWF 10-Day Forecasts

July-August 2007S

tand

ardi

zed

Ano

mal

y

Projections of the raw ECMWF OLR Forecasts in the Indian Ocean-West Pacific Basin onto the First EOF mode.

The different colors are used to distinguished between forecasts of different

dates. The multiple lines for each forecast represent each ensemble member.

Sta

ndar

dize

d A

nom

aly

Projections of the 850mb Relative Vorticity EMCWF Forecasts in the Indian Ocean-West Pacific Basin onto the First EOF mode and then regressed to OLR (using historical data).

Hybrid OLR PC#1 Forecasts

Black Line: Observations (EC Analysis)

51-Ensemble Hybrid 10-Day Forecasts

Dashed Line: “Perfect” forecasts if 850mb R. Vorticity were known.

July-August 2007

Using only one predictor: 850mb Relative Vorticity

The different colors are used to distinguished between forecasts of

different dates. The multiple lines for each forecast represent each

ensemble member.

Thank you

o Numerical hybrid-modeling in early days but shows some promise.

o Further work with SNU Korea using a second hybrid scheme (“slow manifold model”) also appears to reduce the random convective error but keeps the thermal forcing (Kim et al. 2008)

o We hope within the coming months to extend these forecasts to the Americas.

Amplitude of Intraseasonal precipitation variability

1998 Precipitation Annual Cycle of Precipitation

1998 Precipitation Annual Cycle of Precipitation