Long-Term Retrospective Forecasts with CFS: Long-Term Retrospective Forecasts with CFS: Predictability of ENSO and DroughtPredictability of ENSO and Drought

Mark Cane, Dake Chen and Alexey KaplanMark Cane, Dake Chen and Alexey KaplanLamont-Doherty Earth Observatory of Columbia UniversityLamont-Doherty Earth Observatory of Columbia University

Wanqiu Wang and Yan XueWanqiu Wang and Yan XueNational Centers for Environmental PredictionNational Centers for Environmental Prediction

The 4The 4thth Annual CTB SAB Meeting Annual CTB SAB MeetingSeptember 11, 2008September 11, 2008

OutlineOutline

Background and RationaleBackground and Rationale

ObjectivesObjectives and and HypothesesHypotheses

Approach and Work PlanApproach and Work Plan

Summary and DiscussionSummary and Discussion

Chen et al., Nature, 2004

Seager et al., Science, 2007

Cook et al., GRL, 2008

OObjectivesbjectives

Develop coupled data assimilation and Develop coupled data assimilation and model initialization procedure for the CFS;model initialization procedure for the CFS;

Generate retrospective forecasts for the Generate retrospective forecasts for the past one and a half centuries with the CFS;past one and a half centuries with the CFS;

Evaluate the predictability of ENSO and Evaluate the predictability of ENSO and drought using the resulting datasets; anddrought using the resulting datasets; and

Provide the basis for bias correction of Provide the basis for bias correction of operational seasonal climate forecasts.operational seasonal climate forecasts.

Hypothesis IHypothesis I

The CFS can be initialized in a The CFS can be initialized in a

coupled manner by assimilating SST coupled manner by assimilating SST

and SLP data over the past one and a and SLP data over the past one and a

half centuries; the coupled initialization half centuries; the coupled initialization

run and the subsequent retrospective run and the subsequent retrospective

forecasts are realistic enough (at least) forecasts are realistic enough (at least)

for ENSO and drought studies.for ENSO and drought studies.

atmosphere

ocean

atmosphere

ocean

initialization prediction

CDA vs. ODA

Wang et al., Mon. Wea. Rev., 2005

OBSEREVD AND PREDICTED NINO3.4 SSTA

Chen et al., Science, 2004

Hypothesis IIHypothesis II

The large-scale extra-tropical The large-scale extra-tropical

drought event, especially that over drought event, especially that over

North America, is strongly influenced by North America, is strongly influenced by

the variability of the coupled tropical the variability of the coupled tropical

climate system; certain drought patterns climate system; certain drought patterns

are predictable if are predictable if the corresponding the corresponding SST SST

patterns are predictable.patterns are predictable.

Cook et al., Earth-Science Reviews, 2007

Smith et al., Science, 2007

ApproachesApproaches

develop an appropriate coupled data develop an appropriate coupled data assimilation procedure by analyzing the assimilation procedure by analyzing the existing CFS free runs and retrospective existing CFS free runs and retrospective forecasts for the modern era (1981-2004);forecasts for the modern era (1981-2004);

test the procedure for the modern era and test the procedure for the modern era and then use it for a coupled initialization run for then use it for a coupled initialization run for the past 150 years; the past 150 years;

perform retrospective forecasts for lead times perform retrospective forecasts for lead times up to 9 months starting twice a year from up to 9 months starting twice a year from each summer and winter of the past 150 each summer and winter of the past 150 years; years;

assess model skills in predicting ENSO and assess model skills in predicting ENSO and drought using various techniques.drought using various techniques.

Summary and DiscussionSummary and Discussion

The purpose of this project is to generate and evaluate The purpose of this project is to generate and evaluate retrospective forecasts with CFS over the past 150 years retrospective forecasts with CFS over the past 150 years to study the predictability of ENSO and drought.to study the predictability of ENSO and drought.

The key for the success of this study is the development The key for the success of this study is the development of a coupled data assimilation and model initialization of a coupled data assimilation and model initialization procedure using only SST and SLP observations.procedure using only SST and SLP observations.

Computer resources are the most severe limitation for Computer resources are the most severe limitation for carrying out the whole suite of experiments, but even a carrying out the whole suite of experiments, but even a subset of them will prove to be extremely useful.subset of them will prove to be extremely useful.