1

- Implemented

Aug 2004

- Forecast to be analyzed

Jan 2005 – Feb 2008 (~3 years)

- Climatology

1981-2004

The NCEP CFS real-time forecast

CFS forecast Assessment for 2007

2

- Is the forecast skill consistent with the hindcast skill?

- Is there any systematic error during the forecast period?

- How does the forecast skill compare with AMIP runs?

- How does the MJO impact ENSO forecast?

- ….

Related questions

3

Forecast assessment (Jan 2005 – Feb 2008)

- SST, precipitation, T2m, Z200

- Mean forecast errors

- Comparison with AMIP runs

Analysis of Nino34 SST forecast

- Impacts of intraseasonal variability

Outline

4

Climatology

Old climatology 1981-2004 from standard CFS hindcast runs

New climatology 1981-1990 from corrected runs, 1991-2004 from standard runs

Great help from Lindsey, Soo-Hyun, Hui

5

Impact of model climatology

20S-20N anomaly correlation Z200, Jan 2005 – Jul 2007 average, 2-mo-lead forecast

6

Forecast assessment

- SST in the tropics

7

Pacific SST indices

Better forecast towards the west

Delayed transitions between warm and cold phases; forecast failed for 2007 La Nina (Nino12, 3, 34)

8

Indian Ocean SST indices

Better forecast for WTIO than ETIO

More realistic DMI forecast for 2007 and 2006 than 2005

9

Atlantic SST indices

Weaker warm anomalies for TNA in 2005/2006.

Low skill for TSA, TNA-TSA, ATL3

10

Better forecast in the tropical central Pacific and tropical western Atlantic

Western Indian Ocean is more predictable than eastern Indian Ocean

SST temporal correlation 1-mo lead

11

Precipitation skill generally follows SST skill

Better SST forecast toward the end of 2007

Tropical (20S-20N) anomaly correlation 1-mo lead

12

Forecast assessment

- Correlation skill (T2m, precipitation, and z200 )

13

Nino34 SST (K)• Low precipitation skill

• Higher skill in the tropics for Z200 and T2m

• Low T2m skill over North America during northern fall

• Better T2m may not correspond to better Z200

• Small Nino34 SST amplitude during most of the period

Pattern correlation

Z200

2005 2006 2007 2008

0.85

0.33

20S-20N

PNA

Land Precipitation

2005 2006 2007 2008

20S-20N

NA

Land T2m

2005 2006 2007 2008

0.160.40

20S-20N

NA

1-mo lead

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Pattern correlation Forecast with 1981-2004 hindcast skill mask

• Forecast skill is consistent with hindcast skill: Good forecast over areas where hindcast skill is high

• Hindcast statistics are useful to determine forecast reliability

NA Prec

NA T2m

PNA Z200

1-mo lead

0.11

0.19

0.22

-0.05

0.10

0.25

0.24

0.37

0.49

0-mo lead

0.15

0.26

0.23

0.08

0.18

0.30

0.34

0.38

0.50

NA precipitation

NA T2m

PNA Z200

15

NDJ 2006/2007 T2m forecast from Sep 2006

Cor=-0.1

Cor=0.90

Cor=0.96

• The hindcast skill mask helps

16

- Mean errors for the whole forecast period

Forecast assessment

17

T2m (K) Z200 (m)SST (K)

2-month-lead forecast, Jan 2005 – Feb 2007 average

• Cold T2m bias

• These errors may be related to the lack of

- increasing greenhouse gases

- realistic sea ice coverage

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Zonal mean land T2m (K), 2-month-lead forecast

Jan 2005 – Feb 2007 average

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- Comparison with AMIP runs

Forecast assessment

20

AMIP=0.230CFS-1=-0.035CFS-0=0.075

30N-90N land

AMIP=0.375CFS-1=0.431CFS-0=0.450

30S-30N land

Forecast vs AMIP: (1) better land surface/atmosphere initial condition

(2) air-sea interaction

(3) cold bias (lack of CO2 warming, sea-ice change)

Forecast vs AMIP: seasonal-mean correlation T2m

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Tropical SSTs

- CFS tends to delay ENSO phase transition

- Better skill in central Pacific than far EPAC and far WPAC

- Better skill in the west than in the east for Indian and Atlantic Oceans

Forecast of Precipitation, T2m and Z200 - Hindcast skill mask is useful for reliable forecast

- Forecast contains systematic cold bias during the recent years.

Summary of Forecast assessment

22

Analysis of Nino34 SST forecast

- Impacts of intraseasonal variability

2007-2008 La Nina

Demise of 2006-2007 El Nino

- …

23

MJO Activity

200 mb velocity potential, 5S-5N average

One strong MJO event in Dec-Jan 2006/2007

Weaker intraseasonal activities Feb-May 2007

Strong MJO of 2+ cycles in Nov-Feb 2007/2008

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Nino34 SST (K)10S-10N U850 (m/s)

22 Dec 2007-16 Jan 2008

26 Nov 2007-21 Dec 2007

2007-2008 La Nina forecast strongly depends on the MJO phase in initial conditions.

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Forecast March 2008 SST (K)

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Forecast Jan/Feb/Mar 2008 SST (K)

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Analysis of Nino34 SST forecast

- Impacts of intraseasonal variability

2007-2008 La Nina

Demise of 2006-2007 El Nino

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Nino34 SST (K)

CFS tends to prolong and enhance existing anomalies

Dramatic change from Nov to Dec 2006

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10S-10N U850 (m/s) 10S-10N OLR (W/m^2)

Easterly anomalies associated with the MJO in WPAC after 11 Dec 2006.

Easterly anomalies in central-eastern Pacific (180-150W) around 11 Dec 2006.

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Nino34 SST (K)

Substantial change in forecast from Dec 1-5 to Dec 6-10

31

Nino34 SST (K)

Substantial change in forecast from Dec 1-5 to Dec 6-10

Ensemble mean

10S-10N U850 (m/s)

32

Nino34 SST (K)

Uncoupled MOM3 initialized 10 Dec 2006

33

The MJO has strong impacts on

- The demise of 2006-2007 El Nino

- The Evolution of the 2007-2008 La Nina

Forecast of the ENSO events - The MJO is not predictable by CFS beyond 10 days. Impacts of MJO

events that occur 10 days after forecast starts will not be captured by the model

- MJO Impacts on ENSO forecast depend on the phase of the MJO at the initial time.

- For 2006-2007 El Nino, forecast became successful after the Dec 2006 – Jan 2007 MJO information was included in the initial conditions.

- The MJO during Nov 2007 – Feb 2008 was strong and went through 2+ cycles, making the detailed evolution of the La Nina more difficult for predict.

MJO impacts on 2006-2008 ENSO events