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- 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
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- 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
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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
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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
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Impact of model climatology
20S-20N anomaly correlation Z200, Jan 2005 – Jul 2007 average, 2-mo-lead forecast
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Forecast assessment
- SST in the tropics
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Pacific SST indices
Better forecast towards the west
Delayed transitions between warm and cold phases; forecast failed for 2007 La Nina (Nino12, 3, 34)
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Indian Ocean SST indices
Better forecast for WTIO than ETIO
More realistic DMI forecast for 2007 and 2006 than 2005
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Atlantic SST indices
Weaker warm anomalies for TNA in 2005/2006.
Low skill for TSA, TNA-TSA, ATL3
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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
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Precipitation skill generally follows SST skill
Better SST forecast toward the end of 2007
Tropical (20S-20N) anomaly correlation 1-mo lead
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Forecast assessment
- Correlation skill (T2m, precipitation, and z200 )
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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
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NDJ 2006/2007 T2m forecast from Sep 2006
Cor=-0.1
Cor=0.90
Cor=0.96
• The hindcast skill mask helps
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- Mean errors for the whole forecast period
Forecast assessment
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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
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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
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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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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
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Nino34 SST (K)
Substantial change in forecast from Dec 1-5 to Dec 6-10
Ensemble mean
10S-10N U850 (m/s)
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Nino34 SST (K)
Uncoupled MOM3 initialized 10 Dec 2006
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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