subseasonal forecast skill over the northern polar region in … · 2019-04-04 · polar region in...
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Subseasonal Forecast Skill over the Northern
Polar Region in Three Operational S2S Systems
Hai Lin
Recherche en Prévision Numérique,
Environment and Climate Change Canada
Workshop on Predictability, dynamics and applications research
using the TIGGE and S2S ensembles, April 2-5, 2019
ECMWF
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Outlines
• Motivations
• Subseasonal forecast models
• T2m skill
• Influence of the Madden-Julian Oscillation (MJO)
• Summary
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Motivations
• Surface air temperature influences sea ice
• What is the forecast skill of T2m in polar region on the
subseasonal time scale?
• Comparison with other regions
• Coupled model vs atmospheric-only model
• Sources of predictability and skill. e.g., MJO impact
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Data and methods
• Hindcast data of S2S archive
• Models used: ECCC, ECMWF and NCEP
• 12 common years 1999-2010, four members each
model, once a week
• Pentad averaged data
• Verification with ERAinterim and NCEP/NCAR
reanalysis
• Extended winter: NDJFM
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T2m skill (3-model ensemble)
against NCEP/NCARagainst ERA-interim
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T2m skill (north polar region)
against ERA-interim against NCEP/NCAR
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T2m skill
ECCC
Statistical significance
Light green:
0.05
Orange:
0.01
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T2m skill
ECMWF
Statistical significance
Light green:
0.05
Orange:
0.01
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T2m skill
NCEP
Statistical significance
Light green:
0.05
Orange:
0.01
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Composites of tropical
Precipitation rate for 8
MJO phases,
according to Wheeler
and Hendon index.
Xie and Arkin pentad
data, 1979-2003
The MJO
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Polar (60-90N) T2m skill dependence on MJO phase
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MJO impact on NAO and polar temperature
e.g., Lin et al. (2009), Cassou (2008), Lin and Brunet (2010),
Yoo et al. (2011)
10-20 days following MJO phase 3:
positive NAO, Arctic cooling
10-20 days following MJO phase 6:
negative NAO, Arctic warming
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T2m anomaly lagged composites following phase 3
Yellow:
0.05
Orange:
0.01
Polar
cooling
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T2m anomaly lagged composites following phase 6
Yellow:
0.05
Orange:
0.01
Polar
warming
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Observed Sea Ice anomaly lagged composites
ERA interim
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Z500 biasDays 1-15 Days 16-30
ECCC
ECMWF
NCEP
Similar bias amplitude
In the North Pacific in days
16-30.
Resulting in MJO-
teleconnection errors
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Summary
• T2m skill is evaluated for three operational S2S models
• The T2m skill in the polar region is the lowest comparing to the
tropical and middle latitude regions
• Three models have comparable forecast skill in surface air
temperature over the north polar region.
• There is evidence that the tropical MJO contributes to the T2m
skill in the north polar region.
• To improve the polar forecast on the subseasonal time scale, it
is important to have well represented tropical MJO and
teleconnections in the model.
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