Comparative Influence of Snow and SST Variability on Extratropical Climate in Northern Winter

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Comparative Influence of Snow and SST Variability
on Extratropical Climate in Northern Winter

• Fanglin Yang
• RSIS/CPC_NCEP
• Arun Kumar
• CPC/NCEP
• NOAAs 27th Climate Diagnostics and Prediction
  Workshop , October 2002

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Motivitations
In mid-latitudes, air-sea interaction is one
way. Is snow-air interaction also one-way?
Compared to remote tropical SST forcing, how
important is local snow anomaly in modulating
mid-latitude climate variability?
In extreme cases, for instance, in ENSO years,
how snow and local temperature anomalies interact
with each other?
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GCM Experiments (NCEP GSM T42L28)
SST Specification Snow Specification Runs Period of Integration
SST_SNO Observed Predicted 3 1950-1999
SST_CSNO Observed Climatology 3 1950-1999
CSST_SNO Climatology predicted 1 150 years
CSST_CSNO Climatology Climatology 1 150 years
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Model Fidelity, s(Ts) in DJF
Observation, CAMS
Simulation SST_SNO
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Model Fidelity, s(Z200) in DJF
NCEP/DOE R2
Simulation SST_SNO
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Snow Depth Climatology in DJF
Obs SMMR
Simulation SST_SNO
Both are averages for 1979-1987. For model,
assumed snow density 300 kg m-3
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Comparative Impact Snow vs SST

• Analysis of Standard Deviations in DJF

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? s(Ts) in DJF
Impact of Snow Variability
Impact of SST Variability
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? s(Z200) in DJF
Impact of Snow Variability
Impact of SST Variability
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? s(Ts), 30N-60N in DJF
Impact of Snow Variability
Impact of SST Variability
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Rotated EOFs of Z200 in DJF, Atmospheric Modes
SST_CSNO
SST_SNO
EOF 1, 11.6
EOF 1, 13.7
EOF 4, 8.1
EOF 2, 11.2
EOF 3, 9.6
EOF 2, 10.7
EOF 4, 7.3
EOF 5, 7.5
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• Composite Analysis for Extreme Cases
• Impact of Snow Anomaly on the response of
  Mid-Latitude Climate to Tropical SST Forcing in
  ENSO Years

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Composite Sfc Temp Anomalies in ENSO Years
Yang et al., J Climate, 2001
CAMS
SST_CSNO
SST_SNO
SST_SNO - SST_CSNO
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Composite Z500 Anomaly in ENSO Years
SST_SNO
SST_CSNO
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Regression of Z200 and Ts with Nino 3.4 Index
SST_CSNO Z200
SST_CSNO Ts
SST_SNO Z200
SST_SNO Ts
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• Why the the variability (Anomalies) of surface
  air temperature is larger in the runs with
  interactive snow?
• Snow variation can lead to many land surface and
  atmospheric quantities to change, such as surface
  temperature, latent and sensible heat fluxes,
  surface albedo, cloud cover and so on. These
  changes also feed back to snow variation
  (Grossman et al. 1994). Among all these
  feedbacks, we found snow-albedo feedback is the
  most effective one in explaining our GCM results.

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s in DJF from SST_SNO, Snow-Albedo Feedback
Surface Albedo
Snow Depth
Surface Downward Solar
Surface Upward Solar
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Zonal Mean s in DJF from SST_SNO
Why the greatest impact of snow on sfc
temperature variability is found in the
mid-latitudes?
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Amplification by Snow-Albedo Feedback
warm phase PNA pattern
higher surface air temperature
El Niño warmer SST
less snow
smaller surface albedo
more downward solar radiation
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Conclusion Comparative Impact of Snow and SST,
DJF, Mid-Latitide
Sfc Lower Tropospheric Temperature Upper Tropospheric Temperature Large-scale Circulation Characteristics
Snow larger smaller Smaller (re-order internal modes) Local Snow-albedo feedback etc
TropicalSST smaller Larger larger Remote teleconnection
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Conclusion Mid-Latitude Air-Sea and Air-Snow
Interactions at Seasonal time scales
Near Surface Temperature Upper Tropospheric Temperature Large-scale Circulation Mechanism
Air-Snow Large small Small (re-order internal modes) Snow-albedo feedback amplifies near surface temperature variability
Air-Sea Large Small Small (re-order internal modes) Reduction in Thermal damping of near surface temperature Variability by surface energy fluxes