comparative influence of snow and sst variability on extratropical climate in northern winter
DESCRIPTION
Comparative Influence of Snow and SST Variability on Extratropical Climate in Northern Winter. Fanglin Yang RSIS/CPC_NCEP Arun Kumar CPC/NCEP NOAA’s 27th Climate Diagnostics and Prediction Workshop , October 2002. Motivitations. - PowerPoint PPT PresentationTRANSCRIPT
Comparative Influence of Snow and SST Variability on Extratropical Climate in Northern Winter
Fanglin YangRSIS/CPC_NCEP
Arun Kumar CPC/NCEP
NOAA’s 27th Climate Diagnostics and Prediction
Workshop , October 2002
Motivitations
Compared to remote tropical SST forcing, how important is local snow anomaly in modulating mid-latitude climate variability?
In mid-latitudes, air-sea interaction is one way. Is snow-air interaction also one-way?
In extreme cases, for instance, in ENSO years, how snow and local temperature anomalies interact with each other?
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
Snow Depth Climatology in DJF
Both are averages for 1979-1987. For model, assumed snow density 300 kg m-3 Both are averages for 1979-1987. For model, assumed snow density 300 kg m-3
Obs: SMMR Simulation: SST_SNO
Rotated EOFs of Z200 in DJF, Atmospheric Modes
SST_SNO SST_CSNO
EOF 1, 11.6%
EOF 2, 11.2%
EOF 3, 9.6%
EOF 4, 7.3%
EOF 1, 13.7%
EOF 4, 8.1%
EOF 2, 10.7%
EOF 5, 7.5%
Composite Analysis for Extreme Cases
Impact of Snow Anomaly on the response of Mid-Latitude Climate to
Tropical SST Forcing in ENSO Years
Composite Sfc Temp Anomalies in ENSO Years
CAMS
SST_SNO
SST_CSNO
SST_SNO - SST_CSNO
Yang et al., J Climate, 2001
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.
SurfaceAlbedo
Surface DownwardSolar
σ in DJF from SST_SNO, Snow-Albedo Feedback
Snow Depth
Surface Upward Solar
Zonal Mean σ in DJF from SST_SNO
Why the greatest impact of snow on sfc temperature variability is found in the mid-latitudes?
El Niño warmer SST
warm phase PNA pattern
higher surface air temperature
less snow
smaller surface albedomore downward solar radiation
Amplification by Snow-Albedo Feedback
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
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