Low Frequency Atmospheric Variability in GFS Models

Peitao Peng

Acknowledgment:Bhaskar, Arun and Huug

Purposes

• The performance of GFS models in simulating the low frequency variability (LFV) of the atmosphere;

• Differences between the two versions of GFS models in LFV;

• Dynamical interpretation of the differences.

Data

Model:

Monthly Z200 and Prate from the AMIP-type runs (1949-2002) with GFS1 and GFS2.

(Note: the difference between GFS1 and GFS2 is that they uses

different radiation packages)

OBS:

Monthly Z200 from NCEP reanalysis (1949-2002)

“bias” intropical heating

Pacific jet eastward extension

LFV eastward shifting

Mechanism:

Summary

• Either version of the GFS models can generate very realistic LFV patterns.

• Some differences in LFV patterns between the two models can be explained the “bias” in tropical heating.