Remote effect of tropical Atlantic biases on the tropical Pacific

1. Remote effect of tropical Atlantic biases on the tropical Pacific Ping Chang & Link Ji TAMU R. Saravanan NCAR

2. Sperber et al. (2003)

3. Questions? • What causes the large biases in the tropical Atlantic sector? • Do the tropical Atlantic biases contribute to the biases in the tropical Pacific via remote influences? • Can the tropical Atlantic biases alone cause a double ITCZ in tropical Pacific?

4. Coupled Model Experiments • CCM3-ML experiments: 1 Control Simulation where Q-flux is used everywhere. 2 Removed Q-flux experiment where Q-flux is set zero in the tropical Atlantic basin between 20S-20N. • CCM3-MOM3 experiments: 1 100-year Control Simulation with no flux correction. 2 Fixed Atl-SST experiment where Atlantic SST is specified using observed annual cycle.

7. Difference of SST in May between the fixed-SST CCM3-MOM3 experiment and the fully coupled CCM3-MOM3 control simulation. Removing the biases in Atlantic can reduce the cold SST bias in the equatorial Pacific by about 1C.

8. Tentative Conclusions • The fact that the Atlantic systematic biases of the fully coupled GCM can be reproduced by removing the parameterized ocean heat transport in an AGCM coupled to a slab ocean hints that the errors in heat transport of the ocean model may be partially at blame. • The double ITCZ bias in the coupled models may come from two different sources. The large warm SST biases off the coast of South America and the coast of Mexico are likely to be locally induced. The cold SST bias along the equatorial Pacific may contain a significant component that comes from the large biases in the tropical Atlantic via remote influences. • Effort of reducing coupled model biases in tropical Pacific should take into the consideration not only the local processes, but also the remote influence.