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The Equatorial Cold Tongue Bias in a Coupled Climate Model

The Equatorial Cold Tongue Bias in a Coupled Climate Model. Vasu Misra 1 , Larry Marx 1 , M. Brunke 2 and X. Xeng 2 1 Center for Ocean-Land-Atmosphere Studies (COLA), 2 Department of Atmospheric Science, University of Arizona. Variance of MJO mode (30-70days; wn’s 1-6). Courtesy: Jia-Lin.

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The Equatorial Cold Tongue Bias in a Coupled Climate Model

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  1. The Equatorial Cold Tongue Bias in a Coupled Climate Model Vasu Misra1, Larry Marx1, M. Brunke2 and X. Xeng2 1 Center for Ocean-Land-Atmosphere Studies (COLA), 2 Department of Atmospheric Science, University of Arizona

  2. Variance of MJO mode (30-70days; wn’s 1-6) Courtesy: Jia-Lin

  3. Why is one-day coupling interval so popular? Most convenient Best compromise of available resources Practical limitation and reconciliation to approximations Noise is important

  4. Why is one-day coupling interval so popular? • Most convenient • Best compromise of available resources • Practical limitation and reconciliation to approximations • Noise is important

  5. Conducted experiments • CON: Integration of control COLA coupled model • E2D: Coupling frequency changed to 2 days • E3D: Coupling frequency changed to 3 days • E3H: Coupling frequency changed to 3 hours • ESKIN: AGCM interacts with skin SST at every time step All experiments are run for 50 year period from well spun-up ocean and land surface initial conditions.

  6. ESKIN • The coupling interval between OGCM and AGCM is once a day. Therefore, the bulk SST (10m) is updated once a day. • However skin SST is updated at every time step of the AGCM. • Skin SST=f(TB,Q,u*,t)

  7. COLA coupled model • Radiation (CAM) • PBL (NCEP; non-local) • Convection (NASA; RAS) • Land surface (COLA; SSiB) • Resolution T62L28 • Ocean (MOM3)

  8. Climatological monthly mean errors of SST over equatorial Pacific

  9. SST Climatological Dec-Jan-Feb differences. Only significant values are shaded

  10. Velocity potential @ 200 hPa Climatological Dec-Jan-Feb differences. Only significant values are shaded

  11. Velocity potential @ 200 hPa Climatological Dec-Jan-Feb differences. Only significant values are shaded

  12. 1000hPa winds and surface pressure (Pa) Climatological Dec-Jan-Feb differences. Only significant values are shaded

  13. The first EOF of SST

  14. Regression of zonal wind stress anomalies on Nino3 SSTA reconstruced from EOF1

  15. Computational time time On the same machine, for the same number of processors : E3H=38% more than CON ESKIN=CON E2D=3% less than CON E3D=6% less than CON

  16. Conclusions • Diurnal coupling interval even with coarse AGCM’s and OGCM’s has an impact. • Skin SST interactions seem to damp the convection over the oceans-may have huge implications in models that have strong ENSO. • Approach to tropical bias has to come from incremental improvements.

  17. Zonal wind stress Climatological Dec-Jan-Feb differences. Only significant values are shaded

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