AGCMs and Tropical Storms

• Disturbances similar to tropical storms in low-resolution AGCM first reported in 1970 (Manabe et al. 1970).

• Vortices in ECMWF model with structure close to that of observed tropical storms in the same regions at the same time of the year (Bengtsson et al. 1982).

• Many different studies followed: Krishnamurti 1988, Broccoli and Manabe 1990, Wu and Lau 1995, Tsutsui et al. 1995, etc.

• Idea: large scale circulation characteristics of the tropical storm can be captured by low-resolution AGCMs, but not the intense circulation around the eye.

• Studies with ECHAM3 model:
  • High-resolution (T106 - 5yrs): tropical storms with a thermal and dynamic structure close to observed ones, reasonable climatology in all basins and considerable interannual variability without any interannual SST variations (Bengtsson et al. 1995).

  • Low-resolution (T42 - 18 years), North Atlantic Basin: good agreement with climatological number and phase of the interannual variability, but poor
    annual cycle (N. Graham and M. Tyree 1998).

• GFDL model: Potential predictability of seasonal variability is particularly strong over Western and Eastern North Pacific (WNP/ENP)and to a lesser extent over Western North Atlantic (WNA) (Vitart et al. 1997). Positions of storms in WNP dependency with ENSO clearly shown (Vitart et al. 1999).

• Controversial subject: tropical storms generated by AGCMs are not entirely dinamically consistent with observed tropical storms (Mc Bride 1984, Evans 1992, Lander 1993).