Dynamics of Stationary Wave Anomalies Associated with ENSO in the Cola GCM.
Abstract
The performance of the COLA GCM in simulating the stationary wave anomalies observed during recent four ENSO winters has been examined. It is found that the simulation is fairly successful in the tropics and the PNA region, particularly for the 1982/83 and 1988/89 cases. Nevertheless, there still exist noticeable systematic errors. They are the weak signals in the 1982/83 case, the large intersample variability beyond the tropics in other cases and the southward shift of the wave train over the North Pacific in all of the three warm cases, particularly in 1986/87 and 1991/92 cases. A linear stationary wave model with zonally varying basic state has been used to understand the GCM simulated wave train anomalies. When linearized about the GCM climatology and subject to global anomalous diabatic and transient forcing, the linear model successfully reproduces the GCM simulated wave pattern. The effect of the stationary nonlinearity is confined to the tropics and not significant compared to other effects. Its major impact is to support (weaken) the linearly forced wave train in warm (cold) cases. The extratropical wave anomalies are basically maintained by transient eddy anomalies, which result from the stormtrack modulation by tropical disturbances. Anomalous tropical anti-cyclones symmetric about equator are directly forced by anomalous tropical heating and enhanced by extratropical transient anomalies. The primary causes of the systematic errors in the GCM simulations have been traced to the effects of the unrealistically simulated tropical diabatic heating anomalies and the GCM climate drift. The climate drift is very likely due to the GCM's systematic cooling over Indonesia and western tropical Pacific.
- Publication:
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Ph.D. Thesis
- Pub Date:
- January 1995
- Bibcode:
- 1995PhDT........65P
- Keywords:
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- Physics: Atmospheric Science