3.12
ENSO and decadal variations in the U. Hawaii hybrid CGCM
Xiouhua Fu, University of Hawaii, Honolulu, HI; and B. Wang and F. F. Jin
ABSTRACT
A hybrid coupled general circulation model (HGCM) with full coupling (different from other HGCMs, this model produces its own climatology) is developed at U. Hawaii. This HGCM is composed of an ECHAM T30 AGCM and UH intermediate ocean model (active coupling is in the tropical Indian and Pacific Oceans). First 80-year output from this coupled model is used in this study. Our analyses show that the coupled model reasonably simulates both the climatology and climate variability in the tropical Asia-Pacific sector. However, it also suffers some biases commonly existed in most other coupled GCMs, such as the warm bias in the southeast Pacific, which is primarily due to the lack of enough stratocumulus in the atmospheric model. Otherwise, this HGCM simulates fairly realistic mean state and annual cycle in the tropical Pacific. It also produces robust ENSO and decadal variations.
The simulated ENSO is comparable to that observed in terms of the variance and frequency. The model ENSO has two spectral peaks with periods about 2 years and 5 years. The ENSO variance shows enough meridional expansion, but the location of the maximum shifts a bit too westward (~145oW). The simulated ENSO indicates reasonable annual phase locking with minimum (maximum) variance in boreal spring (fall). Both the delayed oscillator and the recharge oscillator contribute to the model ENSO. Significant decadal variations also occur in this HGCM (even without midlatitude ocean variability). Initial analysis suggests that the slow subtropical Rossby waves and recharge oscillator (Jin 2001) are possible causes.
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Session 3, El Nino and the Southern Oscillation (ENSO)
Tuesday, 10 August 2004, 8:00 AM-12:15 PM, New Hampshire Room
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