Comparison of the 200 hPa circulation in CSM and CCM3 simulations and NCEP and ERA reanalysis:
In this paper the interannual variation of monthly mean vorticity and divergence at 200 hPa are compared from four data sources: The NCEP/NCAR reanalyses 1958 through 1994, the ECMWF (ERA) reanalyses, 1979 through 1994, a NCAR CCM3 integration using prescribed SSTs from 1979 through 1993, and the NCAR CSM 300 year integration. Four twenty year periods were taken from the 300 year simulation for analysis. The NCEP, ERA and CCM3 all provide data for the period 1979 through1993. The techniques used are principal and common principal component analyses on the fields transformed to spherical harmonics. The seasonal cycle is removed. For the common time period, 1979 through 1994, the ERA, NCEP and CCM3 display a close correspondence for the leading PC of the 200 hPa vorticity.This mode is closely related to the ENSO variations of the period but the agreement extends to the extratropics. All four CSM periods have similar leading modes which are dominated by a PNA type pattern and lack any Equatorial Pacific ENSO patterns. The agreement between the leading PC for the 200 hPa divergence was somewhat less than that of the vorticity. The CCM3 and ERA indicate a larger magnitude center in the Equatorial Pacific about the dateline than NCEP. The CSM has an intense center a 150E. There are indications in the vorticity and divergence fields that this center is at the source for waves propagating to the midlatitudes. Two twenty year periods of the 1958 to 1996 NCEP reanalyses show a distinct difference between the two periods. The variations are comparable in magnitude if not nature to the variations seen amongst the time sections of the CSM run examined. A CPC analysis of the NCEP, ERA and CCM3 show a common ENS0 type response as the leading common component. The models depart from the reanalyses for the second component. Combining the CCMS, CSM, NCEP and ERA shows that the CSM does have a common component like the other three.
- Research Organization:
- Lawrence Livermore National Laboratory, Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6411731
- Report Number(s):
- UCRL-ID-132248; ON: DE00002902
- Country of Publication:
- United States
- Language:
- English
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