An analysis of the spatial distribution of approximate 8 years periodicity in NCEP/NCAR and ERA-40 temperature fields
The Department of Meteorology and Environment Protection, Charles University in Prague, V Holesovickach 2, 180 00 Prague, Czech Republic
Corresponding author: firstname.lastname@example.org
In the presented paper, we describe an analysis of spatial patterns of the approximate 8 years cycle identified in the NCEP/NCAR and ERA-40 reanalyzed temperature series. The temperature series are examined by the pseudo-2D wavelet transform (p2D-WT) at 17 geopotential levels, ranging from 1000 hPa to 10 hPa. The results differ significantly for the NCEP/NCAR and for the ERA-40 temperature series. For the NCEP/NCAR dataset, oscillation of about 8 years is distinct over large areas at almost every analyzed level. At lower heights, the regions with significant presence of the periodicity are less compact and pronounced than at higher geopotential levels. The occurrence of the analyzed period is generally strongest in the equatorial and tropical areas. For the ERA-40 dataset, the approximate 8 years cycle is detected in substantially fewer grid points and the spatial patterns generally do not conform to the analysis of NCEP/NCAR series. These results indicate that a frequency analysis of the reanalysis datasets should only be interpreted after careful discussion and that the reliability (in the sense of frequency characteristics) of the reanalyzed temperature series still needs to be studied.
© EDP Sciences, Springer-Verlag, 2009