Notes on extended–range atmospheric prediction in the Northern Hemisphere winter |
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| Authors: | Shingo Yamada Shuhei Maeda K Gambo |
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| Institution: | Forecast Division, Japan Meteorological Agency, Tokyo, 100, Japan,Administration Division, Climate and Marine Department, Japan Meteorological Agency, Tokyo, 100, Japan,c / o Department of Earth and Planetary Physics, Faculty of Science, University of Tokyo, Tokyo 113, Japan |
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| Abstract: | We examined the characteristic feature and predictability of low frequency variability (LFV) of the atmosphere in the Northern
Hemisphere winter (January and February) by using the empirical orthogonal functions (EOFs) of the geopotential height at
500 hPa. In the discussion, we used the EOFs for geostrophic zonal wind (Uznl) and the height deviation from the zonal mean
(Zeddy). The set of EOFs for Uznl and Zeddy was denoted as Uznl−1, Uznl−2, …, Zeddy−1, Zeddy−2, …, respectively. We used the
data samples of 396 pentads derived from 33 years of NMC, ECMWF and JMA analyses, from January 1963 to 1995. From the calculated
scores for Uznl−1, Uznl−2, Zeddy-1, Zeddy−2 and so on we found that Uznl−1 and Zeddy−1 were statistically stable and their
scores were more persistent than those of the other EOFs. A close relationship existed between the scores of Uznl−1 and those
of Zeddy−1.
30-day forecast experiments were carried out with the medium resolution version of JMA global spectral model for 20 cases
in January and February for the period of 1984–1992. Results showed that Zeddy−1 was more predictable than the other EOFs
for Zeddy.
Considering these results, we argued that prediction of the Zeddy−1 was to be one of the main target of extended-range forecasting. |
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| Keywords: | Low-frequency variability Empirical orthogonal function Extended-range prediction |
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