ENSO and Decadal Modes Found in SST Field in the North Pacific
Kimio Hanawa
Department of Geophysics, Graduate School of Science, Tohoku University Aoba-ku, Sendai 980-77, Japan
An empirical orthogonal function (EOF) analysis for wintertime SST fields showed existence of two distinctive modes: one is that with the El Nino/Southern Oscillation (ENSO) time scale with period of 3-4 years and the other is that with decadal (DC) time scale. The leading mode of ENSO time scale shows the spatial pattern with 3 poles arranging from west to east, as shown in Fig.1 The leading mode of DC time scale is a meridional dipole pattern: north- south oscillation of low latitude and mid latitude oceans (central North Pacific), as shown in Fig. 2. These modes are very robust and it is also confirmed by a composite analysis (not shown here). Time coefficient of the DC mode showed abrupt change like a step function around 1976 and continued to late 1980s. This is so- called Climatic jump or Regime shift (Trenberth, 1990). A singular value decomposition (SVD) analysis showed that atmospheric general circulation pattern over the North Pacific also varies coherently with SST fields described above. That is, the ENSO mode closely relates with the WP (western Pacific) teleconnection pattern and on the other hand, the DC mode closely relates with the PNA (Pacific/North American) teleconnection pattern. Details will be described in Tanimoto et al. (1996).
Reference
Tanimoto, Y., N. Iwasaka and K. Hanawa, 1996: Relationships between sea surface temperature, the atmosphefic circulation and air-sea fluxes on multiple time scales.
Submitted to J. Meteor. Soc. Japan.
Trenberth, K. E., 1990: Recent observed interdecadal climate changes in the Northern Hemisphere. Bull. Amer. Meteor Soc., 71, 988-993.
