Abstract
The three dimensional structures of sea surface temperature (SST) and atmospheric circulation anomalies associated with ENSO are investigated over the entire globe, by using the objectively analyzed data sets of the years 1964 to 1981. The global data sets of U, V, Z and T are produced by applying the least-square method to fit the time-filtered station data (of more than 320 stations) and NMC tropical wind field data with truncated spherical harmonics of wavenumber 0 to 5. Global SST and sea level pressure data are also utilized. In this paper (Part I) the composite anomaly patterns during El Nino episodes are discussed.
Warm SST anomalies and warm upper troposphere are found to be remarkable not only over the equatorial central Pacific but also over the entire tropics, while the mid-latitudes seem to be characterized as cold SST and cold troposphere as a whole. The increasings of zonal winds in the subtropics and the lower mid-latitudes of the two hemispheres are also prominent. These evidences apparently suggest that the intensified Hadley-type circulation in the low latitudes and the equatorward extent of the circumpolar vortex in the high latitudes are fundamental features during El Nino episodes. A nearly symmetric response pattern of the upper tropospheric flows with respect to the equator is also noted over the northern and the southern Pacific.
It is also suggested that the North Atlantic Oscillation (NAO) is synchronized with the SO during the present analysis period.
