Abstract
Simultaneous and lagged correlation statistics have been calculated between time series of seasonal height anomalies at selected stations and extratropical grid-point anomalies in both hemispheres. The tropical stations in two major tropical precipitation zones, the Indo-China maritime continent and Africa, are well correlated with each other. These stations are also correlated with stations in the North Pacific and Australia, but the coefficients are smaller. The correlations between height anomalies at any of these stations and Northern Hemisphere height anomalies show a well-defined global pattern. Depending upon the location of the stations, the pattern is either a Pacific North American (PNA), a Tropical Northern Hemisphere (TNH) pattern or a mixed pattern having both elements. All three patterns, PNA, TNH and WPO (Western Pacific Oscillation), have been linked to tropical variations. The correlations between height anomalies at these well-correlated stations and the Southern Hemisphere height anomalies at the 500 mb level give the summer teleconnection pattern of Mo and White (1985). The vertical structure of patterns indicate that they are approximately equivalent barotropic.
The TNH pattern tends to be associated more with tropical variability for time scales longer than one season, while the PNA pattern is present in both high- and low-pass filtered analyses, although weakly in the former. Moreover, its low frequency connection to the tropics appears to be confined to ENSO years.
During ENSO years both patterns appear in both simultaneous and lagged maps, but in non-ENSO years, the TNH is weak in simultaneous charts.
