ASSESSMENT OF THE INFLUENCE OF ENSO ON ANNUAL GLOBAL AIR TEMPERATURES

The connection between El Nino-Southern Oscillation (ENSO) as characte rized by the Southern Oscillation Index (SOI) and the global air tempe rature (GAT) is studied in the time and frequency domains, within the framework of bivariate autoregressive (AR) modeling and maximum entrop y spectral analysis. The linear relationship between SOI and GAT is sh own to be statistically significant at the 90% confidence level for th e entire frequency range from 0.0 to 0.5 cycle year(-1). The GAT-SOI t ime series form a closed feedback loop linear system with the damping factor of 0.38 and operating frequency of 0.062 cycle year(-1) The con tribution of ENSO to the overall GAT variance is shown to amount to ab out 30%; it reaches 35% at frequencies between 0.1 and 0.2 cycle year( -1) and is not less than 25% between 0.02 and 0.34 cycle year(-1). At higher frequencies the contribution decreases to about 10%. A unit cha nge in SOI leads to a 0.13 degrees C change in the global air temperat ure at f approximate to 0.06 cycle year(-1), whereas at the higher fre quencies, the response decreases to about 0.04 degrees C. The spectrum of ENSO-subtracted annual variations of GAT has relatively low energy in the low-frequency band and a broad maximum centered at about 0.25 cycle year(-1). The spectrum of the SOI contribution to GAT variations has approximately the same shape as the GAT spectrum, which means tha t ENSO contributes more energy to variations of GAT at large and inter mediate (4-6 years) time scales.