A HISTORY OF INFRARED EXTINCTION AT CTIO, CHILE, AND A POSSIBLE CONNECTION WITH THE EL-NINO PHENOMENON

Extinction coefficients and sensitivity values in the JHKL bandpasses measured on nearly 200 clear nights of observing between 1978 and 1992 on the 1.5 m and the Blanco 4 m telescopes at Cerro Tololo Inter-Amer ican Observatory are presented and discussed. Analysis of these data s hows the following: there are seasonal variations in both the extincti on coefficients and sensitivity values that are qualitatively consiste nt with expected variations in the amount of H2O in the atmosphere-rel atively high in the summer months, lower in the winter months. The lin ear correlation coefficients between most of these quantities are stat istically significant. The yearly mean values of these quantities also show significant variability of a few hundredths of a magnitude, The correlations between these yearly means are again consistent with vari ations in the H2O content of the atmosphere. At least some of these lo nger term variations are closely correlated with quantitative measures of the strength of the atmospheric and oceanic El Nino/Southern Oscil lation phenomenon.