Deterministic signals in precipitation records from the American corn belt

Abstract
Maximum entropy spectrum analysis of 120 yearly total precipitation records in the Corn Belt (States of Illinois, Indiana, Iowa, and Missouri) yield evidence for the 18·6‐year luni‐solar term in 109 instances, while the 10‐ to 11‐year solar cycle signal was found in 100 records. For Illinois, minima in the 19‐year wavetrains were highly correlated with epochs 1898·9, 1917·5, and 1936·1. For eighteen stations wave minima were still correlated with the next epoch, epoch 1954·7; however, a bistable phase switch of 180° then occurred and wave maxima came into phase with epoch 1973·3. In two instances in northern Illinois the switch occurred a cycle earlier at epoch 1954·7, and in five instances a half cycle earlier at mid‐epoch 1964·0. O'Brien and Currie (1989) have provided a construct in mathematical physics that explains how bistability can occur at air‐pressure recording stations, and Currie (1987a) has provided many examples of bistability in air pressure and air temperature data from around the world.