Combination Tone Schematic (image) University of Hawaii ‑ SOEST Share Print E-Mail Caption This is a schematic figure for the suggested generation mechanism of the combination tone: The annual cycle (Tone 1), together with the El Niño sea surface temperature anomalies (Tone 2) produce the combination tone. Credit Malte Stuecker Usage Restrictions For educational purposes only. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.