Combination Tone Schematic (image) University of Hawaii ‑ SOEST 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. 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.