S. Arellano

Volcanoes have been found to display periodicities or cyclic trends in a wide range of phenomena. These include the eruptive activity itself, but also in the time series of geophysical and geochemical monitoring data such as volcanic degassing. Here, we test the existence of periodicities of volcanic degassing at 32 volcanoes using the time series of sulfur dioxide (SO 2 ) emission rates from data of the Network for Observation of Volcanic and Atmospheric Change (NOVAC). We use the Lomb‐Scargle periodogram to analyze the SO 2 data which allows efficient computation of a Fourier‐like power spectrum from unevenly sampled data. We were able to calculate False‐Alarm Probabilities in 28 of the 32 volcanoes, and we identified significant periodicities in the SO 2 emission rates in 17 of the 28 volcanoes. However, we find that most of these periodicities are also present in the plume speeds used to determine SO 2 emission rates. Periodicities at about 30–70, ∼120, and ∼180 days were identified at volcanoes located between 16°N and 16°S and are related to intraseasonality and interseasonality in global trade winds and not volcanic in origin. Periodicities between 30 and 70 days in both plume speed and SO 2 emission rates are associated to the Madden‐Julian Oscillation that is responsible for intraseasonal variability in the tropical atmosphere. Our study highlights the importance of using local wind data for deriving realistic SO 2 emissions and the identification of short‐term periodicity in volcanic behavior.