On the ozone minimum over the equatorial Pacific Ocean

Abstract

Since 1977, several ship and aircraft expeditions to the equatorial Pacific have reported extremely low (≤10 ppbv) or undetectable levels of ozone within the marine boundary layer. Of necessity, field programs from mobile platforms are limited in both their temporal and spatial coverage. However, a 10‐year record of observations at the geophysical monitoring for climatic change site in American Samoa suggests that low ozone mixing ratios are a common occurrence and may reflect a spatially variable but permanent region of low ozone in the equatorial Pacific. The spatial and temporal limits of this feature as well as some aspects of the intensity of the minimum appear to be maintained by the large‐scale atmospheric circulations of the equatorial Pacific. Perturbations in the large‐scale circulations as well as episodic events are reflected in observations of O 3 in the equatorial Pacific. Variations in the large‐scale, zonal circulation patterns (i.e., Walker circulation) of the equatorial Pacific appear to have a major influence on the spatial distribution of O 3 across the equatorial Pacific. The relative importance of variations in large‐scale, meridional circulation patterns on the distribution of O 3 in the tropical Pacific is uncertain; however, they may be important at latitudes somewhat removed from the equator such as at American Samoa.