Ozonesonde profiles from the West Pacific Warm Pool

Abstract

We present a series of ozonesonde profiles measured from Manus Island, Papua New Guinea, during February 2014. The experiment formed a part of a wider airborne campaign involving three aircraft based in Guam, to characterise the atmospheric composition above the tropical West Pacific in unprecedented detail. Thirty-nine ozonesondes were launched between 2 and 25 February, of which 34 gave good ozone profiles. Particular attention was paid to measuring the background current of the ozonesonde before launch, as this can amount to half the measured signal in the tropical tropopause layer (TTL). An unexpected contamination event affected these measurements and required a departure from standard operating procedures for the ozonesondes. Comparison with aircraft measurements allows validation of the measured ozone profiles and confirms that for well-characterized sondes (background current <50 nA) a constant background current should be assumed throughout the profile, equal to the minimum value measured during preparation just before launch. From this set of 34 ozonesondes, the minimum reproducible ozone concentration measured in the TTL was 12-13 ppbv; no examples of near-zero ozone concentration as reported by other recent papers were measured. The lowest ozone concentrations coincided with outflow from extensive deep convection to the east of Manus, consistent with uplift of ozone-poor air from the boundary layer. However, these minima were lower than the ozone concentration measured through most of the boundary layer, and were matched only by measurements at the surface in Manus.