Articles | Volume 16, issue 2
Research article
20 Jan 2016
Research article |  | 20 Jan 2016

Ozonesonde profiles from the West Pacific Warm Pool: measurements and validation

R. Newton, G. Vaughan, H. M. A. Ricketts, L. L. Pan, A. J. Weinheimer, and C. Chemel

Abstract. We present a series of ozonesonde profiles measured from Manus Island, Papua New Guinea, during February 2014, with new insights on the calibration of ozonesondes for measurements in the tropical troposphere. 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 evaluating the background current of the ozonesondes, as this can amount to half the measured signal in the tropical tropopause layer (TTL). An unexpected contamination event affected the measurements and required a departure from standard operating procedures for the ozonesondes. The most significant departure was not exposing the sondes to ozone during preparation, which meant that the background current remained stable before launch. 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 could 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 ozone concentrations  <  5 ppbv, 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.

Short summary
This paper reports the results of a field campaign with ozonesondes held in Manus Island, Papua New Guinea in February 2014. Particular attention is paid to the background current correction for the ozonesondes. We show that the ozonesonde profiles compare very well with near-coincident aircraft measurements, and show no sign of the extremely low ozone concentrations (< 5 ppbv) reported by previous papers. The minimum repeatable ozone concentration just below the tropopause was 12 ppbv.
Final-revised paper