A Tropical Tropospheric Source of High Ozone/Low Water Filaments

Numerous field campaigns have noted the prevalence of filaments of high O₃ and low H₂O (HOLW) in the tropical western Pacific (TWP) troposphere. These filaments can drastically alter the meteorology, climate, and chemistry of the region through suppression of convection, changes in local radiative forcing, and alteration of the OH budget and are often cited as having a dynamical origin caused by transport from either the mid-latitude upper troposphere (mlUT) or stratosphere. We will show that HOLW filaments were a dominant feature observed during the CONTRAST and CAST field campaigns conducted in the TWP during January and February 2014. Our back trajectory analysis connects these filaments to regions of active biomass burning in the tropics, namely Africa and Southeast Asia. The low relative humidity observed in these filaments is consistent with large-scale descent in the tropics, during the transit from the source region to the TWP. The chemical composition of the filaments confirms a biomass burning origin and demonstrates negligible influence from the mlUT and stratosphere. Since the high O₃ in these filaments is of tropical origin, biomass burning likely exerts a stronger influence on earth's climate than commonly appreciated.