Abstract
Air parcels with mixing ratios of high O3 and low H2O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300–700 hPa). Here, using data collected during aircraft sampling of the TWP in winter 2014, we find strong, positive correlations of O3 with multiple biomass burning tracers in these HOLW structures. Ozone levels in these structures are about a factor of three larger than background. Models, satellite data and aircraft observations are used to show fires in tropical Africa and Southeast Asia are the dominant source of high O3 and that low H2O results from large-scale descent within the tropical troposphere. Previous explanations that attribute HOLW structures to transport from the stratosphere or mid-latitude troposphere are inconsistent with our observations. This study suggest a larger role for biomass burning in the radiative forcing of climate in the remote TWP than is commonly appreciated.
Highlights
Air parcels with mixing ratios of high O3 and low H2O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300–700 hPa)
We define a high ozone/low water (HOLW) structure as an air parcel satisfying the simultaneous criteria of O3 440 p.p.b.v. and relative humidity (RH) o20%, where RH in this study is with respect to water for T4273 K and to ice for To273 K
We have shown that the high O3 in the HOLW structures sampled in the TWP during winter 2014 is quantitatively consistent with a tropical, biomass burning source and that the low H2O mixing ratio is consistent with large-scale descent in the tropics
Summary
Air parcels with mixing ratios of high O3 and low H2O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300–700 hPa). Large increases in O3 relative to these low background values have frequently been observed in the TWP midtroposphere[12,14,18,19,20,21,22,23,24,25] Many of these studies note that water vapour tends to be depressed, with respect to the local background, for these high O3 air parcels[12,14,18,19,20,21,22,24], often attributing the HOLW structures to sources outside the tropical troposphere. Our analysis, which focuses on the tropics (20° N–20° S) of the western Pacific, suggests low water is controlled by outflow of the Hadley circulation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
