Observations of ozone-poor air in the tropical tropopause layer

Abstract

Abstract. Ozonesondes reaching the tropical tropopause layer (TTL) over the west Pacific have occasionally measured layers of very low ozone concentrations – less than 15 ppbv – raising the question of how prevalent such layers are and how they are formed. In this paper, we examine aircraft measurements from the Airborne Tropical Tropopause Experiment (ATTREX), the Coordinated Airborne Studies in the Tropics (CAST) and the Convective Transport of Active Species in the Tropics (CONTRAST) experiment campaigns based in Guam in January–March 2014 for evidence of very low ozone concentrations and their relation to deep convection. The study builds on results from the ozonesonde campaign conducted from Manus Island, Papua New Guinea, as part of CAST, where ozone concentrations as low as 12 ppbv were observed between 100 and 150 hPa downwind of a deep convective complex. TTL measurements from the Global Hawk unmanned aircraft show a marked contrast between the hemispheres, with mean ozone concentrations in profiles in the Southern Hemisphere between 100 and 150 hPa of between 10.7 and 15.2 ppbv. By contrast, the mean ozone concentrations in profiles in the Northern Hemisphere were always above 15.4 ppbv and normally above 20 ppbv at these altitudes. The CAST and CONTRAST aircraft sampled the atmosphere between the surface and 120 hPa, finding very low ozone concentrations only between the surface and 700 hPa; mixing ratios as low as 7 ppbv were regularly measured in the boundary layer, whereas in the free troposphere above 200 hPa concentrations were generally well in excess of 15 ppbv. These results are consistent with uplift of almost-unmixed boundary-layer air to the TTL in deep convection. An interhemispheric difference was found in the TTL ozone concentrations, with values < 15 ppbv measured extensively in the Southern Hemisphere but seldom in the Northern Hemisphere. This is consistent with a similar contrast in the low-level ozone between the two hemispheres found by previous measurement campaigns. Further evidence of a boundary-layer origin for the uplifted air is provided by the anticorrelation between ozone and halogenated hydrocarbons of marine origin observed by the three aircraft.

Tropical Cyclones Reduce Ozone in the Tropopause Region Over the Western Pacific: An Analysis of 18 Years Ozonesonde Profiles

“…The western Pacific typhoon season peaks from July to October in the Northern Hemisphere (Matsuura et al., 2003). Several observations have shown that typhoon convection can lift ozone‐poor air from the marine boundary layer into the tropopause region over the Pacific region (Li et al., 2017, 2020; Minschwaner et al., 2015; Newton et al., 2018; Vogel et al., 2014). As a result, low‐ozone values are measured in the upper troposphere within typhoons or hurricanes (Cairo et al., 2008; Fu et al., 2013).…”

Global-scale distribution of ozone in the remote troposphere from the ATom and HIPPO airborne field missions

“…Airborne campaigns have targeted both the Pacific and Atlantic oceans, providing novel characterization of O 3 sources, distribution, and photochemistry in the marine troposphere (Browell et al, 1996a;Davis et al, 1996;Jacob et al, 1996;Pan et al, 2015;Schultz et al, 1999;Singh et al, 1996c) and the low-O 3 tropical Pacific pool (Singh et al, 1996b); the pervasive role of continental outflow on O 3 production (Bey et al, 2001;Crawford et al, 1997;Heald et al, 2003;Kondo et al, 2004;Martin et al, 2002;Zhang et al, 2008); and the marked influence of African and South American biomass burning on O 3 production in the Southern Hemisphere (Browell et al, 1996b;Fenn et al, 1999;Mauzerall et al, 1998;Singh et al, 1996a;Thompson et al, 1996). Ozonesondes have been launched from remote sites for more than 3 decades in some places and have provided additional constraints on the sources and photochemical balance of tropospheric O 3 , including a deep understanding of the vertically resolved tropospheric O 3 climatology in select locations (Derwent et al, 2016;Diab et al, 2004;Jensen et al, 2012;Kley et al, 1996;Liu et al, 2013;Logan, 1985;Logan and Kirchhoff, 1986;Newton et al, 2018;Oltmans et al, 2001;Parrish et al, 2016;Sauvage et al, 2006;. Spatially resolved O 3 climatology has been provided from routine sampling by commercial aircraft, which has mostly been limited to the upper troposphere or over continental regions (Clark et al, 2015;Cohen et al, 2018;Logan et al, 2012;<...>…”

Dehydration and low ozone in the tropopause layer over the Asian monsoon caused by tropical cyclones: Lagrangian transport calculations using ERA-Interim and ERA5 reanalysis data

“…Minschwaner et al (2015) find that Hurricane Henriette uplifted air with low ozone from the boundary layer in the central and eastern Pacific to the upper troposphere with subsequent transport to Socorro (North America) according to balloon-borne ozonesonde and satellite measurements. Newton et al (2018), using aircraft measurements in Guam, show that low ozone values (20 ppbv) in the tropical tropopause layer (TTL) are caused by deep convection, which has lifted ozone-poor boundary layer air to the TTL over the western Pacific in 2014.…”