Direct transport of midlatitude stratospheric ozone into the lower troposphere and marine boundary layer of the tropical Pacific Ocean -: art. no. D23310

The detailed survey of midlatitude stratospheric intrusions penetrating into the Northern Hemisphere tropics was one goal of the Pacific Sub-Tropical Jet Study 2004, conducted from Honolulu, Hawaii, during 19-29 January and 28 February to 15 March. Using the National Oceanic and Atmospheric Administration G-IV jet aircraft, instrumented with dropsondes and a 1-s resolution ozone instrument, we targeted an intrusion above Hawaii on 29 February. The data describe the strongest tropospheric ozone enhancements ever measured above Hawaii (in comparison to a 22 year ozonesonde record) and illustrate the mixing of stratospheric ozone into the midtroposphere as a result of convection triggered by the advection of relatively cold midlatitude air into the tropics. Measurements from the G-IV and Mauna Loa Observatory (3.4 km) show enhanced ozone in the lower troposphere, indicating that the remnants of the intrusion reached these levels. This conclusion is supported by a study using a stratospheric ozone tracer generated by the FLEXPART Lagrangian particle dispersion model. This paper also describes a similar intrusion that enhanced ozone at Mauna Loa on 10 March, as well as Honolulu, which is located in the marine boundary layer. G-IV flights in and out of Honolulu measured enhanced ozone associated with this event on several occasions. The 10 March event transported an estimated 1.75 Tg of ozone into the tropical troposphere, and we suggest that stratospheric intrusions that break away from the polar jet stream as they advect into the tropics are more effective at transporting ozone into the troposphere than intrusions that remain close to the polar jet stream in midlatitudes. Analysis of the dynamic conditions indicates that the frequency of stratospheric intrusions was not anomalous during January-March 2004. While the 10 March event was by itself an extreme event, strong stratospheric intrusions can be expected to influence the tropical lower troposphere in any year.