Intercontinental Chemical Transport Experiment Ozonesonde Network Study (IONS) 2004: 1. Summertime upper troposphere/lower stratosphere ozone over northeastern North America

Coordinate ozonesonde launches from the Intercontinental Transport Experiment (INTEX) Ozonesonde Network Study (IONS) (http:// croc.gsfc.nasa.gov/intex/ions.html) in July-August 2004 provided nearly 300 O₃ profiles from eleven North American sites and the R/V Ronald H. Brown in the Gulf of Maine. With the IONS period dominated by low-pressure conditions over northeastern North America (NENA), the free troposphere in that region was frequently enriched by stratospheric O₃. Stratospheric O₃ contributions to the NENA tropospheric O₃ budget are computed through analyses of O₃ laminae (Pierce and Grant, 1998; Teitelbaum et al., 1996), tracers (potential vorticity, water vapor), and trajectories. The lasting influence of stratospheric contribution into the troposphere is demonstrated, and the computed stratospheric contribution to tropospheric column O₃ over the R/V Ronald H. Brown and six sites in Michigan, Virginia, Maryland, Rhode Island, and Nova Scotia, 23% ± 3%, is similar to summertime budgets derived from European O₃ profiles (Collette and Ancellet, 2005). Analysis of potential vorticity, Wallops ozonesondes (37.9°N, 75.5°W), and Measurements of Ozone by Airbus Inservice Aircraft (MOZAIC) O₃ profiles for NENA airports in June-July-August 1996-2004 shows that the stratospheric fraction in 2004 may be typical. Boundary layer O₃ at Wallops and northeast U.S. sites during IONS also resembled O₃ climatology (June-July-August 1996-2003). However, statistical classification of Wallops O₃ profiles shows the frequency of profiles with background, nonpolluted boundary layer O₃ was greater than normal during IONS.