1. Geophysical Fluid Dynamics Laboratory Footprints of decadal climate variability in ozone at Mauna Loa Observatory Meiyun Lin Coauthors: L.W. Horowitz (NOAA/GFDL), S.J. Oltmans (NOAA/ESRL), A.M. Fiore (Columbia/LDEO), S. Fan (NOAA/GFDL) Acknowledgements: Hiram “Chip” Levy II Levy Symposium (8/16/2013)

2. Geophysical Fluid Dynamics Laboratory We need 30+ years of data for seeing an ozone trend! Changes in ozone (t=22 d) at a remote location can reflect: Trends in hemispheric precursor emissions Variability in large-scale circulation patterns Ozone at Mauna Loa Observatory (MLO) O 3 Anomaly (ppb) GFDL AM3 with fixed emissions (nudged) captures observed O 3 changes Negligible influence from El Niño-related wildfires in equatorial Asia Lin et al (2013), in review

3. Geophysical Fluid Dynamics Laboratory Lin et al (2013), in review The missing puzzle piece on ozone at MLO : No trend in spring but an increase in fall J F M A M J J A S O N D But observed baseline O 3 at NH sites increases most in spring, presumably due to rising Asian emissions [e.g. Cooper et al., 2010; Parrish et al., 2012; Logan et al., 2012; Oltmans et al., 2013] Mauna Loa Observatory No changes in stratospheric influence Circulation-driven changes in Asian pollution influence! What does GFDL AM3 tell us? 1980-1995 1996-2011 % Change in EACOt – (1996-2011) – (1980-1995)

4. Geophysical Fluid Dynamics Laboratory 4 A climate perspective: Mean transport regimes in spring vs. fall Boreal Spring: NCEP 500 hPa winds MLO, located near the edge of midlatitude and Hadley cells  Receives most airflow from Eurasia  Sensitive to varying jet streams with ENSO, PDO, and the Hadley circulation Boreal Fall: MLO, located deep in the tropical belt  Receives least airflow from Eurasia  Transport of Asian pollution to MLO primarily through isentropic subsidence  Sensitive to varying pressure dipoles associated with PNA Lin et al (2013), in review

5. Geophysical Fluid Dynamics Laboratory Interannual variability in spring: ENSO modulates Asian pollution reaching MLO O 3 Anomaly (ppb) Lin et al (2013), in review

6. Geophysical Fluid Dynamics Laboratory Long-term ozone decreases in spring: Role of tropical expansion + fewer El Niño events in 2000s PDO-,tending towards fewer El Niño events [e.g. Chavez et al., 2003; Overland et al., 2008; Meehl et al., 2013] Range of ensemble members (3) Lin et al (2013), in review ElNi ñ o LaNi ñ a Pacific Decadal Oscillation

7. Geophysical Fluid Dynamics Laboratory Long-term ozone decreases in spring: Role of tropical expansion + fewer El Niño events in 2000s Consistent with the observed widening of the tropical belt since 1960s [Seidel et al 2008; Lu et al. 2009; Allen et al., 2012] AM3-AMIP simulated ozone at 675 hPa El Niño Composite La Ni ñ a Composite ENSO Neutral (2000-2012) minus (1960-1975) Lin et al (2013), in review Jet anomaly △ O 3 (ppb) O 3 (ppb)

8. Geophysical Fluid Dynamics Laboratory Decadal ozone increases in fall: Role of a meteorological shift in the mid-1990s O 3 Anomaly (ppb) Lin et al (2013), in review Daily 0-8am average ozone PDF (%) Observations Model

9. Geophysical Fluid Dynamics Laboratory A shift towards predominantly positive PNA enhances transport of midlatitude O 3 to MLO in fall △ Z (m) Changes in NCEP 500 hPa height (1995-2011 minus 1980-1994) Daily Pacific-North American (PNA) Index

10. Geophysical Fluid Dynamics Laboratory A shift towards predominantly positive PNA enhances transport of midlatitude O 3 to MLO in fall Correlations (MLO O 3, NCEP Z), 1980-2011 Changes in 675 hPa O 3 from AM3-FIXEMIS (1995-2011 minus 1980-1994) r △ O 3 (ppb)

11. Geophysical Fluid Dynamics Laboratory Yes, we do need 30+ years of data!!! Lin et al (2013), in review (Correspondence to Meiyun.Lin@noaa.gov) Decadal variability and possibly climate-driven trends in atmospheric circulation must be considered when attributing observed O 3 changes to trends in precursor emissions Need to maintain multi-decadal measurements Potential for atmospheric oxidant measurements to document changes in atmospheric circulation Mar-Apr Sep-Oct 1980201019902000 The short record length complicates the unambiguous attribution to specific processes

12. Geophysical Fluid Dynamics Laboratory Additional slides

13. Geophysical Fluid Dynamics Laboratory Changes in the daily ozone distribution Daily 0-8am average ozone ObservationsModel (GFDL AM3)

14. Geophysical Fluid Dynamics Laboratory Backup slides: Evaluation of NO x emissions Emission data: Lamarque et al., 2010 for 1980-2000 RCP 8.5 for 2005-2010.