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)

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

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? % Change in EACOt – ( ) – ( )

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

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

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

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 ( ) minus ( ) Lin et al (2013), in review Jet anomaly △ O 3 (ppb) O 3 (ppb)

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

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 ( minus ) Daily Pacific-North American (PNA) Index

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), Changes in 675 hPa O 3 from AM3-FIXEMIS ( minus ) r △ O 3 (ppb)

Geophysical Fluid Dynamics Laboratory Yes, we do need 30+ years of data!!! Lin et al (2013), in review (Correspondence to 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 The short record length complicates the unambiguous attribution to specific processes

Geophysical Fluid Dynamics Laboratory Additional slides

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

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