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)Ozone at Mauna Loa Observatory (MLO)

O3

An

om

aly

(pp

b)

GFDL AM3 with fixed emissions (nudged) captures observed O3 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 O3 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?

1980-19951996-2011

% C

hang

e in

EAC

Ot

(199

6-20

11)

––

(198

0-19

95)

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

O3

An

om

aly

(pp

b)

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

ElNiño LaNiña

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 NiñoComposite

La NiñaComposite

ENSO Neutral(2000-2012) minus (1960-1975)

Lin et al (2013), in review

Jet anomaly

△O3 (ppb)

O3 (ppb)

Geophysical Fluid Dynamics Laboratory

Decadal ozone increases in fall: Role of a meteorological shift in the mid-1990s

O3 A

nom

aly

(p

pb)

Lin et al (2013), in reviewDaily 0-8am average ozone

PD

F (

%)

Observations Model

Geophysical Fluid Dynamics Laboratory

A shift towards predominantly positive PNA enhances transport of midlatitude O3 to MLO in fall

△Z (m)Changes in NCEP 500 hPa height(1995-2011 minus 1980-1994)

Daily Pacific-North American (PNA) Index

Geophysical Fluid Dynamics Laboratory

A shift towards predominantly positive PNA enhances transport of midlatitude O3 to MLO in fall

Correlations (MLO O3, NCEP Z), 1980-2011

Changes in 675 hPa O3 from AM3-FIXEMIS (1995-2011 minus 1980-1994)

r

△O3 (ppb)

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 O3 changes to trends in precursor emissions

• Need to maintain multi-decadal measurements

• Potential for atmospheric oxidant measurements to document changes in atmospheric circulation

Mar

-Ap

rS

ep-O

ct

1980 20101990 2000

• 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

Observations Model (GFDL AM3)

Geophysical Fluid Dynamics Laboratory

Backup slides: Evaluation of NOx emissions

Emission data: Lamarque et al., 2010 for 1980-2000 RCP 8.5 for 2005-2010.