Geophysical Fluid Dynamics Laboratory Key drivers of Western U.S. surface O 3 variability over...
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Geophysical Fluid Dynamics Laboratory Key drivers of Western U.S. surface O 3 variability over recent decades: Stratospheric intrusions, Asian pollution,
Geophysical Fluid Dynamics Laboratory Key drivers of Western
U.S. surface O 3 variability over recent decades: Stratospheric
intrusions, Asian pollution, and climate Meiyun Lin Presented at
Air Quality Research Subcommittee Meeting, Feb-19-2015
Acknowledgements: NOAA: L.W. Horowitz, O.R. Cooper, A.O. Langford,
S. J. Oltmans, CalNex Science Team Others: A.M. Fiore and H. Rieder
(Columbia), D. Tarasick (Environment Canada) Zheng Li (Nevada Clark
County DAQ)
Slide 2
Geophysical Fluid Dynamics Laboratory Major challenges for
Western U.S. air quality managements 2 MAJOR CHALLENGES: -Rising
Asian emissions and global CH 4 [e.g. Jacob et al. 1999; Cooper et
al. 2010; Clifton et al. 2014] -More frequent wildfires in summer
[e.g. Westerling et al. 2006; Pfister et al. 2008; Jaffe 2011]
-Frequency of stratospheric intrusions in spring [e.g. Langford et
al., 2009; Lin et al., 2012b] NEED PROCESS-LEVEL UNDERSTANDING ON
DAILY TO MULTI-DECADAL TIME SCALES Annual 4 th Hi MDA8 O 3
(2011-2013 AQS) Mean background, Apr-Jun NA anthrop emis off in
GFDL AM3 (~0.5x0.5) Future NAAQS? Current NAAQS ppb
Slide 3
Trans-Pacific Asian pollution plumes: The view from satellites
Animation of daily AIRS CO columns [10 18 molecules cm -2 ] Lin MY
et al. (JGR, 2012a): AGU Editors Highlight, Featured in Science,
Nature News, NY Times Greenblog) How important is Asian influence
in surface air?
Slide 4
ObservedAM3 Model totalModel Asian June 21 2010 June 22 2010
Asian emissions contribute 8-12 ppb on days when OBS O 3 65 ppb
(future NAAQS) Role of tripling NO x emissions from E. China over
recent decades? Asian pollution contribution to WUS high-O 3 events
Surface MDA8 O 3 [ppb]
Slide 5
Geophysical Fluid Dynamics Laboratory GFDL-AM3 BASE (with both
emis & met varying over time) Long-term U.S. surface ozone
trends: Did regional NO x reductions work? Observed MDA8 O 3 trends
(ppb yr -1 ) 95 th 50 th Larger circles indicate statistically
significant trends MAM 1988-2012 NASA Project PIs (M.Y. Lin and
O.R. Cooper) WUS: High background, thus little response to local NO
x reductions AM3 BASE captures key features of observed surface O 3
trends
Slide 6
Subsidence of stratospheric O 3 to the lower trop of S.
California (May 28, 2010) 30 50 Altitude (km) 70 11015090130 North
South O 3 [ppb] at Joshua Tree (JT) AM3 total zeroNA OBS O 3 O 3
Strat Observed RH (%) [ppb] Sondes over California See more
process-oriented analysis in Lin MY et al (JGR, 2012b) Simulated
enhancements of O 3 Strat consistent with observed low RH Reaching
surface air on the following day
Slide 7
Stratospheric influence on the highest observed surface ozone
events in S. Nevada (e.g. June 5, 2012) What controls year-to-year
variability of such events? Ozone (ppb, 5-min) Wind gust (mph,
hourly) Model O 3 Strat (ppb, 8-h average) Baseline level (~20 ppb)
likely represents an upper limit. Data c/o Zheng Li (Nevada DAQ)
Lin MY et al (in prep, 2015) June 3June 5, Observed Pollution
Slide 8
Geophysical Fluid Dynamics Laboratory Strong stratospheric
influence on year-to-year variability of high-elevation Western
U.S. surface O 3 during April-May Lin MY et al (in review, 2015) 75
th 25 th 50 th O 3 Strat 1990 Emissions held constant Nudged to
real winds Large IAV may complicate the attribution of observed O 3
trends in short records Stratospheric Contribution (ppb)
Slide 9
r 2 (OBS, EACOt ) = 0.09 r 2 (OBS, O 3 Strat) = 0.43
Stratospheric Contribution (ppb) 1990 Asian pollution contributes
less to WUS surface ozone inter-annual variability than the
stratospheric influence Airflow from Eurasia towards the WUS in
spring has weakened in the 2000s Consistent with declines in
Radon-222 and O 3 observed at Mauna Loa, Hawaii (3.4 km altitude)
during spring Too small to be discernable from surface O 3
observations over WUS Lin MY et al (2014) Apr-May
Slide 10
Geophysical Fluid Dynamics Laboratory The high tail of the
observed daily surface O 3 distribution over Western U.S. increases
during La Nia springs Observed daily max 8-h average (MDA8) ozone
[ppb] Neutral: = 56.5, = 7.5 El Nio (1998, 2010): = 56.9, = 7.3 La
Nia (1999, 2008, 2011): = 58.5, = 7.9 Pinatubo (1992, 1993): =
54.3, = 6.5 Lin MY et al (in review, 2015) Changes in the high tail
are statistically significant Probability Density
Slide 11
Geophysical Fluid Dynamics Laboratory 11 1999 (La Nia) 1992
(Pinatubo) Frequent deep stratospheric intrusion events Weaker
events, lower mean values Gothic in the Colorado Rocky Mtn (2.9 km
altitude) NAAQS O 3 Strat BGO 3 Total Following strong La Nia
conditions, deep STT may occur with sufficient frequency as to
confound NAAQS attainment MDA8 O 3 (ppb)
Slide 12
Lin MY et al (in review, 2015) Variance in daily O 3 Strat at
500hPa (April-May) ENSO-related jet characteristics and their
impacts on lower trop. ozone variability over western NA La Nia El
Nio La Nia (ppb 2 ) Lin MY et al (Nature GeoSci., 2014);
Slide 13
Geophysical Fluid Dynamics Laboratory More frequent
stratospheric intrusions expected in the following spring over WUS?
Developing seasonal predictions with a few months of lead time to
aid Western U.S. AQ planning? SST (C) Lin MY et al (in review,
2015) The time lag could allow regional preparations, e.g.
Conducting daily forecasts for public health alerts Deploying
targeted measurements aimed at identifying exceptional events MDA8
O 3 (ppb) Gothic, Colorado winter Tropical SST cooling typically
peaks in winter
Slide 14
Geophysical Fluid Dynamics Laboratory Some Final Thoughts For
Moving Forward Exploiting the linkage between La Nia and WUS
stratospheric intrusion frequency to aid regional preparations for
a high-ozone season? Conducting daily forecast and targeted
measurements Need multi-model assessment of stratospheric influence
Process-oriented evaluation to establish model credibility Focusing
on the known deep SI events as a first step Leveraging CalNex
(2010) and LVOS (2013) measurements The available weekly ozonesonde
measurements are too infrequent to capture the actual variability
of mean O 3 Need more frequent, continuous sonde measurements for
spring? [email protected] GFDL AM3
Slide 15
Additional Slides for Discussions
Slide 16
Geophysical Fluid Dynamics Laboratory SPRING Decreasing ozone
at Mauna Loa in SPRING tied to recent La-Nia-like decadal cooling +
weakening airflow from Asia Decreasing Rn (Bq/m 3 ) Weakening
airflow from Eurasia ElNio LaNia-like decadal cooling [ Chavez2003;
Meehl2013; Kosaka2013 ] Lin MY et al (Nature GeoSci., 2014) AMIP
(fixed emissions) El Nio La Nia (ppb) 40 50 70 60 80 Even higher
Mean background 500 hPa, Apr-May Ozone Anomaly, ppb (25 th
percentile) P