Junhua Liu and Jennifer Logan
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Transcript of Junhua Liu and Jennifer Logan
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Transport analysis and source attribution of the tropical CO seasonal and interannual variability
in the UT/LS
Junhua Liu and Jennifer LoganSchool of Engineering and Applied Sciences, Harvard University, Cambridge,
Massachusetts, USA
Dec 17th 2010, AGU
Acknowledgements: Thanks to the MLS Science team
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Gases exchanged between the UT/LS
Modified from Holton et al. (1995)
H2O tape recorder
Jiang et al. (2010)
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CO Tape RecorderFirst identified by Schoeberl et al. (2006) using MLS data, GCM model analysis by Duncan et al. (2007).
Objective: • To understand the processes that determine observed
temporal and spatial variability in CO signal in the UT/LS.
• Advection of the CO seasonal signal near the tropopause. (Schoeberl et al., 2006)
• Seasonal cycle in upwelling acting on the background vertical gradient in CO (Randel et al., 2007).
Two mechanisms hypothesed:
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MLS (Microwave Limb Sounder)
MLS V3.3 level 2 data• Prelim. validation with MOZAIC aircraft transects at 215 hPa
• the 100% positive bias in MLS v2.2 has been eliminated
MLS
Mozaic
Courtesy of Inna Megretskaia
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GEOS-Chem Model
Standard chemistry run:• 4o × 5o horizontal resolution• Two runs driven by archived GEOS-4 (2005-06) or GEOS-5
(2005-08) assimilated met. fields – diff. convection parameterization
• Model profiles sampled along the MLS orbit track at the obs. time, and vertically smoothed with the MLS AK.
Tagged CO run:• 2o × 2.5o horizontal resolution• OH fields from chemistry run• CO (P-L) rate in stratosphere from GMI model
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CO tape recorder (12ºN- 12ºS)MLS
GEOS-4
GEOS-5
4-yr mean is subtracted from time series
CO from Indonesian fires in late 2006
The GEOS-Chem models capture the main features. Inter-annual variation (IAV) driven by CO fire emissions, especially from Indonesia.
ppb
IAV in emissions in NH fire season apparent (Jan.-Apr.).
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Initial conditions of CO and transport at 226 hPaTagged CO (12N-12S) source contributions
S. America
S. Africa
Indonesia
N. Africa
Isoprene Left: temporal overlapping of surface BB from different continents generates the semi-annual cycle ~200 hPa.
Biomass Burning
max. in Apr-May, min. in Aug-Sep. GEOS-4 stronger than GEOS-5
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70 hPa: CO maximum from SH and NH fires add - shift to annual cycle.100 hPa: MLS : semi-annual cycle Models: • Fall peak damped in 07,
08. • Matches phase of MLS but
amplitude too small. Vert. transport too weak?
215 &147 hPa:: Semi-annual cycle
N.Af, Indo. S.Af, S.Am Indo.
CO
ano
mal
y (p
pb)
Tropical CO - Seasonality and interannual variation
MLS GEOS-4 GEOS-5
4-yr mean is subtracted from time series
CO peak at 70 hPa from NH fires lags peak at 147 hPa by ~0-2 mon.; lag in peak ~3-4 mon. for CO from SH fires.
215 hPa
147 hPa
100 hPa
70 hPa
Jan 05 Jan 06 Jan 07 Jan 08 Jan 09
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Velocity (cm/s)
Winter-spring(Dec-May) Summer-fall (Jun-Nov)
Pres
sure
(hPa
)Seasonality and vertical profile of upward transport
in assimilated met. fields
Transport minimum at ~80 hPa, causing the maximum lag of CO peak from 100 hPa to 70 hPa.
Much slower transport of SH burning signal.
Max. in winter-springMin. in summer-fall
Velo
city
(cm
/s)
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CO mixing ratio and anomaly at 215 & 70 hPa
MLSGEOS-4GEOS-5
• Much less CO has been lofted in GEOS-5.
• CO anomalies show comparable results in GEOS-4 and GEOS-5; Models match the seasonal cycles of MLS - CO tape recorder pattern depends more on phase of vertical transport.
• The model amplitudes are ~10-16 ppb smaller than the obs. at 70 hPa.
CO
mix
ing
ratio
(ppb
)
CO mixing ratio (ppb)
CO
ano
mal
y (p
pb)
CO anomaly (ppb)
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GEOS-5: vertical transport too weak
GEOS-5: 100-75 hPa - Transport too low in all seasons.
GEOS-4:Comparable vertical transport in fall below 90 hPa.
Weaker vertical transport in winter and spring below 90 hPa – possibly causing the damped seasonal cycle in the model
Yang et al., 2008
GEOS vertical velocities computed from mass divergence (zonal mean of 15°S-10°N)
Vertical velocity deduced from heating rates (obs. H2O and O3
Radiative transfer model)Pr
essu
re (h
Pa)
NH spring (MAM)NH summer (JJA)NH fall (SON)NH winter (DJF)
GEOS-4
GEOS-5Pres
sure
(hPa
)
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Conclusion• Semi-annual cycles of CO below 80 hPa in the TTL -
determined by the temporal overlapping of surface BB emissions from different continents.
• Transition from semi-annual to annual cycles around 80 hPa – induced by a combination of the signal at the tropopause and the annual cycle of BDC in the LS
• Strong interannual variation with a CO maximum in boreal fall 2006, mainly caused by fires in the Indonesian region.
• GEOS-5: too weak vertical transport, but matches the phase shift in transport, so similar tape recorder pattern.
• GEOS-4: possibly too weak vertical transport in winter and spring - decreasing the amplitude of the seasonal cycle.