Transcript Transport analysis and source attribution of seasonal and

Transport analysis and source attribution of the
tropical CO seasonal and interannual variability
in the UT/LS
Junhua Liu and Jennifer Logan
School of Engineering and Applied Sciences, Harvard University, Cambridge,
Massachusetts, USA
Dec 17th 2010, AGU
Acknowledgements: Thanks to the MLS Science team
Gases exchanged between the UT/LS
Modified from Holton et al.
(1995)
H2O tape recorder
Jiang et al. (2010)
CO Tape Recorder
First identified by Schoeberl et al. (2006) using MLS data, GCM model
analysis by Duncan et al. (2007).
Two mechanisms hypothesed:
•
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).
•
Objective:
•
To understand the processes that determine observed
temporal and spatial variability in CO signal in the UT/LS.
MLS (Microwave Limb Sounder)
MLS
Mozaic
Courtesy of Inna Megretskaia
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
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
CO tape recorder (12ºN- 12ºS)
MLS
The GEOS-Chem models
capture the main features.
Inter-annual variation (IAV)
driven by CO fire emissions,
especially from Indonesia.
GEOS-4
CO from Indonesian
fires in late 2006
IAV in emissions in NH
fire season apparent
(Jan.-Apr.).
GEOS-5
4-yr mean is subtracted from time
series
ppb
Initial conditions of CO and transport at 226 hPa
Tagged CO (12N-12S) source contributions
Biomass Burning
S. America
S. Africa
N. Africa
Indonesia
Isoprene
max. in Apr-May, min. in Aug-Sep.
GEOS-4 stronger than GEOS-5
Left: temporal overlapping of
surface BB from different
continents generates the semiannual cycle ~200 hPa.
Tropical CO - Seasonality and interannual variation
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.
MLS
GEOS-4
GEOS-5
70 hPa
CO anomaly (ppb)
100 hPa
147 hPa
215 hPa
N.Af, Indo.
Jan 05
S.Af, S.Am
Indo.
Jan 06
Jan 07
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
4-yr mean is subtracted from time
series
Jan 08
Jan 09
Seasonality and vertical profile of upward transport
in assimilated met. fields
Velocity (cm/s)
Max. in winter-spring
Min. in summer-fall
Winter-spring(Dec-May)
Summer-fall (Jun-Nov)
Pressure(hPa)
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.
Velocity (cm/s)
CO mixing ratio and anomaly at 215 & 70 hPa
CO anomaly (ppb)
MLS
GEOS-4
GEOS-5
CO anomaly (ppb)
CO mixing ratio (ppb)
CO mixing ratio (ppb)
•
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.
GEOS-5: vertical transport too weak
Pressure (hPa)
GEOS-4
GEOS vertical
velocities computed
from mass
divergence (zonal
mean of 15°S-10°N)
GEOS-5
NH spring (MAM)
NH summer (JJA)
NH fall (SON)
NH winter (DJF)
Pressure (hPa)
GEOS-5:
100-75 hPa - Transport too
low in all seasons.
Vertical velocity
deduced from
heating rates
(obs. H2O and O3
Radiative transfer
model)
Yang et al., 2008
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
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.