atmospheric chemistry in the tropical tropopause layer
DESCRIPTION
Atmospheric Chemistry in the Tropical Tropopause Layer. Mark G. Lawrence Max Planck Institute for Chemistry Mainz, Germany SPARC/GEWEX/IGAC TTL Workshop Victoria, Canada, 14 June 2006. Flashback to the “dark ages” (about 3-5 years ago). Observations - PowerPoint PPT PresentationTRANSCRIPT
Atmospheric Chemistry in the Tropical Tropopause Layer
Mark G. Lawrence
Max Planck Institute for ChemistryMainz, Germany
SPARC/GEWEX/IGAC TTL WorkshopVictoria, Canada, 14 June 2006
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Flashback to the “dark ages” (about 3-5 years ago)
Observations
• WMO (2002): “Currently very few chemical observations of species other than ozone are available in the TTL”
• Tuck et al. (2004): “There are no published horizontal observations of water, ozone, and tracers in the upper tropical troposphere [ TTL]… recent analysis of this region has worked in terms of single-valued ozone and water vertical profiles…”
Modelling
• WMO (2002): “These estimates…depend strongly on their respective model formulation…such modeling studies, however, are unfortunately rarely repeated once the first ones have been published.”
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
But we’ve not been completely in the dark…
Selected Topics For This Overview
• Low-Ozone Airmasses in the TTL
• Deep Convective Transport of Tracers
• Scavenging – Especially by Ice and Role for HNO3
• Extended Horizontal Observations of a Suite of Gases (ACCENT results)
Largely complementary to topics and more recent results
in other talks / posters (“excess” of MPI results for illustrations)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Why has it been so difficult?
• Tough region to observe in situ
– Only a few aircraft can reach well into the TTL Pickering talk: recent extensive efforts in TROCCINOX, SCOUT-O3, …
– O3-sonde situation improved by SHADOZ…but:• It’s only one gas (albeit important)
• It’s quite long-lived ( ~ 1 year in the TTL) probably tells more about transport than the real “chemical nature”
• Tough region to observe with remote sensing – Satellites: overlying stratospheric columns, steep gradients near the TT– Ground-based (FTIR, LIDAR): far away
• Tough region to model– Heavily dependent on:
• Deep convection and convective transport parameterizations• Representation of the Brewer-Dobson circulation (poor in tropospheric models with caps ~10 hPa)• Representation of complex NMHC chemistry (e.g., acetone as a HOx source) and scavenging, which
are typically poor in middle-atmosphere models
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
What TTL chemistry topics are we interested in for future observations and
model studies?• O3
– Chemistry “driver”– Radiative forcing
• HOx – Intriguing, though not expected to be critical for the global oxidizing
efficiency (e.g., for CH4)
• Halogenated VSLS – Stratospheric source– See WMO, 2002 (and upcoming assessment)
• Aerosols – Cirrus cloud effects – Influence on water transport into the stratosphere
• In situ emissions – Aircraft and Lightning
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Timescales
UT
BL, ~ 5 d
UTUT
LSLS
TTL
TT, ~16-17 km
STT, ~11-13 km
~ 10 (5-20) d
~ months
“potentially significant”
FBL-TT ~ 0.2-6% FBL-STT
(Based on WMO, 2002)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Selected Topics for this Overview
• Low-Ozone Airmasses in the TTL
• Deep Convective Transport of Tracers
• Scavenging – Especially by Ice and Role for HNO3
• Extended Horizontal Observations of a Suite of Gases (ACCENT results)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
CEPEXCentral Equatorial Pacific Experiment
March, 1993
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Observed and MATCH-MPIC vertical O3 profiles
Observations (balloon sondes)Modeled (MATCH-MPIC)
(Kley et al., Science, 1996;Lawrence et al., QJRMS, 1999)
West Middle East
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Western CEPEX regionCentral CEPEX regionEastern CEPEX region
With Convection No O3 Convection
Effect of Convection on Modelled O3
(Lawrence et al., QJRMS, 1999)
(Only convective Transport of ozone was turned off)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Effect of Convection on Modelled O3
(Salzmann, 2005)
WRF Simulation Results for TOGA COARE
TTL – O3 reduced by convective transport
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Other factors possibly influencing the TTL O3 minima?
• Reactions on Ice (HO2, Cl/Br)?– Kley et al., Science, 1996; Lawrence, 1996
• Reactions in the MBL (Halogens)?– Lawrence et al., 1999
• Lightning NOx => Titration?– Wang and Prinn, 2000
Asman et al. (2003): Extreme O3 minima are rare in the MOZAIC data…But flights likely too low and not sampling Pacific enough
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
black lines - average profiles for 1998–2004 colored lines - illustrative reduced ozone events
Ozone Sonde (SHADOZ) Observations
(Solomon et al., GRL, 2005)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Ozone Sonde (SHADOZ) Observations
• Reduced ozone events (< 20 nmol/mol) most common over western Pacific
• Very low ozone events (< 10 nmol/mol) nevertheless quite rare
(Solomon et al., GRL, 2005)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Ozone Sonde (SHADOZ) Observations
(Solomon et al., GRL, 2005)
Ozone frequency distribution changing over time!
Samoa, 200 hPa
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Selected Topics for this Overview
• Low-Ozone Airmasses in the TTL
• Deep Convective Transport of Tracers
• Scavenging – Especially by Ice and Role for HNO3
• Extended Horizontal Observations of a Suite of Gases (ACCENT results)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Deep Convection – Outflow in the TTL
(Folkins and Martin, JAS, 2005)
Airmasses from convection detraining above the transition from radiative cooling to radiative warming (~15 km) have a much greater chance of being transported into the stratosphere
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Yanai et al., 1973; Tiedtke, 1989; Grell, 1993; Pan and Wu, 1995; Zhang and McFarlane, 1995
BulkPlume Ensemble
Arakawa and Schubert, 1974; Lord et al., 1982; Hack et al., 1984; Grell, 1993
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Convective Transport Formulations
(Lawrence and Rasch, JAS, 2005)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Role of Convective Transport Formulations
= 2 d
= 1 d
Zonal Mean, July 2001 (Lawrence and Rasch, JAS, 2005)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
-2 -1 0 1 2 3 Cloud mass flux (kg/m2/s)
-2 -1 0 1 2 3 Cloud mass flux (kg/m2/s)
-.1 -.05 0.0 .05 .1 Cloud mass flux
(kg/m2/s)
-.1 -.05 0.0 .05 .1 Cloud mass flux
(kg/m2/s)
Domain Means Cloudy-Area Means
Convective Mass Flux Characterizations
(Salzmann, 2005)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Selected Topics for this Overview
• Low-Ozone Airmasses in the TTL
• Deep Convective Transport of Tracers
• Scavenging – Especially by Ice and Role for HNO3
• Extended Horizontal Observations of a Suite of Gases (ACCENT results)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Influence of Precipitation Scavenging
Hx in M/atm:
Hx = 0Hx = 103
Hx = 104
Hx = 105
Hx = 106
Ice
(Crutzen and Lawrence, J. Atmos. Chem., 2000)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Influence of Precipitation Scavenging
Hx in M/atm:
Hx = 0Hx = 103
Hx = 104
Hx = 105
Hx = 106
Ice
(Crutzen and Lawrence, J. Atmos. Chem., 2000)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Influence of Precipitation Scavenging: Role of Uptake of HNO3 on Ice
• Large sensitivity to uptake formulation• Based on comparison to observations, some degree of
uptake and scavenging seems very likely, quantification still difficult
• Effects on ozone minor
Focus shifted towards HNO3 itself, especially role for cloud microphys., e.g., -ice (Gao et al., Science, 2004)
• Further laboratory and field work needed!
(von Kuhlmann and Lawrence, ACP, 2006)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Selected Topics for this Overview
• Low-Ozone Airmasses in the TTL
• Deep Convective Transport of Tracers
• Scavenging – Especially by Ice and Role for HNO3
• Extended Horizontal Observations of a Suite of Gases (ACCENT results)
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
ACCENT TTL Chemistry Observations
(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)
20 Sept., 1999 21 Sept., 1999
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)
ACCENT TTL Chemistry Observations
Wide variety of gases and aerosol components observed, large spatial variability
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)
ACCENT TTL Chemistry Observations
• Samples collected between 10 and 19 km altitude (both UT/LS and TTL)
• Chloroform: Continental tracer
• Methyl Nitrate: Marine tracer
• Both continental and marine origins observed at “essentially all latitudes” covered by the flights
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)
ACCENT TTL Chemistry Observations
• Particularly informative: correlations with O3
• Correlations found with tracers with wide range of lifetimes (in this figure: 10-2, 10-1, 10, 102 and 103 years)
• Major identifiable influences:– Marine convection– Continental convection– Stratospheric descent (10% admixture)– Biomass burning– In situ chemistry
• “No large-scale division of these signatures into separate airmasses”
• Key shortcoming: degree of influences only partially quantifiable from the limited data
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Summary/Outlook
• We do know some about TTL chemistry, though much of this is focused on ozone, especially the reduced-ozone observations (CEPEX and SHADOZ sondes)
• Due to the long lifetimes of most key gases in the TTL (e.g., O3 ~ 1 year, NOx ~ 1 week, etc.), transport processes are critical, especially
– Deep convection– Uptake into condensate, especially ice (including subvisible cirrus?), and further lofting
or sedimentation/precipitation – Slow upwelling, especially in the upper TTL– Exchange with the stratosphere (both from above and horizontally)
• More observations needed: major very recent advances through SCOUT-O3, TROCCINOX and others overview in Ken Pickering’s talk
• Modeling studies still tend to be very individual case studies (see several other talks/posters) hope given in Mary Barth’s talk on what we can learn from intercomparisons?
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Outlook: New ECHAM5/MESSy O3 Simulations
• Consistent simulation from surface to 0.01 hPa• No upper boundary near the TTL,
full tropospheric (NMHC) chemistry• Submitted manuscript:
Jöckel et al.,The atmospheric chemistry general circulation model ECHAM5/MESSy1: Consistent simulation of ozone from the surface to the mesosphere, submitted to ACPD. 2006.
Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006
Final Food (and Wine) for Thought
• Adrian Tuck (ACCENT Observations): “As far as transport is concerned, the small-scale variation is not noise, it is music”
• Frank Zappa: “The difference between music and noise is that music is organized – even if it seems like noise to some people”