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

Observations

Flashback to the “dark ages”

(about 3-5 years ago)

• 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 and water vertical profiles…”

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 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 HNO 3 • 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, … – O 3 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 HO x 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?

• O 3 – Chemistry “driver” – Radiative forcing • HO x – Intriguing, though not expected to be critical for the global oxidizing efficiency (e.g., for CH 4 ) • 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

F BL-TT ~ 0.2-6% F BL-STT UT LS

Timescales

(Based on WMO, 2002)

TT, ~16-17 km



~ months TTL



~ 10 (5-20) d STT, ~11-13 km UT “potentially significant” LS UT BL,



~ 5 d 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 HNO 3 • 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

CEPEX Central 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 O 3 profiles

West Middle East

Observations (balloon sondes) Modeled (MATCH-MPIC)

Mark G. Lawrence, Max Planck Institute for Chemistry

(Kley et al., Science, 1996; Lawrence et al., QJRMS, 1999)

TTL Workshop, Victoria, Canada, 14 June 2006

Effect of Convection on Modelled O

3

With Convection No O

3

Convection

Western CEPEX region Central CEPEX region Eastern CEPEX region

Mark G. Lawrence, Max Planck Institute for Chemistry

(Only convective Transport of ozone was turned off)

(Lawrence et al., QJRMS, 1999)

TTL Workshop, Victoria, Canada, 14 June 2006

Effect of Convection on Modelled O

3

WRF Simulation Results for TOGA COARE TTL – O 3 reduced by convective transport Mark G. Lawrence, Max Planck Institute for Chemistry

(Salzmann, 2005)

TTL Workshop, Victoria, Canada, 14 June 2006

Other factors possibly influencing the TTL O 3 minima?

• Reactions on Ice (HO 2 , Cl/Br)?

– Kley et al., Science, 1996; Lawrence, 1996 • Reactions in the MBL (Halogens)?

– Lawrence et al., 1999 • Lightning NO x => Titration?

– Wang and Prinn, 2000

Asman et al. (2003): Extreme O 3 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

Ozone Sonde (SHADOZ) Observations

black lines - average profiles for 1998 –2004 colored lines - illustrative reduced ozone events

Mark G. Lawrence, Max Planck Institute for Chemistry

(Solomon et al., GRL, 2005)

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

Mark G. Lawrence, Max Planck Institute for Chemistry

(Solomon et al., GRL, 2005)

TTL Workshop, Victoria, Canada, 14 June 2006

Ozone Sonde (SHADOZ) Observations

Ozone frequency distribution changing over time!

Samoa, 200 hPa

Mark G. Lawrence, Max Planck Institute for Chemistry

(Solomon et al., GRL, 2005)

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 HNO 3 • 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

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

(Folkins and Martin, JAS, 2005)

TTL Workshop, Victoria, Canada, 14 June 2006

Convective Transport Formulations

Plume Ensemble Bulk

Arakawa and Schubert, 1974; Lord et al., 1982; Hack et al., 1984; Grell, 1993 Yanai et al., 1973; Tiedtke, 1989; Grell, 1993; Pan and Wu, 1995; Zhang and McFarlane, 1995 (Lawrence and Rasch, JAS, 2005)

Role of Convective Transport Formulations



= 1 d



= 2 d

Zonal Mean, July 2001 (Lawrence and Rasch, JAS, 2005)

Convective Mass Flux Characterizations

Domain Means Cloudy-Area Means Cloud mass flux (kg/m 2 /s) Cloud mass flux (kg/m 2 /s) -2 -1 0 1 2 3 Cloud mass flux (kg/m 2 /s) -2 -1 0 1 2 3 Cloud mass flux (kg/m 2 /s)

Mark G. Lawrence, Max Planck Institute for Chemistry

(Salzmann, 2005)

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 HNO 3 • 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

Ice H x in M/atm: H x H x H x H x H x = 0 = 10 3 = 10 = 10 = 10 4 5 6 Mark G. Lawrence, Max Planck Institute for Chemistry

(Crutzen and Lawrence, J. Atmos. Chem., 2000)

TTL Workshop, Victoria, Canada, 14 June 2006

Influence of Precipitation Scavenging

Ice H x in M/atm: H x H x H x H x H x = 0 = 10 3 = 10 = 10 = 10 4 5 6 Mark G. Lawrence, Max Planck Institute for Chemistry

(Crutzen and Lawrence, J. Atmos. Chem., 2000)

TTL Workshop, Victoria, Canada, 14 June 2006

Influence of Precipitation Scavenging: Role of Uptake of HNO

3

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 HNO 3 itself, especially role for cloud microphys., e.g.,  -ice (Gao et al., Science, 2004) Further laboratory and field work needed!

Mark G. Lawrence, Max Planck Institute for Chemistry

(von Kuhlmann and Lawrence, ACP, 2006)

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 HNO 3 • 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

20 Sept., 1999 21 Sept., 1999

Mark G. Lawrence, Max Planck Institute for Chemistry

(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)

TTL Workshop, Victoria, Canada, 14 June 2006

ACCENT TTL Chemistry Observations

Wide variety of gases and aerosol components observed, large spatial variability

Mark G. Lawrence, Max Planck Institute for Chemistry

(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)

TTL Workshop, Victoria, Canada, 14 June 2006

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

(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)

TTL Workshop, Victoria, Canada, 14 June 2006

ACCENT TTL Chemistry Observations

• Particularly informative: correlations with O 3 • Correlations found with tracers with wide range of lifetimes (in this figure: 10 -2 , 10 -1 , 10, 10 2 and 10 3 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

(Tuck et al., JGR, 2004; Ridley et al., Atmos. Env., 2004)

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., O 3 NO x ~ 1 week, etc.), transport processes are critical, especially – Deep convection ~ 1 year, – 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 O

3

Simulations

Mark G. Lawrence, Max Planck Institute for Chemistry

• • • Consistent simulation from surface to 0.01 hPa No upper boundary near the TTL, full tropospheric (NMHC) chemistry Submitted manuscript: J öckel et al.,The atmospheric chemistry general circulation model ECHAM5/MESSy1: Consistent simulation of ozone from the surface to the mesosphere, submitted to ACPD. 2006.

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”

Mark G. Lawrence, Max Planck Institute for Chemistry TTL Workshop, Victoria, Canada, 14 June 2006