Following air masses through the WAM

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Following air masses through the WAM
implications for chemical processing

• Africa Group meeting 24 September 2007
• Michelle Cain
• Supervisors John Methven Ellie Highwood

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Outline

• Nocturnal transport observations modelling
  plans
• Biomass burning plumes observations back
  trajectories

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B219 25 July
A
A
B
B
Benin double header
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B219 nocturnal advection

• On the return leg at night biogenic species were
  observed, transiently, north of the wooded
  region, suggesting nocturnal advection (in
  contrast to the absence of significant advection
  during the day). - From B233 mission
  report.

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B219 meridional wind
Dropsonde quick looks from Doug Parkers website.
B219A day
B219B night
5m/s northward at 950mb
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B233 15 Aug (dawn)
AEJ
Horizontal section at 600hPa showing change in
longitude over the previous 2 days.
Plan view of flight track coloured by time.
Post MCS / intercomparison
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B233 observed winds
Meridional wind data coloured by time.
Dry NE flow
900mb
Monsoon layer SW flow below 950mb
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5N
17N
575 hPa
700 hPa
950hPa
RDF back trajectories
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B233 back trajectories
Trajectories are 3.5 days long.
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B233 back trajectories
Trajectories are 5.5 days long.
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B233 back trajectories
Trajectories are 5.5 days long.
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B233 15 Aug Post MCS
Flight track coloured by time
Flight track coloured by CO
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Nocturnal flow
Bare soil NOx emissions. Is this a significant
source of ozone? Forest Very little ozone
observed. Biogenics emissions. Cooler.
Nocturnal transport
Image from Chris Taylor.
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Nocturnal flow
Nocturnal flow can transport biogenics from a
vegetated region to a region of bare
soil. Photochemistry (e.g. ozone production)
will then occur at dawn.
Nocturnal transport
Image from Chris Taylor.
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Nocturnal flow questions

• How far north are biogenic VOCs transported?
• Do VOCs come into contact with soil NOx and
  produce ozone?
• How does the transport history affect the
  production?
• What other factors affect the production? e.g.
  temperature, concentration and ratio of VOCs /
  NOx

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Modelling nocturnal flow

• Two dimensional meridional section
• Prescribed winds (meridional and zonal)
• Run CiTTyCAT along a trajectory defined by the
  nocturnal flow to model the chemistry(Cambridge
  Tropospheric Trajectory model of Chemistry and
  Transport)

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Meridional winds
00z 28 August 2000
06z 28 August 2000

• Figure from Parker et al (2005). The diurnal
  cycle of the West African monsoon circulation. Q.
  J. R. Meteorol. Soc. 131, 2839-2860
• From ECMWF model
• Section averaged over 2.5W-7.5E
• Colours are humidity

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Modelling nocturnal flow

• Start with a simple setup (no diurnal cycle,
  steady winds)
• Add complexity
• Vary the deposition over different surfaces
• Vary the NOx / VOC sources
• Diurnal cycle e.g. BL, convective clouds, winds
• City
• Biomass burning plume

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No diurnal cycle steady meridional wind, steady
zonally averaged zonal wind
Modelling nocturnal flow
700 hPa
AEJ X
O3
VOCs
NOx
gt900 hPa
ocean moisture
forest O3 deposition, low NOx, VOC source
bare soil low O3 deposition, NOx source
12N
6N
20N
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Add / vary different parameters e.g. emissions,
deposition
Modelling nocturnal flow
AEJ X
O3
VOCs
NOx
ocean moisture
forest vary the O3 deposition VOC source
bare soil vary the NOx source
12N
6N
20N
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Add a diurnal cycle diurnally changing
meridional zonal wind, changing boundary layer,
convection
Modelling nocturnal flow
AEJ X
O3
VOCs
NOx
ocean moisture
forest O3 deposition, low NOx, VOC source
bare soil low O3 deposition, NOx source
12N
6N
20N
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Add a city plume / a biomass plume
Modelling nocturnal flow
AEJ X
Biomass?
O3
VOCs
NOx
City?
ocean moisture
forest O3 deposition, low NOx, VOC source
bare soil low O3 deposition, NOx source
12N
6N
20N
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B231 13 Aug biomass plumes
Flight track coloured by CO
3
2
1
Flight track coloured by time
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B231 back trajs from plumes
Plume 3
Plume 1
Plume 2
5 day back trajectories from plumes seen in
flight.
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B231 back trajs from plumes
Plume 3
Plume 1
Plume 2
10 day back trajectories from plumes seen in
flight.
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B231 back trajs from plumes
Plume 3
Plume 1
Plume 2
15 day back trajectories from plumes seen in
flight.
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B231 back trajs from plumes
Plume 3
Plume 1
Plume 2
20 day back trajectories from plumes seen in
flight.
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B228 elevated biomass plume
Coloured by CO.
Elevated plume
Niamey
Cotonou
Ocean
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B228 back trajs from plume
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B228 back trajs from plume
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B228 back trajs from plume
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B228 back trajs from plume
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