Following air masses through the WAM & implications for chemical processing

Following air masses through the WAM & implications for chemical processing

Africa Group meeting 24 September 2007

Michelle CainSupervisors: John Methven & Ellie Highwood

Outline

Nocturnal transport: observations & modelling plans

Biomass burning plumes: observations & back trajectories

B219 25 July

A

B

AB

Benin double header

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.

B219 meridional wind

~5m/s northward at ~950mb

B219A day

B219B night

Dropsonde quick looks from Doug Parker’s website.

B233 15 Aug (dawn)

Plan view of flight track coloured by time.

Horizontal section at 600hPa showing change in longitude over the previous 2 days.

AEJ

Post MCS / intercomparison

B233 observed winds

Monsoon layer SW flow below ~950mb

Dry NE flow

Meridional wind data coloured by time.

~900mb

5N 17N

950hPa

700 hPa

575 hPa

RDF back trajectories

B233 back trajectories

Trajectories are 3.5 days long.





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.

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.

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

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)

Meridional winds

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

00z 28 August 2000 06z 28 August 2000

No diurnal cycle: steady meridional wind, steady zonally averaged zonal wind

ocean: moisture forest: O3 deposition, low NOx, VOC source

bare soil: low O3 deposition, NOx source

~12N~6N ~20N

O3 VOCs NOx

~700 hPa

>900 hPa

AEJ X

Modelling nocturnal flow

Add / vary different parameters e.g. emissions, deposition

ocean: moisture forest: vary the O3 deposition & VOC source

bare soil: vary the NOx source

~12N~6N ~20N

O3 VOCs NOx

AEJ X


Add a diurnal cycle: diurnally changing meridional & zonal wind, changing boundary layer, convection

ocean: moisture forest: O3 deposition, low NOx, VOC source


~12N~6N ~20N

O3 VOCs NOx

AEJ X


Add a city plume / a biomass plume

ocean: moisture

~12N~6N ~20N

City?

Biomass?

O3 VOCs NOx

AEJ X


forest: O3 deposition, low NOx, VOC source


B231 13 Aug biomass plumes

3

21

Flight track coloured by CO

Flight track coloured by time

B231 back trajs from plumes

Plume 1 Plume 2 Plume 3

5 day back trajectories from plumes seen in flight.










B228 elevated biomass plume

Coloured by CO.

Cotonou Niamey

Elevated plume

Ocean

B228 back trajs from plume




Documents

Following air masses through the WAM & implications for chemical processing