Following air masses through the WAM & implications for chemical processing Africa Group meeting 24 September 2007 Michelle Cain Supervisors: John Methven & Ellie Highwood

Outline Nocturnal transport: observations & modelling plans Biomass burning plumes: observations & back trajectories

B July A B A B 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 Parkers website.

B 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

5N17N 950hPa 700 hPa 575 hPa RDF back trajectories

B233 back trajectories Trajectories are 3.5 days long.

B233 back trajectories Trajectories are 5.5 days long.

B233 back trajectories Trajectories are 5.5 days long.

B Aug Post MCS Flight track coloured by timeFlight track coloured by CO

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, From ECMWF model Section averaged over 2.5W-7.5E Colours are humidity 00z 28 August z 28 August 2000

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

No diurnal cycle: steady meridional wind, steady zonally averaged zonal wind ocean: moistureforest: O3 deposition, low NOx, VOC source bare soil: low O3 deposition, NOx source ~12N~6N~20N O3VOCsNOx ~700 hPa >900 hPa AEJ X Modelling nocturnal flow

Add / vary different parameters e.g. emissions, deposition ocean: moistureforest: vary the O3 deposition & VOC source bare soil: vary the NOx source ~12N~6N~20N O3 VOCsNOx AEJ X Modelling nocturnal flow

Add a diurnal cycle: diurnally changing meridional & zonal wind, changing boundary layer, convection ocean: moistureforest: O3 deposition, low NOx, VOC source bare soil: low O3 deposition, NOx source ~12N~6N~20N O3 VOCsNOx AEJ X Modelling nocturnal flow

Add a city plume / a biomass plume ocean: moisture ~12N~6N~20N City? Biomass? O3 VOCsNOx AEJ X Modelling nocturnal flow forest: O3 deposition, low NOx, VOC source bare soil: low O3 deposition, NOx source

B Aug biomass plumes Flight track coloured by CO Flight track coloured by time

B231 back trajs from plumes Plume 1Plume 2 Plume 3 5 day back trajectories from plumes seen in flight.

B231 back trajs from plumes Plume 1Plume 2 Plume 3 10 day back trajectories from plumes seen in flight.

B231 back trajs from plumes Plume 1Plume 2 Plume 3 15 day back trajectories from plumes seen in flight.

B231 back trajs from plumes Plume 1Plume 2 Plume 3 20 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