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 Cain Supervisors: John Methven & Ellie Highwood

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

B219 25 July A A B 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 Dropsonde quick looks from Doug Parker’s website. B219A day B219B night ~5m/s northward at ~950mb

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

B233 observed winds Meridional wind data coloured by time. Dry NE flow ~900mb Monsoon layer SW flow below ~950mb

5N 17N 575 hPa 700 hPa 950hPa RDF back trajectories

B233 back trajectories Trajectories are 3.5 days long.

B233 back trajectories Trajectories are 5.5 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 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

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

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

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

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

B231 13 Aug biomass plumes Flight track coloured by CO 3 2 1 Flight track coloured by time

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

B228 elevated biomass plume Coloured by CO. Elevated plume Niamey Ocean Cotonou

B228 back trajs from plume

Following air masses through the WAM & implications for chemical processing