Saharan dust episode in June 2012

On 28th June 2012 airborne Saharan dust was observed at the Bayfordbury Observatory.

In the early morning, rain washed some of the dust out of the atmosphere over a wide area in southern England, depositing highly visible yellow-brown layers on windows and cars.

dust 2012 lidar

Later that day the dust was sensed remotely at Bayfordbury. The image above shows the vertical cross-section of the atmosphere (lidar return as "Range Corrected Signal") up to an altitude of 5km, as measured by the lidar, with the dust layer clearly visible below 4km, descending down to 2km in the evening, and eventually disappearing by mixing into the boundary layer (the red spots between 1 and 1.5km casting upwards "shadows" are cumulus clouds). Shown below is the size distribution of the dust retrieved from the sun photometer measurements.

dust 2012 aeronet2

Backtrajectory analysis using the HYSPLIT model indicates that the dust originated in the Sahara desert about six days earlier, around the 22nd of June - see below.

dust 2012 backtrajectory

Remarkable is the large mean size of the dust particles as retrieved by the photometer - around 12 µm diameter. This suggests that the dust may have been processed by clouds, leading to aggregation, as the same dust layer was apparently observed over Tenerife, Canary Islands, on 24/25th of June and it had a more typical 4 µm mean particle size, as shown below.

dust 2012 aeronet1

To find out more about this research, please contact the Light Scattering and Radiative Processes group.