University weather balloon measures volcanic plume

As another plume is due to sweep across the UK in the next few days, researchers are using a newly-developed weather balloon to feed back important information to the Met Office about the make-up of the volcanic ash.

This is the first time that direct measurements of the plume over Scotland have been available.

The measurement technique being used was originally developed to study the properties of Saharan dust clouds for climate models, but has turned out to be ideally suited to measuring a volcanic cloud.

The instrument measures the particle size and concentration using a miniature laser system carried by the balloon. It was specifically designed to take electric charge measurements too, which, as television images of volcanic lightning show, can be an important property of volcanic plumes. The weather balloon technique provides detailed information on the ash plume position, extent and structure.

As well as the particle size and concentration data, the balloon system also reports its position using GPS.

Prof Giles Harrison, Professor of Atmospheric Physics in the Department of Mereorology, and Keri Nicoll, whose PhD project included developing the charge sensor, set up a ground station at Stranraer under the dust cloud.

The RAF helicopter scrambled at the weekend to transport the scientists and equipment to fly to Scotland at low level under the ash plume had to be grounded, forcing a long journey through the night by road.

Professor Harrison said: "To get good measurements of the ash we needed to be both under the ash plume, but in cloud free air. Fortunately the Met Office predictions for an ideal observation window at a site near Stranraer were bang on, allowing us to launch our balloon to pass directly through the volcanic plume.

"Despite the beguilingly blue sky at Stranraer, the weather balloon measurements showed a layer of volcanic dust at 4km aloft. The plume was about 500m thick, with very abrupt edges. Most of the particles sampled were around one millionth of a meter in (1 micron) diameter."

The results will also provide vital data about haazards to aircraft should there be similar events in the future.