LIDAR and 2010 Volcanic dust - Last Update: 20 May 2010

by Massimo Del Guasta - INO CNR

On 20 march, 2010 a new eruption of the volcan Eyjafjallajökull (Island) occurred, after 87 years of inactivity. On 14 April explosive activity begun, producing a plume reaching 8000 m of altitude. The ash plume rapidly reached continental Europe in the next days. The plume was soon detected by means of LIDARs in several European countries (Switzerland, France, Germany, Romania, etc.).

On 19 April the plume was first detected in Italy by means of LIDAR at IFAC CNR and by means of in-situ instrument at ISAC-CNR Mount Cimone station.

For an overview of volcanic ash related problems click here (Wikipedia)

First detection of the volcanic layer: 19 April 2010

In HYSPLIT the origin of airmasses at 2000-4000 m is shown for 19 April, 12 UTC

In this MODIS NAAPS animation,. the (yellow-green) dust plume is shown for 19 April 2010

As shown in this snapshot of the depolarization plot produced by the INO acquisition software, the plume resulted very weak and was evidenced at 2000-3000 m altitude just because of its characteristic depolarization (<10%). The day was quite cloudy and thus the number of valid data above 1000 m altitude was limited. The cloud was above the PBL and its vertical structure resulted quite irregular. In the afternoon, a strong convective activity occurred, resulting into an upward shift of the cloud and its vertical spreading.

At sunset, the presence of volcanic dust was visible at the naked eye because of its charcteristic, reddish blur:

Galliano di Mugello (Florence, Italy), sunset, 19 April 2010

Volcanic dust : 19-20 April 2010

HYSPLIT trajectory analysis for 20 April, 00 UTC:

NAAPS MODIS aerosol concentrations for April 20

In this plot we summarize the raw LIDAR data from 19 and 20 April,2010. The (weak) dust layer is evidenced by a moderate (<10%) total depolarization (dotted lines). The layer is almost invisible in the parallel LIDAR signal. The layer "seated" above the local mixed layer (ML) and resulted relatively uniform with altitude, probably a sign of presence of well mixed, aged aerosols. The contrast between the ML depolarization and the volcanic depolarization is explained by the fact that, in this particular conditions, ML air is less "dusty" than the free troposphere. In the ML, in fact, the parallel signal at 13 UTC was higher than in the overlying cloud (beta p showed a marked downward step in corrispondence with the ML top), but the perpendicular signal is less different.The top of the ML thus marked the base of the volcanic-dust layer . The presence of low clouds from time to time prevented the continuous observation of the volcanic cloud. Because of the very low optical tickness of the volcanic cloud, its presence could not be evidenced by means of other remote sensing techniques

... and a final INO picture of the period 18-22 April 2010! Several PBL structures above Florence are also evidenced

Volcanic dust at INO: 18-20 May 2010

On 18 May 2010 in the evening we started observing a depolarizing structure between 3000 and 4000 m altitude. The weak structure differentiated into several layers between 1000 and 4500 m on May 19, each showing different depolarization. On May, 20 the event decreased in intensity in the morning, but a mixing of volcanic dust with PBL aerosols was apparently occurring in the late morning.
In the plot, several hours show low clouds/rain which prevented a good observation of the cloud. Steps in the raw signal are just due to changes of laser power with time.

A QUESTION FOR TURBINE EXPERTS

As I'm ignorant but curious, I collected from the web the melting temperatures of various compounds which could be present in the Atmosphere as suspended dust.

-In some cases "melting temperature " must be intended as "transformation temperature".
-I cannot exclude some errors (please tell me!).

Compared with the range of temperatures found in a jet engine, many innocent substances such as sea salt or wood ash could melt in the jet turbine, even at tlow temperatures.
My question is: is volcanic ash the only "evil boy?"

Massimo Del Guasta - National Institute of Optics (INO) - National Research Council | Via Madonna del Piano, 10 - 50019 Sesto Fiorentino - Firenze, Italy | Tel (office): +39-055-5226423 - Tel (laboratory) +39-055-5226424 | Email: Massimo Del Guasta | Web: www.ino.it | sito ottimizzato per una risoluzione minima di 1024x768 e firefox