WINTEX: Land-surface-atmosphere interactions in a wintertime boreal landscape

• Research unit: EU RFP
• Project number: 95.0511-1

Key words (English)

Elastic aerosol lidar; polarised lidar; planetary boundary layer; boreal atmospheric conditions

Alternative project number (English)

EU project number: ENV4-CT96-0324

Research programs (English)

EU-programme: 4. Frame Research Programme - 3.1 Environment

Short description (English)

See abstract

Partners and International Organizations (English)

VUA Amsterdam (NL), FMI Helsinki (FIN), DESUA Mytilene (GR), RISOE Roskilde (DK), SLU Uppsala (S), WAU Wageningen (NL), ETHZ Zurich (CH)

Abstract (English)

The largest influence of climatic change is expected at high latitudes and during winter conditions, that is for meteorological conditions for which the planetary boundary layer (PBL) is extremely low or even non-existent in some cases. The climatic change is linked to the land-surface-atmosphere exchange. This WINTEX pilot study aimed at developing a remote sensing technique able to follow the top of the PBL daily evolution in very cold and clean boreal conditions.
Elastic backscatter lidar is known to be a very efficient and rather standard technique for the remote sensing of aerosol in the Planetary Boundary Layer (PBL), in particular for regions and meteorological conditions for which high load of particulate matters are present in the air and essentially trapped into the PBL. Moreover, the top of the PBL is very often associated with a change in the temperature gradient versus altitude and the formation of an inversion layer. The aerosols are condensed at this height and their presence induces a very clear 'signature' on the lidar signal showing the top of the PBL.
For this issue, the performances of the EPFL lidar (light detection and ranging) prototype were adapted to an elastic backscatter lidar operated at 355 nm and 532 nm, thus allowing to extract the corresponding logarithmic derivative of the range coarrected lidar signal, a parameter giving access to the vertical gradients in aerosol backscatter as a clear tracer of the top of the mixed layer.
Furthermore, at 355 nm, both polarizations, parallel and perpendicular to the polarisation of the emitted beam, were measured. As the depolarization ratio depends strongly on the type of particles (spherical vs. non-spherical particles), this measure provided a clear mean to distinguish ice crystals particles from droplets like particles in the PBL.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 95.0511-1