Max Frioud

Aerosols in polar regions: A historical overview based on optical depth and in situ observations

Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and ...

Variation of the aerosol stratification over the Rhine Valley during Foehn development: a backscatter lidar study

The vertical aerosol stratification within and above the Rhine Valley was studied with a backscatter lidar during FORM (Foehn in the Rhine Valley during MAP) IOPs 4-5, October 1-3, 1999. The lidar site was in Trubbach, 9° 28 E, 47° 04 N, 490 m asl. Two scintillometers were used to monitor the horizontal and the vertical wind velocity at 600 m above the Rhine Valley floor. A number of surface stations were operational in the valley, as well as a set of radiosounding stations. This provides a possibility to correlate the measurements of the aerosol stratification with the variation of the meteorological parameters defining the Foehn development. The backscatter lidar measurements during the Foehn development show the variation of the aerosol backscatter at different altitudes of the valley PBL. The combination of lidar signal gradient and lidar signal variance presents the cold-pool as an aerosol-rich layer and suggests a likely mechanism for cold-pool erosion by the Foehn air.

Backscatter lidar observation of the aerosol stratification in the lower troposphere during winter Bise : A case study

This work presents observations of the aerosol mixed layer in the planetary boundary layer and aerosol layers inthe lower troposphere during acaseof winter Bisewind. The Bisewindevent occurred from December 5till December 18, 2001. The observations were performed above Neuchâtel, Switzerland, 47.00 ◦ N, 6.95 ◦ E, 488 m asl, using a ground-based backscatter lidar, operating at a wavelength of 532 nm. The height of the aerosol mixed layer was found to extend up to 0.6–0.8 km agl. Another aerosol layer centred around 1.5 km and 2.5 km agl was also observed. The combination of the lidar-observed profiles with radiosonde measurements from Payerne station shows a coincidence of the altitudes of the observed aerosol layers with the altitudes of the Bise wind layer. Back trajectories were used to trace the incoming Bise air masses showing a likely origin from North America. Zusammenfassung Diese Studie prasentiert Beobachtungen von Aerosolen in der planetaren Grenzschicht und in der freien Troposphare wahrend Bise-Bedingungen. Das diskutierte Bise-Ereignis fand in der Periode vom 5.–18. Dezember 2001 statt. Die Aerosol-Beobachtungen wurden mit einem bodengestutzten Ruckstreulidar bei einer Wellenlange von 532 nm in Neuchâtel, Schweiz (47,00 ◦ N, 6,95 ◦ E, 488 m uber NN), gemacht. Die Hohe der Mischungsschicht, abgeleitet aus den Aerosolbeobachtungen, betrug etwa 0,6–0,8 km uber NN. Eine weitere Aerosolschicht wurde zwischen 1,5 und 2,5 km uber Grund beobachtet. Der Vergleich der LidarProfile mit Radiosondenmessungen aus Payerne belegt, dass die Hohe der Aerosolschichten mit der Hohe der Bise-Winde ubereinstimmt. Ruckwartstrajektorien zeigen, dass die Aerosole in den Bise-Luftmassen ihren Ursprung vermutlich in Nordamerika gehabt haben.

Comparison of lidar methods to determine the aerosol mixed layer top

Backscatter lidar measurements were performed in the atmospheric boundary layer and the troposphere above Neuchatel, Switzerland (47.00°N, 6.95°S, 485m asl). The backscatter lidar is based on Nd:YAG laser. The lidar measurements are done in the period from June 2000 till February 2002 as part of the EU project EARLINET (http://lidarb.dkrz.de/earlinet/). From the lidar measurements, we determine the following values vertical profile of the aerosol backscatter coefficients, the gradient of the range-corrected lidar signal and the variance of the range-corrected lidar signal. These values are used to determine the aerosol mixed layer (AML) height in the atmospheric boundary layer (ABL). In this work, we present a comparison of these different lidar methods to determine the AML height. The lidar-obtained values are also compared with the values for ABL top, as determined from upper air weather parameters. This comparison is performed and presented for various seasons and time in the diurnal cycle.

Observation and characterization of aerosols above ALOMAR (69 degrees N) by tropospheric lidar, sun-photometer, and VHF radar

At ALOMAR (Arctic Lidar Observatory of Middle Atmosphere Research, 69°N, 16°E) an exemplary co-location of tropospheric Lidar, sun-photometer and VHF Radar is used for aerosol investigations. Recently the University of Oslo, the Norwegian Institute for Air Research and the Andøya Rocket Range started to operate a new troposphere Lidar system. The system uses two elastic backscatter channels (1064nm, 355 nm), two polarization channels (532p nm and 532s nm) and a Raman channel (387nm). The co-located sun photometer is of Cimel type and the VHF Radar is operating at 53 MHz. The data from the Cimel instrument are collected in cooperation with a group from Valladolid (Spain) and the Radar is operated by the Institute for Atmospheric Physics from Kühlungsborn. The location of ALOMAR, north of the Arctic Circle and on an island, a few hundred meters from seashore and about 30 km off the continent, makes it ideal for investigations related to Sub-Arctic aerosols. The present paper presents the first results from simultaneous and collocated tropospheric measurements. We compare aerosol stratification derived from Lidar data with simultaneous measurements of total aerosol content, derived from Cimel data in dependence of simultaneous winds, stratified layers and echo power from radar data. Diurnal cycles for both summertime and wintertime are shown.

Determination of the critical system and data processing parameters for Raman-DIAL O3 and H2O measurements: numerical simulation

For the purpose of low tropospheric ozone and water vapor lidar measurements, a recent method, avoiding the high sensitivity to the inhomogeneous aerosols of the elastic DIAL, is offered by the Raman shifts of a single pump beam in the UV. In this work, we investigate the sensitivity of the method to both atmospheric and device perturbations by numerical simulation. The following effects have been modelled: inhomogeneous aerosol load, statistical error, deterioration due to cross-talk between the N2 & O2 Raman-shifted channels, deterioration due to intrusion of the elastically backscattered signal in the Raman-shifted signals, after-pulse noise.