Renaud Matthey

Optical classification, existence temperatures, and coexistence of different polar stratospheric cloud types

Multispectral lidar measurements of polar stratospheric clouds (PSCs) from two winter campaigns in 1994/1995 and 19961997 at Sodankyla, Finland, have been evaluated together with temperature data from local radiosondes to find optical parameters for a PSC classification of different particle types and their existence temperatures. Precise depolarization measurements show that both solid and liquid particles exist below the NAT (nitric acid trihydrate) temperature. A comparison of temperatures at the PSC base and at the cloud top shows a good agreement with the NAT-existence temperature for solid type Ia clouds and a 3–4 K lower temperature for liquid type Ib clouds. The two particle families are therefore consistent with solid NAT particle formation and condensational growth of HNO3, H2O and H2SO4 liquid ternary solutions. The coexistence of solid and liquid particles has been observed by means of the temporal development of parallel and perpendicular polarized lidar signals. These time series of subsequent lidar measurements show stronger and faster fluctuations in the liquid particle mode compared to the solid particles and thus indicate a higher sensitivity toward temperature fluctuations for the liquid PSCs. While the optical properties of most observations are consistent with the definition of PSC type Ia (solid) and type Ib (liquid) clouds, a third type has been observed which does not fit into the current type Ia/Ib optical classification. This cloud type consists of solid particles but has a higher backscatter than type Ia PSC.

Multiwavelength lidar observation of thin cirrus at the base of the Pinatubo stratospheric layer during the EASOE Campaign

Multiwavelength lidar measurements carried out in Sodankyla (Finland, 66°N) during EASOE campaign showed high cirrus clouds growing at the base or within Pinatubo aerosol layer. The temperature was generally below −35°C. The mean peak depolarization at 532 nm for all the campaign was 28%, comparable to the values measured in polar cirrus clouds, observed in Dumont dUrville (Antarctica, 62°S) during 1989, well before the Pinatubo eruption. Optical depth at 532 nm was smaller than 0.3 (thin cirrus). A wavelength dependency was observed in EASOE cirrus backscattering, suggesting a major presence of submicron and micron-sized particles. Such a presence could explain the low depolarization values.

Backscatter-depolarisation lidars on high-altitude research aircraft

This article presents an overview of the development and the applications of two compact elastic backscatter depolarisation lidars, installed on-board the high-altitude research aircraft Myasishchev M-55 Geophysica. The installation of the lidars is intended for simultaneous probing of air parcels respectively upward and downward from the aircraft flight altitude to identify the presence of clouds (or aerosol )above and below the aircraft and to collocate them with in situ instruments. The lidar configuration and the procedure for its on-ground validation is outlined. Example of airborne measurements include polar stratospheric clouds, both synoptical and in lee-waves, ultra-thin cirrus clouds around the tropical tropopause and observation of aerosol layers emerging from the top of deep tropical convection.

Trajectory studies of polar stratospheric cloud lidar observations at Sodankylä (Finland) during SESAME : Comparison with box model results of particle evolution

Polar stratospheric clouds (PSC) were observed with the multi-wavelength lidar of the MOANA project (Modelling and Observations of Aerosols in the Northern Atmosphere) during SESAME (Second European Stratospheric Arctic and Mid-latitude Experiment). The physical state, liquid or solid, of the cloud particles can be inferred from the lidar data. Using isentropic back-trajectories to obtain the thermal history of the sampled air masses, it is possible to reconcile most of the observations with current ideas on PSC formation and evolution. When the cloud particles were identified as liquid, changes in the size distribution of the droplets along the trajectory were calculated using a micro-physical box model. Backscatter ratios calculated from the size distributions are in broad agreement with the lidar data, giving confidence in current understanding of the evolution of ternary solution (H2SO4, HNO3 and H2O) droplets.Results from two soundings are shown which bear on the problem of the formation of solid particles. In the first, solid particles were detected. The air mass had cooled to the frost point 12 hours earlier. In the second no solid particles were detected although the air temperature was below the nitric acid trihydrate existence point, and had decreased by 12K in the previous 14 hours.

Polar Stratospheric Cloud Measurements by Multispectral Lidar at Sodankyla in Winter 1994/95

Lidar measurements at 4 wavelengths and two polarizations were performed during the SESAME campaign in Sodankyla, Finland (67.37N, 26.65E). Using the wavelength dependence of the particle scattering the aerosol size distribution and the refractive index of the PSC particles were retrieved. A liquid PSC with a refractive index of 1.36 could be observed. We assume that this PSC consists of ternary solution particles in contradiction to the NAT-hypothesis.

Depolarization-backscatter lidar for stratospheric studies

The depolarization-backscatter lidar reported here is developed for application in the polar stratospheric and high- tropospheric studies. That includes the following operations: detection of the stratospheric background aerosol, detection of high-altitude cirrus clouds and polar stratospheric clouds (PSC), detection of Rayleigh backscatter signal for subsequent stratospheric temperature retrieval algorithm application. The lidar is stationed in Sodankyla, Finland (67N) and intended for a 2-year operation at that site. It operates with one Nd:YAG laser with second and third harmonics conversion. The detection of the backscatter atmospheric signal is performed at the fundamental, second and the third harmonics of the laser (1 micrometer, 532 nm and 355 nm), as well as the vibrational Raman backscatter from the nitrogen pumped by the third harmonic at 387 nm. The backscatter signal at 532 nm is detected separately in (p) and (s) polarization.

Surface detection performance evaluation of pseudo-random noise continuous wave laser radar

A number of space missions (including in the ESA Exploration Programme) foreseen a use of laser radar sensor (or lidar) for determination of range between spacecrafts or between spacecraft and ground surface (altimetry). Such sensors need to be compact, robust and power efficient, at the same time with high detection performance. These requirements can be achieved with a Pseudo-Random Noise continuous wave lidar (PRN cw lidar). Previous studies have pointed to the advantages of this lidar with respect to space missions, but they also identified its limitations in high optical background. The progress of the lasers and the detectors in the near IR spectral range requires a re-evaluation of the PRN cw lidar potential. Here we address the performances of this lidar for surface detection (altimetry) in planetary missions. The evaluation is based on the following system configuration: (i) A cw fiber amplifier as lidar transmitter. The seeding laser exhibits a single-frequency spectral line, with subsequent amplitude modulation. The fiber amplifier allows high output power level, keeping the spectral characteristics and the modulation of the seeding light input. (ii) An avalanche photodiode in photon counting detection; (iii) Measurement scenarios representative for Earth, Mercury and Mars.

Compact micropulse backscatter lidar: airborne and ground-based applications

This is an overview of the development and the applications of compact elastic backscatter depolarisation lidars. Two of such sensors are installed on-board the high-altitude research aircraft Myasishchev M-55 Geophysica. The installation of the lidars is intended for simultaneous probing of air parcels respectively upward and downward from the aircraft flight altitude to identify the presence of clouds (or aerosol )above and below the aircraft and to collocate them with in situ instruments. The lidar configuration and the procedure for its on-ground validation is outlined. Example of airborne measurements include polar stratospheric clouds, both synoptic and in lee-waves, ultra-thin cirrus clouds around the tropical tropopause and observation of aerosol layers emerging from the top of deep tropical convection. One unit is realized for groundbased application and is extensively used in campaigns and routine measurements of the MLH variation and aerosol backscatter in the lower troposphere.

Backscatter lidar observation of the aerosol stratification over Rhine Valley during a heat wave in September 1999

A backscatter lidar study of the aerosol stratification in PBL over the Rhine valley is presented in this work. The observations have been made from 6 till 14 September 1999 in the Special Observation Period of the Mesoscale Alpine Program at the site of Trubbach, Switzerland [47°04 N, 9°28 E, 490 m above sea level (asl)]. The lidar was operated alongside with a wind-temperature radar, a set of surface meteorological stations and radiosonde observations. The atmospheric conditions for the presented measurements are especially favorable for development of convective PBL. A daily series of range-corrected lidar signal and its gradient are given, showing the diurnal cycle of aerosol layers development in the PBL and lower troposphere over the valley. Averaged altitude distributions of the aerosol backscatter coefficient and the lidar signal gradient are presented and discussed. The results show that the aerosol distribution below the surrounding mountain peaks (approximately 2200 - 2400 m asl) have the diurnal pattern as following from the thermal wind cycle and the temperature inversions in the valley and is characterized by a highly dynamic aerosol stratification. Above this level, we observe a diurnally less variable stratification till altitudes of the highest Alpine peaks (approximately 4500 - 5000 m asl).

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.