Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling (original) (raw)
Related papers
Journal of Geophysical Research, 2002
Mountain wave induced ice clouds in the stratosphere are known to cause the formation of nitric acid hydrate particles downwind. Understanding the microphysical properties of these solid particles is important because they may contribute to a general background of solid polar stratospheric clouds (PSCs) that is observed but whose origin is not understood. Based on the limited set of observations of PSCs directly attributable to mountain waves, it has not been possible to determine their general microphysical properties. Here we analyze lidar observations from the SOLVE/THESEO 2000 campaign. Between December 1999 and March 2000, seven of the twelve flights of the DC-8 aircraft showed clear signs of mountain wave induced clouds, with nitric acid hydrate clouds often extending many hundreds of kilometers downwind of mountains. On the basis of T-matrix calculations, we have developed a technique to estimate the microphysical properties of spherical and nonspherical particles from multiwavelength backscatter and depolarization data from the Goddard Space Flight Center/Langley Research Center (GSFC/LaRC) aerosol lidar. The technique allows particle radius, condensed mass, and number densities of ice, nitric acid trihydrate, and liquid PSCs to be estimated. Ice clouds were found to contain approximately 1-3 ppmv of condensed water with a number density from 1 to 10 cm À3 and a narrow size distribution width with mode radii from 1 to 1.5 mm. Nitric acid hydrate particles downwind of the ice clouds were consistent with 1-5 ppbv condensed HNO 3 , a number density from 0.5 to 2 cm À3 , and mode radius around 0.5 mm. These hydrate clouds are characterized by high aerosol backscatter and depolarization and are distinct from type 1a clouds that are observed away from mountains, which have low aerosol backscatter.
Journal of Geophysical Research, 2009
A case study of a polar stratospheric cloud (PSC) is described using multiwavelength (355, 532, and 1064 nm) lidar measurements performed at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) on 6 December 2005. Rotational Raman signals at 529 and 530 nm are used to derive a temperature field within the cloud using the rotational Raman technique (RRT). The PSC size distributions are retrieved between 1500 and 2000 UTC through a combination of statistical filtering and best match approaches. Several PSC types were detected between 22 and 26 km during the measurement session. Liquid ternary aerosols are identified before about 1600 and after 1900 UTC typically; their averaged retrieved size distribution parameters and associated errors at the backscatter peak are: N o % 1-10 cm À3 (50%), r m % 0.15 mm (20%), and s % 1.2 (15%). A mode of much larger particles is detected between 1600 and 1900 UTC (N o % 0.04 cm À3 (30%), r m % 1.50 mm (15%), and s % 1.37 (10%). The different PSC types are also identified using standard semiempirical classifications, based on lidar backscatter, temperature, and depolarization. Overall, the characteristics of the retrieved size distributions are consistent with these classifications. They all suggest that these very large particles are certainly nitric acid trihydrate that could have been generated by the strong gravity wave activity visible in the temperature profiles. The results demonstrate that multiwavelength lidar data coupled to both RRT temperatures and our size distribution retrieval can provide useful additional information for identification of PSC types and for direct comparisons with microphysical model simulations.
Airborne lidar observation of mountain-wave-induced polar stratospheric clouds during EASOE
Geophysical Research Letters, 1994
The airborne backscatter lidar Leandre was flown during the EASOE campaign on board the French ARAT-Fokker 27, to provide mesoscale observations of scattering layers in the stratosphere. The use of crosspolarization channels at the 532 nm laser emitted wavelength, allowed discrimination between the quasi-spherical particles of the Pinatubo aerosol and the non-spherical frozen particles of polar stratospheric clouds. Measurements taken on December 1 lth 1991 revealed mountain-wave-induced polar stratospheric clouds at 21 km altitude, extending over 300 km west and 300 km east from Kimna. The wavelength and amplitude of the perturbation imply local cooling ranging from 3øK to 10øK in the stratosphere, taking the temperature below the threshold of formation of polar stratospheric clouds.
The microphysical properties of wave PSCs retrieved from lidar measurements during SOLVE/THESEO 2000
J. Geophys. …, 2001
Mountain wave-induced ice clouds in the stratosphere are known to cause the formation of nitric acid-hydrate particles downwind. Understanding the microphysical properties of these solid particles is important because they may contribute to a general background of solid PSCs that is observed, but whose origin is not understood. Based on the limited set of observations of PSCs directly attributable to mountain waves, it has not been possible to determine their general microphysical properties. Here we analyze lidar observations from the SOLVE/THESEO-2000 campaign. Between December 1999 and March 2000 seven of the twelve flights of the DC-8 aircraft showed clear signs of mountain wave-induced clouds, with nitric acid hydrate clouds often extending many hundreds of kilometers downwind of mountains. Based on T-matrix calculations, we have developed a technique to estimate the microphysical properties of spherical and non-spherical particles from multi-wavelength backscatter and depolarization data from the GSFC/LaRC Aerosol lidar. The technique allows particle radius, condensed mass, and number densities of ice, nitric acid trihydrate and liquid PSCs to be estimated. Ice clouds were found to contain approximately 1 to 3 ppmv of condensed water with a number density from 1 to 10 cm −3 , and a narrow size distribution width with mode radii from 1 to 1.5 µm. Nitric acid hydrate particles downwind of the ice clouds were consistent with 1 to 5 ppbv condensed HNO 3 , a number density from 0.5 to 2 cm −3 , and mode radius around 0.5 µm. These hydrate clouds are characterised by high aerosol backscatter and depolarization and are distinct from type 1a clouds that are observed away from mountains, which have low aerosol backscatter.
Airborne lidar observations in the wintertime Arctic stratosphere: Ozone
Geophysical Research Letters, 1990
•. Polar stratospheric cloud (PSC) dis-Lidar Measurement Procedures tributions in the wintertime Arctic stratosphere and their optical characteristics were measured The lidar backscatter return from the atmowith a multi-wavelength airborne lidar system as sphere can be calibrated to determine the part of the 1989 Airborne Arctic Stratospheric atmospheric scattering ratio (R T) at a given Expedition. PSCs were observed on 10 flights altitude, where R T is defined as the sum of the between January 6 and February 2, 1989, into the aerosol and molecular backscatter divided by the polar vortex. The PSCs were found in the 14-27 km molecular backscatter (Kent eta!., 1986). The altitude ran•e in regions where the temperatures scattering ratio can also be written as RT=RA+i, were <-195 K. Two types of aerosols with different where R A is the aerosol scattering ratio or optical characteristics (Types la and lb) were aerosol mixing ratio (Collis and Russell, 1976). observed in PSCs thought to be composed of nitric In this paper, the term "scattering ratio" will acid trihydrate. Type la PSCS typically exhibited refer to R T. To determine the scattering ratio low scattering ratios (1.2-1.5) and high aerosol profile, an accurate estimate of the relative depolarizations (30-50%) at 603 nm, while Type lb molecular scattering profile is needed for each PSCs had higher scattering ratios (3-8) and lower location.. On each flight, the lidar da{'a were aerosol alepolarizations (0.5-2.5%). Water ice used to identify a clean region inside the polar PSCs (Type 2) were observed to have high scatter-vortex at an altitude above ~18 km that had ing ratios (>10) and high aerosol alepolarizations sufficient signal-to-noise to obtain an accurate (>10%) at temperatures <-190 K. ratio of the lidar return to the NMC (National Meteorological Center) molecular density at that
Journal of Aerosol Science, 2003
Observations of Polar Stratospheric Clouds (PSCs) were carried out with an airborne lidar on the stratospheric M55 Geophysica aircraft during a ight from Rovaniemi, Finland, on 9 January, 1997. The clouds were observed at the zenith, downwind from the Norwegian Alps: three PSCs, of somewhat di erent characteristics, were detected at heights between 23 and 28 km. In two of the clouds, di erent types of particles seem to coexist: echoes attributable to types I and II PSCs are found in di erent portions of the clouds. The formation of the PSCs is related to an orographic lee-wave, whose development was forecast by a mesoscale dynamical model used to plan the ight path. The largest observed PSC displays a complex structure, that appears to be in uenced by waves of di erent wavelengths. In particular, lidar and in situ data suggest the presence of a wave having a relatively short length (about 18 km) that overlaps on the main lee-wave. The short wavelength oscillation is thought to play a major role in the cloud development, determining the rapid formation and evaporation of particles and therefore the non-stationary character of the PSC.
Annales Geophysicae, 2007
During the international ASTAR experiment (Arctic Study of Aerosols, Clouds and Radiation) carried out from Longyearbyen (Spitsbergen) from 10 May to 11 June 2004, the AWI (Alfred Wegener Institute) Polar 2 aircraft was equipped with a unique combination of remote and in situ instruments. The airborne AMALi lidar provided downward backscatter and Depolarisation ratio profiles at 532 nm wavelength. The in situ instrumental setup comprised a Polar Nephelometer, a Cloud Particle Imager (CPI) as well as a Nevzorov and standard PMS probes to measure cloud particle properties in terms of scattering characteristics, particle morphology and size, and in-cloud partitioning of ice/water content. The objective of the paper is to present the results of a case study related to observations with ice crystals precipitating down to supercooled boundary-layer stratocumulus. The flight pattern was predefined in a way that firstly the AMALi lidar probed the cloud tops to guide the in situ measurements into a particular cloud formation. Three kinds of clouds with different microphysical and optical properties have therefore been quasi-simultaneously observed: (i) water droplets stratiform-layer, (ii) drizzle-drops fallstreak and (iii) precipitating ice-crystals from a cirrus cloud above. The signatures of these clouds are clearly evidenced from the in situ measurements and from the lidar profiles in term of backscatter and Depolarisation ratio. Accordingly, typical lidar ratios, i.e., extinction-to-backscatter ratios, are derived from the measured scattering phase function combined with subsequent particle shapes and size distributions. The backscatter profiles can therefore be retrieved under favourable conditions of low optical density. From these profiles extinction values in different cloud types can be obtained and compared with the direct in situ measurements.
Large mesospheric ice particles at exceptionally high altitudes
Annales Geophysicae, 2009
We here report on the characteristics of exceptionally high Noctilucent clouds (NLC) that were detected with rocket photometers during the ECOMA/MASS campaign at Andøya, Norway 2007. The results from three separate flights are shown and discussed in connection to lidar measurements. Both the lidar measurements and the large difference between various rocket passages through the NLC show that the cloud layer was inhomogeneous on large scales. Two passages showed a particularly high, bright and vertically extended cloud, reaching to approximately 88 km. Long time series of lidar measurements show that NLC this high are very rare, only one NLC measurement out of thousand reaches above 87 km. The NLC is found to consist of three distinct layers. All three were bright enough to allow for particle size retrieval by phase function analysis, even though the lowest layer proved too horizontally inhomogeneous to obtain a trustworthy result. Large particles, corresponding to an effective radius of 50 nm, were observed both in the middle and top of the NLC. The present cloud does not comply with the conventional picture that NLC ice particles nucleate near the temperature minimum and grow to larger sizes as they sediment to lower altitudes. Strong up-welling, likely caused by gravity wave activity, is required to explain its characteristics.
Polar Science, 2011
Solid polar stratospheric cloud (PSC) layers observed by lidar and a balloon-borne optical particle counter (OPC) on 17 December 1995 are reexamined in a comparative analysis framework. The typical radius of solid particles in the observed PSC is determined through the comparative analysis to have been approximately 2.3 mm. A backward trajectory analysis for the air mass in which the solid particles were observed shows that the air mass had experienced temperatures 2e3 K below the frost point of nitric acid tri-hydrate (NAT) during the 4 days preceding the observations. The back-trajectory analysis traces the air mass back to northern Greenland and Ellesmere Island on 16 December, one day before the observations. A microphysical box model is used to investigate possible mechanisms of formation for the observed solid particles. The results of this model suggest that the solid particles formed under mesoscale temperature fluctuations associated with mountain lee wave activity induced by the relatively high terrestrial elevations of northern Greenland and Ellesmere Island.
Aircraft lidar observations of an enhanced type Ia polar stratospheric clouds during APE-POLECAT
Journal of Geophysical Research, 1999
Polar stratospheric clouds (PSCs) which do not fit into the standard type IaJlb scheme were measured by the airborne lidar OLEX (Ozone Lidar Experiment) on board the Deutsches Zentrum fiir Luft-und Raumfhart (DLR) Falcon during the Airborne Polar Experiment and Polar stratospheric clouds, Leewaves, Chemistry Aerosol and Transport (APE-POLECAT) campaign. In contrast, the standard classification is satisfied by almost all observations for four winters at Ny Alesund, Spitsbergen, which is one of the most comprehensive data sets of ground station lidar measurements presently available. The cloud observed by the Falcon south of Spitsbergen on December 31, 1996, was a 400-km long type I cloud with backscatter ratio S = 2.5 and aerosol depolarization 6A = 15%, which is clearly distinct from the Ny Alesund 4 year record. Using a combination of microphysical and optical modeling, we investigate the possible evolution of this cloud assuming either in situ freezing of ternary HNOa/H2SO4/H20 droplets as nitric acid trihydrate, or the formation of the clouds in mountain waves over the east coast of Greenland, as suggested by a mountain wave model. Best agreement with the observations was obtained by assuming mountain-wave-induced cloud formation, which yields nitric acid trihydrate particles with much higher total mass than achieved by assuming synoptic-scale freezing. Our analysis suggests that this rare type of PSC, which we term type Ia-enh, is characterized by nitric acid hydrate particles rather close to thermodynamic equilibrium, while the more common type Ia PSCs appear to contain much less mass than representative of equilibrium.