Optical classification, existence temperatures, and coexistence of different polar stratospheric cloud types (original) (raw)
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.
Chemical, microphysical, and optical properties of polar stratospheric clouds
2003
1] A balloonborne gondola for a comprehensive study of polar stratospheric clouds (PSCs) was launched on 25 January 2000 near Kiruna/Sweden. Besides an aerosol composition mass spectrometer, the gondola carried optical particle counters, two backscatter sondes, a hygrometer, and several temperature and pressure sensors. A mountain wave induced PSC was sampled between 20 and 23 km altitude. Strongly correlated PSC particle properties were detected with the different instruments. A large variability of particle types was measured in numerous PSC layers, and PSC development was followed for about two hours. Liquid ternary PSC layers were found at temperatures near the ice frost point. A large fraction of the sampled cloud layers consisted of nitric acid trihydrate (NAT) particles with a molar ratio H 2 O:HNO 3 close to 3 at temperatures near and below the equilibrium temperature T NAT . The median radius of the NAT particle size distribution was between 0.5 and 0.75 mm at concentrations around 0.5 cm À3 . Below the NAT layers and above T NAT , thin cloud layers containing a few large particles with radii up to 3.5 mm coexisted with smaller solid or liquid particles. The molar ratio in this region was found to be close to two.
2004
The SAGE-III Ozone Loss and Validation Experiments (SOLVE) were conducted over the Arctic from 29 November 1999 to 16 March 2000 (SOLVE I) and from 9 January to 12 February 2003 (SOLVE II). During these campaigns, a multiple-wavelength lidar system was operated from the NASA DC-8 aircraft to make measurements of background aerosols and polar stratospheric clouds (PSCs) on long-range flights across the wintertime polar vortex. Aerosol backscatter measurements were made at 1064, 622, and 311 nm and aerosol depolarization measurements were made at 1064 (SOLVE I only) and 622 nm. Meteorological analyses from the NASA Goddard Global Modeling and Assimilation Office were also used in this investigation. This paper presents results on the frequency of observation and spatial characteristics of the PSCs observed during the SOLVE campaigns. Optical characteristics of the PSCs are discussed, and their observations are related to temperature distributions and other meteorological conditions.
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.
Tellus B, 2001
Backscatter lidar data from the French Antarctic base in Dumont d'Urville (66.40°S, 140.01°E), including aerosol background and observations of polar stratospheric clouds (PSCs), have been collected since 1989. In the present work we present a climatological study of PSCs, using a data base consisting of almost 90 observations. The seasonal evolution of PSCs, their optical classification, and their relationship with the observation temperature were studied. The first PSC was observed on day number 175 (15 June) and the last on day number 260 (7 September). The characteristic mid-cloud altitude decreases through the season at a rate of 2.5 km/month. Type Ia, Ib, and II PSCs-identified by their optical properties-have been observed. External mixtures of these types have also been observed. These observations have been related to the local temperature measured by radiosondes. The relationship between PSC type and the period of the winter season was also investigated. Mixed (solid and liquid) type I clouds are mostly observed at the beginning of the winter. Type II clouds are observed only during the coldest period around midwinter, although temperatures below the frost point begin earlier and persist longer than this. Type Ia, solid-particle, clouds are observed mostly at the end of the winter.
1992
An optical radar-lidar-has been operational at the Amundsen-Scott South Pole Station since summer 1987-1988. The observations were specially directed to the detection of aerosol layers and polar stratospheric clouds (PSCs). The lidar utilized a Nd-YAG laser followed by a second harmonic generator, and a 0.5-m diameter Cassegrain receiving telescope. Results obtained during the period May-October 1988 are summarized. Some 10,000 profiles of the lidar echoes, each the result of 1-min averaging, were obtained. Data sets consisting of profiles of the scattering ratio and of the backscattering cross section Ba, based on half-hour averaging, are presented. The data can be related to profiles of the atmospheric temperature T, usually obtained on a daily basis at South Pole. Stratifications appear to have two distinct types of structures: one structure shows only a modest variation with height; the other is characterized by sharp features, with large changes of the cross section with height. The basic results, the relationship between B a and T, and their statistical relevance are considered in this paper. The microphysical interpretation, the attribution of these structures to PSC Type ! and Type II, respectively involving the condensation of nitric acid trihydrate and of water ice, and the seasonal evolution of the phenomena are treated in a companion paper.
Comparison of chemical and optical in situ measurements of polar stratospheric cloud particles
Journal of Geophysical Research, 2000
The chemical composition of polar stratospheric cloud (PSC) particles has been measured in a balloon-borne mass spectrometer experiment . The cloud particles have simultaneously been observed by a backscatter sonde flown on the same gondola. Taken separately, the two data sets indicate that the PSC particles are composed of liquid supercooled temary solutions (STS). The chemical analysis shows that the particles contain relatively low concentrations of nitric acid, indicating a not fully developed type lb PSC. Assuming the particles to be composed of STS, it appears that the calculated particle volumes are too small to generate the large observed backscatter ratios. Possible explanations for the apparent discrepancy are discussed, based on STS equilibrium model and microphysical / optical model calculations and including a meteorological mesoscale analysis of the mountain lee wave situation during the flight. Assuming a relatively large value of the real part refractive index of STS particles around 1.50 at 940 nm wavelength would apparently bring the two data sets in agreement. However, this large value seems to be in conflict with previous laboratory measurements and theoretical predictions, although in better agreement with recent balloonborne observations. The limited observational data set does not allow us to assess if the particles could be composed of a metastable dilute solid solution or a higher nitric acid hydrate. , 1988]. However, details in the solid particle formation processes are still unknown , and metastable phases such as nitric acid dihydrate (NAD) or dilute solid solutions could play important roles in their formation. The particle formation may be more complex in the Arctic regions, since winter temperatures typically hover around thresholds for PSC formation, in contrast to Antarctica, where colder and long-1491 1492 LARSEN ET AL.: CHEMICAL AND OPTICAL PSC MEASUREMENTS ß , ß ß ß _m _ [] I1 ! ß _ -
IEEE International Geoscience and Remote Sensing Symposium, 2002
Lidar measurements from the recent SAGE III Ozone Loss and Validation Experiment (SOLVE) have been used to identify the number of classes of Polar Stratospheric Clouds (PSCs) and their corresponding characteristics. The backscatter lidar, flown aboard a DC8 aircraft, measures profiles of backscatter at 532 nm and 1064 nm, and depolarization at 532 nm. These data along with the color ratio were used to categorize PSCs using a clustering algorithm. For each group or cluster, the central values or medoids describe the optical characteristics of the clouds. For this preliminary study, five such groups were determined with medoid scattering ratios of 1.13, 11.90, 47.68, 71.07, and, 88.96 at 532 nm. The mean quality index of 0.82 for the five groups shows that the clusters are sufficiently distinct from each other. I.