Optical classification, existence temperatures, and coexistence of different polar stratospheric cloud types (original) (raw)
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Epic3atmospheric Chemistry and Physics 5 Pp 2081 2090, 2005
The extent of springtime Arctic ozone loss does not reach Antarctic "ozone hole" dimensions because of the generally higher temperatures in the northern hemisphere vortex and consequent less polar stratospheric cloud (PSC) particle surface for heterogeneous chlorine activation. Yet, with increasing greenhouse gases stratospheric temperatures are expected to further decrease. To infer if present Antarctic PSC occurrence can be applied to predict future Arctic PSC occurrence, lidar observations from McMurdo station (78 • S, 167 • E) and NyÅlesund (79 • N, 12 • E) have been analysed for the 9 winters between 1995 (1995/1996) and 2003 (2003/2004). Although the statistics may not completely cover the overall hemispheric PSC occurrence, the observations are considered to represent the main synoptic cloud features as both stations are mostly situated in the centre or at the inner edge of the vortex. Since the focus is set on the occurrence frequency of solid and liquid particles, the analysis has been restricted to volcanic aerosol free conditions. In McMurdo, by far the largest part of PSC observations is associated with NAT PSCs. The observed persistent background of NAT particles and their potential ability to cause denoxification and irreversible denitrification is presumably more important to Antarctic ozone chemistry than the scarcely observed ice PSCs. Meanwhile in Ny-Ålesund, ice PSCs have never been observed, while solid NAT and liquid STS clouds both occur in large fraction. Although they are also found solely, the majority of observations reveals solid and liquid particle layers in the same profile. For the Ny-Ålesund measurements, the frequent occurrence of liquid PSC particles yields major significance in terms of ozone chemistry, as their chlorine activation rates are more efficient.
Atmospheric Chemistry and Physics, 2005
The extent of springtime Arctic ozone loss does not reach Antarctic "ozone hole" dimensions because of the generally higher temperatures in the northern hemisphere vortex and consequent less polar stratospheric cloud (PSC) particle surface for heterogeneous chlorine activation. Yet, with increasing greenhouse gases stratospheric temperatures are expected to further decrease. To infer if present Antarctic PSC occurrence can be applied to predict future Arctic PSC occurrence, lidar observations from McMurdo station (78 • S, 167 • E) and NyÅlesund (79 • N, 12 • E) have been analysed for the 9 winters between 1995 (1995/1996) and 2003 (2003/2004). Although the statistics may not completely cover the overall hemispheric PSC occurrence, the observations are considered to represent the main synoptic cloud features as both stations are mostly situated in the centre or at the inner edge of the vortex. Since the focus is set on the occurrence frequency of solid and liquid particles, the analysis has been restricted to volcanic aerosol free conditions. In McMurdo, by far the largest part of PSC observations is associated with NAT PSCs. The observed persistent background of NAT particles and their potential ability to cause denoxification and irreversible denitrification is presumably more important to Antarctic ozone chemistry than the scarcely observed ice PSCs. Meanwhile in Ny-Ålesund, ice PSCs have never been observed, while solid NAT and liquid STS clouds both occur in large fraction. Although they are also found solely, the majority of observations reveals solid and liquid particle layers in the same profile. For the Ny-Ålesund measurements, the frequent occurrence of liquid PSC particles yields major significance in terms of ozone chemistry, as their chlorine activation rates are more efficient.
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 observations in the wintertime Arctic stratosphere: Ozone
Geophysical Research Letters, 1990
M. R. Schoeberl 5, I. Isaksen 6, and G. Braathen 7 •bstract. Large-scale distributions of ozone characteristics were measured with the DIAL system (03) were measured with an airborne lidar system during these missions, and these results are as part of the 1989 Airborne Arctic Stratospheric discussed in a companion paper by Browell et al. Expedition (AASE). Measurements of 03 distri-(this issue). This paper discusses selected 03 butions were obtained between January 6 and data obtained by the DIAL system on long-range February 15, 1989, on 15 long-range flights into flights into the polar vortex during the AASE, and the polar vortex from the Sola Air Station, relates these observations to dynamical and chemi-Norway. The observed 03 distribution was found to cal processes that act to influence the 03 districlearly indicate the edge of the polar vortex and bution in the wintertime Arctic stratosphere. to be an effective tracer of dynamical processes in the lower stratosphere. On the last two Lidar Technique and Ozone Comparisons flights of the expedition, large regions with reduced 03 levels were observed by the lidar The differential absorption lidar (DIAL) inside the polar vortex. Ozone had decreased by technique has been used to measure 03 distribuas much as 17% in the center of these areas, and tions in numerous airborne lidar investigations using the in situ measurements made on the ER-2 over the past 10 years (see review by Browell aircraft, it was concluded that this decline was (1989)). The airborne DIAL system has been used due to chemical 03 destruction. to study 03 and PSCs during the development of the 1987 ozone hole over Antarctica (Browell et al., Browell et al.-Lidar Observations of Ozone in the Arctic 327 ARCTIC FLT 05 1-6-89
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.
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.
Journal of Geophysical Research, 1993
Simultaneous polar stratospheric cloud (PSC) and ozone measurements were made over South Pole Station using a two-wavelength backscattersonde. This instrument produces aerosol profiles similar to those obtained with a ground-based lidar system but with higher vertical resolution. In one sounding, depolarization of the PSCs was also measured. The backscattersondes were supplemented with occasional frost point soundings. The measurements made before the appearance of PSCs do not show clear evidence of particle deliquescence, suggesting that the background sulfate particles may be frozen solids rather than liquids. PSCs began appearing at-20 km when the temperature at that altitude dropped to-80øC (193 K). Initially, there was apparent evidence of supersaturation (with respect to nitric acid trihydrate) associated with some type I PSCs, while other examples indicated that the condensation of nitric acid was in quantitative agreement with that expected from the saturation vapor pressure and available nitric acid vapor. The apparent supersaturated layers (which occurred within the first 2 weeks of the onset of PSCs) can alternatively be interpreted as denitrified regions. The wavelength dependence of the backscatter is used to deduce rough particle sizes, and in particular, type Ia and Ib population types can be readily identified by the backscattersonde when not occurring as mixed systems. The mode radius of the first observed PSCs of the season was-0.5 tam. In the polarization sensitive sounding, two varieties of type I PSCs were observed, one of which exhibited significant depolarization and another which produced very little depolarization. This observation would be consistent with the classification of types Ia and Ib, respectively. At the precise time that sunlight was returning to the stratosphere near South Pole Station, a strong inverse correlation in the structure of PSCs and ozone mixing ratio was observed. Using trajectory analysis, it is argued that the effect is probably the result of chemical depletion rather than transport processes. This chance observation is consistent with enhanced ozone depletion occurring in association with sunlit PSCs during the early spring. sensors launched at South Pole Station starting just before the beginning of PSC activity and continuing through the initial period of ozone loss. These observations are augmented with frost point soundings and additional ozone soundings, the latter carried out under another program managed by S. J. Oltmans.
Composition analysis of liquid particles in the Arctic stratosphere under synoptic conditions
Atmospheric Chemistry and Physics, 2006
Synoptic scale polar stratospheric clouds (PSCs) that formed without the presence of mountain lee waves were observed in early December 2002 from Kiruna/Sweden using balloon-borne instruments. The physical, chemical, and optical properties of the particles were measured. Within the PSC solid particles existed whenever the temperature was below the equilibrium temperature for nitric acid trihydrate and liquid particles appeared when the temperature fell below an even lower threshold about 3 K above the frost point with solid particles still present. The correlation of liquid supercooled ternary solution aerosols with local temperatures is a pronounced feature observed during this flight; average molar ratios H 2 O/HNO 3 were somewhat higher than predicted by models. In addition HCl has been measured for the first time in liquid aerosols. The chlorine isotope signature served as a unique tool to identify unambiguously HCl dissolved in STS particles. Within a narrow temperature range of about three degrees above the frost point, the measured average amount of HCl in liquid particles is below 1 weight%.