Christine David

Spatial and temporal variability of the stratospheric aerosol cloud produced by the 1991 Mount Pinatubo eruption

Received 25 April 2003; revised 7 July 2003; accepted 22 July 2003; published 17 October 2003. (1) As a critical quality control step toward producing a stratospheric data assimilation system for volcanic aerosols, we conducted a comparison between Stratosphere Aerosol and Gas Experiment (SAGE) II aerosol extinction profiles and aerosol backscatter measured by five lidars, both in the tropics and midlatitudes, for the two-year period following the 1991 Mt. Pinatubo eruption. The period we studied is the most challenging for the SAGE II retrieval because the aerosol cloud caused so much extinction of the solar signal that in the tropics few retrievals were possible in the core of the cloud. We compared extinction at two wavelengths at the same time that we tested two sets of conversions coefficients. We used both Thomason and Jagers extinction-to-backscatter conversion coefficients for converting lidar backscatter profiles at 0.532 mm or 0.694 mm wavelengths to the SAGE II extinction wavelengths of 0.525 mm and 1.020 m mo r the nearby ones of 0.532 mm and 1.064 mm respectively. The lidars were located at Mauna Loa, Hawaii (19.5� N, 155.6� W), Camaguey, Cuba (21.4� N, 77.9� W), Hefei, China (31.9� N, 117.2� W), Hampton Virginia (37.1� N, 76.3� W), and Haute Provence, France (43.9� N, 5.7� W). For the six months following the eruption the aerosol cloud was much more heterogeneous than later. Using two alternative approaches, we evaluated the aerosol extinction variability of the tropical core of the Pinatubo stratospheric aerosol cloud at the timescale of 1-2 days, and found it was quite large. Aerosol variability played the major role in producing the observed differences between SAGE II and the lidars. There was in general a good agreement between SAGE II extinction measurements and lidar derived extinction, and we conclude that all five lidar sets we compared can be used in a future data assimilation of stratospheric aerosols. This is the most comprehensive comparison yet of lidar data with satellite data for the Pinatubo period. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0394 Atmospheric Composition and Structure: Instruments and techniques; 0370 Atmospheric Composition and Structure: Volcanic effects (8409); 3360 Meteorology and Atmospheric Dynamics: Remote sensing; KEYWORDS: volcano, lidar, satellite

Uptake on fractal particles: 2. Applications

This first part of the paper is devoted to the validation of the theoretical framework developed in the companion paper [Coelho et al., this issue] against laboratory data. Although there are limited data suitable for a full-scale validation of the model, model-calculated surface to mass ratios of soot aggregates are found to be consistent with laboratory measurements. Then we use the framework to estimate errors which can be generated in the derivation of fractal aggregate properties from measurements of equivalent sizes. It is shown that the derivations of the aggregate mass and the surface area enhancement factor can be in error by at least an order of magnitude. The calculations are substantially improved when the fractal character of soot is accounted for. Since the gyration radius is a key parameter of the model, useful relationships are provided for converting aggregate equivalent sizes (mass transfer equivalent radius, hydrodynamic radius) into gyration radius. Finally, uptake of chemical species on atmospheric soot is investigated for the lower stratosphere and the boundary layer. The uptake is found to be mostly reaction limited, justifying the assumption of proportionality between the soot surface area and the uptake rate. However, the uptake occurs in the transition regime for the relatively compact aggregates found in urban areas.

Size distribution time series of a polar stratospheric cloud observed above Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) (69°N) and analyzed from multiwavelength lidar measurements during winter 2005

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: No 1–10 cm3 (50%), rm 0.15 mm (20%), and s 1.2 (15%). A mode of much larger particles is detected between 1600 and 1900 UTC (No 0.04 cm3 (30%), rm 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.

Calmyonemin: Identification and distribution throughout thecell cycle in Entodinium bursa (ciliate)

Summary— The ciliature in most entodiniomorphid ciliates is restricted to the cell apex, forming ciliary crowns that can be rapidly retracted under stress conditions. In a previous study, calmyonemin, a 23 kDa analog of centrin, has been characterized from ciliated cortical zones in Eudiplodinium maggii; its localization in subkinetal myonemes, ie bundles of contractile filaments powering retraction of the ciliature, was demonstrated by immunoelectron microscopy (David and Vigues (1994) Cell Motil Cytoskeleton, 27, 169–179). Here we used immunofluorescence microscopy to determine the distribution of calmyonemin and its variations throughout the cell cycle in Entodinium bursa. Labelling of morphostatic cells with anti‐calmyonemin antibody reveals immunoreactivity at the base of the ciliature, in circumciliary lips, around the cytoproct and in an endoplasmic array originating from the post‐oral region and extending down to the posterior part of the cell. All arrays of calmyonemin from the parental cell remain unaffected during cell division except the endoplasmic array which undergoes a transient resorption followed by synchronous reassembly in the two future products of division. The assembly of subkinetal myonemes in the sub‐equatorial zone is described in relation with the main features of oral morphogenesis previously revealed by others using silver impregnation techniques and light microscopy.