Spectral properties of mesospheric ice clouds: Evidence for nonspherical particles

Rapp, Markus; Thomas, Gary E.; Baumgarten, Gerd

doi:10.1029/2006jd007322

Cited by 41 publications

(48 citation statements)

References 35 publications

(87 reference statements)

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“…Eremenko et al (2005) indicate needle-or plate-like particles with ε ≈ 0.5 or ε ≈ 2. Rapp et al (2007) estimated ε ≈ 0.2 or ε ≈ 7. The most extensive data set is from the SOFIE (Solar Occultation For Ice Experiment) instrument, with mean ε ≈ 0.5 or ε ≈ 2 (Hervig et al, 2009a;Hervig and Gordley, 2010).…”

Section: Introductionmentioning

confidence: 99%

Impact of particle shape on the morphology of noctilucent clouds

et al. 2015

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Abstract. Noctilucent clouds (NLCs) occur during summer in the polar region at altitudes around 83 km. They consist of ice particles with a typical size around 50 nm. The shape of NLC particles is less well known but is important both for interpreting optical measurements and modeling ice cloud characteristics. In this paper, NLC modeling of microphysics and optics is adapted to use cylindrical instead of spherical particle shape. The optical properties of the resulting ice clouds are compared directly to NLC three-color measurements by the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) Rayleigh/Mie/Raman (RMR) lidar between 1998 and 2014. Shape distributions including both needle-and disc-shaped particles are consistent with lidar measurements. The best agreement occurs if disc shapes are 60 % more common than needles, with a mean axis ratio of 2.8. Cylindrical particles cause stronger ice clouds on average than spherical shapes with an increase of backscatter at 532 nm by ≈ 30 % and about 20 % in ice mass density. This difference is less pronounced for bright than for weak ice clouds. Cylindrical shapes also cause NLCs to have larger but a smaller number of ice particles than for spherical shapes.

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Section: Introductionmentioning

confidence: 99%

Impact of particle shape on the morphology of noctilucent clouds

et al. 2015

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“…These are the same model runs as previously described and discussed by Rapp et al (2007) in the context of modeling color ratios observed by lidar. The key questions to be addressed with the help of these model runs were: (1) What is the cause for the increase of distribution width with increasing particle size?…”

Section: Model Results and Discussionmentioning

confidence: 99%

“…Jensen and Thomas, 1994;Rapp et al, 2002). For the current study, we use results from a large number of simulations using a one-dimensional version of CARMA which have been described in detail in Rapp and Thomas (2006); Rapp et al (2007).…”

Section: Carmamentioning

confidence: 99%

On microphysical processes of noctilucent clouds (NLC): observations and modeling of mean and width of the particle size-distribution

2010

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Abstract. Noctilucent clouds (NLC) in the polar summer mesopause region have been observed in Norway (69 • N, 16 • E) between 1998 and 2009 by 3-color lidar technique. Assuming a mono-modal Gaussian size distribution we deduce mean and width of the particle sizes throughout the clouds. We observe a quasi linear relationship between distribution width and mean of the particle size at the top of the clouds and a deviation from this behavior for particle sizes larger than 40 nm, most often in the lower part of the layer. The vertically integrated particle properties show that 65% of the data follows the linear relationship with a slope of 0.42±0.02 for mean particle sizes up to 40 nm. For the vertically resolved particle properties ( z = 0.15 km) the slope is comparable and about 0.39±0.03. For particles larger than 40 nm the distribution width becomes nearly independent of particle size and even decreases in the lower part of the layer. We compare our observations to microphysical modeling of noctilucent clouds and find that the distribution width depends on turbulence, the time that turbulence can act (cloud age), and the sampling volume/time (atmospheric variability). The model results nicely reproduce the measurements and show that the observed slope can be explained by eddy diffusion profiles as observed from rocket measurements.

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“…While these two simplifying assumptions have been most commonly used in model simulations, recent model work and comparisons with experimental data (e.g. Baumgarten et al, 2002;Eremenko et al, 2005;Hervig, 2006;Rapp et al, 2007) have shown that a Gaussian size distribution and non-spherical iced particles are more consistent with the observations, and should be considered in the modelling of the PMCs. Rapp et al (2007) have shown that the assumption of spherical particle distribution does not allow a consistent interpretation of available satellite and ground-based observations of PMCs.…”

Section: Model Errorsmentioning

confidence: 99%

“…It has been widely used in the study of the microphysical and physical properties of PMC (e.g. Turco et al, 1982;Jensen and Thomas, 1988;Jensen et al, 1989;Rapp et al, 2002Rapp et al, , 2007Rapp and Thomas, 2006). In the scope of the present study, dust and ice particles are modelled at a latitude of ∼69 • N for the altitude range from 75 to 90 km.…”

Section: The 1-d Carma Modelmentioning

confidence: 99%

Retrieving mesospheric water vapour from observations of volume scattering radiances

Vergados

Shepherd

2009

Ann. Geophys.

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Abstract. This study examines the possibility for a theoretical approach in the estimation of water vapour mixing ratios in the vicinity of polar mesospheric clouds (PMC) using satellite observations of Volume Scattering Radiances (VSR) obtained at the wavelength of 553 nm. The PMC scattering properties perturb the underlying molecular Rayleigh scattered solar radiance of the background atmosphere. As a result, the presence of PMC leads to an enhancement in the observed VSR at the altitude of the layer; the PMC VSRs are superimposed on the exponentially decreasing with height Rayleigh VSR, of the PMC-free atmosphere. The ratio between the observed and the Rayleigh VSR of the background atmosphere is used to simulate the environment in which the cloud layer is formed. In addition, a microphysical model of ice particle formation is employed to predict the PMC VSRs. The initial water vapour profile is perturbed until the modelled VSRs match the observed, at which point the corresponding temperature and water vapour profiles can be considered as a first approximation of those describing the atmosphere at the time of the observations. The role of temperature and water vapour in the cloud formation is examined by a number of sensitivity tests suggesting that the water vapour plays a dominant role in the cloud formation in agreement with experimental results. The estimated water vapour profiles are compared with independent observations to examine the model capability in the context of this study. The results obtained are in a good agreement at the peak of the PMC layer although the radiance rapidly decreases with height below the peak. This simplified scenario indicates that the technique employed can give a first approximation estimate of the water vapour mixing ratio, giving rise to the VSR observed in the presence of PMC.

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Spectral properties of mesospheric ice clouds: Evidence for nonspherical particles

Cited by 41 publications

References 35 publications

Impact of particle shape on the morphology of noctilucent clouds

Impact of particle shape on the morphology of noctilucent clouds

On microphysical processes of noctilucent clouds (NLC): observations and modeling of mean and width of the particle size-distribution

Retrieving mesospheric water vapour from observations of volume scattering radiances

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