Shapes, sizes and light scattering properties of ice crystals in cirrus and a persistent contrail during SUCCESS

Lawson, R. Paul; Heymsfield, Andrew J.; Aulenbach, S.; Jensen, Tara

doi:10.1029/98gl00241

Cited by 80 publications

(91 citation statements)

References 13 publications

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“…Hence the particles in the core remain close to spherical while the particles near the humid boundary of contrails may become large and very complex in shape in particular at high ambient temperature and humidity (Heyms®eld et al, 1998a). The large in¯uence of particle shape on the scattering phase function was demonstrated in measurements and computations (Liou et al, 1998;Raschke et al, 1998;Lawson et al, 1998).…”

Section: Radiative Properties Of Contrailsmentioning

confidence: 97%

“…Strong depolarization of Lidar returns by contrails with growing particles that are a few minutes old indicate aspherical particles (Freudenthaler et al, 1996, Sassen, 1997. Both, complex ice particles (Goodman et al, 1998, Lawson et al, 1998 and nearly spherical ice particles at low ambient temperatures (<A55°C) using replicators in contrail cirrus were identi®ed. It seems that the amount of water vapor available in the core of contrails is too small, in particular at low temperatures, to let very many ice particles grow.…”

Section: Radiative Properties Of Contrailsmentioning

confidence: 99%

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Radiative forcing by contrails

Meerkötter¹,

Schumann²,

et al. 1999

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Abstract. A parametric study of the instantaneous radiative impact of contrails is presented using three di erent radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm A2 daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net e ect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.

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Section: Radiative Properties Of Contrailsmentioning

confidence: 97%

Section: Radiative Properties Of Contrailsmentioning

confidence: 99%

Radiative forcing by contrails

Meerkötter¹,

Schumann²,

et al. 1999

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“…This ensemble is supposed to represent some typical distribution of shapes that is observed in cirrus using the Cloud Particle Imager (CPI) probe due to Lawson et al (1998). However, Westbrook et al (2004) show that realistic ensembles of ice crystal shapes can be generated from some initial monomer crystal, which is allowed to aggregate through collisions until a distribution of aggregates is produced.…”

Section: Introductionmentioning

confidence: 99%

A self‐consistent scattering model for cirrus. I: The solar region

Baran

C.‐Labonnote²

2007

Quart J Royal Meteoro Soc

129

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ABSTRACT:In this paper a self-consistent scattering model for cirrus is presented. The model consists of an ensemble of ice crystals where the smallest ice crystal is represented by a single hexagonal ice column. As the overall ice crystal size increases, the ice crystals become progressively more complex by arbitrarily attaching other hexagonal elements until a chain-like ice crystal is formed, this representing the largest ice crystal in the ensemble. The ensemble consists of six ice crystal members whose aspect ratios (ratios of the major-to-minor axes of the circumscribed ellipse) are allowed to vary between unity and 1.84 for the smallest and largest ice crystal, respectively. The ensemble model's prediction of parameters fundamental to solar radiative transfer through cirrus such as ice water content and the volume extinction coefficient is tested using in situ based data obtained from the midlatitudes and Tropics. It is found that the ensemble model is able to generally predict the ice water content and extinction measurements within a factor of two. Moreover, the ensemble model's prediction of cirrus spherical albedo and polarized reflection are tested against a space-based instrument using one day of global measurements. The space-based instrument is able to sample the scattering phase function between the scattering angles of approximately 60°and 180°, and a total of 37 581 satellite pixels were used in the present analysis covering latitude bands between 43.75°S and 76.58°N. It is found that the ensemble model phase function is well able to minimize significantly differences between satellite-based measurements of spherical albedo and the ensemble model's prediction of spherical albedo. The satellite-based measurements of polarized reflection are found to be reasonably described by more simple members of the ensemble. The ensemble model presented in this paper should find wide applicability to the remote sensing of cirrus as well as more fundamental solar radiative transfer calculations through cirrus, and improved solar optical properties for climate and Numerical Weather Prediction models.

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“…De très nombreux phénomènes physiques sont encore largement hors de portée des Dans ces domaines hautement spécia-lisés, le besoin en observations s'apprécie au cas par cas, en fonction de priorités politiques (surveillance de l'environnement, évolution du climat, prévention des catastrophes...), scientifiques (accent mis sur un processus mal connu identifié comme un « maillon faible » dans la compréhen-sion d'un système) ou techniques (priorité pour l'amélioration des modèles de prévision ou intérêt industriel pour la valorisation d'une technologie instrumentale émergente). On ne saurait en faire ici une énumération à la Prévert : il suffit de feuilleter les sommaires des publications scientifiques (Journal of Applied Meteorology, par exemple) ou l'article de Lawson et al (1998) pour avoir un aperçu de la très grande diversité des instruments utilisés par la recherche atmosphérique et, plus généralement, géophysique et environnementale.…”

Section: La Recherche Et Ses Prioritésunclassified

“…Les lidars Raman (Whiteman et al, 1992) La même association radar-lidar-radiomètre sera utilisée à partir d'avions de recherche atmosphérique et à partir du sol. Ainsi, le réseau européen Cloudpermettront d'améliorer la connaissance et la représentation de la répartition en taille, en phase et en type des hydromé-téores dans les nuages (Gayet et al, 1997 ;Lawson et al, 1998).…”

Section: Pour L'humiditéunclassified