Some Microphysical Properties of an Ice Cloud from Lidar Observation of Horizontally Oriented Crystals

Platt, C. M. R.; Abshire, N. L.; McNice, G. T.

doi:10.1175/1520-0450(1978)017<1220:smpoai>2.0.co;2

Cited by 125 publications

(71 citation statements)

References 5 publications

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“…If the crystals are planar (and, given the lack of active ice nuclei at temperatures warmer than −8 • C, this is the case for many ice-producing supercooled layers (Pruppacher and Klett, 1997)) their basal facets will tend to orient in the horizontal plane, and strong 'mirrorlike' specular reflections are observed as the lidar beam is reflected directly back to the receiver (Platt, 1978;Platt et al, 1978). Simultaneous measurements at vertical and at a few degrees from zenith allow reliable identification of oriented crystal populations from the large difference in backscatter observed at the two angles (Thomas et al, 1990).…”

Section: Introductionmentioning

confidence: 64%

Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds

Westbrook

Illingworth

O’Connor

et al. 2010

Quart J Royal Meteoro Soc

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The properties of planar ice crystals settling horizontally have been investigated using a vertically pointing Doppler lidar. Strong specular reflections were observed from their oriented basal facets, identified by comparison with a second lidar pointing 4 • from zenith. Analysis of 17 months of continuous high-resolution observations reveals that these pristine crystals are frequently observed in ice falling from mid-level mixed-phase layer clouds (85% of the time for layers at −15 • C). Detailed analysis of a case study indicates that the crystals are nucleated and grow rapidly within the supercooled layer, then fall out, forming well-defined layers of specular reflection. From the lidar alone the fraction of oriented crystals cannot be quantified, but polarimetric radar measurements confirmed that a substantial fraction of the crystal population was well oriented. As the crystals fall into subsaturated air, specular reflection is observed to switch off as the crystal faces become rounded and lose their faceted structure. Specular reflection in ice falling from supercooled layers colder than −22 • C was also observed, but this was much less pronounced than at warmer temperatures: we suggest that in cold clouds it is the small droplets in the distribution that freeze into plates and produce specular reflection, whilst larger droplets freeze into complex polycrystals.The

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Section: Introductionmentioning

confidence: 64%

Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds

Westbrook

Illingworth

O’Connor

et al. 2010

Quart J Royal Meteoro Soc

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“…The presence of vertically aligned particles is unexpected, because aligned atmospheric particles, such as column or plate-shaped ice crystals, are typically oriented horizontally due to aerodynamic forces (Platt et al, 1978;Sassen and Benson, 2001). One exception concerns electrically active regions of storm clouds within which ice crystals are thought to align vertically (Vonnegut, 1965, Mendez, Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Section: Introductionmentioning

confidence: 99%

Alignment of atmospheric mineral dust due to electric field

et al. 2007

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Abstract. Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction indicating the presence of vertically aligned particles in the atmosphere. Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here. It is also possible that the alignment and the electric field modify dust transport.

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“…Clouds of this kind show a nondepolarized backscattering echo (Platt 1978;Sakai et al 2006). We demonstrated that this is not the case for the SSSC by the tilted lidar observations.…”

Section: Discussion and Summarymentioning

confidence: 73%

“…Since the cloud layer observed by both lidar systems showed the same small and R profiles (Fig. 2), it is unlikely that the observed small was caused by the horizontally oriented cloud ice crystals (Platt et al 1978). These results indicate that the clouds were not ice clouds, but were composed of liquid phase spherical aerosols.…”

Section: Resultsmentioning

confidence: 99%

Volcanic Clouds from the 2007 Eruption of Jebel at Tair (Yemen) Detected by Ground Based and Space Borne Lidar

Shibata

Kouketsu

2008

SOLA

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Volcanic clouds from the eruption of Jebel at Tair (south-central Red Sea, Yemen) on 30th September 2007 were observed by ground based lidar at Nagoya, Japan, and also by the space borne lidar CALIOP. The cloud was found as a non-depolarized cloud layer in the upper troposphere by ground based Mie/Depolarization lidar. By tilted lidar observations from ground it was demonstrated that these clouds were not composed of ice particles. Clouds with similar characteristics were also observed by CALIOP. Some evidence confirmed their origin to be the said eruption. The estimated total mass of the cloud particles by lidar-observed data coincides with the estimated sulfuric acid oxidized from SO2 included in the volcanic cloud observed by Aura satellite. All of the clouds were observed at altitudes lower than the cold point tropopause for a week after the eruption. Since then parts of the clouds were observed in the stratosphere, indicating transport from the troposphere to the stratosphere.

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Some Microphysical Properties of an Ice Cloud from Lidar Observation of Horizontally Oriented Crystals

Cited by 125 publications

References 5 publications

Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds

Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds

Alignment of atmospheric mineral dust due to electric field

Volcanic Clouds from the 2007 Eruption of Jebel at Tair (Yemen) Detected by Ground Based and Space Borne Lidar

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