Microphysical and Optical Properties of Atmospheric Ice Crystals at South Pole Station

Lawson, R. Paul; Baker, A. B.; Zmarzly, Patrick; O'Connor, D.; Mo, Q.; Gayet, Jean-François; Shcherbakov, Valéry

doi:10.1175/jam2421.1

Cited by 95 publications

(116 citation statements)

References 36 publications

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“…This size appears to delineate the lower limit of ice crystal size responsible (at visible wavelengths) for halo formation according to earlier laboratory studies (Sassen and Liou, 1979;Barkey et al, 2002) and theoretical results (Mishchenko and Macke, 1999). In situ observations at the South Pole station (Shcherbakov et al, 2006a;Lawson et al, 2006) also reported very well-marked 22 • halo peaks with pristine ice crystals no larger than 100 µm. Therefore, the reported ice crystal sizes do not appear to be critical for the halo/no-halo interpretation.…”

Section: Discussionsupporting

confidence: 81%

Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

et al. 2011

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Abstract. In this paper, we describe in situ observations of mid-latitude cirrus cloud band carried out on 16 May 2007 during the CIRCLE-2 experiment. The Polar Nephelometer and the Cloud Particle Imager (CPI) instruments with PMS FSSP-300 and 2D-C probes were used for the description of the optical and microphysical cloud properties. Two selected cloud regions are compared and discussed in detail. Significant differences in optical properties are evidenced in terms of 22 • halo occurrences even though prevalent planarplate ice crystals are observed in both cloud regions. Featureless scattering phase functions are measured in the first cloud region located near the trailing edge of the cirrus-band at about 11 800 m/−57 • C. In contrast, well pronounced 22 • halo peaks are observed with predominant similar-shaped ice crystals near the cirrus-band leading edge at 7100 m/−27 • C. CPI ice crystal images with Polar Nephelometer observations are carefully analysed and interpreted from a theoretical light scattering model in order to explain occurrence and non-occurrence of the 22 • halo feature. The results highlight that the halo peaks are inherent only in perfect plate ice crystals (or pristine crystals). On the basis of previous datasets in mid-latitude cirrus, it is found that simple pristine crystals are uncommon whereas particles with imperfect or complex shapes are prevalent. As a result, phase functions that are smooth and featureless best represent cirrus scattering properties.

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Section: Discussionsupporting

confidence: 81%

Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

et al. 2011

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“…From Walden et al (2003), the atmospheric ice crystals over the Antarctic Plateau in winter is mainly constituted of three major types: diamond dust, blowing snow and snow grains. When sorted by number, Lawson et al (2006) attribute 30 % of the crystals recorded at the Amundsen-Scott South Pole station to rosette shaped (mixed-habit rosettes, plate-like polycrystals and rosette shapes with side planes), 45 % to diamond dust (columns, thick plates and plates) and 25 % to irregular. By mass, the percentages are 57 % rosette shapes, 23 % diamond dust and 20 % irregular.…”

Section: Cloudsmentioning

confidence: 99%

Genesis of diamond dust, ice fog and thick cloud episodes observed and modelled above Dome C, Antarctica

Ricaud¹,

Bazile²,

Guasta³

et al. 2017

Atmos. Chem. Phys.

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Abstract. Episodes of thick cloud and diamond dust/ice fog were observed during 15 March to 8 April 2011 and 4 to 5 March 2013 in the atmosphere above Dome C (Concordia station, Antarctica; 75 • 06 S, 123 • 21 E; 3233 m a.m.s.l.). The objectives of the paper are mainly to investigate the processes that cause these episodes based on observations and to verify whether operational models can evaluate them. The measurements were obtained from the following instruments: (1) a ground-based microwave radiometer (HAM-STRAD, H 2 O Antarctica Microwave Stratospheric and Tropospheric Radiometers) installed at Dome C that provided vertical profiles of tropospheric temperature and absolute humidity every 7 min; (2) daily radiosoundings launched at 12:00 UTC at Dome C; (3) a tropospheric aerosol lidar that provides aerosol depolarization ratio along the vertical at Dome C; (4) down-and upward short-and long-wave radiations as provided by the Baseline Surface Radiation Network (BSRN) facilities; (5) an ICE-CAMERA to detect at an hourly rate the size of the ice crystal grains deposited at the surface of the camera; and (6) space-borne aerosol depolarization ratio from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) platform along orbits close to the Dome C station. The time evolution of the atmosphere has also been evaluated by considering the outputs from the mesoscale AROME and the global-scale ARPEGE meteorological models. Thick clouds are detected during the warm and wet periods (24-26 March 2011 and 4 March 2013) with high depolarization ratios (greater than 30 %) from the surface to 5-7 km above the ground associated with precipitation of ice particles and the presence of a supercooled liquid water (depolarization less than 10 %) clouds. Diamond dust and/or ice fog are detected during the cold and dry periods (5 April 2011 and 5 March 2013) with high depolarization ratios (greater than 30 %) in the planetary boundary layer to a maximum altitude of 100-300 m above the ground with little trace of precipitation. Considering 5-day back trajectories, we show that the thick cloud episodes are attributed to air masses with an oceanic origin whilst the diamond dust/ice fog episodes are attributed to air masses with continental origins. Although operational models can reproduce thick cloud episodes in the free troposphere, they cannot evaluate the diamond dust/ice fog episodes in the planetary boundary layer because they require to use more sophisticated cloud and aerosol microphysics schemes.

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“…The dynamical structure of thunderstorm outflow anvils is of relevance and ha s been discussed extensively (e.g. Lilly, 1988). Its evolution is described as a two-stage process.…”

Section: Tropical Anvil Outflowmentioning

confidence: 99%

“…However, much of the uncertainty in models of storm outflow development and influences on radiative forcing centre on whether the subsequent mixed layer can fully develop before most of the ice within it has precipitated out (Lilly, 1988). Starr and Cox (1985) suggest precipitation is important for the plume development and radiative heating impact, reducing the optical path and hence radiative effect.…”

Section: Tropical Anvil Outflowmentioning

confidence: 99%

Observations and modelling of microphysical variability, aggregation and sedimentation in tropical anvil cirrus outflow regions

et al. 2012

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Abstract. Aircraft measurements of the microphysics of a tropical convective anvil (at temperatures ∼ −60 • C) forming above the Hector storm, over the Tiwi Islands, Northern Australia, have been conducted with a view to determining ice crystal aggregation efficiencies from in situ measurements. The observed microphysics have been compared to an explicit bin-microphysical model of the anvil region, which includes crystal growth by vapour diffusion and aggregation and the process of differential sedimentation.It has been found in flights made using straight and level runs perpendicular to the storm that the number of ice crystals initially decreased with distance from the storm as aggregation took place resulting in larger crystals, followed by their loss from the cloud layer due to sedimentation. The net result was that the mass (i.e. Ice Water Content) in the anvil Ci cloud decreased, but also that the average particle size (weighted by number) remained relatively constant along the length of the anvil outflow. Comparisons with the explicit microphysics model showed that the changes in the shapes of the ice crystal spectra as a function of distance from the storm could be explained by the model if the aggregation efficiency was set to values of E agg ∼0.5 and higher. This result is supported by recent literature on aggregation efficiencies for complex ice particles and suggests that either the mechanism of particle interlocking is important to the aggregation process, or that other effects are occuring, such as enhancement of ice-aggregation by high electric fields that arise as a consequence of charge separation within the storm.It is noteworthy that this value of the ice crystal aggregation efficiency is much larger than values used in cloud resolving models at these temperatures, which typically use E ∼ 0.0016. These results are important to understanding how cold clouds evolve in time and for the treatment of the evolution of tropical Ci in numerical models.

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Microphysical and Optical Properties of Atmospheric Ice Crystals at South Pole Station

Cited by 95 publications

References 36 publications

Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment

Genesis of diamond dust, ice fog and thick cloud episodes observed and modelled above Dome C, Antarctica

Observations and modelling of microphysical variability, aggregation and sedimentation in tropical anvil cirrus outflow regions

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