A new airborne Polar Nephelometer for the measurement of optical and microphysical cloud properties. Part II: Preliminary tests

Abstract. A new optical sensor, the airborne Polar Nephelometer, has been tested in an open wind tunnel. The wind tunnel was operated in cloudy conditions including either cloud water droplets or ice crystals, or a mixture of these particles. The sensor is designed to measure the optical and microphysical parameters of cloud particles sized from a few micrometers to about 500 µm diameter. Basically, the probe measures the scattering phase function of an ensemble of cloud particles which intersect a collimated laser beam near the focal point of a paraboloidal mirror. From the measured scattering phase function the retrieval of the droplet-size spectra and subsequent derived quantities such as liquid water content and size parameters can be calculated using an inversion method. The particle phase discrimination (water droplets/ice particles) can be derived from the shape of the scattering phase function and the sensitivity of the probe allows the detection of small ice crystals (typically of 5 µm diameter). The paper describes the preliminary results obtained by the prototype version of the Polar Nephelometer in various cloudy conditions. These results are compared with direct microphysical measurements obtained by usual PMS probes also mounted in the wind tunnel. Complementary results obtained in a cold chamber are presented in order to illustrate the reliability of the Polar Nephelometer in the presence of small ice crystals.

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A new airborne polar Nephelometer for the measurements of optical and microphysical cloud properties. Part I: Theoretical design

Annales Geophysicae ◽

10.1007/s00585-997-0451-1 ◽

1997 ◽

Vol 15 (4) ◽

pp. 451-459 ◽

Cited By ~ 96

Author(s):

J. F. Gayet ◽

O. Crépel ◽

J. F. Fournol ◽

S. Oshchepkov

Keyword(s):

Phase Function ◽

Focal Point ◽

Ice Crystals ◽

Circular Array ◽

Cloud Properties ◽

Theoretical Design ◽

Microphysical Parameters ◽

Scattering Phase ◽

Scattering Phase Function ◽

Signal Processing Electronics

Abstract. A new optical sensor, the airborne Polar Nephelometer, is described. The sensor is designed to measure the optical and microphysical parameters of clouds containing either water droplets or ice crystals or a mixture of these particles ranging in size from a few micrometers to about 500 µm diameter. The probe measures the scattering phase function of an ensemble of cloud particles intersecting a collimated laser beam near the focal point of a paraboloïdal mirror. The light scattered from polar angles from 3.49° to 169° is reflected onto a circular array of 33 photodiodes. The signal processing electronics and computer storage can provide one measurement of the scattering phase function every 100 ms or every 0.2 ms. The first part of the paper describes the theoretical design of a prototype version of the probe.

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Scattering phase function depolarization parameter model and its application to water droplets sizing using off-axis lidar measurements at multiple angles

Applied Optics ◽

10.1364/ao.57.000969 ◽

2018 ◽

Vol 57 (4) ◽

pp. 969 ◽

Cited By ~ 4

Author(s):

Gilles Roy ◽

Gregoire Tremblay ◽

Xiaoying Cao

Keyword(s):

Phase Function ◽

Water Droplets ◽

Lidar Measurements ◽

Scattering Phase ◽

Scattering Phase Function

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On the interpretation of an unusual in-situ measured ice crystal scattering phase function

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-9355-2012 ◽

2012 ◽

Vol 12 (19) ◽

pp. 9355-9364 ◽

Cited By ~ 14

Author(s):

A. J. Baran ◽

J.-F. Gayet ◽

V. Shcherbakov

Keyword(s):

Phase Function ◽

Asymmetry Parameter ◽

Ice Crystals ◽

Climate Modelling ◽

Ice Crystal ◽

Ice Particles ◽

Scattering Phase ◽

Scattering Phase Function ◽

Phase Functions

Abstract. In-situ Polar Nephelometer (PN) measurements of unusual ice crystal scattering phase functions, obtained near the cloud-top of a mid-latitude anvil cloud, at a temperature of about −58 °C, were recently reported by Gayet et al. (2012). The ice crystal habits that produced the phase functions consisted of aggregates of ice crystals and aggregates of quasi-spherical ice particles. The diameters of the individual quasi-spherical ice particles were estimated to be between about 15 μm and 20 μm. The measured-averaged scattering phase functions were featureless, at scattering angles less than about 100°, but an ice bow-like feature was noted between the scattering angles of about 120° to 160°. The estimated asymmetry parameter was 0.78 ± 0.04. In this paper, the averaged scattering phase function is interpreted in terms of a weighted habit mixture model. The model that provides the best overall fit to the measured scattering phase function comprises of highly distorted ten-element hexagonal ice aggregates and quasi-spherical ice particles. The smaller quasi-spherical ice crystals are represented by Chebyshev ice particles of order 3, and were assumed to have equivalent spherical diameters of 24 μm. The asymmetry parameter of the best overall model was found to be 0.79. It is argued that the Chebyshev-like ice particles are responsible for the ice bow-like feature and mostly dominate the scattered intensity measured by the PN. The results from this paper have important implications for climate modelling (energy balance of anvils), cloud physics and the remote sensing of cirrus properties.

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On the interpretation of an unusual in-situ measured ice crystal scattering phase function

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-12485-2012 ◽

2012 ◽

Vol 12 (5) ◽

pp. 12485-12502 ◽

Cited By ~ 1

Author(s):

A. J. Baran ◽

J.-F. Gayet ◽

V. Shcherbakov

Keyword(s):

Phase Function ◽

Asymmetry Parameter ◽

Ice Crystals ◽

Climate Modelling ◽

Ice Crystal ◽

Ice Particles ◽

Scattering Phase ◽

Scattering Phase Function ◽

Phase Functions

Abstract. In-situ Polar Nephelometer (PN) measurements of unusual ice crystal scattering phase functions were recently reported by Gayet et al. (2012). The ice crystal habits that produced the phase functions were small chain-like aggregates, which had on their surfaces, smaller quasi-spherical ice crystals. The measured-averaged phase functions were featureless, at scattering angles less than about 100°, but an ice bow-like feature was noted between the scattering angles of about 120° to 160°. The estimated asymmetry parameter was 0.78 ± 0.04. In this paper, the phase function is interpreted in terms of a weighted habit mixture model. The best-fit model comprises of highly distorted ten element hexagonal ice aggregates, and the smaller quasi-spherical ice crystals are represented by Chebyshev ice particles. The weighted mean asymmetry parameter was found to be 0.81. It is argued that the Chebyshev-like ice particles are responsible for the ice bow-like feature and mostly dominate the scattered intensity measured by the PN. The results of this paper have important implications for climate modelling (energy balance of anvils) and the remote sensing of cirrus properties.

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On the relationship between the scattering phase function of cirrus and the atmospheric state

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-14109-2014 ◽

2014 ◽

Vol 14 (10) ◽

pp. 14109-14157 ◽

Cited By ~ 1

Author(s):

A. J. Baran ◽

K. Furtado ◽

L.-C. Labonnote ◽

S. Havemann ◽

J.-C. Thelen ◽

...

Keyword(s):

Model Prediction ◽

Phase Function ◽

Weather Prediction ◽

Ice Crystals ◽

Scattering Phase ◽

Scattering Phase Function ◽

Nwp Model ◽

Phase Functions ◽

The Relationship ◽

Good Agreement

Abstract. This is the first paper to investigate the relationship between the scattering phase function of cirrus and the relative humidity with respect to ice (RHi), using space-based solar radiometric angle-dependent measurements. The relationship between RHi, and the complexity of ice crystals has been previously studied using data from aircraft field campaigns and laboratory cloud chambers. However, to the best of our knowledge, there have been no studies to date that explore this relationship, through the use of remotely sensed space-based angle-dependent solar radiometric measurements. In this paper, a case study of semi-transparent cirrus is used to explore the possibility of such a relationship. Moreover, for the first time, RHi fields predicted by a high-resolution numerical weather prediction (NWP) model are combined with satellite retrievals of ice crystal complexity. The NWP model was initialised at midnight, on the 25 January 2010, and the mid-latitude RHi field was extracted from the NWP model at 13:00 UTC. At about the same time, there was a Polarization and Anisotropy of Reflectance for Atmospheric science coupled with Observations from a Lidar (PARASOL) overpass, and the PARASOL swath covered the NWP model predicted RHi field. The cirrus case was located over Scotland, and over the North Sea. From the satellite channel based at 0.865 μm, the directionally averaged and directional spherical albedos were retrieved between the scattering angles of about 80° and 130°. An ensemble model of cirrus ice crystals is used to predict phase functions that vary between phase functions that exhibit optical features (called pristine), to featureless phase functions. For each of the PARASOL pixels, the phase function that best minimised differences between the spherical albedos was selected. This paper reports a positive correlation between the scattering phase function and RHi. That is, the pristine and completely featureless phase functions are found to be correlated with RHi < 100%, and RHi> 100%, respectively. Moreover, it is demonstrated that the NWP model prediction of the vertical profile of RHi is in good agreement with independent aircraft-based physical retrievals of RHi. Furthermore, the NWP model prediction of the cirrus cloud-top height and its vertical extent is also found to be in good agreement with aircraft-based lidar measurements.

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On the relationship between the scattering phase function of cirrus and the atmospheric state

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-1105-2015 ◽

2015 ◽

Vol 15 (2) ◽

pp. 1105-1127 ◽

Cited By ~ 15

Author(s):

A. J. Baran ◽

K. Furtado ◽

L.-C. Labonnote ◽

S. Havemann ◽

J.-C. Thelen ◽

...

Keyword(s):

Phase Function ◽

Ice Crystals ◽

The North ◽

Scattering Phase ◽

Scattering Phase Function ◽

Nwp Model ◽

Phase Functions ◽

The Relationship ◽

Good Agreement

Abstract. This is the first paper to investigate the relationship between the shape of the scattering phase function of cirrus and the relative humidity with respect to ice (RHi, using space-based solar radiometric angle-dependent measurements. The relationship between RHi and the complexity of ice crystals has been previously studied using data from aircraft field campaigns and laboratory cloud chambers. However, to the best of our knowledge, there have been no studies to date that explore this relationship through the use of remotely sensed space-based angle-dependent solar radiometric measurements. In this paper, one case study of semi-transparent cirrus, which occurred on 25 January 2010 off the north-east coast of Scotland, is used to explore the possibility of such a relationship. Moreover, for the first time, RHi fields predicted by a high-resolution numerical weather prediction (NWP) model are combined with satellite retrievals of ice crystal complexity. The NWP model was initialised at midnight, on 25 January 2010, and the mid-latitude RHi field was extracted from the NWP model at 13:00 UTC. At about the same time, there was a PARASOL (Polarization and Anisotropy of Reflectance for Atmospheric science coupled with Observations from a Lidar) overpass, and the PARASOL swath covered the NWP-model-predicted RHi field. The cirrus case was located over Scotland and the North Sea. From the satellite channel based at 0.865 μm, the directionally averaged and directional spherical albedos were retrieved between the scattering angles of about 80 and 130°. An ensemble model of cirrus ice crystals is used to predict phase functions that vary between phase functions that exhibit optical features (referred to as pristine) and featureless phase functions. For each of the PARASOL pixels, the phase function that best minimised differences between the spherical albedos was selected. This paper reports, for this one case study, an association between the most featureless phase function model and the highest values of NWP-predicted RHi (i.e. when RHi > 1.0). For pixels associated with NWP-model-predicted RHi < 1, it was impossible to generally discriminate between phase function models at the 5% significance level. It is also shown that the NWP model prediction of the vertical profile of RHi is in good agreement with dropsonde, in situ measurements and independent aircraft-based physical retrievals of RHi. Furthermore, the NWP model prediction of the cirrus cloud-top height and its vertical extent is also found to be in good agreement with aircraft-based lidar measurements.

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