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

2012 ◽  
Vol 12 (19) ◽  
pp. 9355-9364 ◽  
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.

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

2012 ◽  
Vol 12 (5) ◽  
pp. 12485-12502 ◽  
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.

scholarly journals Pyramidal ice crystal scattering phase functions and concentric halos

1996 ◽  
Vol 14 (11) ◽  
pp. 1192-1197 ◽  
Author(s):  
C. Liu ◽  
P. R. Jonas ◽  
C. P. R. Saunders
Keyword(s):  
Three Dimensional ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Three Dimensional Model ◽  
Model Calculations ◽  
Scattering Phase ◽  
The Common ◽  
Scattering Phase Function ◽  
Phase Functions ◽  
Solar Angle

Abstract. Phase functions have been calculated using the Monte Carlo/geometric ray tracing method for single hexagonal pyramidal ice crystals (such as solid and hollow bullets) randomly oriented in space and horizontal plane, in order to study the concentric halo formations. Results from three dimensional model calculations show that 9° halo can be as bright as the common 22° halo for pyramidal angle of 28°, and the 18°, 20°, 24° and 35° halos cannot be seen due to the strong 22° halo domination in the scattering phase function between 18° and 35°. For solid pyramidal ice crystals randomly oriented horizontally, the 35° arc can be produced and its intensity depends on the incident ray solar angle and the particle aspect ratio.

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

2014 ◽  
Vol 14 (10) ◽  
pp. 14109-14157 ◽  
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.

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

2015 ◽  
Vol 15 (2) ◽  
pp. 1105-1127 ◽  
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.

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

2010 ◽  
Vol 10 (10) ◽  
pp. 24763-24780
Author(s):  
J.-F. Gayet ◽  
G. Mioche ◽  
V. Shcherbakov ◽  
C. Gourbeyre ◽  
R. Busen ◽  
...  
Keyword(s):  
Ice Crystals ◽  
Careful Examination ◽  
Data Sets ◽  
Cloud Particle ◽  
Complex Shapes ◽  
Plate Shape ◽  
Scattering Phase ◽  
Scattering Phase Function ◽  
Phase Functions

Abstract. Preferential horizontally-oriented ice crystals with a prevalent hexagonal-plate shape revealed by the Cloud Particle Imager can explain systematic larger Lidar CALIOP extinctions when compared with extinction derived from co-located in situ measurements. Surprisingly, the Polar Nephelometer does not reveal any signature of 22° (and 46°) halos, showing a rather featureless scattering phase function in this case. In contrast, well pronounced 22° halo peaks are observed with predominant similar-shaped ice crystals in other cirrus situations. This paper discusses the results of a careful examination of CPI images with Polar Nephelometer observations in order to explain occurrence and non occurrence of the 22° halo feature. Observations highlight that halo peaks are evidenced only by the presence of perfect plate ice crystals (or pristine crystals). On the basis of previous data sets 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 are smooth and featureless and best represent cirrus scattering properties.

A Comparison of Aphelion Cloud Belt Phase Functions Before and After the Mars Year 34 Global Dust Storm

2021 ◽  
Author(s):  
Alex Innanen ◽  
Brittney Cooper ◽  
Charissa Campbell ◽  
Scott Guzewich ◽  
Jacob Kloos ◽  
...  
Keyword(s):  
Dust Storm ◽  
Phase Function ◽  
Dust Storms ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Water Ice ◽  
Ice Cloud ◽  
Sky Survey ◽  
Scattering Phase ◽  
Scattering Phase Function

&lt;p&gt;1. INTRODUCTION&lt;/p&gt;&lt;p&gt;The Mars Science Laboratory (MSL) is located in Gale Crater (4.5&amp;#176;S, 137.4&amp;#176;E), and has been performing cloud observations for the entirety of its mission, since its landing in 2012 [eg. 1,2,3]. One such observation is the Phase Function Sky Survey (PFSS), developed by Cooper et al [3] and instituted in Mars Year (MY) 34 to determine the scattering phase function of Martian water-ice clouds. The clouds of interest form during the Aphelion Cloud Belt (ACB) season (L&lt;sub&gt;s&lt;/sub&gt;=50&amp;#176;-150&amp;#176;), a period of time during which there is an increase in the formation of water-ice clouds around the Martian equator [4]. The PFSS observation was also performed during the MY 35 ACB season and the current MY 36 ACB season.&lt;/p&gt;&lt;p&gt;Following the MY 34 ACB season, Mars experienced a global dust storm which lasted from L&lt;sub&gt;s&lt;/sub&gt;~188&amp;#176; to L&lt;sub&gt;s&lt;/sub&gt;~250&amp;#176; of that Mars year [5]. Global dust storms are planet-encircling storms which occur every few Mars years and can significantly impact the atmosphere leading to increased dust aerosol sizes [6], an increase in middle atmosphere water vapour [7], and the formation of unseasonal water-ice clouds [8]. While the decrease in visibility during the global dust storm itself made cloud observation difficult, comparing the scattering phase function prior to and following the global dust storm can help to understand the long-term impacts of global dust storms on water-ice clouds.&lt;/p&gt;&lt;p&gt;2. METHODS&lt;/p&gt;&lt;p&gt;The PFSS consists of 9 cloud movies of three frames each, taken using MSL&amp;#8217;s navigation cameras, at a variety of pointings in order to observe a large range of scattering angles. The goal of the PFSS is to characterise the scattering properties of water-ice clouds and to determine ice crystal geometry.&amp;#160; In each movie, clouds are identified using mean frame subtraction, and the phase function is computed using the formula derived by Cooper et al [3]. An average phase function can then be computed for the entirety of the ACB season.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.eda718c85da062913791261/sdaolpUECMynit/1202CSPE&amp;app=m&amp;a=0&amp;c=67584351a5c2fde95856e0760f04bbf3&amp;ct=x&amp;pn=gnp.elif&amp;d=1&quot; alt=&quot;Figure 1 &amp;#8211; Temporal Distribution of Phase Function Sky Survey Observations for Mars Years 34 and 35&quot; width=&quot;800&quot; height=&quot;681&quot;&gt;&lt;/p&gt;&lt;p&gt;Figure 1 shows the temporal distributions of PFSS observations taken during MYs 34 and 35. We aim to capture both morning and afternoon observations in order to study any diurnal variability in water-ice clouds.&lt;/p&gt;&lt;p&gt;3. RESULTS AND DISCUSSION&lt;/p&gt;&lt;p&gt;There were a total of 26 PFSS observations taken in MY 35 between L&lt;sub&gt;s&lt;/sub&gt;~50&amp;#176;-160&amp;#176;, evenly distributed between AM and PM observations. Typically, times further from local noon (i.e. earlier in the morning or later in the afternoon) show stronger cloud features, and run less risk of being obscured by the presence of the sun. In all movies in which clouds are detected, a phase function can be calculated, and an average phase function determined for the whole ACB season. &amp;#160;&lt;/p&gt;&lt;p&gt;Future work will look at the water-ice cloud scattering properties for the MY 36 ACB season, allowing us to get more information about the interannual variability of the ACB and to further constrain the ice crystal habit. The PFSS observations will not only assist in our understanding of the long-term atmospheric impacts of global dust storms but also add to a more complete image of time-varying water-ice cloud properties.&lt;/p&gt;

scholarly journals A Method for Deriving the Mean Volume Scattering Phase Function for Zodiacal Dust

1985 ◽  
Vol 85 ◽  
pp. 215-218
Author(s):  
S.S. Hong
Keyword(s):  
Linear Combination ◽  
Phase Function ◽  
Dust Particles ◽  
Zodiacal Light ◽  
Volume Scattering ◽  
Zodiacal Dust ◽  
Scattering Phase ◽  
The Mean ◽  
Scattering Phase Function ◽  
Phase Functions

AbstractA linear combination of 3 Henyey-Greenstein phase functions is substituted for the mean volume scattering phase function in the zodiacal light brightness integral. Results of the integral are then compared with the observed brightness to form residuals. Minimization of the residuals provides us with the best combination of Henyey-Greenstein functions for the scattering phase function of zodiacal dust particles.

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

1997 ◽  
Vol 15 (4) ◽  
pp. 451-459 ◽  
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.

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

1997 ◽  
Vol 15 (4) ◽  
pp. 460-470 ◽  
Author(s):  
O. Crépel ◽  
J.-F. Gayet ◽  
J.-F. Fournol ◽  
S. Oshchepkov
Keyword(s):  
Wind Tunnel ◽  
Phase Function ◽  
Focal Point ◽  
Liquid Water Content ◽  
Ice Crystals ◽  
Inversion Method ◽  
Water Droplets ◽  
Scattering Phase ◽  
Cloud Particles ◽  
Scattering Phase Function

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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