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Low-level (cloud tops below 2 km) mixed-phase clouds are important in amplifying warming in the Arctic region through positive feedback in cloud fraction, water content and phase. In order to understand the cloud feedbacks in the Arctic region, good knowledge of the vertical distribution of the cloud water content, particle size and phase is required. Here we investigate the vertical extent of the cloud-phase and ice-phase optical properties in six case studies measured in the European Arctic during the ACLOUD campaign. Late spring- and summertime stratiform clouds were sampled in situ over pack ice, marginal sea ice zone and open-ocean surface, with cloud top temperatures varying between −15 and
−1.5 ∘C. The results show that, although the liquid phase dominates the upper parts of the clouds, the ice phase was frequently observed in the lower parts down to cloud top temperatures as warm as −3.8 ∘C.
In the studied vertical cloud profiles, the maximum of average liquid phase microphysical properties, droplet number concentration, effective radius and liquid water content, varied between 23 and 152 cm−3, 19 and
26 µm, 0.09 and 0.63 g m−3, respectively.
The maximum of average ice-phase microphysical properties varied between 0.1 and 57 L−1 for the ice number concentration, 40 and 70 µm for the effective radius, and 0.005 and 0.08 g m−3 for the ice water content. The elevated ice crystal number concentrations and ice water paths observed for clouds, with cloud top temperatures between −3.8 and −8.7 ∘C can be likely attributed to secondary ice production through rime splintering.
Low asymmetry parameters between 0.69 and 0.76 were measured for the mixed-phase ice crystals with a mean value of 0.72.
The effect of the ice-phase optical properties on the radiative transfer calculations was investigated for the four cloud cases potentially affected by secondary ice production. Generally the choice of ice-phase optical properties only has a minor effect on the cloud transmissivity and albedo, except in a case where the ice phase dominated the upper cloud layer extinction. In this case, cloud albedo at solar wavelengths was increased by 10 % when the ice phase was given its measured optical properties instead of treating it as liquid phase.
The presented results highlight the importance of accurate vertical information on cloud phase for radiative transfer and provide a suitable data set for testing microphysical parameterizations in models.

Atmospheric chemistry and physics, 2023-07, Vol.23 (13), p.7611-7633

Investigating the vertical extent and short-wave radiative effects of the ice phase in Arctic summertime low-level clouds

This data set consists of microphysical and light scattering properties of bullet rosette ice crystals as measured by the airborne Particle Habit Imaging and Polar Scattering (PHIPS) probe. This includes maximum dimension, bullet aspect ratio, number of bullets, projected area, bullet hollowness, derived mass, derived effective density, derived terminal velocity, asymmetry parameter and the optical complexity parameter. The PHIPS consists of two CCD cameras and a nephelometer which simultaneously acquire stereo image and angular scattering functions of individual ice crystals and water droplets. Information on the design, operation, and characterization of the PHIPS can be found in Abdelmonem et al. (2016), doi: https://doi.org/10.5194/amt-9-3131-2016, and Schnaiter et al. 2018, https://doi.org/10.5194/amt-11-341-2018. The data was acquired during the DLR sponsored CIRRUS-HL campaign using the High Altitude and Long Range (HALO) research aircraft from June 6th to July 28th 2021 (https://halo-db.pa.op.dlr.de/mission/125). During the campaign, high altitude cirrus were sampled between Northern and Southern Europe during 22 research flights. The PHIPS was operated by the Karlsruhe Institute of Technology Airborne Research Group. Microphysical properties of the bullet rosettes were determined through a combination of automated and manual PHIPS image analysis, using IDL and MATLAB. Environmental variables were provided through the HALO BAHAMAS basic data sensor.  A complete analysis of the data can be found in Wagner et al. 2024, doi: https://doi.org/10.5194/egusphere-2024-3316 (preprint). Funding for the generation and analysis of the data set was provided by the Helmholtz Association’s Initiative and Networking Fund (grant agreement no. VH-NG-1531), the Helmholtz Association research program "Atmosphere and Climate".
File Contents:
This netCDF4 file contains PHIPS measurements taken during the CIRRUS-HL field campaign. The variables in the file are:
AllRosetteFlightNumbersMicroAnalysis: Flight Numbers For All Rosettes Used in the Microphysical Analysis (unitless)
SolidRosetteFlightNumbersMicroAnalysis: Flight Numbers For Solid Rosettes Used in the Microphysical Analysis (unitless)
HollowRosetteFlightNumbersMicroAnalysis: Flight Numbers For Hollow Rosettes Used in the Microphysical Analysis (unitless)
InclusionRosetteFlightNumbersMicroAnalysis: Flight Numbers For Inclusion Rosettes Used in the Microphysical Analysis (unitless)
AllRosetteImageNumbersMicroAnalysis: Image Numbers For All Rosettes Used in the Microphysical Analysis (unitless)
SolidRosetteImageNumbersMicroAnalysis: Image Numbers For Solid Rosettes Used in the Microphysical Analysis (unitless)
HollowRosetteImageNumbersMicroAnalysis: Image Numbers For Hollow Rosettes Used in the Microphysical Analysis (unitless)
InclusionRosetteImageNumbersMicroAnalysis: Image Numbers For Inclusion Rosettes Used in the Microphysical Analysis (unitless) 
AllRosetteFlightNumbersScattAnalysis: Flight Numbers For All Rosettes Used in the Scattering Analysis (unitless) 
SolidRosetteFlightNumbersScattAnalysis: Flight Numbers For Solid Rosettes Used in the Scattering Analysis (unitless)
HollowRosetteFlightNumbersScattAnalysis: Flight Numbers For Hollow Rosettes Used in the Scattering Analysis (unitless)
InclusionRosetteFlightNumbersScattAnalysis: Flight Numbers For Inclusion Rosettes Used in the Scattering Analysis (unitless)
AllRosetteImageNumbersScattAnalysis: Image Numbers For All Rosettes Used in the Scattering Analysis (unitless) 
SolidRosetteImageNumbersScattAnalysis: Image Numbers For Solid Rosettes Used in the Scattering Analysis (unitless)
HollowRosetteImageNumbersScattAnalysis: Image Numbers For Hollow Rosettes Used in the Scattering Analysis (unitless) 
InclusionRosetteImageNumbersScattAnalysis: Image Numbers For Inclusion Rosettes Used in the Scattering Analysis (unitless) 
BulletHollownessFactors: Mean Hollowness Factors Per Bullet Rosette (unitless)
MeanBulletAspectRatios: Mean Bullet Aspect Ratios Per Rosette (unitless) 
MeanBulletLength: Mean Bullet Length Per Rosette (μm)
MeanBulletWidth: Mean Bullet Width Per Rosette (μm)
NumberOfBullets: Number of Bullets Per Rosette (unitless) 
RosetteEffectiveDensity: Effective Density Per Rosette (g cm^-3)
RosetteMass: Mass Per Rosette (mg)
RosetteMaxDimensionsBulletAnalysis: Maximum Dimensions Per Rosette Included in the Bullet Analysis (μm)
RosetteMaxDimensionsMassAnalysis: Maximum Dimensions Per Rosette Included in the Rosette Mass Analysis (μm)
RosetteMaxDimensionsAll: Maximum Dimensions Per Rosette (μm)
RosetteProjectedArea: Projected Area Per Rosette (μm^2)
RosetteTerminalVelocity: Terminal Velocity Per Rosette (m s^-1)
TemperaturesAll: Environmental Temperatures for All Rosettes (°C)
TemperaturesBulletAnalysis: Environmental Temperatures for Rosettes Included in the Bullet Analysis (°C)
TemperaturesHollowRosettes: Environmental Temperatures for Hollow Rosettes Included in the Bullet Analysis (°C)
AreaEquivalentDiameter: Area Equivalent Diameters Included in the Scattering Analysis (μm)
AllDSCS: Differential Scattering Cross Section For All Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
SolidDSCS: Differential Scattering Cross Section For Solid Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
HollowDSCS: Differential Scattering Cross Section For Hollow Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
InclusionDSCS: Differential Scattering Cross Section For Inclusion Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
MeanAllDSCS: Mean Differential Scattering Cross Section After Legendre Polynomial Fitting For All Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
MeanSolidDSCS: Mean Differential Scattering Cross Section After Legendre Polynomial Fitting For Solid Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
MeanHollowDSCS: Mean Differential Scattering Cross Section After Legendre Polynomial Fitting For Hollow Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
MeanInclusionDSCS: Mean Differential Scattering Cross Section After Legendre Polynomial Fitting For Inclusion Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
AED60DSCS: Differential Scattering Cross Section For 60 μm Area Equivalent Diameter Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
AED80DSCS: Differential Scattering Cross Section For 80 μm Area Equivalent Diameter Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
AED125DSCS: Differential Scattering Cross Section For 125 μm Area Equivalent Diameter Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
AED175DSCS: Differential Scattering Cross Section For 175 μm Area Equivalent Diameter Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
AED225DSCS: Differential Scattering Cross Section For 225 μm Area Equivalent Diameter Rosettes Included in the Scattering Analysis (μm^2 sr^-1)
gByType: Asymmetry Parameters Included in the Scattering Analysis by Rosette Type (All, Solid, Hollow, Inclusion) (unitless)
gByAED: Asymmetry Parameters Included in the Scattering Analysis by Rosette Area Equivalent Diameter (60, 80, 125, 175, 225 μm) (unitless)
More information on the data products can befound in "Light scattering and microphysical propertier of atmospheric bullet rosette ice crystals" - Atmospheric Chemistry and Physics.

Bullet Rosette Light Scattering and Microphysical Data from CIRRUS-HL

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Investigating the vertical extent and short-wave radiative effects of the ice phase in Arctic summertime low-level clouds

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Bullet Rosette Light Scattering and Microphysical Data from CIRRUS-HL

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