scholarly journals A New Parameterization of an Asymmetry Factor of Cirrus Clouds for Climate Models

2007 ◽  
Vol 64 (11) ◽  
pp. 4140-4150 ◽  
Author(s):  
Qiang Fu
Keyword(s):  
Surface Roughness ◽  
Solar Radiation ◽  
Climate Models ◽  
Particle Surface ◽  
Visible Spectrum ◽  
Cirrus Clouds ◽  
Asymmetry Factor ◽  
Hexagonal Ice ◽  
Ice Particles ◽  
The Asymmetry

Abstract The aspect ratio (AR) of a nonspherical ice particle is identified as the key microphysical parameter to determine its asymmetry factor for solar radiation. The mean effective AR is defined for cirrus clouds containing various nonspherical ice particles. A new parameterization of the asymmetry factor of cirrus clouds in terms of AR and mean effective size, Dge, is developed for solar radiation. It is based on geometric ray-tracing calculations for hexagonal ice crystals with a simple representation of particle surface roughness. The present parameterization well reproduces the asymmetry factors of complicated ice particles such as bullet rosettes, aggregates with rough surfaces, and fractal crystals and agrees well with observations. It thus can be properly applied to cirrus clouds containing various nonspherical ice particles. The asymmetry factor from this parameterization in the visible spectrum ranges from about 0.73 to more than 0.85. Radiative transfer calculations show that for a cirrus cloud with an optical depth of 4 and a solar zenith angle of 60°, changes in AR from 1.0 to 0.5 or from 1.0 to 0.1 result in differences in reflected solar fluxes of about −30 or −70 W m−2, respectively. For the same cloudy conditions, the effect of ice particle surface roughness on the reflected solar flux is found to be about 20 W m−2.

scholarly journals Captured Cirrus Ice Particles in High Definition

2020 ◽  
Author(s):  
Nathan Magee ◽  
Katie Boaggio ◽  
Samantha Staskiewicz ◽  
Aaron Lynn ◽  
Xuanyi Zhao ◽  
...  
Keyword(s):  
Climate Models ◽  
Multiple Scales ◽  
Experimental System ◽  
Particle Morphology ◽  
Technical Difficulty ◽  
Cirrus Clouds ◽  
Environmental Sensors ◽  
High Definition ◽  
Ice Particles ◽  
Particle Imaging

Abstract. Cirrus clouds composed of small ice crystals are often the first solid matter encountered by sunlight as it streams into Earth’s atmosphere. A broad array of recent research has emphasized that photon-particle scattering calculations are very sensitive to ice particle morphology, complexity, and surface roughness. Uncertain variations in these parameters have major implications for successfully parameterizing the radiative ramifications of cirrus clouds in climate models. To date, characterization of the microscale details of cirrus particle morphology has been limited by the particles’ inaccessibility and technical difficulty in capturing imagery with sufficient resolution. Results from a new experimental system achieve much higher resolution images of cirrus ice particles than existing airborne particle imaging systems. The novel system (Ice Cryo-Encapsulation by Balloon, ICE-Ball) employs a balloon-borne payload with environmental sensors and hermetically-sealed cryo-encapsulation cells. The payload captures ice particles from cirrus clouds, seals them, and returns them via parachute for vapor-locked transfer onto a cryo-scanning electron microscopy stage (cryo-SEM). From 2016–2019, the ICE-Ball system has successfully yielded high resolution particle images on nine cirrus-penetrating flights. On several flights, including one highlighted here in detail, thousands of cirrus particles were retrieved and imaged, revealing unanticipated particle morphologies, extensive habit heterogeneity, multiple scales of mesoscale roughening, a wide array of embedded aerosol particles, and even greater complexity than expected.

Influence of Ice Particle Surface Roughening on the Global Cloud Radiative Effect

2013 ◽  
Vol 70 (9) ◽  
pp. 2794-2807 ◽  
Author(s):  
Bingqi Yi ◽  
Ping Yang ◽  
Bryan A. Baum ◽  
Tristan L'Ecuyer ◽  
Lazaros Oreopoulos ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Particle Surface ◽  
Radiation Budget ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Radiative Effect ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Ice Particles ◽  
Cloud Radiative Effect

Abstract Ice clouds influence the climate system by changing the radiation budget and large-scale circulation. Therefore, climate models need to have an accurate representation of ice clouds and their radiative effects. In this paper, new broadband parameterizations for ice cloud bulk scattering properties are developed for severely roughened ice particles. The parameterizations are based on a general habit mixture that includes nine habits (droxtals, hollow/solid columns, plates, solid/hollow bullet rosettes, aggregate of solid columns, and small/large aggregates of plates). The scattering properties for these individual habits incorporate recent advances in light-scattering computations. The influence of ice particle surface roughness on the ice cloud radiative effect is determined through simulations with the Fu–Liou and the GCM version of the Rapid Radiative Transfer Model (RRTMG) codes and the National Center for Atmospheric Research Community Atmosphere Model (CAM, version 5.1). The differences in shortwave (SW) and longwave (LW) radiative effect at both the top of the atmosphere and the surface are determined for smooth and severely roughened ice particles. While the influence of particle roughening on the single-scattering properties is negligible in the LW, the results indicate that ice crystal roughness can change the SW forcing locally by more than 10 W m−2 over a range of effective diameters. The global-averaged SW cloud radiative effect due to ice particle surface roughness is estimated to be roughly 1–2 W m−2. The CAM results indicate that ice particle roughening can result in a large regional SW radiative effect and a small but nonnegligible increase in the global LW cloud radiative effect.

scholarly journals The accommodation coefficient of water molecules on ice-cirrus cloud studies at the AIDA simulation chamber

2012 ◽  
Vol 12 (9) ◽  
pp. 24351-24393 ◽  
Author(s):  
J. Skrotzki ◽  
P. Connolly ◽  
M. Schnaiter ◽  
H. Saathoff ◽  
O. Möhler ◽  
...  
Keyword(s):  
Climate Models ◽  
Interaction Model ◽  
Particle Growth ◽  
Accommodation Coefficient ◽  
Cirrus Clouds ◽  
Radiative Properties ◽  
Water Molecules ◽  
Cirrus Cloud ◽  
Cloud Data ◽  
Ice Particles

Abstract. Cirrus clouds and their impact on the Earth's radiative budget are subjects of current research. The processes governing the growth of cirrus ice particles are central to the radiative properties of cirrus clouds. At temperatures relevant to cirrus clouds, the growth of ice crystals smaller than a few microns in size is strongly influenced by the accommodation coefficient of water molecules on ice, αice, making this parameter relevant for cirrus cloud modeling. However, the experimentally determined magnitude of αice for cirrus temperatures is afflicted with uncertainties of almost three orders of magnitude and values for αice derived from cirrus cloud data lack significance so far. This has motivated dedicated experiments at the cloud chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) to determine αice in the cirrus-relevant temperature interval between 190 K and 235 K under realistic cirrus ice particle growth conditions. The experimental data sets have been evaluated independently with two model approaches: the first relying on the newly developed model SIGMA (Simple Ice Growth Model for determining Alpha), the second one on an established model, ACPIM (Aerosol-Cloud-Precipitation Interaction Model). Within both approaches, a careful uncertainty analysis of the obtained αice values has been carried out for each AIDA experiment. The results show no significant dependence of αice on temperature between 190 K and 235 K. In addition, we find no evidence for a dependence of αice on ice particle size or on water vapor supersaturation for ice particles smaller than 20 μm and supersaturations of up to 70%. The temperature averaged and combined result from both models is αice=0.6−0.4+0.4 which implies that αice may only exert a minor impact on cirrus clouds and their characteristics when compared to the assumption of αice=1. Impact on prior calculations of cirrus cloud properties, e.g. in climate models, with αice typically chosen in the range 0.2–1 is thus expected to be negligible. In any case, we provide a well constrained αice which future cirrus model studies can rely on.

scholarly journals Properties of Cirrus Clouds over the European Arctic (Ny-Ålesund, Svalbard)

2021 ◽  
Vol 13 (22) ◽  
pp. 4555
Author(s):  
Konstantina Nakoudi ◽  
Christoph Ritter ◽  
Iwona S. Stachlewska
Keyword(s):  
Optical Properties ◽  
Particle Surface ◽  
Visible Spectral Region ◽  
Cirrus Clouds ◽  
The Arctic ◽  
Specular Reflections ◽  
Ice Particles ◽  
Westerly Flow ◽  
European Arctic ◽  
Winter Time

Cirrus is the only cloud type capable of inducing daytime cooling or heating at the top of the atmosphere (TOA) and the sign of its radiative effect highly depends on its optical depth. However, the investigation of its geometrical and optical properties over the Arctic is limited. In this work the long-term properties of cirrus clouds are explored for the first time over an Arctic site (Ny-Ålesund, Svalbard) using lidar and radiosonde measurements from 2011 to 2020. The optical properties were quality assured, taking into account the effects of specular reflections and multiple-scattering. Cirrus clouds were generally associated with colder and calmer wind conditions compared to the 2011–2020 climatology. However, the dependence of cirrus properties on temperature and wind speed was not strong. Even though the seasonal cycle was not pronounced, the winter-time cirrus appeared under lower temperatures and stronger wind conditions. Moreover, in winter, geometrically- and optically-thicker cirrus were found and their ice particles tended to be more spherical. The majority of cirrus was associated with westerly flow and westerly cirrus tended to be geometrically-thicker. Overall, optically-thinner layers tended to comprise smaller and less spherical ice crystals, most likely due to reduced water vapor deposition on the particle surface. Compared to lower latitudes, the cirrus layers over Ny-Ålesund were more absorbing in the visible spectral region and they consisted of more spherical ice particles.

Radiative Transfer in Cirrus Clouds: Light Scatting and Spectral Information

Cirrus ◽  
2002 ◽  
Author(s):  
K.N. Liou ◽  
Y. Gu
Keyword(s):  
Radiative Transfer ◽  
Cloud Cover ◽  
Climate Models ◽  
The United States ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Ice Particles ◽  
Ground Based Lidar ◽  
Composition Structure

The importance of cirrus clouds in climate has been recognized in the light of a number of intensive composite field observations: the First ISCCP Regional Experiment (FIRE) I in October-November 1986; FIRE II in November-December 1991; the European experiment on cirrus (ICE/EUCREX) in 1989; Subsonic Aircraft: Contrail and Cloud Effect Special Study (SUCCESS) in April 1996. Based on observations from the ground-based lidar and radar, airborne instrumentation, and satellites, cirrus clouds are typically located in the upper troposphere and lower stratosphere (Liou 1986). The formation, maintenance, and dissipation of cirrus clouds are directly associated with synoptic and mesoscale disturbances as well as related to deep cumulus outflows. Increases of high cloud cover have been reported at a number of urban airports in the United States based on surface observations spanning 40 years (Liou et al. 1990; Frankel et al. 1997). These increases have been attributed to the contrails and water vapor produced by jet airplane traffic. Satellite observations from NOAA polar-orbiting High-Resolution Infrared Radiation Sounder (HIRS) using the CO2 slicing method (Wylie et al. 1994) also show that cirrus cloud cover substantially increased between 60° S and 60° N during a 4-year period from June 1989 to September 1993. Understanding the role of cirrus clouds in climate must begin with reliable modeling of their radiative properties for incorporation in climate models as well as determination of the global variability of their composition, structure, and optical properties. Development of the remote sensing methodologies for the detection and retrieval of the ubiquitous visible and subvisual cirrus clouds requires the basic scattering, absorption, and polarization data for ice crystals in conjunction with appropriate radiative transfer models. We present the fundamentals involving radiative transfer in cirrus clouds and review pertinent research. In section 13.1, an overview of the subject of light scattering by ice crystals is presented in which we discuss a unification of the geometric optics approach for large ice particles and the finite-difference time domain numerical solution for small ice particles, referred to as the unified theory. Section 13.2 presents radiative transfer in cirrus clouds involving two unique properties: orientation of nonspherical ice crystals and cloud inhomogeneity.

scholarly journals Captured cirrus ice particles in high definition

2021 ◽  
Vol 21 (9) ◽  
pp. 7171-7185
Author(s):  
Nathan Magee ◽  
Katie Boaggio ◽  
Samantha Staskiewicz ◽  
Aaron Lynn ◽  
Xuanyi Zhao ◽  
...  
Keyword(s):  
Climate Models ◽  
Multiple Scales ◽  
Experimental System ◽  
Particle Morphology ◽  
Technical Difficulty ◽  
Cirrus Clouds ◽  
Environmental Sensors ◽  
High Definition ◽  
Ice Particles ◽  
Particle Imaging

Abstract. Cirrus clouds composed of small ice crystals are often the first solid matter encountered by sunlight as it streams into Earth's atmosphere. A broad array of recent research has emphasized that photon particle scattering calculations are very sensitive to ice particle morphology, complexity, and surface roughness. Uncertain variations in these parameters have major implications for successfully parameterizing the radiative ramifications of cirrus clouds in climate models. To date, characterization of the microscale details of cirrus particle morphology has been limited by the particles' inaccessibility and technical difficulty in capturing imagery with sufficient resolution. Results from a new experimental system achieve much higher-resolution images of cirrus ice particles than existing airborne-particle imaging systems. The novel system (Ice Cryo-Encapsulation by Balloon, ICE-Ball) employs a balloon-borne payload with environmental sensors and hermetically sealed cryo-encapsulation cells. The payload captures ice particles from cirrus clouds, seals them, and returns them via parachute for vapor-locked transfer onto a cryo-scanning electron microscopy stage (cryo-SEM). From 2015–2019, the ICE-Ball system has successfully yielded high-resolution particle images on nine cirrus-penetrating flights. On several flights, including one highlighted here in detail, thousands of cirrus particles were retrieved and imaged, revealing unanticipated particle morphologies, extensive habit heterogeneity, multiple scales of mesoscopic roughening, a wide array of embedded aerosol particles, and even greater complexity than expected.

scholarly journals The accommodation coefficient of water molecules on ice – cirrus cloud studies at the AIDA simulation chamber

2013 ◽  
Vol 13 (8) ◽  
pp. 4451-4466 ◽  
Author(s):  
J. Skrotzki ◽  
P. Connolly ◽  
M. Schnaiter ◽  
H. Saathoff ◽  
O. Möhler ◽  
...  
Keyword(s):  
Climate Models ◽  
Interaction Model ◽  
Particle Growth ◽  
Accommodation Coefficient ◽  
Cirrus Clouds ◽  
Radiative Properties ◽  
Water Molecules ◽  
Cirrus Cloud ◽  
Cloud Data ◽  
Ice Particles

Abstract. Cirrus clouds and their impact on the Earth's radiative budget are subjects of current research. The processes governing the growth of cirrus ice particles are central to the radiative properties of cirrus clouds. At temperatures relevant to cirrus clouds, the growth of ice crystals smaller than a few microns in size is strongly influenced by the accommodation coefficient of water molecules on ice, αice, making this parameter relevant for cirrus cloud modeling. However, the experimentally determined magnitude of αice for cirrus temperatures is afflicted with uncertainties of almost three orders of magnitude, and values for αice derived from cirrus cloud data lack significance so far. This has motivated dedicated experiments at the cloud chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) to determine αice in the cirrus-relevant temperature interval between 190 K and 235 K under realistic cirrus ice particle growth conditions. The experimental data sets have been evaluated independently with two model approaches: the first relying on the newly developed model SIGMA (Simple Ice Growth Model for determining Alpha), the second one on an established model, ACPIM (Aerosol-Cloud-Precipitation Interaction Model). Within both approaches a careful uncertainty analysis of the obtained αice values has been carried out for each AIDA experiment. The results show no significant dependence of αice on temperature between 190 K and 235 K. In addition, we find no evidence for a dependence of αice on ice particle size or on water vapor supersaturation for ice particles smaller than 20 μm and supersaturations of up to 70%. The temperature-averaged and combined result from both models is αice = 0.7−0.5+0.3, which implies that αice may only exert a minor impact on cirrus clouds and their characteristics when compared to the assumption of αice =1. Impact on prior calculations of cirrus cloud properties, e.g., in climate models, with αice typically chosen in the range 0.2–1 is thus expected to be negligible. In any case, we provide a well-constrained αice which future cirrus model studies can rely on.

Sign in / Sign up

Export Citation Format

Share Document