Impact of ice aggregate parameters on microwave and sub-millimetre scattering properties

Ekelund, Robin; Eriksson, Patrick

doi:10.1016/j.jqsrt.2018.11.013

Cited by 12 publications

(7 citation statements)

References 52 publications

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“…Regardless, Figure 8a–c reveals a clear and consistent trend relating to the orientation of the analogues, whereby at low Reynolds number analogues were observed to fall with the largest principal axis approximately aligned with the vertical fall direction (and the intermediate and smallest principal axes approximately aligned normal to the fall direction), in line with commonly used assumptions (see e.g. Ekelund and Eriksson, 2019). However, the data indicate that, as the Reynolds number increases, the orientation that the analogues adopt changes such that the largest principal axis is aligned further from the vertical fall direction whilst the intermediate principal axis is also aligned further from the horizontal plane; the smallest principal axes remains approximately aligned with the horizontal fall‐normal direction.…”

Section: Case Studysupporting

confidence: 78%

TRAIL: A novel approach for studying the aerodynamics of ice particles

McCorquodale

Westbrook

2020

Quart J Royal Meteoro Soc

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A novel experimental approach for studying the aerodynamics of ice particles is presented. The Trajectory Reconstruction Algorithm implemented through Image anaLysis (TRAIL) produces digital reconstructions of the trajectory and orientation of 3D-printed analogues of ice particles that fall through a quiescent viscous liquid. Data extracted from this analysis can be used to test fall speed parametrisations and investigate the preferred orientation of analogues with complex irregular geometries. Experiments using thin circular discs are used to validate this approach. Measurements from a case study in which an analogue of an aggregate ice particle is used are also reported. Data extracted from the analysis clearly demonstrate important, but poorly understood, aspects of the aerodynamics of atmospheric ice particles. For example, the orientation that the analogue adopts in free fall is shown to depend not only on the geometric shape of the particle, but also on the Reynolds number at which it falls. In addition, measurements of the drag coefficient indicate that the accuracy of fall speed parametrisations reduces at high Reynolds number due to the onset of unsteady motions.

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Section: Case Studysupporting

confidence: 78%

TRAIL: A novel approach for studying the aerodynamics of ice particles

McCorquodale

Westbrook

2020

Quart J Royal Meteoro Soc

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“…Rosenkranz (1998) and nitrogen absorption using the standard profile by Liebe et al (1993). Furthermore, liquid clouds are treated using the absorption model by Ellison (2007) (scattering by liquid clouds is omitted).…”

Section: Arts Setupmentioning

confidence: 99%

Using passive and active observations at microwave and sub-millimetre wavelengths to constrain ice particle models

2020

Self Cite

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Abstract. Satellite microwave remote sensing is an important tool for determining the distribution of atmospheric ice globally. The upcoming Ice Cloud Imager (ICI) will provide unprecedented measurements at sub-millimetre frequencies, employing channels up to 664 GHz. However, the utilization of such measurements requires detailed data on how individual ice particles scatter and absorb radiation, i.e. single scattering data. Several single scattering databases are currently available, with the one by Eriksson et al. (2018) specifically tailored to ICI. This study attempts to validate and constrain the large set of particle models available in this database to a smaller and more manageable set. A combined active and passive model framework is developed and employed, which converts CloudSat observations to simulated brightness temperatures (TBs) measured by the Global Precipitation Measurement (GPM) Microwave Imager (GMI) and ICI. Simulations covering about 1 month in the tropical Pacific Ocean are performed, assuming different microphysical settings realized as combinations of the particle model and particle size distribution (PSD). Firstly, it is found that when the CloudSat inversions and the passive forward model are considered separately, the assumed particle model and PSD have a considerable impact on both radar-retrieved ice water content (IWC) and simulated TBs. Conversely, when the combined active and passive framework is employed instead, the uncertainty due to the assumed particle model is significantly reduced. Furthermore, simulated TBs for almost all the tested microphysical combinations, from a statistical point of view, agree well with GMI measurements (166, 186.31, and 190.31 GHz), indicating the robustness of the simulations. However, it is difficult to identify a particle model that outperforms any other. One aggregate particle model, composed of columns, yields marginally better agreement with GMI compared to the other particles, mainly for the most severe cases of deep convection. Of the tested PSDs, the one by McFarquhar and Heymsfield (1997) is found to give the best overall agreement with GMI and also yields radar dBZ–IWC relationships closely matching measurements by Protat et al. (2016). Only one particle, modelled as an air–ice mixture spheroid, performs poorly overall. On the other hand, simulations at the higher ICI frequencies (328.65, 334.65, and 668.2 GHz) show significantly higher sensitivity to the assumed particle model. This study thus points to the potential use of combined ICI and 94 GHz radar measurements to constrain ice hydrometeor properties in radiative transfer (RT) using the method demonstrated in this paper.

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“…For example, the large plate aggregate habit is complemented with the thick plate crystal. These three particle models are intended to be generic, exhibiting different levels of extinction (Ekelund and Eriksson, 2019). The name used to represent the habit mixture under 'Habit' in 5 of Delanoë et al (2014).…”

Section: Ice Hydrometeor Particle Modelsmentioning

confidence: 99%

“…Particle habit and PSD can both depend strongly on environmental conditions and cloud-type (Yau and Rogers, 1989) and therefore do not occur at the same rate (O'Shea et al, 2016). Additionally, the parameters describing the assumed particle model (including the aARO factor) can have a strong impact on the mapping of IWC from reflectivity inversions (Ekelund and Eriksson, 2019). In light of these considerations, the six particle models are not used with equal frequency within the simulations.…”

Impact of ice aggregate parameters on microwave and sub-millimetre scattering properties

Cited by 12 publications

References 52 publications

TRAIL: A novel approach for studying the aerodynamics of ice particles

TRAIL: A novel approach for studying the aerodynamics of ice particles

Using passive and active observations at microwave and sub-millimetre wavelengths to constrain ice particle models

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