Light scattering by airborne ice crystals – An inventory of atmospheric halos

Moilanen, Jarmo; Gritsevich, Maria

doi:10.1016/j.jqsrt.2022.108313

Cited by 7 publications

(2 citation statements)

References 32 publications

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“…When ice crystals are horizontally oriented, this gives them distinctive optical characteristics (Cho et al, 1981;Sassen, 1987). For instance, horizontal crystals can create a range of atmospheric optical phenomena such as sun dogs, light pillars, and Parry arcs, among others (Moilanen and Gritsevich, 2022). Additionally, spiralling ice crystals have been hypothesized to cause the rare 'Bottlinger's rings' effect (Lynch et al, 1994;Tränkle and Riikonen, 1996).…”

Section: Importance Of Orientation Of Ice Crystalsmentioning

confidence: 99%

Stable and unstable fall motions of plate-like ice crystal analogues

Stout,

Westbrook,

Stein

et al. 2024

Preprint

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Abstract. The orientation of ice crystals affects their microphysical behaviour, growth, and precipitation. Orientation also affects interaction with electromagnetic radiation, and through this, influences remote sensing signals, in-situ observations, and optical effects. Fall behaviours of a variety of 3D-printed plate-like ice crystal analogues in a tank of water-glycerine mixture are observed with multi-view cameras and digitally reconstructed to simulate falling of ice crystals in the atmosphere. Four main falling regimes were observed: stable, zigzag, transitional, and spiralling. Stable motion is characterised by no resolvable fluctuations in velocity or orientation, with the maximum dimension oriented horizontally. The zigzagging regime is characterised by a back-and-forth swing, corresponding to a time series of inclination angle approximated by a rectified sine wave. In the spiralling regime, analogues consistently incline at an angle between 7 and 28 degrees, depending on particle shape. Transitional behaviour exhibits motion in between spiral and zigzag, similar to that of a falling spherical pendulum. The inclination angles that unstable planar ice crystals make with the horizontal plane are found to have a non-zero mode. This observed behaviour does not fit the Gaussian model of inclination angle that is common in the literature. The typical Reynolds number when oscillations start is strongly dependent on shape: solid hexagonal plates begin to oscillate at Re = 237, whereas several dendritic shapes remain stable throughout all experiments, even at Re > 1000.

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Section: Importance Of Orientation Of Ice Crystalsmentioning

confidence: 99%

Stable and unstable fall motions of plate-like ice crystal analogues

Stout,

Westbrook,

Stein

et al. 2024

Preprint

View full text Add to dashboard Cite

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“…An attempt is also being made to achieve automated observations of halos using a sun-tracking camera (Forster et al, 2017) or a total sky imager (Boyd et al, 2019). Image processing techniques can be used to observe even faint halos or other atmospheric optical phenomena in photographs more clearly, which can greatly aid in these types of studies (Riikonen et al, 2000;Moilanen and Gritsevich, 2022;Großmann et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Revealing halos concealed by cirrus clouds

Ayatsuka

2024

Atmos. Meas. Tech.

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Abstract. Many types of halos (including arcs) appear in the sky. Each type of halo corresponds to the shape and orientation of ice crystals in clouds, and reflects the state of the atmosphere; therefore observing them from the ground greatly helps in understanding the state of the atmosphere. However, halos are easily obscured by the contrast of the cloud itself, making it difficult to observe them. This difficulty can be overcome by enhancing halos in images, for which various techniques have been developed. This study describes the construction of a sky-color model for halos and a new effective algorithm to reveal halos in images.

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Unraveling the optical shape of snow

et al. 2023

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The reflection of sunlight off the snow is a major driver of the Earth’s climate. This reflection is governed by the shape and arrangement of ice crystals at the micrometer scale, called snow microstructure. However, snow optical models overlook the complexity of this microstructure by using simple shapes, and mainly spheres. The use of these various shapes leads to large uncertainties in climate modeling, which could reach 1.2 K in global air temperature. Here, we accurately simulate light propagation in three-dimensional images of natural snow at the micrometer scale, revealing the optical shape of snow. This optical shape is neither spherical nor close to the other idealized shapes commonly used in models. Instead, it more closely approximates a collection of convex particles without symmetry. Besides providing a more realistic representation of snow in the visible and near-infrared spectral region (400 to 1400 nm), this breakthrough can be directly used in climate models, reducing by 3 the uncertainties in global air temperature related to the optical shape of snow.

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Light scattering by airborne ice crystals – An inventory of atmospheric halos

Cited by 7 publications

References 32 publications

Stable and unstable fall motions of plate-like ice crystal analogues

Stable and unstable fall motions of plate-like ice crystal analogues

Revealing halos concealed by cirrus clouds

Unraveling the optical shape of snow

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