Fig 7 - uploaded by Maria Gritsevich
Content may be subject to copyright.
Ice crystals and their orientations that create rare halos. From left to right: A column ice crystal in Parry orientation, a plate ice crystal in Lowitz orientation, and a pyramidal ice crystal in plate orientation.
Source publication
Atmospheric halos are a light scattering phenomenon caused by airborne ice crystals in the atmosphere. Halos can be seen by the naked eye. They provide the observer the information on the kinds of ice crystals present in the sky during a halo display. A combination of ice crystals’ shape, their orientation, and light ray paths through the crystals...
Contexts in source publication
Context 1
... between two prism faces. An alternative Lowitz orientation is similar, but the horizontal axis goes through two opposite prism faces. Although the so-called alternative Lowitz orientation has been discussed in halo literature for decades, arcs produced by ice crystals in this orientation were documented first time on 28 June 2019 in Finland. In Fig. 7 Parry orientation is on the left. In ray paths in Parry orientated ice crystals the horizontal crystal face on the top is agreed to be the face number 3. A usual assumption is that to attain a Parry orientation, a column ice crystal has to be longer (c/a ratio is bigger) than to attain a column orienta- tion, but there are observations ...
Context 2
... ray paths in Parry orientated ice crystals the horizontal crystal face on the top is agreed to be the face number 3. A usual assumption is that to attain a Parry orientation, a column ice crystal has to be longer (c/a ratio is bigger) than to attain a column orienta- tion, but there are observations contradicting the assumption that the orientation and the c/a ratio are always correlated. The Lowitz orientation in the middle ( Fig. 7 ), where only A-axis is horizontal, is called a classical or a spinning Lowitz orientation [2] . Observations have proven that the limited or restricted Lowitz orientation where the crystal is only tilted around the A-axis may be more common. ...
Citations
... Ice crystals formed in the atmosphere show a large variety of sophisticated and, often, near-perfect geometric shapes 1 (Fig. 1a). The interaction of sunlight with such crystals sometimes results in well-known optical phenomena, called halos 2 , whose nature is directly related to the shape of the crystals 3 . ...
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.
