Snow Crystals in Hokkaido ( Note of the Snow Crystal Observation )

Ⅰ Needle crystals	1. Simple needle	a. Elementary needle b. Bundle of elementary needles
	2. Combination
Ⅱ Columnar crystal	1. Simple column	a. Pyramid, Bullet type b. Hexagonal column
	2. Combination	a. Combination of bullets b. Combination of columns
Ⅲ Plane crystal	1. Regular crystal developed in 　　one plane	a. Symple plate b. Blanches in sector form c. Plate with simple extensions d. Broad branches e. Simple stellar form f. Ordinary dendritic form g. Fernlike crystal h. Stellar crystal with plates at ends i. Plate with dendritic extensions.
	2. Crystal with irregular number 　　of branches	a. Three-branched crystal b. Four-branched crystal c. Others
	3. Crystal with twelve branches	a. Fernlike crystal b. Broad branches
	4. Malformed crystal	Many varieties
	5. Spacial assemblage of plane 　　branches	a. Special hexagonal type b. Radiating type
Ⅳ Combination of 　　column and plane 　　crystals	1. Column with plane crystals at 　　both ends	a. Column with plates b. Column with dendritic crystal c. Complicated capped column
	2. Bullets with plane crystals	a. Bullets with plates b. Bullets with dendritic crystals
	3. Irregular assemblage of columns and plates
Ⅴ Columnar crystals with extended side planes
Ⅵ Rimed crystals 　　(crystals with 　　cloud particles 　　attathed )	1. Rimed crystal
	2. Thick plate
	3. Graupellike snow	a. Hexagonal type b. Lump type
	4. Graupel	a. Hexagonal graupel b. Lump graupel c. Conelike graupel
Ⅶ Irregular snow 　　particle	1. Ice particle
	2. Rimed particle
	3. Miscellaneous

References

　1) Nakaya, U., 1954: Snow Crystals, Natural and Artifical. Harvard University Press, Cambridge, 510pp,
　2) Magono, C. and C. W. Lee, 1966: Meteorological classificasion of natural snow crystals. J. Fac. Sci., Hokkaido Univ., Ser. Ⅶ 4, 321-335.
　3) Kikuchi, K., T. Kameda, K. Higuchi, A. Yamashita and Working group members for new classification of snow crystals, 2013: A global
　　　classification of snow crystals, ice crystals, and solid precipitation based on observations from middle latitudes to polar regions. Atmos.Res.,
　　　132-133, 460-472(doi.org/10.1016/j.atmosres.2013.06.006).
　4) 小林貞作，1983：雪の結晶　冬のエフェメラル．北海道大学図書刊行会，39pp．
　5) 村上正隆，2005：降雪雲と降雪分布（降雪の気象）．雪と氷の辞典，（社）日本雪氷学会監修，朝倉書店，59-80．
　6) Kobayashi, T., 1967: On the variation of ice crystal habit with temperature. Physics of snow and ice: Proceedings, 1(1), 95-104.
　7) Auer Jr., A. H., 1971: Observation of ice crystal nucleation by droplet freezing in natural clouds. J. Atmos. Sci., 28, 285-290.
　8) Magono, C, 1973: Recent problems on the study of snow crystals. Geophysical Bulletin of Hokkaido Univ., 29, 33-50 (in Japanese).
　9) Kikuchi, K., 1987: The Discovery of Eighteen-Branched Snow Crystals. J. Met. Soc. Japan., 65, 309-311.
　10) Kikuchi, K. and H. Uyeda, 1998: Formation mechanisms of multibranched snow crystals (twelve-, eighteen-, twenty-four-branched crystals).
　　　 Atmos. Res. 47-48, 169-179.

Introduction

　In Hokkaido, Japan, it begins to snow with periodic wind of winter becoming strong. The temperature gradually lowers every day and becomes less than 0 ℃ all day. So, the snow becomes leave on ground without melting. I consider this is the same process anywhere in the world if it is Temperate Zone district in a high latitude area.

　We usually distinguish a snowy state from powdery snow, large - snowflakes, or sleet. But there can recognize a figure of a snow crystal when I enlarge it with a microscope even at the time of any kind of snow.

　It is said that a snow crystal does not have a thing of form same for two
because the form is delicately different when observe it with a microscope.
Therefore, there is fresh surprise whenever I watch another one.

　But, I think there may be completely a crystal of the same form when I
see innumerable snow falling in sequence from the sky bacause a snow
crystal such as a minute glasswork continues to fall unlimitedly as far as
the eye can see.

　In this site, I show snow crystals which photographed in Hokkaido and
photographed it since I make a replica once. I want to introduce one part
of its mysterious figure.

Classification of snow crystals

　It is known that form of a snow crystal changes by climatic condition when it falls. In other words, it is changed mainly by temperature and the humidity. Dr. Ukichiro Nakaya who clarified it stated that "the snow crystal is a letter sent from the sky" and showed that a state of the atmosphere from the upper air at that time to the surface of the ground was ticked away in form and a design of a snow crystal¹⁾.

　In his study, Dr. Nakaya repeated observation in Sapporo City and Mt. Tokachi and took a picture of more than 3,000 pieces of natural snow. And he made general classification list of snow crystals which classified snow crystals as seven kinds greatly.

　In his classification, snow crystals are classified into "Needle crystal", "Columnar crystal", "Plane crystal", "Combination of column and plane crystals", "Columnar crystal with extended side planes", "Rimed crystal", and "Irregular snow particle". In the later study, snow crystals seem to be classified more finely^{2), 3)}. But, I think to call snow crystals along his classification in this site because a study of Dr. Nakaya was carried out mainly in Hokkaido.

　In above table, I showed only the name of snow crystals which came out to his general classification . So, it may be difficult for you to imagine the form of each snow crystal. I hope to look at figures indicated in his report, if you want to know them preciously. But, it is able to understand by this table that a regular form of snow crystal which we have an image generally is only one part of snow crystals which falls on ground innumerably.

Climatic condition of winter and snowfall in Hokkaido

　When it snows in Hokkaido, it is brought in West area by periodic wind type, and in East area by a low pressure type. In this way, by the difference of a snowy model to fall, there is the case that kinds of snow crystal observed by an area are different.

　For example, in West area, line-shaped snow cloud flocks with periodic wind in sequence and brings snow. In this area, Rimed crystals, that is a lot of cloud particles were attached-shaped snow, and hail-shaped snow is mainly observed. Otherwise, in area of Daisetsuzan National Park (Middle area of Hokkaido), I can observe beautiful plane crystals which has a large smooth surface. It is said that these beautiful snow crystals are shaped in snow cloud which occurs in Middle area by conflicting in a mountain after the periodic wind has once brought snow in West area⁴⁾.That is snow of periodic wind type.

　In contrast, fine weather continues day after day in East area of Hokkaido
in winter. The reason is that most of snow cloud disappear while the periodic
wind reches there. In East area, a large quantity of snow is often brought
when the low pressure with a font passes by. And it is known that snow
crystals which shaped simple hexagonal plate or column are mainly formed
in a cloud which opens in the north side of a warm front⁵⁾. Thus, the kind
of snow crystals observed on the ground is different from that of West and
MIddle area.

　In addition, I meet with really various snowfalls when I repeat observation
of snow crystals. I have surprised to meet with the scene where needle
crystals fell into suddenly from the dusky snow cloud which wrapped up the
sky. I have met the mysterious scene that large fernlike crystals fell under
the night sky where stars shined. And I have admired to fall without being
broken when I found the dendritic crystal which grew up greatly in a blizzard
of a low pressure.

　In such a weather phenomenon, I am made to realize that there is a lump
of changing various atmosphere. Therefore, I think that repeating observation
in various areas is more important than going to one area where the beautiful
crystals are falling in order to observe every kind of snow crystals falling in
Hokkaido.

About form of snow crystals

　The regular crystal developed in one plane is very beautiful because the symmetry form is not able to consider as a natural product.

　It is known that the form of a snow crystal is basically a hexagonal column which consist of two pieces, that is two basal surfaces and six pieces of cylinder surfaces. And it grows up in the plane crystals such as the simple plate or the fernlike crystal if growth of the cylinder surface is fast.

　Otherwise, it grows up to a slim crystal when growth of the basal surface is fast, such as the needle crystal or the columnar crystal. And it seems to change by the temperature when it grows up whether growth of which surface is fast.

　Why the growth direction of a crystal turns into by the temperature is not mentioned here, but this is the crystal habit change of snow. It is appeared the tempereture of changing is 0 ℃> plane >-4 ℃> columnar >-10 ℃> plane >-22 ℃> columnar⁶⁾. There is three changing point as temperature falls.

　Thus, snow crystals grow up in the form of both the column and the planes are combinationed when it step over the temperature of a crystal habit change during it falls on ground.

　The difference of form by such a crystal habit change is also seen in frost crystals as well as snow crystals. I introduce about frost crystals in page 4.

　Sometimes, I find a small hexagonal plane existing in the center of a plane crystal. Such a crystal becomes structure of two pieces of planes so that both basal surfaces of small hexagonal column develop. Therefore, It should become "H" structure when I observe it from the side.This type of plane crystal is called "double plate type".

　In addition, when I repeated the observation, it is noticed that some plane clystals have a small circular pattern in the center. It is known that this type of crystals are also double plate type. But, in this case, both planes are connected by spherical structure derived from frozen water droplets that became origin of the snow crystal^{7), 8)}. Therefore, the small circular pattern is recognized in some plane crystals of double plate type.

　A crystal of twelve-branched is also consisted with some pieces of planes but it seems to be divided from the crystals of doble plate type described above. In recent report, twelve-branched crystals are classified in "Saparated and multiple dendrite type"³⁾. Thus, the formation mechanism of twelve-branched crystals is seemed to be different from that of general double plate type of plane crystals.

　Dr. Nakaya describes in his book that these three pieces of basic crystals were sometimes piled up and become a crystal of eighteen-branched. There are really the reports that eighteen-branched or twenry-four crystals were observed in the Arctic area of Canada^{9), 10)}. So, it may be falling somewhere in Hokkaido.