For visitors from abroad From a Water Molecule to a Snowflake
This is a Japanese-language educational site that follows the physics of snow, in twelve stages, from a single H2O molecule (0.3 nm) to a falling snowflake (~2 cm) — with 25 interactive 3D models you can rotate and adjust.
Reading this site in your language.
All pages declare lang="ja", so modern browsers (Chrome, Edge, Safari, Firefox with a
translation extension) will offer to translate each page automatically — look for the translate
icon in the address bar or the context menu. Machine translation of the prose is generally good;
please treat translated technical terms with care and refer to the glossary below,
which uses the official English names from the global classification papers.
What this site tries to be
Every factual claim on the site has been checked against primary sources where possible — the global classification of snow crystals (Kikuchi et al. 2012, 2013), crystal-structure analyses of low-temperature types (Sato & Kikuchi 1985, 1989), electron-microscope studies of riming (Rango et al. 2003), laboratory aggregation efficiencies (Connolly et al. 2012), the Japan Meteorological Agency's official definitions, and others. Model assumptions and simplifications are disclosed on each page; claims we could not source have been removed, and every correction is logged on the notes page (Japanese). The interactive models are pedagogical schematics — they encode real crystallographic constraints (hexagonal symmetry, axis orientations) but are not quantitative simulations, and each page says exactly which is which.
The twelve stages
| Stage | Page (Japanese) | What it covers |
|---|---|---|
| 1 | 水分子 | The water molecule: bent shape, polarity, hydrogen bonding, tetrahedral coordination. |
| 2 | 六員環 | Six-membered rings of ice: chair form within layers, boat form between layers. |
| 3 | 氷Ihの結晶 | The ice Ih lattice, basal and prism faces, ice rules and proton disorder. |
| 4 | 表面とステップ | Crystal surfaces at the nm scale: steps, terraces, the quasi-liquid layer. |
| 5 | 初期氷晶 | Freezing droplets, droxtals, germ crystals (G group), pyramidal faces and odd-radius halos. |
| 6 | 晶癖 | Habit changes with temperature: plates vs. columns, capped columns, a KMC toy model. |
| 7 | 薄板・中空・表裏 | Hollow columns and sheaths, double plates, face asymmetry. |
| 8 | 主枝 | Branching: diffusion instability, the Berg effect vs. Mullins–Sekerka, sector plates. |
| 9 | 副枝 | Sidebranches, 60° geometry on plate-type dendrites, a Reiter-style cellular automaton. |
| 10 | 立体・多結晶 | Polycrystals: bullet rosettes, crossed plates, and the low-temperature types — skeletal tetragons, Gohei twins, spearheads, seagull crystals. |
| 11 | 雲粒付着 | Riming: cloud droplets freezing onto crystals, R1–R4, graupel; JMA definitions. |
| 12 | 雪片 | Aggregation into snowflakes: collision, interlocking, sintering; new-snow porosity. |
Glossary of key crystal types
Official English names follow Table 3 of Kikuchi et al. (2012) and the global classification (Kikuchi et al. 2013, Atmospheric Research 132–133).
| Japanese | Official English name | Code |
|---|---|---|
| 御幣 | Gohei twin | CP7a |
| 矛先 | Spearhead | CP8a |
| 多重矛先 | Multiple spearhead | CP8d |
| 鴎状結晶 | Seagull-type crystal | CP9 |
| 骸晶四角形 | Skeletal tetragon | CP6a |
| 多重骸晶四角形 | Multiple skeletal tetragon | CP6c |
| 砲弾集合 | Combination of bullets (bullet rosettes) | C4d |
| 鞘 | Sheath | C2a |
| 骸晶角柱 | Skeletal column | C3b |
| 細長角柱 | Long solid column | C3d |
| 鼓状結晶 | Column with plane-type crystals (capped column) | CP1 |
| 交差角板 | Crossed plates | CP4a |
| 初期結晶群 | Germ of ice crystal group | G |
| 十四面体氷晶／二十面体氷晶 | 14-faces / 20-faces polyhedral ice crystal | G3a / G3b |
| 雲粒付結晶 | Rimed crystal | R1 |
| 霰（あられ） | Graupel | R4 |
| 樹枝六花 | Dendrite (dendrite-type crystal) | P3b |
Using the interactive models
Model labels and readouts are in Japanese, but the controls are simple sliders and buttons — drag to rotate, use the viewpoint buttons (真上から = from above, 真横から = from the side, 斜めから = oblique), and move sliders to change the labelled quantity. Browser translation also translates most model text in place.
Selected references
Kikuchi, Kameda, Higuchi, Yamashita and working group (2012), Seppyo 74(3), 223–241 (Japanese, with the official English name table) · Kikuchi et al. (2013), Atmospheric Research 132–133, 460–472 · Sato & Kikuchi (1985), Annals of Glaciology 6 · Sato & Kikuchi (1989), J. Meteor. Soc. Japan 67(4) · Rango et al. (2003), Scanning 25 · Connolly et al. (2012), Atmos. Chem. Phys. 12 · Reiter (2005), Chaos, Solitons & Fractals 23. A full list, with what was verified against which source and every logged correction, is on the notes page.
A full English edition? This overview is hand-written; the twelve main pages are currently Japanese-only, by design — we did not want to bake in machine translations of carefully verified scientific prose. If a fully translated English edition would be useful to you, the correction-log workflow of this site makes it feasible as a maintained parallel edition.