Characterization of the texture of large hailstones

Maurine Montagnat , Mathieu Bourcier (1) , Armelle Philip (1) , Paul D Bons (2) , Catherine C Bauer (2) , Paul Deconinck (3) , Pierre Hereil (3)

1 IGE - Institut des Géosciences de l’Environnement
2 Department of Geosciences [Tübingen]
3 Thiot ingénierie, Puybrun

Hailstone structures have been studied for over a century, but so far mainly by manual optical means. This paper presents new texture and microstructure data (i.e. crystal lattice orientations, grain sizes and shapes) measured with an Automatic Ice Texture Analyzer (AITA) which gives access to high spatial and angular resolutions. The hailstones show two main characteristics; (i) they are structured with several concentric layers composed of alternating fine equi-axed grains and coarse elongated and radially oriented grains, (ii) they show two texture types with c-axes oriented either parallel or perpendicular to 5 the radial direction. Such textures are compared with the ones observed in lake S1 and S2 ices, respectively. The S1 texture type (with c-axes parallel to the columnar crystals that grew in the radial direction) may result from epitaxial growth from a polycrystalline embryo, while S2 texture (c-axes in the plan perpendicular to the column direction) may result from the growth from an embryo made of large crystals with only one or few crystallographic orientations. Owing to these high resolution measurements of both microstructure and texture, we are able to come back to a long-term discussion concerning the growth 10 mechanisms of large hailstones and clarify the main processes at play.

Domaines: Glaciologie

Maurine Montagnat, Mathieu Bourcier, Armelle Philip, Paul D Bons, Catherine C Bauer, et al.. Characterization of the texture of large hailstones. 2020. ⟨hal-02942822⟩