Caaml V5.0 2010-08-05 Avisualanche Consulting CAAML dictionary for enumerations defined in IACS document on the classification for seasonal snow on the ground (Fierz, C., Armstrong, R.L., Durand, Y., Etchevers, P., Greene, E., McClung, D.M., Nishimura, K., Satyawali, P.K. and Sokratov, S.A. 2009. The International Classification for Seasonal Snow on the Ground. IHP-VII Technical Documents in Hydrology N°83, IACS Contribution N°1, UNESCO-IHP, Paris) IACS2009 The International Classification for Seasonal Snow on the Ground GrainShape Grain Shape (Form) IACS document section 1.1 and appendix A PP Precipitation Particles Prismatic crystal, solid or hollow PPco Precipitation Particles - Columns Needle-like, approximately cylindrical PPnd Precipitation Particles - Needles Plate-like, mostly hexagonal PPpl Precipitation Particles - Plates six-fold star-like, planaer or spatial PPsd Precipitation Particles - Stellars, Dendrites Clusters of very small crystals PPir Precipitation Particles - Irregular crystals Heavily rimes particles, spherical, conical, hexagonal or irregular in shape PPgp Precipitation Particles - Graupel Laminar internal structure, trnalucent or milky glazed surface PPhl Precipitation Particles - Hail Transparent, mostly small spheriods PPip Precipitation Particles - Ice pellets Irregular depsosits or longer cones and needles pointing into the wind PPrm Precipitation Particles - Rime MM Machine Made Snow Small spherical particles, often showing protrusions, a result of the freezing process; may be partially hollow MMrp Machine Made Snow - Round polycrystaline particles Ice plates, shard-like MMci Machine Made Snow - Crushed ice particles DF Decomposing and Fragmented precipitation particles Characteristic shapes of precipitation particles still recognizable; often partly rounded. DFdc Partially decomposed precipitation particles DFbk Wind-broken precipitation particles RG Rounded Grains Rounded, usually elongated particles of size < 0.25 mm; highly sintered RGsr Rounded Grains - Small rounded particels Rounded, usually elongated particles of size > 0.25 mm; well sintered RGlg Rounded Grains Small, broken or abraded, closely-packed particles; well sintered RGwp Rounded Grains - Wind packed Rounded, usually elongated particles with developing facets RGxf Rounded Grains FC Faceted Crystals Solid faceted crystals; usually hexagonal prisms FCso Solid faceted particles Faceted crystals in surface layer FCsf Near surface faceted particles Faceted crystals with rounding facets and corners FCxr Rounding faceted particles DH Depth Hoar Striated, hollow skeleton type crystals; usually cup-shaped DHcp Depth Hoar - Hollow cups Prismatic, hollow skeleton type crystals with glassy faces but few striations DHpr Depth Hoar - Hollow prisms Hollow skeleton type crystals arranged in chains DHch Chains of depth hoar Large, heavily striated crystals; either solid or skeleton type DHla Depth Hoar - large striated crystals Hollow skeleton type crystals with rounding of sharp edges, corners, and striations DHxr Rounding depth hoar SH Surface Hoar Striated, usually flat crystals; sometimes needle-like SHsu Surface Hoar crystals Striated, planar or hollow skeleton type crystals grown in cavities; orientation often random SHcv Cavity or cravasse hoar Surface hoar crystal with rounding of sharp edges, corners and striations SHxr Rounding surface Hoar MF Melt Forms Clustered rounded crystals held by large ice-to-ice bonds; water in internal veins among three crystals or two grain boundaries MFcl Melt Forms - Clustered round grains Individual crystals are frozen into a solid polycrystalline particle, either wet or refrozen MFpc Melt Forms - Rounded polycrystals Separated rounded particles completely immersed in water MFsl Melt Forms - Slush Crust of recognizable melt-freeze polycrystals MFcr Melt Forms - Melt-freeze crust IF Ice Formations Horizontal ice layer IFil Ice Formations - Ice layer Vertical ice body IFic Ice Formations - Ice column Basal ice layer IFbi Ice Formations - Basal ice Thin, transparent glaze or clear film of ice on the surface IFrc Ice Formations - Rain crust Thin, transparent and shiny glaze or clear film of ice on the surface IFsc Ice Formations - Sun crusts, firnspiegel Hardness is the resistance to penetration of an object into snow. Hardness measurements produce a relative index value that depends on both the operator and the instrument; therefore, the device has to be specified. A widely accepted instrument is the Swiss rammsonde. Using this instrument, ‘ram resistance’ is a quasi-objective measure of snow hardness in newtons. Profiles of snow hardness can be obtained from the wall of a snow pit using so called push-pull gauges (see, e.g., Takeuchi et al., 1998). De Quervain (1950) introduced a hand test with five steps that he assigned rather intuitively to ram resistance ranges. The test uses objects of decreasing areas. For any single layer of the snowpack, hand hardness index corresponds to the first object that can be gently pushed into the snow, thereby not exceeding a penetration force of 10–15 N. The hand test is a relative, subjective measurement. It is thus suggested that operators ‘calibrate’ themselves against colleagues or against another snow hardness measuring instrument such as the ramsonde. Hardness Snow Hardness IACS document section 1.4 Fist F Very soft 4 fingers 4F Soft 1 finger 1F Medium Pencil - tip of a sharpened pencil P Hard Knife blade K Very Hard Ice I Ice Liquid water content is defined as the amount of water within the snow that is in the liquid phase. This parameter is synonymous with the free-water content of a snow sample. Liquid water in snow originates from either melt, rain, or a combination of the two. Measurements of liquid water content or wetness are expressed as either a volume (Omegaw,V or LWCV) or mass (Omegaw,m or LWCm) fraction. Both can be reported as a percent (%), which usually requires a separate measurement of density. A general classification of liquid water content Omegaw,V in terms of volume fraction is given in Table 1.5. Lwc Liquid Water Content IACS document section 1.5 Usually Ts is below 0°C, but dry snow can occur at any temperature up to 0°C. Disaggregated snow grains have little tendency to adhere to each other when pressed together, as in making a snowball. D Dry Ts = 0°C. The water is not visible even at 10x magnification. When lightly crushed, the snow has a distinct tendency to stick together. M Moist Ts = 0°C. The water can be recognised at 10x magnification by its meniscus between adjacent snow grains, but water cannot be pressed out by moderately squeezing the snow in the hands (pendular regime). W Wet Ts = 0°C. The water can be pressed out by moderately squeezing the snow in the hands, but an appreciable amount of air is confined within the pores (funicular regime). V Very wet Ts = 0°C. The snow is soaked with water and contains a volume fraction of air from 20 to 40% (funicular regime). S Soaked This subsection refers to the general appearance of the snow surface. These surface features are due to the following main processes: deposition, redistribution and erosion by wind, melting and refreezing, sublimation and evaporation, and rain. A classification that allows the characterisation of vast areas as found in polar and sub-polar regions as well as alpine snow surfaces has not yet been developed. However, the snow surface can be described more generally in terms of roughness elements that are not related to snow microstructure. The surface roughness types are given in Table 2.3. The average vertical extent of any of these roughness elements, measured in centimetres, can be combined with the relevant symbol or code, e.g., SFrcv 10. The wavelength and compass direction may also be of interest. Note that surface features are not a substitute for the characterisation of the topmost snowpack layer according to Part I and Appendix C. SfcRough Surface Roughness IACS document section 2.9 Deposition without wind rsm Smooth No roughness elements Wind deposited snow rwa wavy Roughness elements: ripples Melt and submilmation rcv Concave furrows Roughness elements: ablation hollows, sun cups, penitents Rain or melt rcx Smooth Roughness elements: rain or melt groves Erosion rrd Random furrows Roughness elements:zastrugi, erosion features