Lecturer: Sandra Vázquez Martin (LTU)
Date: 2019-03-28 10:00
Place: Aniara

Ground-based in-situ measurements and shape classification of natural snow crystals and snowflakes in Kiruna

Sandra Vázquez Martin
Luleĺ University of Technology
Department of Computer Science
Electrical and Space Engineering,
Division of Space Technology
Kiruna, Sweden

Thomas Kuhn, LTU, and Salomon Eliasson, SMHI.

Knowledge of snow microphysical properties, including particle shape, is required for snow retrievals from remote sensing methods. Particle shape and morphology affect radar measurements and microwave brightness temperatures. In this work, we present ground-based in-situ measurements of the shape and other microphysical properties of snow crystals, ice crystals, aggregates, and other hydrometeors covering sizes from 50 μm to 4 mm. Our measurements have been carried out in Kiruna during the snowfall seasons from 2014 to present between the beginning of November and the middle of May. These measurements of natural snow crystals and other hydrometeors are classified using an updated classification with over 100 shapes. Our classification includes new snow shapes that have been found in Kiruna. To carry out this study, our ground-based in-situ instrument D-ICI has been used, which takes high-resolution side- and top-view images of falling hydrometeors. With these dual images, ambiguities in shape determination can be minimized. In addition to assigning a shape to each particle, our proposed classification sorts particle shapes into 15 different shape groups depending on their shape and morphology. These groups are: Needles and thin or long columns; Crossed needles and crossed columns; Thick columns and bullets; Capped columns and capped bullets; Plates; Stellar crystals; Bullet rosettes; Branches; Side planes; Spatial plates; Spatial stellar crystals; Graupel; Ice, melting or evaporating particles; Irregulars and aggregates; and Droplets. Then, with the help of this classification, microphysical properties such as particle size, area, area ratio, aspect ratio, shape, and fall speed are studied for the different shape groups. From this, relationships between these microphysical properties specific for shape groups, for instance, particle size and area can be derived, which will be useful for climate and forecast models, and also will help to improve our understanding of precipitation in cold climate.

Created 2018-10-26 16:14:17 by Uwe Raffalski
Last changed 2019-03-27 16:08:24 by Uwe Raffalski