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Water Storage: Atmospheric
Published in Yeqiao Wang, Atmosphere and Climate, 2020
Visible clouds are formed when the water vapor in large volumes of moist air is transformed into liquid droplets or ice crystals. While clouds contain considerable amounts of liquid or frozen water, they remain suspended in the air because their density is slightly less than or equal to the volume of dry air. Cloud droplets or ice crystals are initially only a fraction of a micrometer in diameter. They grow in size as they merge into drops a few millimeters in diameter that fall from the cloud when the tug of gravity exceeds the force of convective updrafts or as ice crystals that grow by deposition of water vapor and by the collision and collection of ice crystals to make snowflakes. Falling snowflakes can melt into raindrops if the lower atmosphere is above the freezing point.
Mineral Crystals
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
The first crystallographic investigations occurred in the 1600s. Johannes Kepler studied the symmetry of snowflakes and concluded that the hexagonal shapes were due to water particles packed together in hexagonal patterns. In 1669, Nicolas Steno showed that the angles between crystal faces were the same for all samples of any particular mineral. Eventually, in 1784, René Hauy deduced that crystal faces result from the stacking together of fundamental building blocks in regular ways. Subsequent studies concluded that crystals contain an ordered arrangement of atoms that repeat indefinitely in three directions that need not be perpendicular. Because the repeat distance in crystals is on the order of angstroms, we can think of crystals as many identical unit cells of angstrom scale stacked together to create the entire crystal. Consequently, crystals of a given compound have the same composition and same relative arrangement of atoms no matter their sizes. The existence of a unit cell and the repetitive nature of the overall structure set crystals apart from other solid materials.
The Hydrology of Snow and Ice
Published in Richard J. Chorley, Introduction to Physical Hydrology, 2019
Ice is characterized by crystals of the hexagonal system, and commonly takes on a variety of prismatic, pyramidal, or dipyramidal forms. Hexagonal symmetry occurs, and is especially prominent in the aggregates of ice crystals which form snowflakes. Crystal size, form, and aggregate structure are highly variable and depend greatly on mode of formation and local environment. Crystals in a glacier, for example, may vary from less than 1 mm to over 1 m in length.
Numerical study of dry snow accretion characteristics on the bogie surfaces of a high-speed train based on the snow deposition model
Published in International Journal of Rail Transportation, 2022
Lu Cai, Zhen Lou, Tian Li, Jiye Zhang
The experimental results of snowflakes impact with a snow surface are obtained by using artificial snowflakes and are summarized as follows: when U1 < 3 m/s (U1 is the wind speed at 1 m above the ground) [31], the snowflake will not break; when 2≤ U1 ≤ 3 m/s, the snowflake is partially broken and accumulates; when U1 ≥ 5 m/s, the snowflake is completely decomposed into snow crystals and blown away by the wind. When U1 ≈ 4 ~ 5 m/s, the snowflake deposition rate is close to zero, therefore, this paper takes the corresponding snowflake incident velocity amplitude as the critical capture velocity. The corresponding vertical incident velocity of the snowflake is 0.8 ~ 1.0 m/s, and the horizontal incident velocity is 0.74U1, the incident speed of the snow is 3.0 ~ 3.8 m/s. In this paper, the critical capture velocity is set as 3.0 m/s, and the critical wind friction speed is set as 1.0 m/s. The normal rebound coefficient is 0.01, and the tangential rebound coefficient is 0.2. The impact results between the snow particles and the bogie surface was implemented with user-defined functions (UDF) with details that can be seen in [33]. The calculation processes can be seen in Figure 4.