# Relationships between Surface Properties and Snow Adhesion and Its Shedding Mechanisms
## 4 Conclusions  
A non-destructive apparatus was developed to accurately measure the shear adhesion strength of snow without changings its properties (i.e., liquid water content) during the measurement. The setup involved using a surface-mountable sensor to monitor the liquid water content in snow and its  
Figure 7: **(a–d)** The time progression of the liquid layer in snow (LWC \(\sim\)22%) infiltrating the surface roughness (RMS = 36.4 \(\upmu\)m) of Al 6061 substrate at a substrate temperature of 2 \({}^{\circ}\)C: **(a)** Water is above the surface roughness. **(b)** As time progresses, the water begins to seep into the roughness, shown with a dashed white line. **(c)** Water continues to flow into the surface roughness until **(d)** the roughness is completely infiltrated with water. The arrow in each section shows the front of the water progressively moving into the surface roughness. After liquid water infiltration, when temperatures rise above the freezing point, this liquid layer results in snow gliding on rough surfaces with reduced shear adhesion strength; however, post infiltration, when temperatures go below freezing point, the liquid layer forms a thin ice layer at the snow–substrate interface, leading to enhanced snow shear adhesion strength. temperature during experiments. An internal mixing snow gun was also developed that includes ball valves to control air and water flow to the mixing chamber for snow formation with controlled liquid water content. To the best of our knowledge, this is closest attempt in forming artificial snow comparable to natural snow, considering the limited size of our freezing room and the lack of temperature gradients that real snow experiences falling from the atmosphere. We report that shear adhesion strength of snow peaks near 20% liquid water content when the substrate temperature is at 0 \({}^{\circ}\)C. At lower than \(\sim\)20% LWC, snow is powdery with little free liquid water content to form capillary action, leading to low snow adhesion strength. As the LWC increases to around 20%, a strong adhesive bond is formed by capillary forces at the interface. This strong bond begins to diminish as the snow becomes slushy and a thin layer of water forms at the interface and allows sliding action to occur, when the LWC is greater than 20%. We also found that when surface roughness nears the size of the snow particles, the shear adhesion strength of snow is maximum due to the enhanced surface area between the snow and the substrate. As the roughness increases, snow adhesion strength decreases because multiple lubricating snow particles can fit inside the roughness, resulting in local cohesive failures in snow which are much weaker than adhesive failures. We also show that reducing the surface polarity leads to lower snow adhesion strength. Finally, we report three snow shedding/de-adhering mechanisms depend on the temperature during the adhesion measurement. At temperatures below \(-2\)\({}^{\circ}\)C a quasi-ice layer forms at the interface, allowing for the snow mass to shed in one piece. At temperatures above 2 \({}^{\circ}\)C a liquid layer forms at the interface, allowing for lower shear adhesion strength and a compressive failure mechanism. Between \(-2\) and 2 \({}^{\circ}\)C, a combination of the two failure mechanisms occurs, such that an ice layer and liquid layer may form at different locations on the substrate. The different interface layers allow for the combination of the two failure mechanisms to occur on the same substrate. In conclusion, adding the liquid water content sensor allowed for tracking the temperature and wetness of the snow throughout the adhesion experiments. The ability to ensure constant liquid water content and temperature profiles throughout the experiments allowed for failure mechanisms to be explored. It also enabled determining the impact of surface properties on snow shear adhesion strength.