What type of icing does "clear ice" refer to?

Clear ice refers to a specific type of ice accumulation that forms when supercooled water droplets freeze upon contact with a surface, typically an aircraft's wings or control surfaces, leading to a smooth, transparent layer of ice. This type of icing is characterized by its high density and weight, which can significantly affect an aircraft's aerodynamic performance. The presence of clear ice can cause issues such as increased drag and altered stall characteristics, making it dangerous for flight operations.

The other options describe different forms of ice or icing phenomena: thin layers of frost tend to occur in warmer conditions and do not significantly impact performance as clear ice does. Solid chunks of ice commonly refer to larger accumulations, which are more associated with severe icing conditions and can detach, leading to ice that is less uniform than clear ice. Water droplets freezing upon contact is a basic description of the process contributing to clear ice but does not capture the full implications of its density and impact on aircraft performance.