ATPL Meteorology Test 2025 – 400 Free Practice Questions to Pass the Exam

Sublimation is the process in which a substance transitions directly from a gas to a solid without going through the liquid phase. For vapor to turn into ice, the presence of freezing nuclei is crucial. These nuclei act as sites around which ice crystals can form, allowing the vapor to crystallize and transition into solid ice.

Freezing nuclei provide the necessary framework for the water vapor to organize into a solid structure. This is particularly important in the atmosphere, where ice crystals form in clouds. Without these nuclei, the process of sublimation would be significantly hindered, as there would be no substrate for the water vapor to effectively solidify into ice.

Heat energy is typically associated with the melting or sublimation processes in that energy absorption leads to changes in state, but in the context of sublimation to ice, it is the presence of freezing nuclei that is the primary requirement. The other options, such as condensation nuclei, relate to different phase changes and support processes that involve liquid water, not directly applicable to the transition from vapor to ice. Similarly, simply increasing humidity does not guarantee the formation of ice; the proper conditions must be met rather than just an increase in moisture.