Final answer:
The freezing level is the altitude where the temperature is 0°C, while the rain-snow line is where precipitation falls as snow, influenced by temperature and other atmospheric conditions. Snow persists on slopes above the freezing level due to the heat needed for melting.
Step-by-step explanation:
The freezing level and the rain-snow line exist at different elevations because the freezing level is determined by temperature, whereas the rain-snow line is influenced by precipitation type which can also include additional atmospheric conditions. Simply put, the freezing level refers to the altitude at which the air temperature is at the freezing point of water, which is 0°C (32°F).
Above this level, precipitation is more likely to fall as snow if the atmospheric conditions are suitable. On the other hand, the rain-snow line is the elevation level where precipitation falls as snow rather than rain. This line can be affected by multiple factors, including not just temperature, but also humidity, pressure differences, and the presence of warm air which can cause snow to melt as it descends, turning it back into rain before reaching the ground.
Snow tends to remain on mountain slopes even at temperatures slightly above freezing due to the significant amount of heat required for the snow to transition from a solid to a liquid state. Conditions such as direct sunlight, air humidity, and wind can all influence how quickly this melting occurs. Understanding these processes is essential in fields like meteorology and climatology, where predicting weather patterns and precipitation types is vital.