A warm front is formed when a warm air mass replaces a cold air mass. Which term describes this boundary?

A warm front is formed when a warm air mass replaces a cold air mass. Which term describes this boundary?

• A. Unstable atmosphere
• B. Cold front
• C. Thermal layer
• D. Warm front

Answer: (D)

A front is the boundary between air masses with different temperatures and densities. When a warmer air mass moves in and slides over a cooler air mass, the leading edge between them is called a warm front. This matches the idea of a boundary formed as warm air replaces cold air. The other terms don’t describe this specific boundary: an unstable atmosphere is a weather condition, not a boundary; a cold front is where cold air replaces warm air; a thermal layer isn’t the standard term for the boundary between air masses. So the term that fits the description is a warm front.

A front is the boundary between air masses with different temperatures and densities. When a warmer air mass moves in and slides over a cooler air mass, the leading edge between them is called a warm front. This matches the idea of a boundary formed as warm air replaces cold air.

The other terms don’t describe this specific boundary: an unstable atmosphere is a weather condition, not a boundary; a cold front is where cold air replaces warm air; a thermal layer isn’t the standard term for the boundary between air masses. So the term that fits the description is a warm front.