Under which of the following condition(s) the occluded fronts are created ? 1. When the front remains stationary 2. When cold air mass moves to warm air mass 3. When warm air mass moves to cold air mass 4. When an air mass is fully lifted above the land surface Select the correct answer using the code given below :

An occluded front is formed during the mature stage of an extratropical cyclone when a faster-moving cold front catches up with and overtakes a slower-moving warm front [3]. This process, known as occlusion, occurs because cold fronts generally move at higher velocities than warm fronts [3]. As the cold front undercuts the warm front, the warm air mass that was wedged between them is forced upward and completely lifted off the ground surface [3]. Statement 1 describes a stationary front, where air masses do not move against each other [2]. Statements 2 and 3 describe the basic movements of cold and warm fronts respectively, but occlusion specifically requires the overtaking and subsequent lifting of the warm air mass above the surface [3]. Therefore, only statement 4 correctly identifies the definitive condition for an occluded front.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 28: Temperate Cyclones > Occluded Front > p. 403
2. [3] https://www.bom.gov.au/resources/learn-and-explore/climate-knowledge-centre/climate-factors/frontal-systems
3. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 28: Temperate Cyclones > Explanation > p. 406