In mid-latitude regions, the diurnal variation in weather is mainly due to option 3, advection. Advection refers to the horizontal movement of air masses. During the day, the sun heats up the Earth`s surface, causing warm air to rise and creating low-pressure areas. This leads to the movement of air from high-pressure to low-pressure areas, bringing in different air masses and causing changes in weather patterns.

Option 1, raising air/convection, is partially correct as convection also plays a role in the diurnal variation. Convection is the process of heat transfer through the vertical movement of air. Warm air near the surface rises, creating upward air currents that can lead to the development of clouds and precipitation. However, advection is the predominant factor in mid-latitude regions.

Option 2, sinking air/conduction, is not the primary driver of diurnal variation. Conduction refers to the transfer of heat within a substance or between objects in contact. While sinking air may contribute to stable weather conditions, it does not significantly impact the diurnal variation.

Option 4, radiation, is not as significant in causing diurnal variation in mid-latitude regions. Radiation refers to the transfer of energy through electromagnetic waves, such as heat from the sun