What is the primary cause of mechanical turbulence?

Mechanical turbulence primarily occurs when wind flows are disrupted by obstructions such as buildings, trees, or terrain features. These obstructions create eddies and irregular air movements as the wind encounters them, leading to turbulent conditions. This type of turbulence is most commonly observed close to the ground and can significantly affect aircraft during takeoff and landing phases. Other options represent different atmospheric phenomena or types of turbulence. For instance, temperature variations and vertical wind shear pertain to other processes contributing to turbulence but do not specifically address the disruption of airflow caused by physical objects. Movement through a stable air mass might result in less turbulence, rather than mechanical disruptions that cause it. Understanding mechanical turbulence is crucial for pilots and air traffic control personnel to ensure safe operations in the vicinity of obstacles.