Which of the following is NOT a type of mechanical turbulence?

Thermal turbulence is associated with the heating of the Earth's surface, which causes variations in air density and creates rising thermal currents. This type of turbulence occurs primarily due to the uneven heating caused by solar radiation, especially during the day when the ground heats up and then transfers heat to the air above it.

In contrast, the other types of turbulence mentioned—shear turbulence, frontal turbulence, and mechanical turbulence—are categorized as forms of turbulence caused by mechanical factors, such as wind shear and interactions with physical structures (like buildings or mountains). Shear turbulence occurs due to speed differences in the wind at various altitudes or within a layer, while frontal turbulence is the result of various air masses colliding.

Understanding these distinctions helps in recognizing how different factors contribute to turbulence during flight, particularly in relation to environmental conditions and topographical influences.