Define "wind shear."

Wind shear refers to a change in wind speed or direction with altitude or along a horizontal plane. It is a critical concept in aviation and meteorology because it can significantly impact aircraft performance, especially during takeoff and landing. A sudden shift in wind direction or speed can create turbulence that may be hazardous to pilots. For example, if an aircraft is ascending and encounters an area of wind shear where the wind suddenly shifts to come from the opposite direction, it can cause the aircraft to lose altitude abruptly.

Understanding wind shear is essential for aviation safety, as it affects flight dynamics and can contribute to hazardous conditions such as low-level wind shear during thunderstorms or microbursts. The other choices do not capture this dynamic nature of wind shear, focusing instead on static or less relevant wind conditions.