What does vertical windshear refer to?

Vertical windshear refers to the change in wind speed or direction with altitude. Specifically, it involves a variation in horizontal wind components as one moves vertically through the atmosphere. This phenomenon is crucial for pilots to understand, as it can significantly impact aircraft performance during takeoff and landing phases, especially in the presence of thunderstorms or when flying near mountains.

The term "vertical windshear" emphasizes that we are observing changes as a function of height—thus the correct choice relates to the variation of horizontal wind, which can include changes in both speed and direction, as you rise through the atmosphere. This understanding is vital for anticipating how wind conditions may affect flight dynamics, especially in critical flight phases.