Task: Class Definition Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes 'head wind'?

A. 1. A sudden, brief increase in the speed of the wind. It is of a more transient character than a squall and is followed by a lull or slackening in the wind speed. Generally, winds are least gusty over large water surfaces and most gusty over rough land and near high buildings. According to U.S. weather observing practice, gusts are reported when the peak wind speed reaches at least 16 knots and the variation in wind speed between the peaks and lulls is at least 9 knots. The duration of a the concept is usually less than 20 s. 2. With respect to aircraft turbulence, a sharp change in wind speed relative to the aircraft; a sudden increase in airspeed due to fluctuations in the airflow, resulting in increased structural stresses upon the aircraft. 3. (Rare.) Same as cloudburst.
B. Small-scale downward moving air current in a cumulonimbus cloud.
C. When dust, sand, snow, and/or spray is raised by the wind to a height of 6 feet or more
D. A wind that opposes the intended progress of an exposed, moving object, for example, rendering an airborne object's airspeed greater than its groundspeed; the opposite of a tailwind.

Answer: A wind that opposes the intended progress of an exposed, moving object, for example, rendering an airborne object's airspeed greater than its groundspeed; the opposite of a tailwind.