Which term describes pressure variations that can affect aircraft performance?

The correct choice is isobar divergence, as this term specifically refers to variations in pressure that can influence aircraft performance. Isobar divergence occurs when there are changes in the spacing of isobars, which are lines on a weather map that connect points of equal atmospheric pressure. This divergence indicates differing pressure systems that can result in gusts, turbulence, or shifts in wind direction, all of which can significantly impact an aircraft's performance dynamics.

Understanding isobar divergence is crucial for dispatchers and pilots because it helps in anticipating how pressure changes might lead to alterations in flight conditions. Isobar divergence can indicate areas of increasing or decreasing wind speeds, which are essential considerations during takeoff, cruising, and landing phases.