What is a feature of jet streams regarding their wind pattern?

Jet streams are characterized by their variability in strength, which can change significantly due to various meteorological factors. This feature is crucial because these winds can influence aircraft performance, flight routes, and weather patterns. The intensity of jet streams can fluctuate due to changes in temperature gradients, pressure systems, and seasonal variations. Understanding this variability helps pilots and meteorologists predict weather conditions and optimize flight planning.

While the other statements present information that might seem relevant, they do not capture the defining aspect of jet streams as effectively. For instance, jet streams do not always have a consistent direction; they can change course frequently. Similarly, while they do exert a tendency to flow generally from west to east in the mid-latitudes, this is not absolute. Additionally, describing them as unsteady at all altitudes oversimplifies their characteristics, as jet streams are most pronounced at certain altitudes, particularly in the upper troposphere.