What is the minimum speed for a jet stream?

The minimum speed typically associated with a jet stream is indeed considered to be over 100 knots. Jet streams are fast-flowing, narrow air currents found in the atmosphere at higher altitudes, generally occurring at around 30,000 to 39,000 feet. These high-altitude winds usually have speeds well above the minimum threshold of 100 knots, and can at times exceed 200 knots.

The other options fall below this threshold typically associated with jet streams. For instance, a speed of 50 knots is considered too low to classify as a jet stream, as this speed is more characteristic of surface winds or lower altitude wind patterns instead. Therefore, the understanding of jet streams is grounded in their significant altitude and associated wind speeds, which is crucial for flight planning and navigation.