Jet streams are upper-level tropospheric winds. Which one of the following statements about jet streams is NOT correct?

Introduction / Context:
Jet streams are fast flowing, narrow air currents found in the upper levels of the atmosphere, particularly near the tropopause. They play a crucial role in weather patterns, storm tracks, and aviation. Understanding their typical characteristics, such as location, continuity, and seasonal variation, is important in both meteorology and general geography. This question asks you to identify which statement about jet streams is not correct.

Given Data / Assumptions:
• Jet streams are upper-level winds, especially in the troposphere near the tropopause. • They are associated with strong horizontal temperature gradients, often near frontal zones. • We focus on the polar front jet stream as a typical example. • We consider seasonal variations between winter and summer.

Concept / Approach:
Jet streams are relatively narrow bands of high-speed winds that flow from west to east along wave-like paths. They are typically located near the tropopause at altitudes roughly between 8 km and 15 km. These currents can extend over thousands of kilometres, making them continuous over long distances, though their position and strength vary. The polar front jet stream is stronger in winter when the temperature contrast between polar and mid-latitude air masses is greatest. In summer, this temperature contrast weakens, and the polar front jet generally becomes weaker and shifts poleward. Therefore, any statement claiming that the polar front jet reaches maximum strength in summer is not correct.

Step-by-Step Solution:
Step 1: Confirm that jet streams are narrow, high-velocity wind bands; this is a standard definition. Step 2: Recognise that they occur near the tropopause, typically between 8 km and 15 km altitude, and follow wave-like (meandering) paths. Step 3: Note that jet streams are often continuous over long distances, sometimes encircling the globe in segments. Step 4: Remember that the polar front jet is strongest in winter due to the large temperature gradient between polar and mid-latitude air. Step 5: In summer, this temperature gradient is weaker, so the polar front jet stream usually weakens instead of strengthening. Step 6: Thus, the statement that the polar front jet achieves its maximum force (strength) in summer is not correct.

Verification / Alternative check:
Meteorological data and textbooks describe how jet streams shift and change strength with the seasons. The polar front jet intensifies in winter in both hemispheres, while subtropical jets behave differently. Airline flight planning also uses stronger winter jet streams for faster eastbound flights. The seasonal pattern is therefore opposite of what the incorrect statement suggests, confirming that summer is not when the polar front jet is at its maximum strength.

Why Other Options Are Correct (and therefore not the answer):
Option a: Jet streams are indeed narrow bands of very high-speed winds compared to surrounding airflows. Option b: They run near the tropopause and follow meandering, wave-like paths influenced by large-scale atmospheric waves. Option c: Jet streams typically extend over thousands of kilometres and can be considered continuous over long stretches. Option e: They are associated with strong horizontal temperature gradients, especially around fronts and the polar jet region.

Common Pitfalls:
A frequent confusion is mixing up which season has stronger jet streams. Because winter has larger temperature differences between air masses, the polar front jet is stronger in winter, not summer. Another mistake is thinking of jet streams as short or local winds, when they actually extend over large distances. Keeping the association between strong temperature gradients and stronger jets helps avoid these errors.

Final Answer:
The incorrect statement is: In summer, the polar front jet achieves its maximum strength.