In winter, how do the upper-level westerlies in the northern hemisphere generally compare to those in summer?

• A. Weaker and extend further north
• B. Stronger and extend further south
• C. Stronger and extend further north
• D. Weaker and extend further south

Answer: (B)

In winter, the upper-level westerlies in the northern hemisphere are generally stronger and extend further south compared to those in summer. This is primarily due to the significant temperature differences between the polar regions and the mid-latitudes during the winter months. The contrast in temperatures causes a steepening of the pressure gradients, which increases wind speeds at upper levels.

During winter, the polar areas are very cold while the mid-latitudes can be relatively warm, leading to a stronger jet stream. Additionally, the location of the jet stream tends to shift southward during winter, allowing it to extend further into the southern regions compared to summer, when the temperature gradient is less pronounced. The dynamics of the atmosphere also promote more active weather patterns in winter, resulting in stronger and more prominent upper-level westerlies.

In contrast, during summer, the upper-level winds tend to weaken and shift northward as the temperature gradients diminish, leading to a more stable atmosphere with less pronounced wind patterns. Therefore, the comparison highlights the seasonal variations in wind strength and positioning influenced by temperature differences across the hemisphere.