Correct Response: C. Colder and warmer air masses have different densities and consequently different atmospheric pressures. Where cold and warm air masses meet, such as along the polar front, the difference in atmospheric pressure causes wind. The strong pressure gradient along the polar front drives the concentrated winds of the polar jet stream near the altitude of the tropopause. Although fluctuations in the Arctic Oscillation can affect the position and strength of jet stream winds, it is not a major factor driving their development (A). The decrease in atmospheric pressure between the troposphere and stratosphere (B) is also not a major factor driving the polar jet stream. Seasonal changes in atmospheric instability in temperate and tropical regions (D) can be affected by the position of the polar jet stream and subtropical jet stream, but are not a factor in their development.
