Jet streams form where cold polar air meets warm tropical air. This creates a very steep “pressure gradient” in the upper atmosphere. Think of it like a steep hill; the steeper the temperature difference, the faster the air “rolls” down that pressure hill. Earth’s rotation then turns this fast-moving air into the narrow Jet Stream. ANSWER: (B) The sharp temperature contrast at the Polar Front
What is the primary cause of the “Jet Stream’s” extreme speed? (A) The pull of the moon’s gravity (B) The sharp temperature contrast at the Polar Front (C) Rapid evaporation over the tropical oceans (D) High-altitude volcanic ash
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The speed of the wind is determined by how quickly pressure changes over a distance. At the “Polar Front,” you have a massive block of freezing air next to a block of very warm air. In the upper atmosphere, this creates a dramatic pressure slope. Air rushes to equalize this pressure, but the Coriolis effect deflects it into a tight, eastward-moving tube of air. This is why the Jet Stream is strongest in the winter—the temperature difference between the Equator and the Pole is much bigger in winter than in summer, making the “pressure hill” even steeper.
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