The polar vortex in the stratosphere affects the weather in the troposphere. When the polar vortex is strong, the jet streams in the troposphere are stronger and closer to the pole, keeping cold air in the Arctic. This leads to stormy and wet conditions in places like the British Isles. When the polar vortex is weak, the jet stream is weaker and wavier, allowing cold air to move southward. This creates different weather patterns known as the positive and negative phases of the Arctic Oscillation. The strength of the polar vortex can vary, influencing how much it impacts the troposphere.