Which statement about the planetary boundary layer height is accurate?

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Multiple Choice

Which statement about the planetary boundary layer height is accurate?

PBL height controls how far vertical mixing reaches from the surface into the lower atmosphere. When the boundary layer is shallow, vertical mixing is limited to a small depth, so moisture and heat can accumulate near the surface. Under nighttime radiative cooling with clear skies and light winds, the near-surface air can reach the dew point, forming surface fog. If the boundary layer is tall, stronger mixing brings drier air down from above and spreads moisture through a larger layer, which tends to prevent fog from forming at the surface. So a shallow PBL promotes surface fog formation, while a tall PBL generally reduces it.

PBL height controls how far vertical mixing reaches from the surface into the lower atmosphere. When the boundary layer is shallow, vertical mixing is limited to a small depth, so moisture and heat can accumulate near the surface. Under nighttime radiative cooling with clear skies and light winds, the near-surface air can reach the dew point, forming surface fog. If the boundary layer is tall, stronger mixing brings drier air down from above and spreads moisture through a larger layer, which tends to prevent fog from forming at the surface. So a shallow PBL promotes surface fog formation, while a tall PBL generally reduces it.

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