Which statement best describes the Maritime Arctic (mA) air mass?

Which statement best describes the Maritime Arctic (mA) air mass?

• A. Hot, very moist, unstable air mass.
• B. Cold, dry, stable air mass.
• C. Cold, moist, unstable (in lower levels) air mass.
• D. Hot, dry, stable air mass.

Answer: (C)

Air masses are described by where they form and how moist or dry they are, plus how stable the air is. A Maritime Arctic air mass forms over the Arctic Ocean, so it is very cold and carries a lot of moisture from the sea. The cold, dense air gives it a strong low-level temperature contrast with the surface or with air over warmer ground, which can make the lower part of the atmosphere prone to buoyant lifting and convection. That combination—cold and moist, with potential instability in the lower levels—is the most accurate way to describe it. The other options conflict with its origin (Arctic) and moisture content (maritime) or describe conditions that don’t match an Arctic maritime air mass.

Air masses are described by where they form and how moist or dry they are, plus how stable the air is. A Maritime Arctic air mass forms over the Arctic Ocean, so it is very cold and carries a lot of moisture from the sea. The cold, dense air gives it a strong low-level temperature contrast with the surface or with air over warmer ground, which can make the lower part of the atmosphere prone to buoyant lifting and convection. That combination—cold and moist, with potential instability in the lower levels—is the most accurate way to describe it. The other options conflict with its origin (Arctic) and moisture content (maritime) or describe conditions that don’t match an Arctic maritime air mass.