Question

What is the occurrence of orographic precipitation?

• A. When the warm air raises over a cold air mass
• B. By frontal lifting of air masses
• C. When the moist air raises over a mountain barrier
• D. By convection in the atmosphere

Hint:

• Orographic precipitation is mountain-induced. Moist air is forced upward by a mountain range, cools, and condenses, leading to precipitation on the windward side.
• Frontal precipitation occurs at the boundary (front) between warm and cold air masses.
• Convective precipitation is caused by surface heating and subsequent rising of warm, moist air.

Answer 1

The Correct Option is C

Precipitation occurs when moist air rises, cools adiabatically (due to expansion at lower pressures), and its water vapor condenses into clouds and eventually falls as rain, snow, etc. There are different mechanisms that cause air to rise:

• Orographic Precipitation (option c): This occurs when moist air is forced to rise as it encounters a topographic barrier, such as a mountain range. As the air ascends the windward slope of the mountain, it expands and cools, leading to condensation and precipitation. The leeward side of the mountain often experiences a rain shadow effect (drier conditions) because the air has lost much of its moisture and descends, warming and drying.
• Frontal Precipitation (options a and b): This occurs when two air masses with different temperatures and moisture content meet.
  • At a warm front, warm, less dense air rises gently over a colder, denser air mass (as suggested by option a).
  • At a cold front, cold, denser air actively pushes under warmer, less dense air, forcing it to rise rapidly.
  Option (b) "By frontal lifting of air masses" is a general term for this.
• Convective Precipitation (option d): This results from localized heating of the Earth's surface. The warmed surface heats the air above it, causing the air to become less dense and rise (convection). As it rises, it cools, and if enough moisture is present, clouds and precipitation (often thunderstorms) can form.

Therefore, orographic precipitation specifically refers to precipitation caused by moist air rising over a mountain barrier. \[ \boxed{\text{When the moist air raises over a mountain barrier}} \]