What is the primary cause of convectional rainfall?

Correct — C. NCERT explains convectional rain as one chain. Air heated at the surface becomes light and rises in convection currents.

As it rises it expands and loses heat, condensation follows, and cumulus clouds form. Heating, rising, cooling: option (c).

Why the others are wrong

• (a)
  Cold fronts meeting warm air — A cold front meeting warm air gives frontal (cyclonic) rain, where warm air is forced up over colder air. Convectional rain needs no front, only strong surface heating.
• (b)
  Mountains forcing air to rise — Mountains forcing air to rise give orographic or relief rain, heaviest on the windward slopes. There the lift comes from the mountain, not from heating.
• (d)
  Moist air from polar regions — Polar air is cold and holds little moisture. Convectional rain comes from strong heating, which is why NCERT finds it in summer, the hotter part of the day and equatorial regions.

NCERT classifies rainfall by what makes the air rise: convectional (heating), orographic or relief (a mountain in the way) and cyclonic or frontal (air masses meeting).

Convectional rain falls as heavy showers with thunder and lightning, but it does not last long. It is common in summer or the hotter part of the day, and very common in equatorial regions and the interiors of continents.

Key facts

• Convectional rain: heated air rises in convection currents, expands, cools and condenses.
• Orographic rain: a mountain forces saturated air to rise, and the windward slopes get the most rain.
• The leeward side of the mountain gets less rain and is called the rain-shadow area.
• Convectional rain is very common in equatorial regions, and in the hotter part of the day.

Common traps

• Picking (b) because air rises in both cases. Ask what lifts the air: heat for convectional, a mountain for orographic.

No directly related past PYQ was found.