Rain-gauge catch deficiency caused by upward vertical air acceleration over the gauge orifice is generally greater for which type of rain or drop size?

Introduction / Context:
Wind and aerodynamic effects around a rain gauge can lead to undercatch, meaning the measured rainfall is less than the true precipitation. The magnitude of undercatch depends on drop size and rainfall intensity.

Given Data / Assumptions:

• Vertical upward air acceleration over the gauge opening reduces drop entry.
• Smaller, lighter drops are more affected by aerodynamic deflection.
• Heavier rainfall typically has larger drops and higher momentum.

Concept / Approach:
The physics is governed by drop inertia and aerodynamic drag. Small/light drops (drizzle, light rain) have low terminal velocity and are more easily deflected by turbulent, upward-moving air, leading to greater undercatch. Large, heavy drops have higher momentum and are less deflected, so undercatch is smaller for heavy rain.

Step-by-Step Solution:

Verification / Alternative check:
Gauge-exposure correction studies and WMO guidance note increased undercatch for snowfall and light rain (small particles), consistent with this reasoning.

Why Other Options Are Wrong:

• Greater for heavy rain / large drops: Large drops have higher momentum, so less deflection.
• Lesser for small drops: Opposite of observed behavior; small drops give greater undercatch.

Common Pitfalls:

• Assuming intensity alone controls undercatch without considering drop size.
• Ignoring shield and site-exposure effects on measurements.

Final Answer:
Greater for lighter rain