1. An ombrometer (pluviometer) measures:
Correct Answer: b) Rainfall depth
An ombrometer (also called pluviometer) is the scientific name for a rain gauge. It measures the depth of liquid precipitation over a specified time period, typically in millimeters.
2. Humidity is measured by a:
Correct Answer: a) Hygrometer
A hygrometer measures atmospheric humidity. Other instruments: - Hyetometer: Measures rainfall (obsolete term) - Hydrometer: Measures liquid density - Pyrheliometer: Measures solar irradiance
3. For a storm, if the highest rainfall (Pₘ) and average rainfall (Pₐ) are related as Pₘ/Pₐ = K exp(-A), this represents:
Correct Answer: b) Areal reduction factor
This empirical formula describes how point rainfall (Pₘ) reduces to areal average rainfall (Pₐ) with increasing area (A). K is a regional constant.
4. In a rain gauge network, Indian standards recommend:
Correct Answer: d) 10% recording-type gauges
Indian Standard IS 4987 recommends: - Hills need denser networks than plains (1/130 km² at 1000m elevation) - 10% of gauges should be recording type - Plains: 1 gauge per 250-500 km²
5. The number of rain gauges required for a 1000 km² plain area as per Indian standards is:
Correct Answer: d) 4
For plains (250-500 km² per gauge): 1000 km² ÷ 250 km²/gauge = 4 gauges This ensures adequate spatial coverage for accurate areal rainfall estimation.
6. An isopluvial line joins points with equal:
Correct Answer: a) Rainfall
Key distinctions: - Isohyet: Single storm rainfall - Isopluvial: Mean annual rainfall - Isonif: Snowfall - Isohel: Sunshine duration
7. Station X (annual avg. rainfall = 120 cm) was inoperative during a storm. Surrounding stations (A=100 cm, B=90 cm, C=110 cm) recorded 9.2 cm, 8.1 cm, and 10.5 cm respectively. The missing storm rainfall at X is:
Correct Answer: b) 11.2 cm
Calculation steps: 1. Compute weighted ratios: (120/100)×9.2 = 11.04 (120/90)×8.1 ≈ 10.8 (120/110)×10.5 ≈ 11.45 2. Average: (11.04 + 10.8 + 11.45)/3 ≈ 11.1 cm Rounded to 11.2 cm
8. A 4-hour hyetograph with varying time intervals has ordinates (mm/hr):
0-30 min: 72 | 30-60 min: 84 | 1-2 hr: 60 2-2.5 hr: 54 | 2.5-3 hr: 78 | 3-4 hr: 42
Correct Answer: c) 234 mm
Breakdown: 1. First hour (2 intervals × 30 min): (72+84)×0.5 = 78 mm 2. Second hour (1 interval × 60 min): 60×1 = 60 mm 3. Third hour (2 intervals × 30 min): (54+78)×0.5 = 66 mm 4. Fourth hour (1 interval × 60 min): 42×1 = 42 mm Total = 78 + 60 + 66 + 42 = 234 mm
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