Atmosphere & Weather — Set 5

Correct Answer: A. Nitrogen

• **Nitrogen (N2)** = the most abundant gas in Earth's atmosphere at approximately 78%, acting as a diluent for oxygen and essential for life. • **78%** — nitrogen's share of the atmosphere; it is chemically inert under normal conditions, making the atmosphere stable for life. • 💡 Wrong-option analysis: Oxygen: second most abundant at ~21%; Argon: third most abundant at ~0.93%; Carbon Dioxide: only ~0.04% (400 ppm), despite its important greenhouse role.

Correct Answer: C. Oxygen

• **Oxygen (O2)** = the second most abundant gas in Earth's atmosphere at approximately 21%, essential for respiration and combustion. • **21%** — oxygen's share of the atmosphere; it supports both aerobic respiration in living organisms and combustion reactions. • 💡 Wrong-option analysis: Argon: third most abundant at ~0.93%, an inert noble gas; Helium: trace gas at only ~0.0005%, much less than argon; Carbon Dioxide: only ~0.04%, though important as a greenhouse gas.

Correct Answer: D. Mesosphere

• **Mesosphere** = the coldest layer of the atmosphere where temperatures can drop as low as -90°C, located between the stratosphere and thermosphere. • **-90°C** — minimum temperature recorded at the mesopause (top of mesosphere), making it the coldest region in the entire atmosphere. • 💡 Wrong-option analysis: Thermosphere: paradoxically hot (1500°C+) due to direct solar radiation absorption; Troposphere: cools with altitude but starts warm near surface; Stratosphere: temperature actually increases with altitude due to ozone absorption.

Correct Answer: A. Thermosphere/Exosphere

• **Thermosphere/Exosphere** = the upper atmosphere layers where satellites orbit, with extremely low air density and temperatures exceeding 1500°C. • **International Space Station** — orbits at approximately 400 km altitude within the thermosphere, where air density is nearly zero. • 💡 Wrong-option analysis: Stratosphere: 12-50 km, ozone layer, jet aircraft fly here; Mesosphere: 50-80 km, coldest layer, meteors burn here; Troposphere: 0-12 km, lowest layer, all weather occurs here.

Correct Answer: D. Wind Direction

• **Wind Vane** = one of the oldest weather instruments, used to measure the direction from which the wind is blowing, with an arrow pointing into the wind. • **Direction indicator** — wind direction is named after the source; a 'south wind' blows from the south toward the north. • 💡 Wrong-option analysis: Wind Speed: measured by anemometer, not wind vane; Air Pressure: measured by barometer; Humidity: measured by hygrometer.

Correct Answer: A. Hygrometer

• **Hygrometer** = the instrument used to measure relative humidity (water vapor content) in the air, critical for weather forecasting. • **Psychrometer** — a type of hygrometer using wet and dry bulb thermometers to calculate relative humidity; hair hygrometer uses hair expansion. • 💡 Wrong-option analysis: Anemometer: measures wind speed; Barometer: measures atmospheric pressure; Thermometer: measures temperature only.

Correct Answer: D. Cirrus

• **Cirrus** = high-altitude clouds (above 6 km) composed of ice crystals that appear as delicate, feathery, or wispy streaks in the sky. • **Ice crystals** — cirrus clouds are formed entirely of ice crystals due to extreme cold at high altitudes; they often signal approaching weather changes. • 💡 Wrong-option analysis: Stratus: flat, gray, low-lying layer clouds; Nimbus: dark rain-bearing clouds (nimbostratus/cumulonimbus); Cumulus: fluffy cotton-wool clouds at lower-to-medium altitude.

Correct Answer: D. Isobars

• **Isobars** = lines on a weather map connecting all points with equal atmospheric pressure at a given time, used to identify weather systems. • **Closely spaced isobars** — indicate strong pressure gradient and high wind speeds; widely spaced isobars indicate calm conditions. • 💡 Wrong-option analysis: Isohalines: lines of equal ocean salinity; Isohyets: lines of equal rainfall; Isotherms: lines of equal temperature.

Correct Answer: C. Cold

• **Mistral (Cold)** = a strong, cold, northwesterly wind that blows from southern France into the Gulf of Lion in the northern Mediterranean. • **Winter and spring** — Mistral is most prevalent in these seasons, causing rapid temperature drops along the French Riviera and Rhone Valley. • 💡 Wrong-option analysis: Warm: Foehn/Chinook are warm local winds; Wet: Mistral is characteristically dry; Hot: Sirocco and Loo are hot local winds.

Correct Answer: A. Trade Wind

• **Trade Wind** = a planetary (permanent) wind that blows consistently in the same direction throughout the year from subtropical highs toward the equatorial low. • **Year-round consistency** — trade winds blow from northeast in the Northern Hemisphere and southeast in the Southern Hemisphere without seasonal reversal. • 💡 Wrong-option analysis: Chinook: a local wind, only in Rocky Mountain region; Monsoon: seasonal wind that reverses direction twice a year; Sea Breeze: local diurnal wind that reverses between day and night.