Important Questions: Atmospheric Circulation & Weather Systems | Geography Class 11 - Humanities/Arts PDF Download

Very Short Answer Type Questions

Q1: What is atmospheric pressure at sea-level?
Ans: The atmospheric pressure at sea level is about 1 kilogram per cm².

Q2: How the air pressure is the measure?
Ans: The air pressure is measured as a force per unit area. The units of measurements are millibar (Mb).

Q3: In which direction the earth rotates on its axis?
Ans: On its axis, the earth rotates from west to east.

Q4: Give the latitudinal extent of the sub-polar low-pressure belt.
Ans: Between 45” North and Arctic Circle in the northern hemisphere, and 45° South and Antarctic Circle in the southern hemisphere.

Q5: Name two places with the heaviest rainfall in India.
Ans: The two places with the heaviest rainfall in India are Mawsinram and Cherrapunji.

Q6: Where are the polar maritime air masses located?
Ans: They are located over warmer high latitude oceans of North Pacific, North Atlantic Ocean, and entire sweep of southern hemisphere oceans, fringing Antarctica.

Q7: What is a millibar?
Ans: It is a unit of measurement of atmospheric pressure.

Q8: What is a pressure gradient?
Ans: The pressure gradient is defined as the decrease in pressure per unit distance in the direction in which the pressure decreases most rapidly.

Short Answer Type Questions

Q9: What is Coriolis force and who discovered it first?
Ans: On the rotating earth, a point on the equator moves the fastest. As we go towards the poles, the speed decreases, reaching about zero at the pole. It is because of this difference in speed that any moving body, such as winds and ocean currents, gets deflected when it moves towards the equator or away from the equator. This force or deflection is called Coriolis. It was discovered by Coriolis, a French mathematician.

Q10: Explain the occurrence and importance of ITCZ.
Ans: The ITCZ means Inter-Tropical Convergence Zone. It is also known as Inter-Tropical Front (ITF). It is an equatorial front. It is a broad trough of low pressure defined more sharply over land than over the ocean. The tropical maritime air masses converge here. In ITCZ, the north-east trade winds and the south-east trade winds meet. This zone is mainly stationed over the equator but moves north and south according to the season. The air mass may be almost stagnant, the winds light and variable. Hence the air belt is calm, known as doldrums.

Q11: What are tertiary winds?
Ans: These winds are generated by the influence of the surrounding terrain. They include mountain and valley winds, land and sea-breezes, and other local winds such as loo, foehn, chinook and mistral, etc. Some winds are hot and some winds are cold winds. All are local winds.

Q12: Give the relation between pressure and temperature.
Ans: The pressure and temperature have an inverse relationship with each other. As the air gets heated, it expands and rises upwards. The higher the temperature, the lower is the pressure. On the other hand, cold air contracts and becomes heavy. It results in high pressure.

Q13: What is a jet stream? Explain.
Ans: The winds with a high velocity which blow at high altitude are called the jet stream. This strong current of air is located near 90° north latitude. It affects the weather patterns of the world. High flying planes use these as super tailwinds to save time and fuel.

Long Answer Type Questions

Q14: Describe the global pattern of the distribution of pressure.
Ans: The global pattern of pressure distribution on Earth's surface is largely influenced by the movement of air masses due to differences in temperature and the Earth's rotation. This results in the creation of high-pressure and low-pressure systems. Here's an overview of the global pressure patterns:

• Equatorial Low-Pressure Belt: Near the equator, the Sun's energy heats the Earth's surface intensely. This warming causes the air to rise, creating a low-pressure zone known as the equatorial low. Here, warm, moist air rises and cools, forming clouds and contributing to high levels of precipitation. This area of low pressure is also known as the Intertropical Convergence Zone (ITCZ).
• Subtropical High-Pressure Belts: Around 20 to 30 degrees north and south of the equator, the descending air from the upper atmosphere creates high-pressure areas known as the subtropical high-pressure belts. These regions are characterized by descending, dry air. The descending air suppresses cloud formation and leads to arid conditions, making many deserts, such as the Sahara in Africa and the Sonoran Desert in North America, located within these belts.
• Subpolar Low-Pressure Belts: Around 60 to 70 degrees north and south of the equator, warm air from the subtropical high-pressure areas meets cold polar air. This contrast in temperature creates low-pressure areas, where rising warm air meets descending cold air. These zones are associated with the formation of mid-latitude cyclones and are characterized by stormy weather and significant precipitation.
• Polar High-Pressure Belts: Near the poles, cold, dense air descends, creating high-pressure areas. These polar high-pressure belts are characterized by cold, stable air. The frigid conditions and low temperatures at the poles contribute to the formation of polar deserts.
• Seasonal Variations: The global pressure patterns also shift with the seasons due to the tilt of the Earth's axis. For example, during the northern hemisphere's winter, the subtropical high-pressure belt moves southward, and during summer, it moves northward.

These global pressure patterns, driven by solar radiation, the Earth's rotation, and the movement of air masses, play a fundamental role in shaping weather patterns, winds, and ocean currents around the world.

Q15: What are cyclones? Describe the various types of cyclones.
Ans: Cyclones are large-scale atmospheric systems characterized by inward spiraling winds around a central low-pressure area. They are natural disasters that can cause severe damage due to high winds, heavy rainfall, storm surges, and flooding. There are several types of cyclones, each with specific characteristics:

Tropical Cyclones:

• Formation: Tropical cyclones, also known as hurricanes or typhoons in different regions, form over warm ocean waters near the equator. They require sea surface temperatures of at least 26.5°C (80°F) to intensify.
• Structure: Tropical cyclones consist of an eye, which is a calm, low-pressure center, surrounded by a wall of thunderstorms with strong winds and heavy rain. They can cause extensive damage to coastal areas due to storm surges and high winds.
• Categories: Tropical cyclones are categorized based on their wind speeds. The Saffir-Simpson Hurricane Wind Scale classifies them from Category 1 (weakest) to Category 5 (strongest) based on sustained wind speeds.

Extratropical Cyclones:

• Formation: Extratropical cyclones form outside the tropics, usually in the mid-latitudes. They often develop along weather fronts, where warm and cold air masses meet.
• Structure: Extratropical cyclones have a more complex structure than tropical cyclones. They consist of warm and cold fronts, and the interaction between these air masses leads to the development of strong winds and precipitation.
• Impact: Extratropical cyclones are responsible for most of the weather experienced in mid-latitude regions, bringing rain, snow, and wind. They can cause heavy snowfall, blizzards, and severe storms.

Tornadoes:

• Formation: Tornadoes are small-scale cyclones that form within severe thunderstorms. They develop when there are strong wind shears (changes in wind speed and direction with height) within the storm.
• Structure: Tornadoes are characterized by a rotating column of air extending from the base of a thunderstorm to the ground. They often appear as a funnel-shaped cloud, with winds reaching extremely high speeds.
• Impact: Tornadoes are highly destructive, capable of causing widespread damage with their intense winds. The Enhanced Fujita (EF) scale rates tornadoes from EF0 (weakest) to EF5 (strongest) based on the damage they cause.

Each type of cyclone has specific conditions for formation and varying degrees of intensity. Understanding these cyclones is crucial for predicting and mitigating the impact of these natural disasters.

Q16: Define and describe the fronts.
Ans: The contact line between air masses of different properties is called a front. A cold front develops where the cold air mass moves under warm air mass and lifts it up. On the other hand, the trailing edge of a cold air mass that is followed by warm air is called a warm front. In each case, precipitation is likely to occur because warm air is rising over the cold air. Thus duration and intensity of precipitation along the few from.s are quite different. The cold front is steep and produces showery and sometimes violet precipitation for a longer period of time. If the cold front moves faster than the warm front in such a trap, part or all the pocket of warm air may be lifted from the surface, thus producing air occluded front. Often exculpation of the air masses lose earlier characters and form new fronts.