Worksheet Solutions: Atmospheric Circulation and Weather Systems | Geography Class 11 - Humanities/Arts PDF Download

Fill in the Blanks

Q1: Air expands when heated and gets compressed when __________.
Ans: cooled
When air is heated, the molecules gain energy and move farther apart, causing the air to expand. Conversely, when air is cooled, the molecules lose energy and move closer together, resulting in compression.

Q2: The weight of a column of air from mean sea level to the top of the atmosphere is called __________.
Ans: atmospheric pressure
Atmospheric pressure is the force exerted by the weight of the overlying air in a vertical column, extending from sea level to the top of the Earth's atmosphere. It decreases with increasing altitude.

Q3: Atmospheric pressure is measured in units of __________.
Ans: millibar
Millibars (mb) are the most commonly used units for measuring atmospheric pressure. Other units like pascals (Pa) and inches of mercury (inHg) are also used, but millibars are widely adopted in meteorology.

Q4: Isobars are lines connecting places having equal __________.
Ans: pressure
Isobars are contour lines on weather maps that connect points with the same atmospheric pressure. They help meteorologists analyze pressure patterns and identify areas of high and low pressure.

Q5: Near the equator, the sea-level pressure is known as __________.
Ans: equatorial low
The equatorial low is a region near the equator where the sea-level pressure is relatively low due to the warm air rising and converging, creating a low-pressure zone.

Q6: The force exerted by the rotation of the earth is called __________.
Ans: Coriolis force
The Coriolis force is an effect of the Earth's rotation that causes moving air or water to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Q7: The Coriolis force deflects the wind to the right direction in the __________ hemisphere.
Ans: Northern
In the Northern Hemisphere, the Coriolis force causes moving air or wind to be deflected to the right of its original path. In the Southern Hemisphere, it deflects to the left.

Q8: The low pressure gets filled instead of intensifying near the __________.
Ans: equator
Near the equator, the Coriolis force is weak, so low-pressure areas do not intensify into cyclones or hurricanes. Instead, they tend to fill with rising warm air.

Q9: The general circulation of the atmosphere sets in motion the ocean water circulation which influences the __________.
Ans: Earth's climate
The general circulation of the atmosphere, driven by the movement of air masses and pressure systems, influences the circulation of ocean currents. This interaction between the atmosphere and oceans plays a significant role in regulating the Earth's climate.

Q10: The phenomenon of southern oscillation and El Nino is known as __________.
Ans: ENSO (El Niño-Southern Oscillation)
ENSO refers to the combined phenomenon of El Niño and the Southern Oscillation. El Niño is the warming of ocean waters in the central and eastern Pacific, and the Southern Oscillation is the atmospheric pressure variation in the tropical Pacific. These events can have a significant impact on global weather patterns.

Assertion and Reason Based

Q1: Assertion: Atmospheric pressure decreases rapidly with height in the lower atmosphere.
Reason: The decrease in pressure with height is caused by the increasing concentration of water vapor.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Both assertion and reason are false.
Ans: (c)
The decrease in atmospheric pressure with height is primarily caused by decreasing air density as one moves higher in the atmosphere, not the concentration of water vapor. Water vapor content can affect air density, but it is not the primary factor in pressure changes with height.

Q2: Assertion: The Coriolis force is maximum at the equator.
Reason: The Coriolis force is directly proportional to the angle of latitude.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Both assertion and reason are false.
Ans: (d)
The Coriolis force is directly proportional to the angle of latitude, and it is maximum at the poles and absent at the equator. This directly influences the direction of wind.

Q3: Assertion: The general circulation of the atmosphere is influenced by the distribution of continents and oceans.
Reason: Oceans provide input of energy and water vapor into the atmosphere.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Both assertion and reason are false.
Ans: (a)
Oceans provide energy and moisture to the atmosphere, which, in turn, influences the general circulation of the atmosphere. The assertion and reason are both true and interrelated.

Q4: Assertion: El Nino is associated with the appearance of cool water off the coast of Peru.
Reason: El Nino is caused by the southern oscillation.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Both assertion and reason are false.
Ans: (b)
El Nino is associated with the appearance of warm water off the coast of Peru, not cool water. The southern oscillation is indeed linked to El Nino, but it does not explain the cooling of the water.

Q5: Assertion: Subtropical highs are located between 30° N and 30° S.
Reason: These high-pressure areas are associated with sinking air and clear skies.
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Both assertion and reason are false.
Ans: (a)
Subtropical highs are located between 30° N and 30° S, and they are associated with sinking air and clear skies. The assertion and reason are both true and related.

Very Short Answer Type Questions

Q1: Define atmospheric pressure.
Ans: Atmospheric pressure is the force exerted by the weight of the atmosphere on the Earth's surface.

Q2: What is the primary cause of air motion (wind)?
Ans: The primary cause of air motion (wind) is variations in atmospheric pressure.

Q3: Explain the concept of isobars.
Ans: Isobars are lines connecting places having equal atmospheric pressure. They are used to study the horizontal distribution of pressure.

Q4: Differentiate between a low-pressure system and a high-pressure system.
Ans: A low-pressure system is enclosed by one or more isobars with the lowest pressure in the center. A high-pressure system is also enclosed by one or more isobars with the highest pressure in the center.

Q5: What is the Coriolis force, and in which direction does it deflect wind in the northern hemisphere?
Ans: The Coriolis force is an apparent force that deflects the motion of objects, including wind, due to the rotation of the Earth. In the northern hemisphere, it causes moving air to be deflected to the right.

Q6: Why are tropical cyclones not formed near the equator?
Ans: Tropical cyclones are not formed near the equator because the Coriolis force is nearly absent at the equator.

Q7: Define geostrophic wind.
Ans: Geostrophic wind refers to the horizontal wind flow at high altitudes. It is the result of a balance between the pressure gradient force and the Coriolis force. Geostrophic winds blow parallel to isobars.

Q8: What is a cyclonic circulation?
Ans: Cyclonic circulation refers to the counterclockwise flow of air around a low-pressure center in the northern hemisphere (and clockwise in the southern hemisphere). It is associated with the inward movement of air and the potential for stormy weather.

Q9: What are the three cells that set the pattern for the general circulation of the atmosphere?
Ans: The three cells that establish the general circulation pattern of the atmosphere are the Hadley cell, Ferrel cell, and Polar cell. These cells are responsible for redistributing heat and moisture across the globe.

Q10: What is ENSO, and how does it affect weather patterns?
Ans: ENSO (El Nino-Southern Oscillation) is a climate phenomenon associated with the periodic warming and cooling of the central and eastern Pacific Ocean.

Short Answer Type Questions

Q1: Explain how variations in atmospheric pressure cause the movement of air and the formation of wind.
Ans: Variations in atmospheric pressure cause the movement of air from high pressure to low pressure, creating wind. When moist air rises due to lower pressure, it cools, forms clouds, and brings precipitation.

Q2: Describe the vertical variation of pressure in the atmosphere and its significance.
Ans: The vertical variation of pressure in the atmosphere is significant because it results in the formation of pressure gradients, which drive air motion. As altitude increases, atmospheric pressure decreases. The decrease is about 1 millibar for every 10 meters in elevation.

Q3: How is atmospheric pressure measured, and why does it decrease with height?
Ans: Atmospheric pressure is measured in units like pascals, millibars, or inches of mercury. It decreases with height due to the decreasing density of air molecules. Pressure decreases because there is less air above exerting a downward force.

Q4: Discuss the forces affecting the velocity and direction of wind, including the Coriolis force.
Ans: The velocity and direction of wind are affected by three forces: the pressure gradient force, the frictional force, and the Coriolis force. The pressure gradient force results from differences in atmospheric pressure. The Coriolis force is caused by the Earth's rotation and deflects the wind to the right in the northern hemisphere.

Q5: Explain the concept of Hadley cells and their role in the general circulation of the atmosphere.
Ans: Hadley cells are tropical atmospheric circulation cells that consist of rising air near the equator, moving air at higher altitudes toward the poles, and sinking air around 30° N and 30° S. They play a crucial role in the general circulation of the atmosphere.

Q6: Describe the general atmospheric circulation and its influence on the oceans.
Ans: The general atmospheric circulation is the pattern of global wind systems that influences the Earth's climate. It involves the Hadley cell, Ferrel cell, and polar cell, which are responsible for transferring heat energy from lower latitudes to higher latitudes.

Q7: What is El Nino, and how is it related to the southern oscillation? How does it impact weather patterns?
Ans: El Nino is a climate phenomenon characterized by the periodic warming of central and eastern Pacific Ocean waters. It is related to the southern oscillation, which is the shifting of atmospheric pressure patterns. El Nino can lead to worldwide climate disruptions.

Q8: How do the interactions between the atmosphere and oceans affect long-range weather forecasting?
Ans: Large-scale wind patterns in the atmosphere influence ocean currents and heat transfer. For example, the trade winds push warm surface waters westward in the tropical Pacific, leading to the upwelling of cold waters off the coast of Peru. This interaction impacts weather and climate on a global scale.

Long Answer Type Questions

Q1: Discuss the role of atmospheric pressure in weather systems, including its impact on the formation of clouds and precipitation.
Ans: Atmospheric pressure plays a crucial role in the formation of weather systems and influences the occurrence of clouds and precipitation. Atmospheric pressure refers to the force exerted by the weight of the air above a particular location. It varies with altitude and is commonly measured using a barometer.
In weather systems, areas of high and low pressure are key elements. High-pressure systems are associated with sinking air, resulting in stable atmospheric conditions. These systems often bring clear skies and fair weather. Low-pressure systems, on the other hand, are associated with rising air, leading to unstable atmospheric conditions. These systems typically bring clouds, storms, and precipitation.
The gradient of atmospheric pressure, known as the pressure gradient, influences the movement of air. Air flows from areas of high pressure to areas of low pressure, creating wind patterns. This movement of air is essential for the formation and movement of weather systems.
When air rises in a low-pressure area, it cools and reaches its dew point, causing water vapor to condense and form clouds. As the air continues to rise, the clouds can grow and develop into precipitation, such as rain, snow, or hail. The intensity and type of precipitation depend on various factors, including temperature, humidity, and the presence of other atmospheric particles.
In summary, atmospheric pressure affects weather systems by creating areas of high and low pressure, which in turn influence the movement of air and the formation of clouds and precipitation.

Q2: Explain the concept of general atmospheric circulation and how it influences the Earth's climate and weather patterns.
Ans: The concept of general atmospheric circulation refers to the large-scale movements of air in the Earth's atmosphere. It is driven by the uneven heating of the Earth's surface by the Sun, resulting in variations in temperature and pressure.
The primary driver of general atmospheric circulation is the differential heating between the equator and the poles. At the equator, solar radiation is more intense, causing the air to warm and rise. This creates a region of low pressure known as the Intertropical Convergence Zone (ITCZ). As the air rises, it cools and moves towards the poles, forming the Hadley cells.
The air in the upper levels of the atmosphere moves towards the poles, gradually descending around 30 degrees latitude in both hemispheres. This creates regions of high pressure known as the subtropical high-pressure belts. The descending air warms and forms the trade winds, which blow towards the equator.
At higher latitudes, the polar cells form as the cool air near the poles sinks and moves towards lower latitudes. The polar cells meet the warmer air from the Ferrel cells around 60 degrees latitude, creating the polar front, a region of low pressure. This frontal boundary is associated with the formation of mid-latitude weather systems and storms.
The general atmospheric circulation has significant impacts on the Earth's climate and weather patterns. It helps distribute heat from the equator towards the poles, resulting in the moderation of global temperatures. It also influences the global wind patterns, which affect the movement of weather systems and the distribution of moisture and precipitation.
Furthermore, the general atmospheric circulation plays a role in the formation of the major climate zones, such as the tropical, temperate, and polar regions. These climate zones have distinct characteristics in terms of temperature, precipitation, and vegetation, which are influenced by the patterns of atmospheric circulation.

Q3: Describe the complex interactions between El Nino, the southern oscillation, and their global effects on weather and climate.
Ans: El Niño and the Southern Oscillation (ENSO) are interconnected phenomena that have significant global effects on weather and climate. El Niño refers to the warming of the eastern Pacific Ocean, while the Southern Oscillation refers to the atmospheric pressure changes between the eastern and western Pacific.
During a typical year, a strong easterly trade wind blows across the Pacific Ocean, pushing warm surface waters towards the western Pacific. This causes the sea level to be higher in the western Pacific compared to the eastern Pacific. The temperature difference across the Pacific generates atmospheric circulation patterns known as the Walker Circulation.
However, during an El Niño event, the trade winds weaken or reverse, reducing the upwelling of cold, nutrient-rich waters in the eastern Pacific. This leads to a decrease in the temperature gradient across the Pacific and a weakening of the Walker Circulation. As a result, warm oceanic waters move eastward, leading to a rise in sea surface temperatures along the coasts of South America.
The complex interactions between El Niño and the Southern Oscillation have several global effects on weather and climate. These include:

• Changes in rainfall patterns: El Niño can cause drought conditions in some regions, such as Australia and Southeast Asia, while increasing rainfall in others, such as the southwestern United States and Peru. The altered atmospheric circulation disrupts normal precipitation patterns.
• Impact on tropical cyclones: El Niño tends to suppress the formation of tropical cyclones in the Atlantic basin, while increasing their occurrence in the central and eastern Pacific.
• Shifts in temperature patterns: El Niño events can lead to warmer-than-average surface temperatures in various parts of the world, including the equatorial Pacific, North America, and parts of Africa.
• Disruption of fisheries: Changes in oceanic conditions during El Niño events can have detrimental effects on marine ecosystems, leading to reduced fish populations and affecting the livelihoods of fishing communities.

Overall, El Niño and the Southern Oscillation have far-reaching impacts on weather and climate patterns globally, affecting precipitation, temperature, storm activity, and marine ecosystems.

Q4: How do large-scale wind patterns in the atmosphere influence ocean currents and the transfer of heat energy across the Earth's surface?
Ans: Large-scale wind patterns in the atmosphere play a crucial role in influencing ocean currents and the transfer of heat energy across the Earth's surface. These wind patterns are driven by the unequal heating of the Earth by the Sun and the resulting pressure gradients.
The major wind patterns include the trade winds, prevailing westerlies, and polar easterlies. Near the equator, the trade winds blow from east to west, driven by the temperature difference between the equator and the poles. These trade winds help drive the ocean currents in the tropical regions, such as the warm eastward-flowing currents in the Pacific and Atlantic Oceans.
The prevailing westerlies, located between 30 and 60 degrees latitude in both hemispheres, blow from west to east. These winds influence the movement of both surface and deep ocean currents in the mid-latitudes. In the Northern Hemisphere, they contribute to the Gulf Stream, a warm ocean current that transports heat towards Europe.
The polar easterlies blow from east to west near the poles. They play a role in the formation of polar surface currents that circulate around the polar regions.
The interaction between these wind patterns and the ocean currents has several effects on the transfer of heat energy across the Earth's surface:

• Upwelling and downwelling: Winds blowing parallel to the coastline can cause the upwelling or downwelling of ocean waters. Upwelling brings cold, nutrient-rich waters from the deep ocean to the surface, supporting marine ecosystems. Downwelling, on the other hand, can transport warm surface waters to deeper layers.
• Heat redistribution: Ocean currents driven by wind patterns transport heat from the equator towards the poles, helping to regulate global temperatures. Warm currents carry heat away from the tropics, while cold currents transport heat towards the equator.
• Influence on climate: The transfer of heat energy by ocean currents influenced by wind patterns can affect regional climates. For example, the Gulf Stream helps moderate the climate of western Europe, keeping it warmer than other regions at similar latitudes.

In conclusion, large-scale wind patterns in the atmosphere drive ocean currents, which play a crucial role in the transfer of heat energy across the Earth's surface. These interactions contribute to the regulation of global temperatures and influence regional climates.