Class 11 Geography (Fundamental of Physical Geography) Chapter 8 Solar Radiation, And Balance And temperature

Key Concept: Cause Analysis

c) Temperature inversion

[Solution Description] In winter, temperature inversion often occurs more frequently, trapping pollutants near the ground level. This happens when a layer of warm air overlays cooler air at the surface, preventing the rise and dispersal of pollutants which increase smog levels.

Key Concept: Latitude Effect

b) Higher latitude, more slant rays

[Solution Description] As latitude increases, the angle of incoming solar radiation becomes more oblique, resulting in less intense solar energy received per unit area. At higher latitudes, solar rays strike at a slanting angle leading to less direct sunlight.

Key Concept: Real-World Application, Climate Regulation

b) It drives wind and ocean currents for heat redistribution.

[Solution Description] To understand how the variation in net radiation balance influences global climate regulation, we need to consider how heat is absorbed and distributed on a planetary scale. The tropics receive more solar insolation than they emit back into space, resulting in surplus heat, while polar regions lose more heat than they gain, leading to a deficit. This imbalance drives atmospheric and oceanic circulation patterns that redistribute heat from the equator towards the poles, regulating the global climate. Hence, this variation leads to the formation of distinct climatic zones and plays a crucial role in maintaining thermal equilibrium.

Key Concept: Heat Redistribution, Insolation and Latitude

d) Ocean currents can modify insolation by altering atmospheric conditions such as cloud cover.

[Solution Description] The redistribution of heat by ocean currents impacts the temperature distribution across various latitudes. Warm ocean currents transfer heat from lower to higher latitudes, moderating temperatures in those regions. This process indirectly affects insolation as areas with warmer temperatures due to ocean currents can lead to changes in atmospheric conditions that may influence cloud cover, thereby altering the amount of solar radiation absorbed or reflected.

Key Concept: Complex Interaction, Hemisphere Comparison

a) Cold currents cause a sharper drop in temperature in the Northern Hemisphere due to larger landmass.

[Solution Description] Cold ocean currents can influence coastal temperatures by lowering them. In the Northern Hemisphere, due to larger land masses and less ocean coverage, cold currents cause isotherms to bend south over continents. The Southern Hemisphere has more ocean coverage, causing isotherms to remain more parallel to latitudes even with the presence of cold currents.

Key Concept: Heat Transfer Processes

c) Advection

[Solution Description] Advection is the primary heat transfer process responsible for the horizontal movement of warm air masses across regions. In contrast to convection, which involves vertical movements, advection refers to the transport of properties like heat in a fluid by the flow of the fluid itself.

Key Concept: Real-World Application

c) Due to the equilibrium between incoming solar and outgoing terrestrial radiation.

[Solution Description] The earth’s heat budget remains balanced because the total incoming solar radiation equals the outgoing terrestrial radiation. Specifically, the 65 units of solar radiation absorbed by the earth are eventually returned to space through processes like radiation and absorption by the atmosphere, ensuring no net gain or loss in heat over time.

Key Concept: Rotation and Gravitational Variation, Rotation and Earth’s Shape

a) It makes Earth an oblate spheroid and reduces gravity at the equator.

[Solution Description] The Earth’s rotation causes a centrifugal force that is perpendicular to the axis of rotation and acts outward from the center of the Earth. This force has the maximum effect at the equator and decreases to zero at the poles. As a result, Earth is not a perfect sphere but an oblate spheroid, slightly flattened at the poles. Due to this oblate shape, the gravitational force is weaker at the equator compared to the poles because the distance from the center of mass of the Earth is greater at the equator.

Key Concept: Effects of Inversion

b) Dense fog

[Solution Description] Surface inversion causes stability in the lower atmosphere, which inhibits the vertical mixing of air, leading to the accumulation of smoke, dust, and moisture beneath the inversion layer. This can contribute to the formation of dense fogs, particularly in winter mornings.

Key Concept: Critical Thinking, Real World Application

c) Terrestrial radiation would decrease, causing a deficit in the heat budget.

[Solution Description] Doubling the concentration of $CO_2$ will increase the absorption of terrestrial radiation by greenhouse gases. This means more heat is trapped in the atmosphere, reducing the amount of heat radiated back to space. Consequently, the heat budget will be affected as incoming solar radiation exceeds outgoing radiation, leading to an increase in Earth’s temperature.

Key Concept: Seasonal Variation

c) 30°C

[Solution Description] The temperature range is influenced by factors such as latitude, altitude, and proximity to the sea. At 45° N latitude on land, which is a mid-latitude region in the Northern Hemisphere, there is significant variation between winter and summer temperatures due to the tilt of Earth’s axis and its orbit around the sun. This creates a notable seasonal variation. Typically, the temperature range could be moderate. For example, if the average January temperature is around -5°C and the average July temperature is about 25°C, the temperature range would be calculated as follows:

$\text{Temperature Range} = 25\,^{\circ}\mathrm{C} – (-5\,^{\circ}\mathrm{C}) = 30\,^{\circ}\mathrm{C}$

Thus, the typical temperature range at this latitude is approximately 30°C.

Key Concept: Real-World Application, Heat Balance Analysis

b) Equinox results in equal distribution of insolation over all latitudes

[Solution Description]

On an equinox, the Earth’s axis is not tilted toward or away from the Sun, resulting in nearly equal daylight and darkness at all latitudes. Insolation is uniformly distributed across the hemisphere receiving sunlight. The heat budget remains balanced as the hemispheres receive similar amounts of solar energy due to the perpendicular angle of solar rays at the equator and the decreased angle towards the poles. This uniformity balances incoming and outgoing radiation.

Key Concept: Basic Definition

a) Temperature inversion

[Solution Description] The reversal of the typical decrease in temperature with elevation is known as a temperature inversion.

Key Concept: Complex Problem Solving, Advanced Cause and Effect

b) It decreases transparency, thereby decreasing insolation.

[Solution Description] Increasing water vapor content leads to more absorption of near-infrared radiation by water molecules, reducing atmospheric transparency. This lowers the insolation reaching the Earth’s surface because less solar radiation can pass through the atmosphere. Additionally, increased water vapor enhances cloud formation, further reflecting and absorbing solar radiation.

Key Concept: Conduction vs. Convection

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion describes the process of conduction correctly, where energy is transferred between vibrating molecules and atoms within a substance or between substances in contact, without any movement of the medium itself. The reason also accurately describes convection, where fluid motion (such as liquid or gas) carries heat from one place to another. Both statements are true, but they describe two different processes; hence the Reason is not the correct explanation for the Assertion.

Key Concept: Analytical Thinking, Real-world Application

a) Less variation between summer and winter insolation

[Solution Description] A decrease in Earth’s axial tilt would result in milder seasons, as the angle of inclination of the sun’s rays would vary less between summer and winter. Equatorial regions would experience relatively stable insolation, while polar and temperate zones would witness lesser seasonal extremes, impacting ecosystems and climate patterns.

Key Concept: Real-world Application, Advanced Atmospheric Dynamics

c) Design better ventilation systems for enhanced air circulation.

[Solution Description] The goal is to reduce trapped pollutants by enhancing air circulation and reducing emissions. Planting more trees can absorb some pollutants but doesn’t directly address inversion issues. However, designing better ventilation systems can help break through the inversion layer allowing for dispersal of pollutants.

Key Concept: Inversion Mechanism

a) Long winter nights, clear skies, and still air

[Solution Description]

Temperature inversion typically occurs when the normal lapse rate is reversed, meaning warmer air resides above cooler air. Conditions such as long winter nights allow more heat loss from the earth’s surface, clear skies facilitate radiation cooling, and still air prevents mixing, all contributing to this phenomenon.

Key Concept: Temperature Inversion

b) On a long winter night with clear skies

[Solution Description] Temperature inversion often occurs during a long winter night with clear skies because the ground loses heat rapidly without cloud cover to trap it. This leads to cooler temperatures near the surface than aloft, causing an inversion layer.

Key Concept: Simple Definition

c) Percentage of visible light reflected by an object

[Solution Description] Albedo is the percentage of visible light that is reflected by an object. It is a measure of how much light is reflected as opposed to absorbed.

Key Concept: Basic Concept

c) 3

[Solution Description] Ozone is a molecule that consists of three oxygen atoms. It is represented by the chemical formula $O_3$.

Key Concept: Conceptual Understanding

a) Higher cloud cover

[Solution Description] The main reason why the equator receives less insolation than some parts of the tropics is due to higher cloud cover over the equatorial regions, which results in more scattering and reflection of solar radiation. In contrast, certain tropical regions, especially subtropical deserts, have much clearer skies, allowing for maximum insolation.

Key Concept: Complex Heat Budget, Real-World Application

c) 9 units

[Solution Description] Initially, with an albedo of 35 units, the Earth absorbs 65 units of solar radiation. Increasing the albedo to 40 units reduces the absorption to 60 units because $100 – 40 = 60$. If the Earth’s surface absorbs all remaining after atmospheric absorption, we let $x$ be the units absorbed by the atmosphere. Then $x + 51 = 60$, thus $x = 9$.

Key Concept: Complex Heat Balance, Advanced Insolation Variability

c) 58.5

[Solution Description] Normally, 65 out of 100 units are absorbed. A reduction of 10% in insolation implies only 90 units are received. The reflection remains proportional since albedo is unchanged: $35/100 = x/90 \Rightarrow x = 31.5$. Hence, $90 – 31.5 = 58.5$ units are absorbed.

Key Concept: Analytical Thinking, Problem Solving

d) Less energy will be absorbed, causing possible cooling.

[Solution Description] Initially, Earth reflects 35 units of solar radiation back to space. If the albedo increase causes an additional reflection of 5 units, the new total reflected will be $35 + 5 = 40$ units. Since the Earth initially absorbs 65 units and radiates back 51 units, with this increase in reflection, only $65 – 5 = 60$ units will be absorbed. The Earth’s heat balance would be disrupted unless there is a compensatory decrease in outgoing terrestrial radiation or atmospheric radiation.

Key Concept: Concept Understanding

b) Humidity

[Solution Description] Among the given options, humidity is not typically considered a primary factor affecting the distribution of temperature. Latitude, altitude, ocean currents, and landmass are the main factors.

Key Concept: Integrated Concepts, Problem Solving

d) Terrestrial radiation, as increased surface temperature raises emitted energy drastically.

[Solution Description]

To solve this problem, we must consider how various components of the heat budget react to changes in surface temperature. An increase in surface temperature would result in a rise in emitted terrestrial radiation according to the Stefan-Boltzmann law, which states that energy radiated per unit area is proportional to the fourth power of temperature $(E = \sigma T^4)$. This rapid adjustment helps to restore balance by increasing outgoing longwave radiation.

Given $T_{new} = T_{initial} + 5$, the relative increase in radiation is determined by evaluating $(T_{new}/T_{initial})^4$. This shows that even a small increase in temperature leads to a significant rise in radiant energy output, making terrestrial radiation the primary process adjusting to counteract the imbalance.

Key Concept: Synthesis of Information, Analytical Thinking

c) They absorb and re-radiate longwave terrestrial radiation.

[Solution Description] Greenhouse gases like water vapor and carbon dioxide play a crucial role in absorbing and reradiating long-wave terrestrial radiation back towards Earth. This process is called the “greenhouse effect.” When solar energy reaches the Earth’s surface, it is absorbed and then re-emitted as infrared radiation. Greenhouse gases absorb this infrared radiation and emit it in all directions, including back towards the surface, thus warming the lower atmosphere and the surface. The correct understanding involves synthesizing how these gases interact with both incoming shortwave radiation and outgoing longwave radiation to regulate the Earth’s heat budget.

Key Concept: Latitude Effect

b) Temperature decreases with higher latitude

[Solution Description] Temperature generally decreases with an increase in latitude because regions at higher latitudes receive less direct insolation as compared to those near the equator.

Key Concept: Basic Concept

c) As the main source of energy driving weather systems on Earth

[Solution Description] Solar radiation is the primary source of energy for Earth’s climate system. It drives atmospheric and oceanic circulation, contributes to weather patterns, and affects the global temperature distribution by being absorbed, reflected, or re-emitted by Earth’s surface and atmosphere.

Key Concept: Temperature Distribution

d) Location at 30° N latitude

[Solution Description] The Northern Hemisphere experiences summer in July, leading to higher temperatures. Among given locations, 30° N latitude will have higher temperatures compared to 60° N because it is closer to the equator where solar radiation is more direct.

Key Concept: Advanced Application, Complex Analysis

d) It raises temperatures by reducing cloud cover and altering wind patterns.

[Solution Description] An anticyclone typically involves descending air which suppresses cloud formation and leads to atmospheric stability. During summer, the reduced cloud cover increases solar radiation reaching the surface, thus raising temperatures. Additionally, if the wind direction is from the sea towards the land, the relatively cooler oceanic air could moderate these effects. However, in the presence of an anticyclone over the ocean, the prevailing winds may change, causing warm continental air to dominate. Therefore, the overall effect would likely be an increase in temperature due to more direct sunlight and warmer air flow.

Key Concept: Insolation and Earth’s Orbit, Seasonal Variation

b) Perihelion, due to closer proximity to the Sun.

[Solution Description] Milder winters in the Northern Hemisphere typically occur when Earth is near perihelion, where it is closest to the Sun. This proximity leads to slightly stronger solar radiation reaching Earth, offsetting some cold conditions otherwise expected in winter.

Key Concept: Complex Heat Balance, Real World Application

b) 65 units

[Solution Description] In the initial state, 17 units go directly to space while 34 units are absorbed by the atmosphere. The atmosphere radiates 48 units back to space. With an increase of 10 units absorbed due to more greenhouse gases, the atmosphere would now absorb $34 + 10 = 44$ units. Assuming that all other processes remain constant, these extra absorbed units will eventually be balanced by the same amount being radiated back to space to maintain equilibrium. Thus, the total radiation returning to space would be $17 + 48 = 65$ units, as initially it was maintained at 65 units.

Key Concept: Real-world Application, Complex Energy Flow

c) Enhances the greenhouse effect

[Solution Description] An increase in atmospheric $$\text{CO}_2$$ leads to more terrestrial radiation being absorbed and re-emitted back towards the earth, enhancing the greenhouse effect. This results in a net gain of heat within the earth’s system, as $$\text{CO}_2$$ is effective in trapping long-wave radiation emitted by the Earth. The enhanced greenhouse effect causes an imbalance in the heat budget, leading to warming.

Key Concept: Complex Heat Budget Analysis, Real-World Application

a) 0 units

[Solution Description]

The problem involves analyzing the given data on terrestrial radiation and its interaction with greenhouse gases. Given that the earth radiates 51 units, and 34 units are absorbed by the atmosphere, we have:

$$\text{Direct emission to space} = 17 \text{ units}$$

Since these 17 units are not interacting with the atmosphere or greenhouse gases, they must be subtracted from the total terrestrial radiation:

$$\text{Remaining for atmospheric absorption} = 34 \text{ units}$$

In order to maintain an energy surplus, total absorption minus direct emissions should equal the additional required retention by greenhouse gases:

Since the units already exceed what is emitted directly (17 units), there is no requirement for additional greenhouse gas absorption to maintain a surplus because the atmosphere is already absorbing all excess terrestrial radiation.

Therefore, the amount needing further greenhouse gas retention beyond normal levels is effectively zero.

Key Concept: Temperature Distribution, Insolation and its Variability

b) The equatorial region receives more concentrated sunlight leading to warmer temperatures.

[Solution Description] During the solstices, the Earth’s axial tilt causes significant differences in the angle of incidence of sunlight at various latitudes. At the equator, the sun is nearly directly overhead, resulting in higher insolation and warmer temperatures. Conversely, at the poles, the sun’s rays strike at a very shallow angle, spreading over a larger area and resulting in lower insolation and colder temperatures. This difference accounts for the extreme temperature variations between equatorial and polar regions.

Key Concept: Isotherm Deviation Analysis, Advanced Temperature Calculation

d) Increased deviation of isotherms toward the continent

[Solution Description] The warm ocean current moving northward will cause local temperatures to rise, altering the typical isotherm patterns. Normally, isotherms deviate northward over oceans and southward over continents in January due to prevailing currents and continental influences. With an anomalous warm current, this effect amplifies, making the land warmer. To calculate the change in mean daily temperature, consider initial temperatures $T_{\text{initial}} = 5^\circ C$ and let the ocean current increase it by $+3^\circ C$. Therefore, final temperature $T_{\text{final}} = T_{\text{initial}} + 3^\circ C = 8^\circ C$.

Key Concept: Temperature Extremes

c) North-eastern Eurasian continent

[Solution Description]

The highest range of temperature between January and July is observed in the North-eastern Eurasian continent. This region experiences extreme cold winters and hot summers leading to a large annual temperature range.

Key Concept: Insolation and Atmospheric Composition, Heat Balance Dynamics

c) Water vapor absorbs infrared radiation, trapping heat

[Solution Description]

Water vapor is a greenhouse gas present in the atmosphere that absorbs infrared radiation emitted by Earth. It traps heat within the atmosphere, contributing to Earth’s overall heat balance. When solar radiation enters the atmosphere, part of it is absorbed by water vapor, which increases atmospheric temperature. This absorption of radiation affects the amount of insolation that reaches the Earth’s surface. The process can be broken down as follows:

– Solar radiation enters the atmosphere.

– Water vapor absorbs part of this radiation.

– Absorbed energy increases atmospheric temperature.

– Less radiation reaches Earth’s surface, altering insolation.

Hence, water vapor acts both as an absorber of incoming solar radiation and a contributor to the warming of the atmosphere, affecting how much insolation reaches the surface.

Key Concept: Direct Fact

c) 60° N

[Solution Description] During the summer months, higher latitudes such as those closer to the poles experience longer durations of daylight due to the tilt of the Earth’s axis, which causes the sun to stay above the horizon for extended periods.

Key Concept: Insolation and Heat Redistribution, Insolation and Temperature Distribution

c) Ocean currents and atmospheric circulation

[Solution Description]

The surplus heat from the tropics is redistributed toward higher latitudes through atmospheric circulation (winds and jet streams) and ocean currents (like the Gulf Stream). This process balances temperatures across different latitudes by transporting warm air and water towards colder regions, while cold air and water move towards warmer areas. Without such systems, the temperature differences between the equator and poles would be much more extreme.

Key Concept: Complex Interactions, Isotherm Deviation

d) Warm ocean currents cause northward bending of isotherms.

[Solution Description] The deviation of isotherms over the North Atlantic during winter is influenced significantly by both latitude and ocean currents. Latitude determines the general temperature gradient from equator to poles. However, the presence of warm or cold ocean currents can alter this pattern by either warming or cooling the air above them. In the North Atlantic, the Gulf Stream, a warm ocean current, causes isotherms to bend northwards, indicating warmer temperatures than typical for those latitudes.

Key Concept: Insolation and Earth’s Orbit, Insolation and Climate

b) Subtropical deserts receive reduced insolation but more than equatorial regions due to clearer skies.

[Solution Description] At aphelion, Earth is farthest from the Sun, which means that less solar radiation reaches the earth overall. However, in subtropical deserts, clear skies allow for a relatively higher proportion of incoming solar energy to reach the surface compared to equatorial regions where frequent cloud cover reflects or absorbs much of the radiation. Hence, despite being farther from the sun, subtropical deserts can still receive significant insolation due to atmospheric conditions.

Key Concept: Insolation and Latitude, Solar Radiation and Atmospheric Gases

a) Due to less atmospheric absorption and scattering caused by low water vapor content.

[Solution Description] Subtropical deserts receive more insolation because they typically experience clearer skies with fewer clouds due to high-pressure systems dominating these areas. The lack of cloud cover means less solar radiation is reflected or absorbed before reaching the surface, unlike equatorial regions where frequent cloud cover absorbs and scatters sunlight. Also, subtropical regions often receive direct overhead sunlight during certain periods of the year, further maximizing insolation.

Key Concept: Insolation and Heat Redistribution, Insolation and Earth’s Energy Balance

b) Atmospheric circulation transports warm air from low to high latitudes.

[Solution Description]

The solar energy received in Region A is much higher than that in Region B. This excess heat in Region A needs to be redistributed to maintain thermal equilibrium. One primary method for this energy transfer is through atmospheric circulation patterns, where warm air moves from low latitudes to high latitudes. Ocean currents also play a significant role by transporting warm water poleward and returning cold water equatorward. Conduction is negligible on a global scale and radiation alone cannot account for the observed heat transport.

Key Concept: Advanced Application, Real-World Problem Solving

a) The room with wooden walls due to better insulation properties.

[Solution Description] Wood is generally a better insulator than glass. Insulators prevent heat from escaping or entering easily, thus maintaining a more stable temperature inside. Glass has higher thermal conductivity compared to wood, meaning it allows heat transfer more readily. Therefore, the room with wooden walls will likely maintain a more stable and consistent temperature over time compared to the room with glass walls.

Key Concept: Heat Transfer Mechanisms, Atmospheric Stability

c) Radiative cooling

[Solution Description] During winter nights, the Earth’s surface loses heat through terrestrial radiation more rapidly than the air above it. This radiative cooling leads to a layer of cooler air near the surface under warmer air aloft. Since radiation is the primary heat loss at night, and without incoming solar radiation to warm the surface, convection is limited, leading to temperature inversion.

Key Concept: Critical Analysis, Complex Problem Solving

b) Decrease in winter insolation as sun’s path moves further overhead.

[Solution Description] Shifting the Earth’s axis by 5 degrees towards the poles would alter the length of the day and the angle at which sunlight hits various parts of Earth. In subtropical deserts, this might lead to a decrease in winter insolation as the sun’s path shifts away from direct overhead positions. Conversely, summer insolation may marginally increase or remain stable but will not be drastically altered. Therefore, the most significant change would occur during winter months, impacting overall annual insolation patterns.

Key Concept: Seasonal Temperature Changes

c) July

[Solution Description] In the Southern Hemisphere, July is winter when compared to January, which is summer. The temperature deviations from the latitudinal pattern are more pronounced during winter months due to greater variability in insolation and atmospheric conditions.

Key Concept: Insolation Distribution

c) It results in lower average temperatures and longer winters.

[Solution Description] The polar regions receive low amounts of insolation due to the angle at which sunlight strikes these areas, leading to colder climates. This reduced solar energy results in higher albedo effect with snow and ice reflecting most of the sun’s rays.

Key Concept: Complex Interactions, Heat Transfer Mechanisms

c) Temperatures remain relatively stable through winter.

[Solution Description] The interaction between warm air masses and cold ocean currents can lead to interesting temperature patterns along coastlines. When a warm air mass meets a cold ocean current, it is often cooled by the underlying water. This results in cooler temperatures along the coast compared to the inland areas, which are under the direct influence of the warm air mass. The cooling effect is more pronounced during winter months when the temperature differences between land and sea are greater. Therefore, the coastal regions tend to have milder winters than the interior parts due to this moderating effect.

Key Concept: Net Radiation Balance, Convection and Advection

b) Influence of warm or cold ocean currents

[Solution Description] The primary factor causing variation in temperature between coastal and inland areas at similar latitudes is due to the influence of ocean currents and air masses which impact the net radiation balance. Coastal areas are moderated by the presence of large water bodies where convection and advection play significant roles. Warm or cold ocean currents can transport heat away from or towards a location, moderating the temperatures. Inland areas lack this moderation, resulting in more extreme temperatures.

Key Concept: Complex Analysis, Synthesis of Concepts

c) 5.5°C

[Solution Description] To find the temperature at 3000 meters, we can use the lapse rate concept. The formula for calculating temperature change with altitude is:

$\text{Temperature drop} = \left(\frac{\text{Altitude height}}{1000}\right) \times \text{Lapse rate}$

Given the initial temperature $T_0 = 25^\circ C$, lapse rate $6.5^\circ C/1000m$, and altitude 3000m, calculate:

$\text{Temperature drop} = \left(\frac{3000}{1000}\right) \times 6.5 = 19.5^\circ C$

Subtract the temperature drop from the initial temperature:

$T_{\text{at 3000m}} = 25 – 19.5 = 5.5^\circ C$

Therefore, the predicted temperature at 3000 meters is 5.5°C.

Key Concept: Latitudinal Variation, Energy Redistribution

c) Enhanced poleward heat transfer regulates climate stability.

[Solution Description]

Between latitudes 35°N and 35°S, a surplus in net radiation causes excess heat in these regions, which drives atmospheric circulation patterns like Hadley cells. This surplus results in heat moving towards higher latitudes, moderating climates there. Without this redistribution, equatorial regions would overheat while polar areas would become excessively cold. Therefore, any change in this surplus will significantly alter global climate through disruption of these atmospheric circulations.