PHSI 243 Environmental Physics Course Notes

Flashcards generated from the provided lecture notes on Environmental Physics, covering topics from the Sun's energy to global climate models.

What is the primary source of energy, besides nuclear and geothermal, used in human activities?

The Sun emits energy in the form of electromagnetic radiation, produced by nuclear fusion reactions in its core, primarily converting hydrogen into helium. This radiation spans a broad spectrum, crucial for various processes on Earth including weather patterns, photosynthesis, and maintaining surface temperatures. The energy output is immense, providing nearly all the energy for Earth's climate system and driving many human activities.

What is the main process in star formation?

Star formation begins with the gravitational collapse of dense regions within interstellar molecular clouds. These regions, composed mainly of gas (primarily hydrogen and helium) and dust, contract under their own gravity. The collapse can be triggered by various events such as supernova explosions, which compress the surrounding interstellar medium, or by density waves in spiral galaxies. As the cloud collapses, it fragments and forms individual stars, often in clusters.

What was the approximate composition of the material from which the earliest stars were formed?

The earliest stars, known as Population III stars, formed from a primordial gas cloud composed almost entirely of hydrogen and helium, with trace amounts of lithium. This composition reflects the conditions shortly after the Big Bang. Specifically, it was approximately 90% hydrogen and 10% helium by number density, which translates to about 75% hydrogen and 25% helium by mass. The absence of heavier elements (metals) significantly influenced the formation and evolution of these first stars.

How do many stars explode at the end of their life-cycle?

Stars with sufficient mass (typically more than 8 times the mass of the Sun) end their lives in a spectacular supernova explosion. This occurs when the core of the star, having exhausted its nuclear fuel, collapses under its own gravity. The collapse triggers a rebound effect, releasing vast amounts of gravitational energy. This energy blows away the outer layers of the star in a violent explosion, creating heavy elements and dispersing them into the interstellar medium. The remnant of the core may form a neutron star or a black hole, depending on its mass.

What is the equation for gravitational force (F) between two bodies with masses m1 and m2 separated by a distance r?

The gravitational force F between two bodies with masses m1 and m2 separated by a distance r is given by the equation F = G \frac{m1 m2}{r^2}, where G is the universal gravitational constant, approximately 6.674 × 10^{-11} N(m/kg)^2. This force is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.

What is the Ideal Gas Law?

The Ideal Gas Law is expressed as PV = nRT, where P is the pressure of the gas, V is the volume, n is the number of moles of the gas, R is the ideal gas constant (approximately 8.314 J/(mol·K)), and T is the absolute temperature in Kelvin. This law describes the state of an ideal gas, relating pressure, volume, and temperature.

What is the mean kinetic energy of each atom in an ideal gas?

The mean kinetic energy Ek of each atom in an ideal gas is given by Ek = \frac{3}{2} kB T, where kB is Boltzmann’s constant (approximately 1.38 × 10^{-23} J/K) and T is the absolute temperature in Kelvin. This equation shows that the average kinetic energy of gas particles is directly proportional to the absolute temperature of the gas.

What temperature must be reached in a proto-star's core for hydrogen fusion to occur?

For hydrogen fusion to occur in a proto-star's core, the temperature must reach approximately 10 × 10^6 K (10 million Kelvin). At this temperature, the kinetic energy of the hydrogen nuclei is high enough to overcome the electrostatic repulsion between them, allowing them to fuse and release energy. This ignition temperature marks the transition from a proto-star to a main-sequence star.

Summarize the reaction for Helium (4 2He) formation.

The formation of Helium-4 (2^4 \text{He}) from Hydrogen-1 (1^1 \text{H}) can be summarized by the nuclear fusion reaction: 4 \, _1^1 \text{H} \rightarrow \, _2^4 \text{He} + 2e^+ + 2\nu + 2\gamma + (2 × 0.42 + 2 × 5.49 + 12.86) \text{MeV}. In this process, four protons fuse to form a helium nucleus, releasing two positrons (e^+), two neutrinos (\nu), and two gamma rays (\gamma), along with energy.

What is the total energy released in producing 4 2He from 4 1 1H?

The total energy released in producing one Helium-4 (2^4 \text{He}) nucleus from four Hydrogen-1 (1^1 \text{H}) nuclei is approximately 26.72 \text{MeV}. This energy is released in the form of kinetic energy of the particles produced and as gamma radiation. Note that about 1% of this energy is carried away by neutrinos, which interact very weakly with matter.

What is luminosity of the sun?

The Sun's luminosity is the total amount of electromagnetic energy that the Sun emits per unit time. It is a measure of the Sun's absolute brightness. The Sun's luminosity is approximately 3.828 × 10^{26} \text{W}, representing the total radiative power output from the Sun.

What is albedo of Earth and what does Albedo measure?

The albedo of Earth is approximately 0.3, indicating that 30% of the solar radiation incident on Earth is reflected back into space. Albedo is a measure of a surface's ability to reflect solar radiation. Surfaces with high albedo, like snow and ice, reflect a large fraction of incoming solar radiation, whereas surfaces with low albedo, like forests and oceans, absorb most of the incoming solar radiation.

What is the natural greenhouse effect?

The natural greenhouse effect is a process by which certain gases in the Earth's atmosphere absorb and re-emit infrared radiation, which warms the planet's surface. Without this effect, the Earth's surface temperature would be significantly colder, making it uninhabitable. The atmosphere absorbs most of the radiation emitted from the Earth’s surface, trapping heat and maintaining a stable, habitable temperature.

What does the Planck radiation law describe?

The Planck radiation law describes the spectral distribution of electromagnetic radiation emitted by a black body at a given temperature. It is fundamental to understanding the radiation emitted by the solar photosphere. It quantifies the amount of energy emitted per unit area, per unit solid angle, and per unit frequency as a function of temperature. This law is crucial for analyzing the spectral characteristics of solar radiation.

What affects the shape of the spectral irradiance?

The shape of the spectral irradiance is affected by absorption in the Sun’s outer layers, where specific elements absorb radiation at characteristic wavelengths, creating absorption lines in the solar spectrum. Additionally, absorption in the Earth's atmosphere by gases such as ozone, water vapor, and carbon dioxide also modifies the spectral irradiance, particularly in the ultraviolet and infrared regions.

What factors determines the intensity of solar radiation on a surface?

The intensity of solar radiation on a surface is determined by several factors: (1) the orientation of the surface relative to the daily and seasonal movement of the solar beam, which affects the angle of incidence; (2) absorption and scattering of the solar beam by atmospheric gases, aerosols, and clouds, which reduce the amount of radiation reaching the surface; and (3) possible reflections from surrounding surfaces, which can increase the radiation received.

What is Irradiance?

Irradiance is defined as the rate at which radiant energy is incident on a surface per unit area of the surface. It is typically expressed in watts per square meter (Wm^{-2}). Irradiance measures the power of electromagnetic radiation arriving at a surface, providing a quantitative measure of the solar energy input.

What is Irradiation or radiant exposure?

Irradiation, also known as radiant exposure, is the incident energy per unit area on a surface, found by integrating the irradiance received during a specified time interval. This is usually measured over an hour or a day and is expressed in units such as joules per square meter (Jm^{-2}) or watt-hours per square meter (Whm^{-2}). Irradiation provides a measure of the total energy received over a period.

What are the principal mechanisms of attenuation in the atmosphere?

The principal mechanisms of attenuation in the atmosphere are scattering and absorption. Scattering involves the dispersion of solar radiation by atmospheric particles, redirecting the energy in various directions. Absorption, on the other hand, involves the conversion of solar radiation into other forms of energy, such as heat, by atmospheric gases.

What are the most important absorbers?

The most important absorbers in the Earth's atmosphere are ozone (O3), water vapor (H2O), carbon dioxide (CO2), and oxygen (O2). Ozone primarily absorbs ultraviolet (UV) radiation in the stratosphere, while water vapor and carbon dioxide absorb infrared (IR) radiation in the troposphere, contributing to the greenhouse effect. Oxygen also absorbs UV radiation at high altitudes.

What pressure gradients are strong?

Strong pressure gradients are most evident in the vertical structure of the atmosphere. The vertical pressure gradient is significant because it determines how the atmosphere responds to and absorbs the Sun’s radiation. Understanding this vertical structure is essential for modeling atmospheric dynamics and energy balance.

What does establish the barometric law from basic principles?

The barometric law, which describes how atmospheric pressure decreases with altitude, can be derived from basic principles by considering the equilibrium of a gas (the atmosphere) in gravitational equilibrium. This equilibrium is established by balancing the gravitational force pulling the gas downwards with the pressure gradient force pushing it upwards.

How is Earth surface divided?

The Earth's surface is divided into 29.2% land and 70.8% ocean. This distribution significantly influences climate patterns, as oceans have a much higher heat capacity than land and play a key role in the global transport of heat and moisture.

In a well mixed atmospheric layer, what is q?

In a well-mixed atmospheric layer, q refers to the specific humidity, which represents the mass of water vapor per unit mass of air. It indicates the amount of moisture present in the air, influencing atmospheric stability and weather phenomena.

What does the term Coriolis effect refer to?

The Coriolis effect is an apparent force that acts on objects moving within a rotating frame of reference. On Earth, this force arises from the planet's rotation and deflects moving objects (such as air masses and ocean currents) to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The Coriolis effect is crucial for understanding large-scale atmospheric and oceanic circulation patterns.

What does the Geostrophic equation do?

The geostrophic equation relates wind speed to the horizontal pressure gradient. The resulting wind, called the geostrophic wind, flows parallel to isobars (lines of constant pressure) due to the balance between the pressure gradient force and the Coriolis force. This equation is fundamental in understanding large-scale atmospheric dynamics and weather patterns, particularly in areas where frictional forces are negligible.

What can the natural greenhouse effect be attributed to?

The natural greenhouse effect can be attributed to the molecular components of the atmosphere, primarily greenhouse gases such as water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These gases absorb and re-emit infrared radiation, trapping heat within the atmosphere and warming the Earth's surface.

What is the most effective greenhouse gas?

Water vapor is the most effective greenhouse gas in the atmosphere due to its abundance and strong absorption of infrared radiation. Although its concentration varies regionally and is influenced by temperature, it plays a crucial role in regulating Earth's temperature and climate.

What is the radiative forcing?

Radiative forcing is defined as the change in net downward radiative flux at the tropopause after allowing for stratospheric temperatures to readjust to radiative equilibrium, while holding surface and tropospheric temperatures and state variables such as water vapor and cloud cover fixed at the unperturbed values. It quantifies the impact of different factors (such as greenhouse gas emissions or changes in solar radiation) on the Earth's energy balance and is a key metric for assessing climate change.

Why could be climate behavior hard to model?

Climate behavior can be hard to model accurately due to the complex interactions and feedbacks between various components of the climate system. For example, low clouds tend to reflect incoming solar radiation, reducing warming, but do not significantly affect radiative heat loss because most outgoing radiation originates from higher elevations. These types of intricate relationships make it challenging to develop precise climate models.