Basic Chemistry and Physics Flashcards
Define the concept of a black body.
A black body is a theoretical body that absorbs all incoming electromagnetic radiation, reflecting or transmitting none, and emits electromagnetic radiation called black body radiation. The radiation emitted by a black body depends only on its temperature.
Explain the physical process behind CO2 molecules only absorbing radiation at specific wavelengths.
Radiation at specific IR wavelengths is usually not energetic enough to excite electrons, but it will cause the chemical bonds within molecules to vibrate in different ways. The resonance frequency for molecules are fixed depending on the type of bonds present and the symmetry of the molecule. Because each of these bonds is different, each will vibrate in a different way, and absorb IR radiation of different wavelengths. When the COs molecules is bent, the oxygens, carrying slight negative charges swing from one side of the molecule to the other. The CO2 bending vibration absorbs and emits IR light - CO2 is infrared active. The CO2 bending vibration absorbs right at the peak of the blackbody spectrum of the Earth.
Around which wavelength is the main CO2 absorption band centered? And what is the relevance of this absorption band, i.e. which key role does CO2 have because of it?
The main CO2 absorption band is centered around 15 um.
It corresponds to the radiation emitted from the warm ground, the center of the blackbody spectrum, of the Earth. So, CO2 absorbs the intense “warm” IR from the ground at theis frequency and re-emits the same frequency but at a lower intensity, because of its colder temp. higher up in the atmosphere.
Emissions of a GHG to the atmosphere will change the concentration of the gas and change its radiative forcing. How is radiative forcing defined? Give a description of the specifics of the definition.
- Definition: Radiative forcing (RF) is a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the troposphere and is an index of the importance of the factor as a potential climate change mechanism.
- Different factors that can change the climate can be compared in terms of their effect on the energy budget of the earth in units of W/m2, which is called their global average RF values. For example, 1 W/m2 of IR light by CO2. Not exactly, but close enought for the radiative forcing to make a convenient starting point for comparing different drivers of climate change.
- The radiative forcing is defined as the energy imbalance immediately after the change has been enacted but before the climate has had a chance to respond. It’s defined this way because when the climate responds, it eventually drives the energy in balance back to zero. Some factors that affect climate are considered internal to the climate system, like the water vapour feedback, clouds and changes in the albedo of the land surface and from melting ice. These are not considered forcing, which should be externally driven, because they are internal to the climate system, they are considered feedbacks.
Describe the relationship between the GHG concentration and radiative forcing. Explain specifically how the relationship differs among different GHG as well as the physical mechanisms causing the difference.
Without GHG the earth would glow with IR radiation corresponding to the same amount of energy absorbed by the sun. But because of the gases in the atmosphere the IR radiation is interrupted and depending on the gases, some of the IR radiation wavelengths gets absorbed and trapped in the atmosphere, thereby reducing earths radiative forcing.
Different gases absorb different bands of wavelengths depending on the radiative forcing. The higher concentration of the gas the radiation has to travel through, the higher chance it has of being absorbed when leaving the planet.
Define the residence time and residence age when dealing with material fluxes in the environment.
- The residence time is the time spent in a reservoir by an individual atom or molecule.
- The age of a molecule is how old it is when it leaves the reservoir, and the age started when it enters the reservoir.
- Different molecules and atoms have different residence times in different reservoirs. For the fluxes in the environment, this can be used to look at different substances and how they move between different parts and how long they will be there.
Explain the relation () between average residence time and average age for carbon, C, in the soil.
As the average residence time is the time spent in a reservoir from the inlet to outlet. The age of an atom/molecule in a reservoir is the time since it entered the reservoir. Therefore, in a steady-state reservoir, the average residence time ≈ average age.
However, in a case where most atoms leave the reservoir soon and few remain, the average residence time < average age. Like for ex. that average age in Sweden is 40 years while the average length of life (residence time) is 80 years.
What is meant by parameterization in atmospheric model?
- Parameterized = sub-grid processes summerized in a statistical fashion in a way related to the large-scale flow.
- For a model of the atmosphere the large scale will have grid size of 100 km or more. But the connective motion systems in ocean and atmosphere occur on spacial scale of a few km or less, and thus cannot be resolved in large scale models. But the combined effect of such models is of fundamental importance when looking at the atmosphere. So parametarization schemes can be used to describe how the small-scale influences the large-scale flow.
How does the wavelength corresponding to the peak of blackbody radiation spectrum vary with temperature?
The spectral distribution of the black body radiation depends only on the temperature. As the temperature goes up, the wavelength becomes shorter and they come at a higher frequency. Secondly, as the temperature goes up, the total energy emitted by the object goes up (which is the area under the canvas). (see picure in notes)
What is the equilibrium impact on the temperature T(t) in a step response?
When the system is in equilibrium everything is balanced, so the temperature T(t) will remain the same over time as long as in equilibrium.
What is the e-folding time?
E-folding time is the time it takes to reach the 1-e^(-1) (≈63%) fraction of the steady state level for the step response.
