Wave propagation and radiative transfer in the atmosphere, the greenhouse effect and global warming
Other project members
Christian Engström, Linnaeus University; Pieter Tans, NOAA Global Monitoring Laboratory, USA
Electrical engineering (Department of Physics and Electrical Engineering, Faculty of Technology)
More about the project
The topic of wave propagation and radiative transfer in the atmosphere, the greenhouse effect and global warming is a timely subject area embracing many scientific and technological advancements and challenges. Not only does it provide a basic understanding of the physical principles underlying the climate changes, it also provides a unifying interdisciplinary theme connecting many interesting research areas within the natural and technological sciences. Some of these are Earth and environmental sciences, chemistry, physics, electrical engineering and applied mathematics.
The research project is addressing the following specific areas:
1) Statistical analysis of climate data and short-term global trends
Nowadays, the amount of greenhouse gases as well as mean surface temperatures are routinely measured around the world. This provides an irreplaceable source of data, information and analyses as a basis for policymakers in their quest to mitigate the global warming. It is therefore of utmost importance to understand precisely the variability and accuracy in these measurements in order to make correct interpretations of the data.
Our research is aiming to develop new tools based on estimation and statistical theory to provide analysis and validation of short-term global trends in the abundance of the atmospheric greenhouse gases and other climate related data.
2) Radiative transfer and quantitative spectroscopy
The theory of radiative transfer in the atmosphere is an important tool for being able to predict the greenhouse effect, the radiation budget of the planet and the global warming in different scenarios. Quantitative spectroscopy is in the core of the radiative transfer calculations and constitute a modern research field with many recent results of great importance. Today, researchers are speaking about spectral profiles "beyond Voigt" (i.e., beyond the classical spectral profiles) and are continuously trying to improve and implement new spectroscopic models, e.g., by taking into account line mixing and velocity changes due to molecular collisions.
Our research is aiming to analyze and refine these models by taking into consideration the fundamental mathematical and physical properties relating to passivity, positive real (or Herglotz) functions and the associated optical theorems and sum rules. The research is also aiming to develop more efficient numerical implementations of advanced spectral profiles in computer programs that are based on "line-by-line" calculations.
The project is part of the research in the Waves, Signals and Systems research group.
Example of an atmospheric model
In the video above, an atmospheric model is illustrated, comprising some given vertical profiles of temperature, mixing ratios for the five most important greenhouse gases and atmospheric pressure, all between 0 and 65 km height. The lower plot shows the spectrum of the outgoing thermal infrared radiation (irradiance) transmitted by the Earth at different altitudes in the atmosphere.
The video sequence can be stepped up or down in order to study the impact of the various greenhouse gases in different frequency bands and different altitudes. As can be seen in this video, the rotational-vibrational bands of water and carbon dioxide are responsible for most of the attenuation, whereas the effect of methane and nitrous oxide are partly masked by the more abundant absorbers. Clearly, the attenuation of ozone stems from the ozone layer at 20–40 km altitude.
An interesting quantum mechanical feature to note here is the bending mode Q-branch of carbon dioxide at 667 cm-1 which is saturated up to 25 km height, and which then becomes visibly resolved due to the positive temperature gradient at higher altitudes. In contrast, the peak seen at the central 1043 cm-1 resonance in the non-saturated absorption band of ozone is due to the absence of a Q-branch of its stretching mode.
All these features are due to well established principles of radiative transfer and quantum mechanics, and have been validated by satellite measurements since the 70’s. Today, this kind of modeling is an important tool in the study of radiative forcing and global warming due to the increased amounts of greenhouse gases in the atmosphere.
Explanation of the model above
The video above is also explained in Sven Nordebo's recent talk The greenhouse effect, radiative transfer in the atmosphere and quantum mechanics, recorded at the conference Quantum Information and Probability: From Foundations to Engineering (QIP) held August 25–27, 2021 at Linnaeus University. You can also download the presentation from the talk (pdf file).