5th School on Cosmic Rays and Astrophysics La Paz, Bolivia August 22nd to 31st , 2012 High Energy Radiation Phenomena in the AtmospherePart I Prof. Marcelo A. Leiguide Oliveira CCNH – UFABC firstname.lastname@example.org
Structure of the Atmosphere • The atmosphere is a thin layer of gases: • 90,0% (h < 10 km); • 99,0% (h < 20 km); • 99,9% (h < 30 km); • etc.
Atmospheric layers Troposphere*: 0 – (7 – 18) km Stratosphere*: 18 – 50 km Mesosphere: 50 – 80 km Thermosphere: 80 – 480 km Exosphere: > 480 km * most important for CRs physics
Chemical composition of the atmosphere From Wikipedia
Basic concepts of energy transport in the atmosphere: • Radiation: energy transfer by electromagnetic waves which takes place in vacuum • Conduction: transfer of kinetic energy by collisions of molecules • Convection: transport of energy by bulk motion of a fluid
Electromagnetic waves: • oscillating electric and magnetic fields that travel in vacuum in the speed of light: c = 299.792.458 m/s ≈ 3 × 108 m/s • the electromagnetic spectrum is continuous and we distinguish • different types of waves based on bands of frequency or wavelength • within each band different processes may • occur, leading to different opacities to the waves
Insolation: the amount of solar radiation received at Earth’s surface The Earth is closest to the Sun on January 3 (perihelion) an farthest from the Sun on July 4 (aphelion)and the revolution axis of the Earth is tilted by 23.5° with respect to the orbital plane, giving rise the seasons, e.g.: winter (summer) in the northern (southern) hemisphere in December.
Radiation Balance on Earth • The Sun is the major source of energy on Earth • The incident energy is partially reflected and partially absorbed in the atmosphere • The Earth emits energy by blackbody radiation • The radiation is partially scattered by air and aerosol molecules
Radiation Balance on Earth The relevant photons fall into two classes: Short wavelength (emitted by the Sun): 0.1 < λ < 4.0 µm (ultraviolet, visible and infrared) Long wavelength (emitted by the Earth’s surface and atmosphere): 4.0 < λ < 100.0 µm (infrared)
Stefan-Boltzmann law: Rate at which objects emit radiation is proportional to the fourth power of the temperature thus the Sun radiates from its photosphere: more power than the Earth system.
Albedo average Earth’s albedo ≈ 30%
Radiation Balance + Greenhouse Effect The atmosphere is our blanket
Atmospheric Influence on Radiation • Upon entering the atmosphere the solar radiation encounters: • Gases: atoms and molecules • Particles (aerosols): large molecules and dust • Clouds: water and 3 processes may happen: Scattering Transmission Absorption
Atmospheric Scattering This is the process where an atom or a molecule redirects the energy: if the outgoing energy (wavelength) is the same: Elastic Scattering if the outgoing energy (wavelength) is different: Inelastic Scattering and there may be 3 types of scatterings: Rayleigh Scattering: by atoms and small molecules Mie Scattering: by large molecules or aerosols Non-selective Scattering: by clouds
Rayleigh Scattering This is the process caused by atoms or small molecules (size < ): if the outgoing energy (wavelength) is different: Raman Scattering
Rayleigh Scattering The Rayleigh scattering is nearly isotropic:and is inversely proportional to 4Conclusion: the sky is blue!! … and the sunset is red
Mie Scattering This is the process caused large molecules & aerosols (size > ): It is not (hardly) dependent on , but on the size of the particles. The radiation is scattered predominantly in the forward direction.
Non-selective Scattering This is the process caused by water droplets which are translucent and curved, (acting like lenses) bending and reflecting the light: the size of water droplets is important, since it will influence on the curvature of the water droplets. Light passing though clouds is an excellent example of non-selective scattering
Transmission • Direct passage of light though the atmosphere: • on a sunny day, without pollution and water vapor as much as 80% of sunlight may reach the surface • as the pollution, water vapor and the amount of clouds increase, the amount of light reaching the surface can drop to zero.
Absorption Any specie that absorbs solar radiation reducing its intensity while passing through the atmosphere. Molecular collisions are always occurring and are likely to take place while some of the colliding molecules happens to be in an excited state (due to a previous process) before the reemission. In this case, the excitation is transferred to other kinds of energy: kinetic, rotational, vibrational, ionization …
Absorption Absorptions don’t occur in the same way for all the wavelengths
5th School on Cosmic Rays and Astrophysics La Paz, Bolivia August 22nd to 31st , 2012 High Energy Radiation Phenomena in the AtmospherePart II Prof. Marcelo A. Leiguide Oliveira CCNH – UFABC email@example.com
Electromagnetic Processes Coulomb scattering
Electromagnetic Processes Ionization loss
Electromagnetic Processes Ionization loss
Electromagnetic Processes Air Fluorescence Measured fluorescence spectrum in dry air at 800 hPa and 293 K F Arqueros, F Blanco and J Rosado, New J. Phys. 11 (2009) 065011 AIRFLY Collaboration, Astroparticle Physics, Volume 28, Issue 1, September 2007, Pages 41-57,
Electromagnetic Processes Cherenkov light
Electromagnetic Processes Compton scattering