5th School on Cosmic Rays and Astrophysics, Aug-2012, La Paz, Bolivia.
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
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.
Annual Heat Inbalances and Convections
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)
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.
average Earth’s albedo ≈ 30%
The atmosphere is our blanket
and 3 processes may happen:
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
This is the process caused by atoms or small molecules (size < ):
if the outgoing energy (wavelength) is different: Raman Scattering
The Rayleigh scattering is nearly isotropic:and is inversely proportional to 4Conclusion: the sky is blue!! … and the sunset is red
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.
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
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 …
Absorptions don’t occur in the same way for all the wavelengths
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,
Inverse Compton Effect
EAS particles dissipates energy through ionization
A weakly ionized plasma is formed at T ~ 104 K
This plasma cools down very fast (10 ns) though collisions with air molecules
Bremsstrahlung from free electrons (f ~ GHz: microwave band)
EAS produces e± in the shower front (2-3 m thick)
These e±bend in the geomagnetic field (~ 0.3 G), generating synchrotron radiation (geosynchrotron)
Emissions for all e± add up coherently
The radiation can be detected by antennas at f ~ 100 MHz (FM band)
1994 The AGASA Group in Japan and the Yakutsk group in Russia each reported an event with an energy of 2x1020eV.
Pierre Auger Observatory: taking data since 2004
HESS I and HESS-II: four 12 m telescopes andone 28 m telescope
MAGIC: a 17 m telescope
VERITAS: four 12 m telescopes
1991 The Fly's Eye cosmic ray research group in the USA observed a cosmic ray event with an energy of 3x1020eV.
The Telescope Array
The Pierre Auger Fluorescence Detector
this event: intial viewing angle 15°, i.e. large direct Cherenkov contribution
iterative procedure, converges in < 4 steps; energy here ~ 2x1018 eV
20 May 2007 E ~ 10 Cherenkov contribution19eV
FD: 24 (+3) Cherenkov contributionfluorescence
telescopes (30° x 30° FOV):
S Cherenkov contribution38 (1000)vs. E(FD)
661 hybrid events
J. Abraham etal, Phys. Rev. Lett. 101, (2008) 061101.
Flux Cherenkov contributioncalculation:
J. Abraham etal, Phys. Lett. B 685 (2010) 239-246.
A bit of propaganda: Cherenkov contribution
Light pollution in Brazil: Cherenkov contribution