99511 - RADIATION, CLOUDS AND CLIMATE

Conoscenze e abilità da conseguire

Through this course, the student will learn the basics physical mechanisms underlying the interaction between electromagnetic radiation and the atmospheric components and the role of radiative transfer of energy in the climate system. The student will learn the optical properties of radiatively active gaseous species, aerosol particles, and different cloud types, and will be able to understand the greenhouse effect mechanism. The impact of multiple atmospheric components on Earth's energy budget will be assessed. A special focus will be set on clouds, their radiative forcing, and the feedback mechanisms involving water vapor and aerosols. The effect of climate change on cloud structure will also be considered. Finally, the students will learn to use a radiative transfer model to simulate the signature of different atmospheric components on the radiation field in relevant regions of the electromagnetic spectrum.

Contenuti

Module 1 “Clouds” (FP)

introduction to the Module,

thermodynamics: water in the atmosphere,

cloud’s elements formation and growth,

precipitation processes,

cloud structures,

the aerosol system,

clouds in the Tropics,

clouds at mid-latitude,

clouds in polar regions,

precipitation features and extreme events,

cloud parameterization,

clouds in climate models.

Module 2 “Radiative processes” (TM)

1 Interaction between Electromagnetic radiation and atmospheric components

• A physical overview of the Earth atmosphere
• The electro-magnetic spectrum
• Radiatively active gases: historical viewpoint
• Interaction between radiation and gas: molecular energy levels and transitions
• The solid angle
• The concept of radiance and irradiance

 

2 Emission of radiation

 

• The Planck equation and the local thermodynamic equilibrium
• Features of the black body radiation model
• Real bodies and the concept of Emissivity

3 Solar radiation

• Sun luminosity and the solar spectrum
• Measurements of the solar total irradiance (TSI)
• Natural variation of the TSI
• Insolation at the top of the atmosphere

4 The law of absorption and emission of radiation

• The Bouger-Lambert-Beer law
• Monochromatic transmissivity, absorptivity and reflectivity
• The Schwarzschild’s equation

5 Shortwave absorption in the atmosphere

• Absorption of solar radiation in the atmosphere
• The Ozone layer
• The Chapman model

6 Longwave absorption and emission

• Longwave radiative transfer in clear sky
• The Schwarzschild’s equation in presence of non-scattering clouds
• Brightness temperature
• Weighting functions

7 Introduction to scattering

• Surface reflection
• Scattering regimes for isolated scatterer
• Scattering cross section and phase function
• Rayleigh scattering vs Mie scattering
• The radiative transfer equation in presence of multiple scattering

   

 

8 Radiative properties of clouds and aerosols

 

• Interaction between radiation and matter: refractive index
• Size distributions of liquid, ice and aerosol particles
• Bulk optical properties of clouds and aerosols
• Cloud radiative properties parametrization in climate models

9 Energy balance 1-D models and greenhouse effect

• The concept of spherical albedo
• Radiative equilibrium of a planet
• Greenhouse parameter
• The window-grey radiative equilibrium model
• The role of convection and clouds

10 Climate sensitivity and feedbacks

• Climate radiative forcing: external and anthropogenic
• Climate sensitivity of greenhouse and window-gray models
• Equilibrium response to radiative forcing
• Volcanic eruption
• CO2 forcing
• Feedbacks

11 Diabatic radiative processes in the atmosphere

• SW heating and LW cooling rates in clear and cloudy sky
• Radiative cooling of the atmosphere and time constant
• Thermal inertia for a mixed layer

12 Energy budget at the surface and at toa: role of clouds

• Global energy balance and Trenberth plot
• Cloud forcing and feedback
• Latitudinal mean distribution of radiative fluxes
• Mean energy balance at the surface

Testi/Bibliografia

• notes of the teachers
• Pruppacher and Klett, 1997, Microphysics of clouds and precipitation, Kluwer Academic Publishers, pp. 954.
• Wang, P.K., 2014, Physics and Dynamics of Clouds and Precipitation, Cambridge University Press, pp 451
• Siebesma, Bony, Jakob and Stevens, 2020, Clouds and Climate, Climate's Greatest Challenge. Cambridge University Press, pp. 409

Metodi didattici

Frontal lectures with slide projector

Modalità di verifica e valutazione dell'apprendimento

The final examination aims at verifying the acquired knowledge and abilities by means of an oral exam (50 minutes) that covers the topics of the two modules.

Strumenti a supporto della didattica

Video projector and blackboard.

Orario di ricevimento

Consulta il sito web di Federico Porcù

Consulta il sito web di Tiziano Maestri