Computer Modeling Laboratory 4

Written report due: 13 February

Modeling of optical characteristics with Mie theory.
Remote sensing based on direct solar radiation. AERONET.

RELATED MATERIALS:
Lecture 5, S 6.1

TASK 1

To compute optical characteristics of a single spherical particle run MIE_sphere

  1. Compute and plot (as a function of size parameter in a range from 0.2 to 20) the extinction Qe, scattering Qs, and absorption Qa efficiencies for non-absorbing (m = 1.5) and strong-absorbing (m=1.5-i0.5) aerosols. Identify and briefly discuss the main differences in Qe, Qs and Qa of these aerosol types.
  2. Calculate the total aerosol optical depth and the effective single scattering albedo at the 500 nm wavelength of a 1 km layer containing these two aerosol types. Assume that all particles have a radius of 0.2 μm, and both aerosol types have a particle number concentration of N= 100 #/cm3.

 

TASK 2

Aerosol Robotic Network (AERONET) is an automatic sun and sky scanning measurement program established by NASA to perform systematic ground-based observations of aerosols and water vapor. Remote sensing of aerosols with a ground-based sunphotometer utilizes the direct beam of solar radiation transmitted through the atmosphere. Sunphotometer measurements at several wavelengths are used to retrieve the spectral aerosol optical depth (AOD), several other aerosol properties (e.g., Angstrom exponent, fine mode fraction, single scattering albedo, size distribution), and water vapor. Learn how measurements of AOD are performed with the AERONET sunphotometer.
Read more http://aeronet.gsfc.nasa.gov/new_web/aerosols.html  Measurements of AOD

  1. In this task you will analyze AERONET data from two sites: Bondville, IIllinois, and Agoufou, Mali. On the AERONET website, go to Aerosol Optical Depth and then to Data Display. Find these two stations on the map (also see the list of stations below the map).
    Plot and analyze AOD and Angstrom exponent for 2010 at these two sites. Briefly describe similarities and explain differences in aerosol properties measured at these two sites. HINT: Take a look at other AERONET aerosol products.
  2. On the AERONET website, go to Climatology Maps. By clicking at 500 nm Aerosol Optical Thickness (Level 2.0), you will see animation of the global AOD climatology.
    Note that the representative range of monthly mean AOD at 500 nm is from about 0.05 to 1.5 depending on location and time. Taking these two AOD values, calculate a fraction of direct solar radiation that would reach surface in each case. Compare these fractions to that in aerosol-free conditions, considering the Rayleigh scattering but ignoring absorption by gases. HINT: Optical depth due to molecular scattering is given by Eq.[5.27]