Computer Modeling Laboratory 3

Written report due: 16 February

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

RELATED MATERIALS:
Lecture 4, S 6.1

TASK 1

To compute the 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), absorbing (m =1.5-i0.01), and strong-absorbing (m=1.5-i0.5) aerosols. Identify and briefly discuss the main differences between 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 two aerosol types: absorbing and non-absorbing aerosols. Use the refractive indices given above. Assume that all particles have a radius of 0.2 μm, 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. The remote sensing of aerosols from a ground-based sunphotometer utilizes the direct beam of solar radiation transmitted through the atmosphere. The sunphotometer measurements at several wavelengths are used to retrieve the spectra 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 collected at 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 AOD for 2010 and compare the AOD behavior at these sites in terms of the AOD range, and max/min values. Then examine the Angstrom exponent. Based on your analysis, briefly discuss similarities and explain the differences between aerosol properties at these two sites. HINT: You may also look at other products (fine mode fraction, water vapor) provided by AERONET along with AOD.
  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.
    Identify regions with the largest values of AOD. What type of aerosol is likely to be responsible for these large AODs?
  3. In the regions with largest and lowest aerosol loads, select representative AOD values at 500 nm and calculate a fraction of direct solar radiation that will be attenuated by aerosol in each case. Contrast this to aerosol-free conditions, considering the Rayleigh scattering but ignoring absorption by gases.