Computer modeling of light scattering by atmospheric dust particles with spheroids and ellipsoids

Sini Merikallio

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

I have studied how well average optical properties of different mineral dust and ash samples can be modeled using simplified model particle shapes, and whether using these kinds of model particles could be used to improve the accuracy of models involving scattering. Measured scattering matrices have been emulated by modeling light scattering from an ensemble of different shapes of spheroids and ellipsoids and adjusting their shape distributions for improved fits. By using these model particles, it is not suggested that dust particles really have ellipsoidal or spheroidal forms, but rather that the single-scattering properties of dust particle ensembles might be simulated numerically by using suitable ensembles of ellipsoidal or spheroidal model particles. The results are encouraging in that the simplified model particles, spheroids and ellipsoids, when used in ensembles of differently shaped particles, seem to work well e.g. by providing considerably better agreements with the measurements than do plain spheres. They however were also found to have shortcomings and proved to be insufficient for retrievals of refractive index. This might imply inadequacies as well in other retrieval usages of ellipsoidal model particles. Balancing our efforts between seeking an easily managed model with a low number of parameters, yet one that accurately works both in forward modeling and retrievals, will thus need to continue further into the future. In this thesis, I have found that ellipsoidally or spheroidally shaped model particles could be used to improve modeling of the light scattering by atmospheric mineral dust, Martian dust analog particles (namely palagonite dust) and volcanic ash particles. Results of these studies have been used to improve ECHAM climate models of the Finnish Meteorological Institute, and plans are also in place to incorporate the results into remote sensing data analysis software of AATSR satellite instrument.
Translated title of the contributionIlmakehän pienhiukkasten valon sironnan mallinnus käyttäen sferoideja ja ellipsoideja mallihituja
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Tulkki, Jukka, Supervising Professor
  • Nousiainen, Timo, Thesis Advisor, External person
  • Harri, Ari-Matti, Thesis Advisor
Publisher
Print ISBNs978-952-60-6657-8
Electronic ISBNs978-952-60-6658-5
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • light
  • scattering
  • atmosphere
  • dust
  • ash
  • particle
  • aerosol
  • modeling

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