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The Attenuation of Sunlight by Airborne Dust Particles on Earth and Mars Thesis Open Research Online The Open University’s repository of research publications and other research outputs The Attenuation of Sunlight by Airborne Dust Particles on Earth and Mars Thesis How to cite: Mason, Jonathon Peter (2013). The Attenuation of Sunlight by Airborne Dust Particles on Earth and Mars. PhD thesis The Open University. For guidance on citations see FAQs. c 2013 The Author https://creativecommons.org/licenses/by-nc-nd/4.0/ Version: Version of Record Link(s) to article on publisher’s website: http://dx.doi.org/doi:10.21954/ou.ro.0000f114 Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online’s data policy on reuse of materials please consult the policies page. oro.open.ac.uk «no r-c ts i(Z-\ C L T B l^ The Attenuation of Sunlight by Airborne Dust Particles on Earth and Mars Jonathon P. Mason September 2012 The Open University Department of Physical Sciences A THESIS SUBMITTED TO THE OPEN UNIVERSITY IN THE SUBJECT OF PLANETARY SCIENCES FOR THE DEGREE OF DOCTOR OF PHILOSOPHY soErAiSSion z 56prent uatZ. ProQuest Number: 13835946 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13835946 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 Dedicated to the loving memory of Grandad Peter Acknowledgements First and foremost I would like to express my sincere gratitude to my supervisors Dr. Manish Patel and Dr. Stephen Lewis for giving me the opportunity to undertake this PhD project. The journey was arduous at times and I would like to show my appreciation for their patience and supporting me during the hardships of this PhD. A big thank you also goes out to them for commenting and reviewing thesis drafts which came at short notice towards the end. I would like to thank Dr. Jon Menison at the University of Aarhus for allowing me to use the Mars Simulation Wind Tunnel Facility and answering endless streams of email. I am also indebted to my friends in the Mars comer, Euan Monaghan, Samantha Rolfe, Adam Stevens and Daniel Dawson for proof reading multiple thesis drafts and endlessly correcting what could only be described as some questionable English grammar. I would like to express my thanks to my family and friends that supported me in the decision to study for my PhD. Most importantly a special thanks to Zoe Wathen for her love and unwavering support during this endeavour and I would just like to acknowledge that without her I’m not sure I would have made it. Finally I would like to show my appreciation to my friends in PS SRI for helping me see that there is life outside the office, even if it did take dragging me away from my desk. A special acknowledgement goes out to Farrer’s™ coffee for creating their fabulous No. 1 blend, without which this thesis would never have been completed. Abstract This thesis details an investigation into how dust and ice aerosols in the atmosphere of Earth and Mars affect the solar spectrum from the ultraviolet to the near infrared, allowing the characterisation of the aerosols using broad band surface measurements. A Monte Carlo Light Scattering Model (MCLSM) was developed to predict the optical signature of terrestrial and martian dust devils. The MCLSM was applied to measurements taken in the Eldorado Valley, U.S.A. Transit signatures were found to be dependent on the method of observation. The transit signature measured in scattered light depends on the dust concentration and distribution in contrast to the total light transit signature, which depends primarily on the column-integrated dust optical depth. On Mars the high diffuse irradiance provides better definition of the vortex interior within the transit signature, with wavelengths between 600-750 nm optimal for detecting a transit. To determine the vortex size and dust concentration, both the total and the scattered light must be measured. Retrieval of the dust optical properties showed that spectral measurements and the calculated mass concentration were sensitive to the presence of small particles (0.5-5.0 pm). A comparison of the downward irradiance for two distinct dust components suggests that dust with a higher absorption at visible wavelengths causes increased heating at higher altitudes, leading to a more statically-stable atmosphere, which may result in more rapid decay of large-scale dust storms. The investigations have also shown that variations in single scattering properties can lead to -20% difference in the daily UV-C dose. A method was devised to distinguish compositional changes in the ubiquitous martian dust haze and validated against wind tunnel experiments. This technique is applicable to determine the size of water-ice crystals in clouds and the optical depth of the dust haze at the time of the cloud passage. Publications As an outcome of this study, the following manuscript has been accepted for publication: J.P Mason, M.R Patel and S.R Lewis. (2013). Radiative Transfer Modelling of Dust Devils. Icarus, 233, pp. 1-10 The following are conference presentations given over the course of this study: J.P Mason, M.R Patel and S.R Lewis. Retrieving Dust Properties by Radiative Transfer Modelling of Dust Devils on Earth and Mars. European Planetary Science Congress, Madrid, Spain, 23rd - 28th September, 2012. J.P Mason, M.R Patel and S.R Lewis. Effects of Aerosols on the Observed Irradiance from the Ultraviolet to Near-Infrared at the Surface of Mars. Fourth International Workshop on the Mars Atmosphere: Modelling and Observations, Paris, France, 8th- 11th February, 2011. J.P Mason, M.R Patel and S.R Lewis. Airborne Dust and Water Vapour at Visible Wavelengths in the Martian Atmosphere. European Workshop on Astrobiology, Brussels, Belgium, 12rd - 14th October, 2009. Table of Contents 1 Chapter One: Introduction................................................................................................ 1 1.1 Aim of the thesis ............................................................................................................ 1 1.2 The planet Mars . .................................................................................................. 2 1.3 History of optical depth measurements from the surface of Mars ................................. 2 1.4 The atmosphere of Mars ......................................................................................... 6 1.5 Aeolian mineral dust ......................................................................................................9 1.5.1 Sources of aerosol dust ........................................................................................10 1.5.2 Seasonal variation ...................................................................................11 1.6 Condensate clouds ........................................................................................................ 12 1.6.1 Physical characteristics of martian H20 aerosols .................................................14 1.7 Vertical distribution of dust and water-ice aerosols ............................................... 14 1.8 Diurnal variation of optical depth: Morning fogs ......................................................... 15 1.9 Thesis outline ............................................................................................................... 16 2 Chapter Two: Dust aerosols in the martian atmosphere............................................. 19 2.1 Light scattering by aerosols .......................................................................................... 20 2.1.1 Single scattering theory ........................................................................................ 21 2.1.2 Spherical particles (Mie theory) ........................................................................... 25 2.1.3 Non-spherical particles (discrete dipole approximation) ...................................... 29 2.2 Optical properties of martian aeolian dust .....................................................................34 2.2.1 Overview of the different observations .................................................................35 2.2.2 Single scattering albedo .........................................................................................36 2.2.3 Asymmetry parameter and extinction efficiency ...................................................38 2.2.4 Complex refractive index ......................................................................................40 2.3 Dust devil phenomena .................................................................................................42 2.3.1 Dust devil formation ............................................................................................43 2.3.2 Lower dust devil structure ........................................................................ 45 2.3.3 Dust devils on Mars .................................................................................... 47 2.4 Previous radiative transfer modelling of dust
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