Prosiectau Ffiseg ar gyfer myfyrwyr bl.3 a bl.4

Disgrifiad prosiect

Rainbows and glories - atmospheric scattering processes

(supervisor: Rudi Winter)

Nature of project: data analysis, theory

Available to students on full-time physics degree schemes or joint students.

Project description and methodology

Sunlight is scattered by a variety of processes in the atmosphere, including refraction, total reflection and diffraction. We can learn about water droplets, ice crystals and dust particles from analysing visible patterns generated by these scattering processes.

In this project, we will investigate how subtle changes to the size and composition of droplets and particles in the atmosphere affect the optical phenomena that can be observed. The project uses the free MS-Windows software Mieplot to study these effects.

Mie scattering theory, on which the software is based, is used to interpret the results in order to get a quantitative understanding of how different environmental parameters affect optical phenomena such as rainbows, glories or coronas.

A successful project will develop beyond the above in one/some of the following directions:
(1) Investigate how pollution affects the scattering phenomena. For example, substances dissolved in mist droplets could change the refractive index of the droplet. Dust particles could provide a multitude of nuclei for the formation of droplets, resulting in a very fine spray. When freezing over, droplets may obtain a shell structure. How do these effects change the patterns observed?

(2) Investigate how different atmospheric conditions affect the scattering patterns by sourcing geo-located images of rainbows from the internet and comparing the observed phenomena with Mieplot simulation results.

(3) Calculate how rainbows and other atmospheric phenomena work on other planets. Are they even possible in a dilute atmosphere? Compare terrestrial rainbows with ones one might observe on a variety of planets with different atmospheres.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

This project is only available as a Y3 project.

Please speak to Rudi Winter (ruw) if you consider doing this project.

Initial literature for students:

  1. HC van de Hulst: Light scattering by small particles; Wiley (1957)
  2. The Mieplot program: http://www.philiplaven.com/mieplot.htm
  3. WJ Markiewicz et al., Icarus 234 (2014) 200

Novelty, degree of difficulty and amount of assistance required

The Mieplot website has a wealth of detail on atmospheric optics and the theory underlying the simulation program. Once a few of the examples shown have been reproduced using the software, parameters can be varied to investigate the scenarios detailed above. There is no need to program anything yourself for this project, but in order to obtain physically truthful results it is important to understand the theory behind the program rather than just using it as a black box.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Familiarisation with Mieplot and reproduction of a few simulations from its websiteend of November
Decide which variations of atmospheric conditions you want to study in detailChristmas
Mieplot simulations of chosen atmospheric conditions completedmid-March
Comparison of simulation results with imagery or data sourced onlineEaster