Numerical prediction of the night sky quality
IDPASC Portugal - PHD Programme 2016
2016 / 2017
Universidade de Évora
Artificial light at night from ground sources produces light pollution and is the cause of skyglow. Part of the light emitted from those sources, either directly or by reflection off the ground, propagates horizontally and upward. The resulting brightening of the night sky is detectable up to dozens or hundreds of kilometres from the sources compromising, together with the transparency of the atmosphere, astronomical and astrophysical observations. A model of light propagation that can predict the effect of a ground source at a known distance relies on a thorough knowledge of the diffusion of the light on the atmosphere. Actually, the scattering of the light from ground sources depends on the molecules and aerosols present on the atmospheric layers, on cloud cover and air humidity. Some of these physical parameters are operationally anticipated by the Numerical Weather Prediction (NWP) systems. The main objective of this PhD programme is the study of the predictability of the nocturnal darkness and of the atmospheric transparency by linking a nocturnal light propagation tested model (Kocifaj, 2007) with a NWP model and a scheme to compute the moon brightness. The work-plan includes the study of the dependence of the scattering of the light on the local atmospheric characteristics. Measuring simultaneously, in situ, both night sky brightness and the concentration of aerosols and molecules, would allow the refinement of current light diffusion models. As we know, it will be the first attempt to get sky quality forecasts based on NWP, which will be of high interest to astronomers and astrophysics. The Dark Sky Alqueva Reserve, in Alentejo, will be the field laboratory to test the methodologies. As it was the first Starlight Tourism Destination in the world, the Alqueva reserve has optimal conditions to perform such a study, taking advantage of previous studies (Lima, 2015) and of the development of a new project (ALOP: ALT20-03-0145-FEDER-000004), in which a meteorological station will be installed together with a Sky Quality Meter. The PhD programme includes the following tasks: 1. Investigate the state of the art of nocturnal artificial light propagations models and possible advantages of use of NWP results as input parameters 2. Participation in the Installation and test of a Sky Quality Meter in a meteorological station. 3. Monitoring and control the operation of the Sky Quality Meter and processing of the collected data. 4. Use calibrated satellite remote sensing information in order to map night light sources in the region of interest. 5. Study the relationships between night sky brightness and the local concentration of aerosols and molecules and use this information to introduce refinements in current light diffusion models. 6. Learning how to use a numerical weather prediction model. The Meso-NH research model (Lafore et al., 1998) will be the model to be used in the case studies simulations. 7. Carry out the (one way) coupling of the nocturnal light propagation model to the Meso-NH model. 8. Perform and analyze numerical simulations of well documented real case studies, using the coupled NWP-Night-Darkness model 9. Based on the above results, investigate the feasibility of the use of operational weather forecast information currently made available for Portugal by the IPMA (based on IFS and AROME models) in predicting the sky quality for astronomers and astrophysics. 10. Writing papers and the thesis. References Kocifaj, Miroslav (2007). Light-pollution model for cloudy and cloudless night skies with ground-based light sources. Applied Optics, 46(15), pp. 3013–3022. Lafore JP, Stein J, Asencio N, Bougeault P, Ducrocq V, Duron J, Fischer C, Héreil P, Mascart P, Masson V, Pinty JP, Redelsperger JL, Richard E, Vilà-Guerau de Arellano J. 1998. The Meso-NH Atmospheric Simulation System. Part I: adiabatic formulation and control simulations. Annales Geophysicae. 16: 90-109. DOI: 10.1007/s00585-997-0090-6 LIMA, R., (2015). Light pollution : measuring and modelling skyglow: an application in two portuguese reserves. Coimbra [s.n.]. Tese de doutoramento. http://hdl.handle.net/10316/28773.