The propagation of light pollution in the atmosphere

Europe, North Africa and Western Asia photographed at night. April - October 2012. (c)
NASA Earth Observatory

P. Cinzano and F. Falchi from Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso and Osservatorio Astronomico ‘G. V. Schiaparelli’ studied the light pollution related to artificial night-sky brightness. The abstract follows.

Recent methods to map artificial night-sky brightness and stellar visibility across large territories or their distribution over the entire sky at any site are based on computation of the propagation of light pollution with Garstang models, a simplified solution of the radiative transfer problem in the atmosphere that allows fast computation by reducing it to a ray-tracing approach. They are accurate for a clear atmosphere, when a two-scattering approximation is acceptable, which is the most common situation. We present here up-to-date extended Garstang models (EGM), which provide a more general numerical solution for the radiative transfer problem applied to the propagation of light pollution in the atmosphere. We also present the lptran software package, an application of EGM to high-resolution Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) satellite measurements of artificial light emission and to GTOPO30 (Global 30 Arcsecond) digital elevation data, which provides an up-to-date method to predict the artificial brightness distribution of the night sky at any site in the world at any visible wavelength for a broad range of atmospheric situations and the artificial radiation density in the atmosphere across the territory. EGM account for (i) multiple scattering, (ii) wavelengths from 250 nm to infrared, (iii) the Earth's curvature and its screening effects, (iv) site and source elevation, (v) many kinds of atmosphere with the possibility of custom set-up (e.g. including thermal inversion layers), (vi) a mix of different boundary-layer aerosols and tropospheric aerosols, with the possibility of custom set-up, (vii) up to five aerosol layers in the upper atmosphere, including fresh and aged volcanic dust and meteoric dust, (viii) variations of the scattering phase function with elevation, (ix) continuum and line gas absorption from many species, ozone included, (x) up to five cloud layers, (xi) wavelength-dependent bidirectional reflectance of the ground surface from National Aeronautics and Space Administration (NASA) Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite data, main models or custom data (snow included) and (xii) geographically variable upward light-emission function given as a three-parameter function or a Legendre polynomial series. Atmospheric scattering properties or light-pollution propagation functions from other sources can also be applied. A more general solution allows us to account also for (xiii) mountain screening, (xiv) geographical gradients of atmospheric conditions, including localized clouds and (xv) geographic distribution of ground surfaces, but suffers from too heavy computational requirements. Comparisons between predictions of classic Garstang models and EGM show close agreement for a US62 standard clear atmosphere and typical upward emission function.

Follow this link for more information about this article: Monthly Notices of the Royal Astronomical Society, 427: 3337–3357

Authors and affiliations:

Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso (ISTIL), Thiene, Italy

Cinzano, P.

CieloBuio, Coordinamento per la Protezione del Cielo Notturno, Osservatorio Astronomico ‘G. V. Schiaparelli’, Varese, Italy

Falchi, F.

The near-Earth objects and their potential threat to our planet

Comet Bradfield from Cactus Flats in NE Colorado. (c) TheStarmon

D. Perna, M. A. Barucci, M. Fulchignoni published on the journal The Astronomy and Astrophysics Review a very interesting article concerning the potential threat from the near-Earth objects, namely asteroids, comet nuclei.

Here the abstract of the article.

The near-Earth object (NEO) population includes both asteroids (NEAs) and comet nuclei (NECs) whose orbits have perihelion distances q<1.3 AU and which can approach or cross that of the Earth. A NEA is defined as a “potentially hazardous asteroid” (PHA) for Earth when its minimum orbit intersection distance (MOID) comes inside 0.05 AU and it has an absolute magnitude H<22 mag (i.e. mean diameter > 140 m). These are big enough to cause, in the case of impact with Earth, destructive effects on a regional scale. Smaller objects can still produce major damage on a local scale, while the largest NEOs could endanger the survival of living species. Therefore, several national and international observational efforts have been started (i) to detect undiscovered NEOs and especially PHAs, (ii) to determine and continuously monitor their orbital properties and hence their impact probability, and (iii) to investigate their physical nature. Further ongoing activities concern the analysis of possible techniques to mitigate the risk of a NEO impact, when an object is confirmed to be on an Earth colliding trajectory. Depending on the timeframe available before the collision, as well as on the object’s physical properties, various methods to deflect a NEO have been proposed and are currently under study from groups of experts on behalf of international organizations and space agencies. This paper will review our current understanding of the NEO population, the scientific aspects and the ongoing space- and ground-based activities to foresee close encounters and to mitigate the effects of possible impacts.

Follow this link for more information about this article: The Astronomy and Astrophysics Review September 2013, 21:65

Authors and affiliations:

LESIA—Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 Place Jules Janssen, 92195, Meudon Principal Cedex, France

D. Perna, M. A. Barucci, M. Fulchignoni

Solar Irradiance Variability and Climate

Sun in X-ray. (c) NASA Goddard Laboratory for Atmospheres

The prestigious journal Annual Review of Astronomy and Astrophysics (impact factor 23.3) published an interesting article written by Sami K. Solanki, Natalie A. Krivova and Joanna D. Haigh regarding the relationship between ht solar irradiance and the climate on the Earth. Here below the abstract of the article.
The brightness of the Sun varies on all timescales on which it has been observed, and there is increasing evidence that this has an influence on climate. The amplitudes of such variations depend on the wavelength and possibly the timescale. Although many aspects of this variability are well established, the exact magnitude of secular variations (going beyond a solar cycle) and the spectral dependence of variations are under discussion. The main drivers of solar variability are thought to be magnetic features at the solar surface. The climate response can be, on a global scale, largely accounted for by simple energetic considerations, but understanding the regional climate effects is more difficult. Promising mechanisms for such a driving have been identified, including through the influence of UV irradiance on the stratosphere and dynamical coupling to the surface. Here, we provide an overview of the current state of our knowledge, as well as of the main open questions.

The link of the article website is: Annual Review of Astronomy and Astrophysics Vol. 51: 311-351 (August 2013)

Affiliations:

Max-Planck-Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
Sami K. Solanki, Natalie A. Krivova
School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701, Korea
Sami K. Solanki
Imperial College, London SW7 2AZ, United Kingdom

Joanna D. Haigh

Home