Twilight Sky Background Research Articles

Optical depths and vertical profiles of stratospheric aerosol based on multi-year polarization measurements of the twilight sky

ABSTRACT The method of detection of light scattering on stratospheric aerosol particles on the twilight sky background is considered. It is based on the data on sky intensity and polarization in the solar vertical at zenith distances of up to 50° from the sunset till the moment of the Sun depression to 8° below the horizon. The measurements conducted in central Russia since 2011 had shown the negative trend of stratospheric aerosol content, this can be related with the relaxation of the stratosphere after the number of volcanic eruptions during the first decade of XXI century.

Detection of Molecular Scattering Field from a Polarization Analysis of the Sky Background during Transitive Twilight and Temperature Measurements near the Stratopause

The simplest version of the method of detection of single molecular scattering basing on the polarization measurements of the twilight sky background by all-sky cameras is considered. The method can be used during the transitive twilight (solar zenith angles 94-98 degrees), when effective single scattering takes place in upper stratosphere and lower mesosphere. The application of the method to the multi-year measurements in the vicinity of Moscow and Apatity allows determination of temperature of these atmospheric layers and estimation of contribution and properties of multiple scattering during the transitive twilight period.

Analysis of the direction of the twilight sky background polarization as a tool for selecting single scattering

The direction of the twilight sky background polarization on the celestial sphere far from the solar vertical depends on the ratio of single and multiple scattering contributions. Variations in the polarization direction during twilight reflect the evolution of the properties and background emission components and can be used to control the procedure of selecting single scattering. This makes it possible to specify the temperature measurements according to the molecular scattering of solar emission and the contribution of dust scattering in the upper mesosphere. The results of the temperature measurements during the observations in 2011–2015 have been presented.

Noctilucent cloud polarimetry: Twilight measurements in a wide range of scattering angles

Wide-field polarization measurements of the twilight sky background during several nights with bright and extended noctilucent clouds in central and northern Russia in 2014 and 2015 are used to build the phase dependence of the degree of polarization of sunlight scattered by cloud particles in a wide range of scattering angles (from 40° to 130°). This range covers the linear polarization maximum near 90° and large-angle slope of the curve. The polarization in this angle range is most sensitive to the particle size. The method of separation of scattering on cloud particles from the twilight background is presented. Results are compared with T-matrix simulations for different sizes and shapes of ice particles; the best-fit model radius of particles (0.06μm) and maximum radius (about 0.1μm) are estimated.

Mesosphere light scattering depolarization during the Perseids activity epoch by wide-angle polarization camera measurements

The paper describes the study of scattered radiation field in the mesosphere basing on wide-angle polarization camera (WAPC) measurements of the twilight sky background and single scattering separation procedure. Mid-August observations in 2012 and 2013 show the decrease of single scattering polarization value probably related with Perseids meteor dust moderation in the upper mesosphere. Effect correlates with activity of tiny fraction of Perseids shower. Polarization and temperature analysis allows estimating the altitude of dust layer and character polarization of dust scattering.

Summer mesosphere temperature distribution from wide-angle polarization measurements of the twilight sky

The paper contains the results of wide-angle polarization camera (WAPC) measurements of the twilight sky background conducted in summer 2011 and 2012 at 55.2°N, 37.5°E, southwards from Moscow. The method of single scattering separation based on polarization data is suggested. The obtained components of scattering matrices show the domination of Rayleigh scattering in the mesosphere over the majority of observation time. It made possible to retrieve the altitude distribution of temperature in the mesosphere. The results are compared with the temperature data by TIMED/SABER and EOS Aura/MLS instruments averaged over the nearby dates and locations.

Scattering function of tropospheric aerosol according to the data of polarimetry of the twilight and night sky background

The paper contains the photometric and polarimetric analysis of the sky background near the zenith during the twilights and the nights of different years and seasons. The period of enhanced tropospheric aerosol content during the summer 2009 is noticed. The aerosol scattering of solar emission is separated from the total twilight sky background, and similar data on lunar emission is taken from the night sky background. The results are compared with the data of relatively clear troposphere of winter 2006. The observational data are used to construct the polarization scattering function of tropospheric aerosol particles during the nighttime.

Studies of the stratosphere aerosol layer based on polarization measurements of the twilight sky

The paper is devoted to an analysis of observational manifestations of the aerosol layer in the Earth’s stratosphere and to a method of determining their optical properties. It is based on polarization measurements of the twilight sky background in the zenith vicinity and in a broad spectral band with an effective wavelength of 5250 A. An increased abundance of the stratosphere aerosol was found in December 2006 for the first time in several years of observation. The suggested method allows one to determine the ratio of radiation scattering coefficients by the stratosphere aerosol and by air molecules, as well as the degree of polarization of aerosol scattering in the stratosphere. The appearance of the stratosphere aerosol is associated with explosive eruption of Rabaul volcano having occurred in the beginning of October 2006.

Polarization measurements of twilight sky: Studies of atmospheric aerosol from the troposphere to mesosphere

The results of polarization measurements of the twilight sky background are described. The measurements were carried out in the Crimean Laboratory of the Sternberg Astronomical Institute. The main regularities in the behavior of the twilight zenith sky polarization with the Sun zenith distance at wavelengths 513–525 nm, as well as the effects of the atmospheric aerosol on these dependences, are analyzed. The effects of enhanced aerosol scattering in the stratosphere in December 2006 and January 2008 are considered in detail.

Polarization Studies of Contribution of Aerosol Scattering to the Glow of Twilight Sky

The paper is devoted to studies and a quantitative estimation of the influence of scattering of direct solar radiation by particles of tropospheric aerosols in the period of light twilight, close to sunrise and sunset. Polarization measurements of the twilight sky in two broad spectral bands lying near the standard bands V and R form the basis of these studies. The measurements were carried out in 2002 and 2003 at the Southern Laboratory (Crimea) of the Sternberg Astronomical Institute. The twilight period during which the single aerosol scattering becomes significant is isolated. The character of its influence on the intensity and polarization of the twilight sky is demonstrated. A method is suggested to evaluate polarization of the single aerosol scattering and its contribution to the general brightness of the twilight sky background. The method is based on differential characteristics of the background near the zenith and on their correlations with each other.

Multicolor Polarimetry of the Twilight Sky: The Role of Multiple Light Scattering as a Function of Wavelength

This paper is devoted to the investigation of the role of multiply scattered light of different wavelengths in clear twilight, as well as to the influence of multiple scattering and scattering by atmospheric aerosol particles on the polarization of the twilight sky background during this period. The work is based on wide-angle polarimetric CCD-observations of the twilight sky near zenith in the U, B, V, and R bands, which were carried out in summer 2000 at the South Laboratory of the Moscow Shternberg Astronomical Institute. Based on the data obtained, we have determined the fraction of single-scattered light in clear twilight in the zenith for the U, B, and V bands and have estimated the lower limit of this value for the R band. The analysis of color and polarimetric evolution of the sky background was made taking into account single and multiple scattering properties. The characteristic height of the upper boundary of the tropospheric aerosol layer in the Earth's atmosphere was also obtained.