Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

“Physics o f Auroral Phenomena”, Proc. XL Annual Seminar, Apatity, pp. 116-119, 2017 © Polar Geophysical Institute, 2017 ^ Polar j Geophysical f Institute MULTI-COLOR PHOTOMETRY OF TWILIGHT SKY BACKGROUND USING RGB ALL-SKY CAMERAS: MICROPHYSICAL INVESTIGATIONS OF AEROSOL IN MIDDLE AND UPPER ATMOSPHERE O.S. Ugolnikov1,1.A. Maslov1, A.V. Roldugin2, S.V. Pilgaev2, A.A. Galkin2 1Space Research Institute, Russian Academy o f Sciences, Moscow, Russia zPolar Geophysical Institute, Apatity’, Russia e-mail: ougolnikov@gmail.com Abstract. We consider the possibilities of three-color (RGB) photometry of twilight background by all-sky cameras for study o f microphysical properties of aerosol particles in stratosphere and mesosphere of Earth. Background stratospheric aerosol causes the effect of sky reddening in the dusk area during the light stage of twilight. Measurements conducted during spring and summer of 2016 near Moscow allow finding the size distribution of stratosphere aerosol particles. The same was done for particles of polar mesospheric (or noctilucent) clouds during their display in August 2016 at Lovozero station. The results are in good agreement with the data of direct, lidar and satellite measurements. The method suggested here seems to be simplest and most effective for systematic measurements of aerosol properties in middle and upper atmosphere. In a present time, a large number o f all-sky color cameras is installed in high latitudes for regular aurora monitoring. They operate during the night. However, their work period can be expanded to the twilight, that can be effective for middle and upper atmospheric research. Climate changes observed in mesosphere during recent decades are most sufficient in polar latitudes [Beig et a l, 2003]. Negative trend of summer temperature leads to the increase of frequency of appearance of polar mesospheric clouds (or noctilucent clouds, NLC). Anthropogenic sulfur dioxide emission is considered as possible reason o f increase of background stratospheric aerosol observed at the altitudes around 20 km even in the case of volcanic-free periods [Solomon etal., 2011]. 120 100 80 -o 2 E 60 с <>T 40 20 0 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 COS 8 Figure 1. Mie scattering functions S of sphere with radius 60 nm for wavelengths 463 (1), 526 (2), and 590 nm (3), and their ratio. The observational ratio of NLC scattering for bands 1 and 2, Ьг/bi (single image) is shown in the top, normalized by b2/bi(90°) for convenience. Aerosol particles scatter the solar radiation. This effect is mostly noticeable during the twilight, when lower dense atmospheric layers are immersed in the Earth's shadow. Stratospheric aerosol reveals itself during the light stage of twilight (solar zenith angles 92°-94°), noctilucent clouds are seen during the darker stages (solar zenith angles 96°- 98°). Aerosol scattering is seen on the background of single and multiple scattering o f solar radiation in the atmosphere. Spectral properties of aerosol component differ from the ones of twilight background. This is related with physical characteristics of scattering on aerosol particles described by Mie theory and also with different conditions 116