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.

Multi-colorphotometry oftwilight sky background using RGB all-sky cameras of solar illumination (the last is the reason of red color of tropospheric clouds at the sunset). These effects also depend on the sky point and scattering angles. Basing on this effects, aerosol scattering can be separated in studied in all-sky RGB-images. Figure 2. Possible values of volume-equivalent radius and axes' ratio o f ice spheres and spheroids basing on polarization (dashed lines) and color analysis (comparison of NLC in wavelengths 2-1 and 3- 1, see Fig. 1). a x e s ' ra tio , a j/e 2 80 x> со i— с CO <0 £ 60 20 Figure 3. Possible parameters of lognormal size distribution of spherical particles of NLC. The results of this work are shown by bold lines and error areas (the same wavelengths 1 , 2 and 3 as in Figs. 1-2). Dashed lines correspond to polarization analysis. 1.0 1.2 1.4 1.6 lo g n o rm a l d istrib u tio n w id th , <r 1.8 ^Polarization ч N • Ч ч ч Ч ’4 4 \ * ♦ Lidars * * Rockets > ... ч # • Satellites Noctilucent clouds are formed of water ice at the temperatures below 150 К in upper mesosphere (80-90 km). The condensation nuclei are hydrate ions [ Wilt, 1969] or fragments of meteor particles moderated in the same atmospheric layer [Hunten et a l, 1980]. NLC particles consist of tiny ice particles with scattering properties close to Rayleigh law (~X~4), that explains their color. However, the color ratio of scattering coefficients slightly depend on scattering angle 0. As we can see in Fig. 1, this dependence is close to linear by cos 0. To fix this effect, NLC must be observed in the most part of the sky, including the dusk-opposite part. These bright clouds were observed at August, 12,2016, by all- sky RGB-camera in Lovozero station (68.0°N, 35.1 °E). We should note that it happened less than one day after Perseid meteor shower maximum. Increased level of dust in mesosphere in the same season was fixed earlier by polarization measurements [Ugolnikov and Maslov, 2013, 2014]. As we see in upper panel o f Fig. 1, color ratio of NLC light scattering actually turns red from dusk area to the opposite sky part. This effect is also influenced by the conditions of solar illumination, absorption by stratospheric ozone in Chappuis bands. Procedure of separation of twilight background and analysis of NLC light scattering is described in details in [Ugolnikov et a l, 2017]. Results are shown in Figs. 2 and 3. Analysis o f monodisperse models of spherical and non-spherical particles is performed in Fig. 2 in comparison with polarization analysis [Ugolnikov et a l, 2016ab]. Good agreement is clearly seen, effective size of monodisperse ice particle in NLC is close to 60 nm. Possible parameters of lognormal size distribution of NLC spherical particles are shown in diagram in Fig. 3 in comparison with polarization measurements [Ugolnikov et a l, 2016ab] and recent lidar, rocketbome and satellite data (see references in [Ugolnikov et a l, 2017]). Agreement is seen again; if we assume that particles have a lognormal 117