High‐frequency heating of the ionosphere is effective for generating extremely low frequencies (ELF, 3–3000 Hz) through modulation of the auroral electrojet current. While the amplitudes of the resulting ELF waves depend on the auroral electrojet current strength, the polarization of their horizontal magnetic field remains relatively stable. In this work, we determined that at the distance of several wavelengths from an ionospheric ELF source created by two HF heating waves separated by an ELF frequency, polarization parameters are influenced by the Earth‐ionosphere waveguide. Previous experiments in the vicinity of the ionospheric ELF source have determined that the right‐hand polarization of the magnetic field measured at the ground typically prevails, whereas in this paper we demonstrate that at the distance of 660 km to the east of the European Incoherent Scatter, a circular left‐hand polarization dominates. We interpret this effect as a result of “trapping” of the left‐hand mode between the upper and lower boundaries of the Earth‐ionosphere waveguide, while the right‐hand or whistler mode leaks into the ionosphere.

The article deals with the analysis of color distribution in noctilucent clouds (NLC) in the sky based on multi-wavelength (RGB) CCD-photometry provided with the all-sky camera in Lovozero in the north of Russia (68.0°N, 35.1°E) during the bright expanded NLC performance in the night of August 12, 2016. Small changes in the NLC color across the sky are interpreted as the atmospheric absorption and extinction effects combined with the difference in the Mie scattering functions of NLC particles for the three color channels of the camera. The method described in this paper is used to find the effective monodisperse radius of particles about 55 nm. The result of these simple and cost-effective measurements is in good agreement with previous estimations of comparable accuracy. Non-spherical particles, Gaussian and lognormal distribution of the particle size are also considered.

Routine observations of the aurora are conducted in Apatity by a set of five cameras: (i) all-sky TV camera Watec WAT-902K (1/2"CCD) with Fujinon lens YV2.2 × 1.4A-SA2; (ii) two monochromatic cameras Guppy F-044B NIR (1/2"CCD) with Fujinon HF25HA-1B (1:1.4/25 mm) lens for 18° field of view and glass filter 558 nm; (iii) two color cameras Guppy F-044C NIR (1/2"CCD) with Fujinon DF6HA-1B (1:1.2/6 mm) lens for 67° field of view. The observational complex is aimed at investigating spatial structure of the aurora, its scaling properties, and vertical distribution in the rayed forms. The cameras were installed on the main building of the Apatity division of the Polar Geophysical Institute and at the Apatity stratospheric range. The distance between these sites is nearly 4 km, so the identical monochromatic cameras can be used as a stereoscopic system. All cameras are accessible and operated remotely via Internet. For 2010–2011 winter season the equipment was upgraded by special blocks of GPS-time triggering, temperature control and motorized pan-tilt rotation mounts. This paper presents the equipment, samples of observed events and the web-site with access to available data previews

[1] By observations at Lovozero station (64.3 N, 114.3 E CGM coordinates), we have investigated two events of auroral pulsations of Pc1-2 type with periods in the range 2.5-7 s accompanied by similar geomagnetic pulsations. Luminous variations in different parts of the sky were found by photometric measurements of the frames of all-sky camera, which was operated at the rate of one frame per second. The pulsations under study are associated with the diffuse aurora. For the event with 7 s period, a phase relationship between auroral and magnetic pulsations is as follows: the luminosity bursts are coincident with positive half periods in the Z component and negative ones in the D component, while positive peaks in the H component lag behind the luminous peaks by about p/2. For the event with 2.5 s period, this relationship appears different. Within one of 10-min intervals, Pc2 pulsations observed in both magnetic field and aurora were superposed by regular Pc4 pulsations of 1-min period. For these, the luminosity bursts corresponded to negative half periods in the Z component. A connection between auroral and magnetic pulsations is discussed.