Abstract. Global ultraviolet auroral images from the IM-AGE satellite were used to investigate the dynamics of the dayside auroral oval responding to a sudden impulse (SI) in the solar wind pressure. At the same time, the TV all-sky camera and the EISCAT radar on Svalbard (in the pre-noon sector) allowed for detailed investigation of the auroral forms and the ionospheric plasma flow. After the SI, new discrete auroral forms appeared in the poleward part of the auroral oval so that the middle of the dayside oval moved poleward from about 70 • to about 73 • of the AACGM latitude. This poleward shift first occurred in the 15 MLT sector, then similar shifts were observed in the MLT sectors located more westerly, and eventually the shift was seen in the 6 MLT sector. Thus, the auroral disturbance "propagated" westward (from 15 MLT to 6 MLT) at an apparent speed of the order of 7 km/s. This motion of the middle of the auroral oval was caused by the redistribution of the luminosity within the oval and was not associated with the corresponding motion of the poleward boundary of the oval. The SI was followed by an increase in the northward plasma convection velocity. Individual auroral forms showed poleward progressions with velocities close to the velocity of the northward plasma convection. The observations indicate firstly a pressure disturbance propagation through the magnetosphere at a velocity of the order of 200 km/s which is essentially slower than the velocity of the fast Alfvén (magnetosonic) wave, and secondly a potential (curl-free) electric field generation behind the front of the propagating disturbance, causing the motion of the auroras. We suggest a physical explanation for the slow propagation of the disturbance through the magnetosphere and a model for the electric field generation. Predictions of the model are supported by the global convection maps produced by the SuperDARN HF radars. Finally, the interchange instability and the eigenmode toroidal Alfvén oscillations areCorrespondence to: A. Kozlovsky (alexander.kozlovsky@oulu.fi) discussed as possible generation mechanisms for the dayside auroral forms launched by the SI.
[1] In the first part of our paper, we consider the pattern of geomagnetic pulsations in the Pc5 range in the North European area, based on an event of 19 January 2005. Intense pulsations, observed in Lovozero at Kola Peninsula, were accompanied by auroras north of the station, recorded by an all-sky TV camera. In the second part, we consider the global pattern of amplitudes and phases of geomagnetic pulsations for this event, which includes data from nearly conjugate stations and the magnetic data of GOES 10 and 12, confirming the quasi-stationary model for magnetic field distribution on the ground. In the event, the auroral luminosity oscillated with the same 5 min period as the magnetic field. Magnetic data from Scandinavia and data from North Europe riometers show analogous pulsations. The maximal intensity of geomagnetic pulsations in this region occurred near the pulsating aurora, but there was a reversal of pulsation polarity in the X-component. In the area of phase change the value of the Z-component is maximal. We suggest that geomagnetic pulsating variations, observed on the surface, are determined by Biot-Savart's law for a three-dimensional current system, the extra-ionospheric part of which is spatially coincident with auroral electron flux. The electric field in the ionosphere is found from the current continuity condition and the value of Pedersen conductivity. The directions to the pulsating current, calculated by using the magnetic data from Lovozero, are close to the directions of the auroral area. We also claim that this approach is applicable to all short periodic oscillations observed on the surface. Satellite data indicates the same periods, but with oscillations that appear to be poloidal on GOES10 and toroidal on GOES12, suggesting the traveling character of the wave.
A prototype auroral hyperspectral all-sky camera has been constructed and tested. It uses electro-optical tunable filters to image the night sky as a function of wavelength throughout the visible spectrum with no moving mechanical parts. The core optical system includes a new high power all-sky lens with F-number equal to f/1.1. The camera has been tested at the Kjell Henriksen Observatory (KHO) during the auroral season of 2011/2012. It detects all sub classes of aurora above ~½ of the sub visual 1kR green intensity threshold at an exposure time of only one second. Supervised classification of the hyperspectral data shows promise as a new method to process and identify auroral forms.
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.
[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.
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