Tima Sergienko

Optical effects in the aurora caused by ionospheric HF heating

Abstract Ionospheric heating experiments were done by the EISCAT Heater in Tromso on 15–19 November, 1993. A low-light TV camera was installed at the VLF receiving station at Porojarvi about 100 km to the south-east of Tromso. The spectral analysis of the auroral luminosity variations showed that the brightness of the aurora varied at the modulation frequency of the heating wave. The results of this analysis and the numerical simulations of the auroral luminosity variations caused by the HF heating are shown. The variations of the optical emission intensity at the heating frequency occur during the auroral ionosphere modification. The observed intensity variation of the auroral green line during the interval of enhanced electron temperature is explained by a decreasing rate of the O2+ ion dissociative recombination when the electron temperature increases. The brightness variation depends on the characteristic energy and the intensity of the auroral electron flux and the heating wave parameters. The artificial luminosity pulsations caused by HF heating are estimated.

Fine structure of aurora

Fine structure is present in most types of aurora, but much of it has previously not been possible to study properly because of instrument limitations. However, recent advances in optical instrumentation have provided considerable improvements in temporal and spatial resolution. Optical measurement systems are able to use a higher resolution than other types of ground-based instruments used in auroral studies. New results have been obtained regarding, for example, elemental structures in discrete auroras, generation of flickering aurora, generation of Alfvén waves in shear regions, dynamic rayed aurora, fine structure of diffuse auroras and fine structure of auroral curls. Outstanding questions are highlighted and recommendations for future research are given. The importance of a coordinated infrastructure for ionospheric research, simultaneous measurements on different scales, optical calibration facilities and the development of time-dependent high-resolution models is stressed.

Estimate of auroral electron spectra, the power of ground-based multi-station optical measurements

Abstract Ground-based multi-station optical imaging has a great inherent scientific potential for investigations of the magnetosphere-ionosphere-thermosphere interactions by using inversions of the ionospheric optical signal, the aurora. Two methods for estimating characteristics of primary auroral electron spectra are compared and used to describe an auroral event. One method uses the spectral information in the images and the other method is based on the inversion of the N 2 + 1 NG 4287 A altitude distribution. With the second method ALIS can currently give estimates of the primary electron distribution with medium time resolution (10 s). The auroral event, a passage of an eastward moving fold in a pre-existing auroral arc, is analysed and characteristics of the precipitating electrons show regions with different fluxes, e.g. a soft region that has previously been found inside the fold appears to belong to a wider region of soft precipitation that emerges as the arc activates.

A Non-linearity Correction Method for Calibration of Optical Sensor at Low Level Light

This paper describes a methodology developed for calibrating optical detector for light engineering, especially for devices used at low level light, including auroral imager, star sensor, astronomical camera and similar optical instruments. In order to know the physical meaning of optical sensor output, calibration is the first and most important process in a complete analysis of observed data. It is found that optical sensors, like CCDs, are not perfectly linear systems as they were assumed. After bias frame subtraction, the number of ADU counts is not exactly proportional to the number of incident photons. A key component of this paper is non-linearity correction. One of current applications using this method is auroral imager which is used for measuring aurora, high-altitude clouds, and other atmospheric optical objects light intensity, which is the first step to complete an optical object tomography simulation.

On the possibility of coupling satellite and ground-based optical measurements in the region of pulsating auroras

The possibility of comparing in detail CLUSTER satellite data with data on pulsating spots registered with a TV camera at the Lovozero Observatory when the satellite crossed the magnetospheric region related to the camera’s field of view is discussed. The satellite ionospheric projections were calculated using the T89, T96, and T01 models. It was shown that the projection allows us to judge with confidence whether or not a satellite will find itself in a region of pulsating auroras when only the level of geomagnetic activity and the characteristics of the interplanetary medium are a priori known. When different models are used in the projection, the spread is not less than the characteristic dimensions of the pulsating spots and can be as high as 100 km. The corresponding satellite flight time is ∼4 min. Such a large spatial and time uncertainty does not allow us to compare in detail the satellite data with ground-based optical measurements without a priori information on, e.g., the character of precipitation above a spot, as has been done by other researchers in the case of auroral arcs. The situation becomes even more complex if a satellite is in the region of greatly stretched magnetic field lines.

Electric Field Enhancement in an Auroral Arc according to the Simultaneous Radar (EISCAT) and Optical (ALIS) Observations

The character of a change in the ionospheric electric field when several auroral arcs crossed the region of radar measurements has been analyzed. In one case the plasma conductivity and electric field normal component in an arc increased as compared to their undisturbed values. In another case the field and conductivity changed traditionally (in antiphase). Arcs with an increased field were previously classified as correlating arcs, but their existence was subsequently open to question during optical observations. The usage of the ALIS system of digital cameras made it possible to decrease the errors introduced by optical equipment. The measurements in the vicinity of correlating arcs were performed when these arcs were generated, and a traditional arc was a completed formation. In an originating arc, the field value can depend not only on the ionospheric plasma conductivity but also on the processes in the magnetospheric-ionospheric system resulting in the field enhancement.

Dynamics of field-aligned currents reconstructed by the ground-based and satellite data

Parameters of field-aligned currents reconstructed by ground-based measurements of magnetic field in the Scandinavian countries (IMAGE) and ionospheric conductivity for specific events of the 6 and 8 December 2004 are represented here. Ionospheric conductivity was calculated from precipitating electron flux measured at DMSP-13 satellite and electron density EISCAT incoherent scattering radar direct measurements. There is a high correlation between field-aligned currents, calculated from DMSP-13 satellite data and field-aligned currents calculated from radar measurements for the December 6, 2004 in the presence of developed ionospheric current system. The comparison of field-aligned currents, reconstructed by the proposed method, with the currents calculated by the variation of magnetic field on the DMSP satellites, confirms correctness of the offered algorithm.

Ionospheric Response Observed by EISCAT During the 6–8 September 2017 Space Weather Event: Overview

We present ionospheric plasma conditions observed by the EISCAT radars in Tromso and on Svalbard, covering 68°–81° geomagnetic latitude, during 6–8 September 2017. This is a period when X2.2 and X9 ...

Project "Development of the Methodology of Experiment and Technical Support for Studies of the Flow Cyclotron Maser in the Earth's Magnetosphere by Creating an Artificial Ionization Cloud From a Geophysical Rocket"

Investigation of the wave particle interaction in the magnetosphere and ionosphere by controllable experiment in near Earth space is in focus of modern space geophysics. We propose to stimulate auroral precipitation by changing parameters of the Flow Cyclotron Maser (FCM) and test the FCM model itself. One of the main goals of the project is inducing of artificial pulsating aurora.