Laevskii Yu.M., Rudenko O.V. «On the convergence of locally one-dimensional schemes for solving the third boundary value parabolic problem in nonrectangular domains» Доклады академии наук, 354, № 4, с. 452-455 (1997)

Mityurich G.S., Lebedeva E.V., Aleksiejuk M., Serdyukov A.N. «Thermooptical excitation of sound by Bessel light beams in layered media with internal stress» Проблемы физики, математики и техники, № 3, с. 39-43 (2018)

Представлены результаты исследования фотоакустического преобразования различных мод БСП в гиротропных слоистых средах при пьезоэлектрическом методе регистрации результирующего сигнала. Показано, что амплитуда фотоакустического сигнала определяется теплофизическими характеристиками слоистых сред с внутренними напряжениями, коэффициентом поглощения и параметром кругового дихроизма гиротропных слоистых сред, поляризацией и энергетическими характеристиками БСП, частотой амплитудной модуляции, а также геометрией системы «пьезоэлектрический датчик–гиротропный слоистый образец».

Leonovich A.S., Quigang Z., Kozlov D.A., Yongfu W. «Alfven waves in the magnetosphere generated by shock wave/plasmapause interaction» Солнечно-земная физика, 5, № 2, с. 11-16 (2019)

We study Alfven waves generated in the magnetosphere during the passage of an interplanetary shock wave. After shock wave passage, the oscillations with typical Alfven wave dispersion have been detected in spacecraft observations inside the magnetosphere. The most frequently observed oscillations are those with toroidal polarization; their spatial structure is described well by the field line resonance (FLR) theory. The oscillations with poloidal polarization are observed after shock wave passage as well. They cannot be generated by FLR and cannot result from instability of high-energy particle fluxes because no such fluxes were detected at that time. We discuss an alternative hypothesis suggesting that resonant Alfven waves are excited by a secondary source: a highly localized pulse of fast magnetosonic waves, which is generated in the shock wave/plasmapause contact region. The spectrum of such a source contains oscillation harmonics capable of exciting both the toroidal and poloidal resonant Alfven waves.

Leonovich L.A., Tashchilin A.V., Lunyushkin S.B., Karavaev Yu.A., Penskikh Yu.V. «Studying 630 nm atomic oxygen emission sources during strong magnetic storms in the night mid-latitude ionosphere» Солнечно-земная физика, 5, № 2, с. 35-41 (2019)

We analyze significant increases in 630 nm atomic oxygen night emissions during very strong geomagnetic storms, using optical measurements, theoretical modeling, and magnetogram inversion technique (MIT) data. It is shown that during strong magnetic storms when electron precipitation equatorial boundary at the night sector expands up to ∼40°, the interaction of energetic electron flux with thermospheric components may cause extreme increases in the 630 nm emission intensity. Model calculations of the red line intensity show good agreement with observational data. Using the November 20, 2003 magnetic storm as an example, we have found that oxygen atom collisions with thermal Maxwell and superthermal electrons make a major contribution to the integral emission intensity. Thermospheric density variations during the magnetic storm significantly affect the red line generation.

Zhenghua H., Bo Li., Lidong X. «Observations of small-scale energetic events in the solar transition region: explosive events, UV bursts, and network jets» Солнечно-земная физика, 5, № 2, с. 63-73 (2019)

In this paper, we review observational aspects of three common small-scale energetic events in the solar transition region (TR), namely TR explosive events, ultraviolet bursts and jets. These events are defined in either (both) spectral or (and) imaging data. The development of multiple instruments capable of observing the TR has allowed researchers to gain numerous insights into these phenomena in recent years. These events have provided a proxy to study how mass and energy are transported between the solar chromosphere and the corona. As the physical mechanisms responsible for these small-scale events might be similar to the mechanisms responsible for large-scale phenomena, such as flares and coronal mass ejections, analysis of these events could also help our understanding of the solar atmosphere from small to large scales. The observations of these small-scale energetic events demonstrate that the TR is extremely dynamic and is a crucial layer in the solar atmosphere between the chromosphere and the corona.

Chengming T., Baolin T., Yihua Ya., Wei W., Linjie Ch., Fei L., Yujiang D. «Fine structure events in microwave emission during solar minimum» Солнечно-земная физика, 5, № 2, с. 4-10 (2019)

The solar minimum is a period with a relatively smaller number of sunspots and solar eruptions, and has been less studied before. Since the radio signal rapidly responds to the change of solar plasma and magnetic field, we perform a comprehensive analysis of high resolution spectrum data from SBRS and MUSER: 1) a search for solar radio bursts of different kinds in recent solar minima (2007–2009 and 2016–2018); 2) an analysis of several typical radio burst events, negative and positive drifting bursts, for example the November 22, 2015 and August 29, 2016 events; superfine spectral structure events with mini-flares and even without sunspots, for example the March 28, 2008 and July 04, 2017 events. These results show that there were many radio bursts with a fine structure during solar minima. These events occurred not only in powerful flares, but also in faint flares (class C and B by GOES) or even without flares, but in regions related to weak brightenings or ejecta. We assume that the weak solar radio bursts observed by telescopes with high sensitivity and low interference will help us to understand the basic physical characteristics of small-scale solar eruptions.

Dali Ya., Tiemin Zh., Jihong W., Jianqing Wu., Linmao W., Xu Z., Hongyan P. «Characteristics of double sodium layer over Haikou, China (20.0°N, 110.1°E)» Солнечно-земная физика, 5, № 2, с. 30-34 (2019)

We study the property of double sodium layer structures (DSLs) in the mesosphere and lower thermosphere (MLT) by a lidar at the low-latitude location of Haikou (20.0°N, 110.1°E), China. From April 2010 to December 2013, 21 DSLs were observed within a total of 377 observation days. DSLs were recorded at middle latitudes of Beijing and Wuhan, China, but were rarely observed at low latitudes. We analyze and discuss characteristics of DSLs such as time of occurrence, peak altitude, FWHM, duration time, etc. At the same time, the critical frequency f_oE_s and the virtual height h E_s of the sporadic E layer E_s were observed by an ionosonde over Danzhou (19.0°N, 109.3°E). We discuss such their characteristics as differences of time, differences of altitude compared to DSLs. We used an Nd:YAG laser pumped dye laser to generate the probing beam. The wavelength of the dye laser was set to 589 nm by a sodium fluorescence cell. The backscattered fluorescence photons from the sodium layer were collected by a telescope with the ∼1000 mm primary mirror.

Jun Ch., Yihua Ya., Dong Zh., Long Xu. «Scale sequentially CLEAN for MingantU SpEctral Radioheliograph» Солнечно-земная физика, 5, № 2, с. 55-62 (2019)

MingantU SpEctral Radioheliograph (MUSER) is a solar-dedicated radio heliograph, adopting aperture synthesis technique to image the Sun in the frequency range of 0.4 GHz to 15 GHz. MUSER has extremely high spatial resolution, temporal resolution, and frequency resolution beyond those of contemporary devices of the same category. For aperture synthesis, the number of antennas is limited, so sparse sampling of Fourier components is actually obtained for solar observation, which corresponds to the situation that a clean image is convolved by a dirty beam with strong sidelobe in a spatial domain. Thus, the deconvolution, such as CLEAN, is generally required for imaging the aperture synthesis to remove artifacts caused by the convolving dirty beam. The traditional Hogbom CLEAN is based on the assumption that an observed object is only composed of point sources. This assumption does not hold for solar observation, where the solar disk is an extended source containing complex structures and diffuse features. In this paper, we make the first attempt to employ scale sequentially CLEAN for MUSER imaging, including Multi-Resolution CLEAN and Wavelet CLEAN. The experimental results demonstrate that the scale sequentially CLEAN, especially wavelet CLEAN, is superior to the traditional CLEAN algorithm in smaller number of iterations and improved image quality. We provide optimized wavelet parameters to further improve the performance of wavelet CLEAN.

Lunyushkin S.B., Mishin V.V., Karavaev Yu.A., Penskikh Yu.V., Kapustin V.E. «Studying the dynamics of electric currents and polar caps in ionospheres of two hemispheres during the August 17, 2001 geomagnetic storm» Солнечно-земная физика, 5, № 2, с. 17-29 (2019)

The magnetogram inversion technique (MIT), developed at ISTP SB RAS more than forty years ago, has been used until recently only in the Northern Hemisphere. In recent years, MIT has been improved and extended to make instantaneous calculations of 2D distributions of electric fields, horizontal and field-aligned currents in two polar ionospheres. The calculations were carried out based on one-minute ground-based geomagnetic measurements from the worldwide network of stations in both hemispheres (SuperMAG). In this paper, this extended technique is used in the approximation of uniform ionospheric conductance and is applied for the first time to calculations of equivalent and field-aligned currents in two hemispheres through the example of the August 17, 2001 geomagnetic storm. We have obtained the main and essential result: the advanced MIT-ISTP can calculate large-scale distributions of ionospheric convection and FACs in the Northern (N) and Southern (S) polar ionospheres with a high degree of expected hemispheric similarity between these distributions. Using the said event as an example, we have established that the equivalent and field-aligned currents obtained with the advanced technique exhibit the expected dynamics of auroral electrojets and polar caps in two hemispheres. Hall current intensities in polar caps and auroral electrojets, calculated from the equivalent current function, change fairly synchronously in the N and S hemispheres throughout the magnetic storm. Both (westward and eastward) electrojets of the N hemisphere are markedly more intense than respective electrojets of the S hemisphere, and the Hall current in the north polar cap is almost twice as intense as that in the south one. This interhemispheric asymmetry is likely to be due to seasonal conductance variations, which is implicitly contained in the current function. From FAC distributions we determine auroral oval boundaries and calculate magnetic fluxes through the polar caps in the N and S hemispheres. These magnetic fluxes coincide with an accuracy of about 5% and change almost synchronously during the magnetic storm. In the N hemisphere, the magnetic flux in the dawn polar cap is more intense that that in the dusk one, and vice versa in the S hemisphere. These asymmetries (dawn-dusk and interhemispheric) in the polar caps are consistent with the theory of reconnection for IMF B_y>0 and with satellite images of auroral ovals; both of these asymmetries decrease during the substorm expansion phase.

Leonovich L.A., Tashchilin A.V., Lunyushkin S.B., Karavaev Yu.A., Penskikh Yu.V. «Studying 630 nm atomic oxygen emission sources during strong magnetic storms in the night mid-latitude ionosphere» Солнечно-земная физика, 5, № 2, с. 35-41 (2019)

We analyze significant increases in 630 nm atomic oxygen night emissions during very strong geomagnetic storms, using optical measurements, theoretical modeling, and magnetogram inversion technique (MIT) data. It is shown that during strong magnetic storms when electron precipitation equatorial boundary at the night sector expands up to ∼40°, the interaction of energetic electron flux with thermospheric components may cause extreme increases in the 630 nm emission intensity. Model calculations of the red line intensity show good agreement with observational data. Using the November 20, 2003 magnetic storm as an example, we have found that oxygen atom collisions with thermal Maxwell and superthermal electrons make a major contribution to the integral emission intensity. Thermospheric density variations during the magnetic storm significantly affect the red line generation.

L'vov V.S., Rudenko O.V. «Analytic Model of the Universal Structure of Turbulent Boundary Layers» Письма в ЖЭТФ, 84, № 2, с. 67-72 (2006)