Статьи журнала - Солнечно-земная физика
Все статьи: 599
02 density and temperature profiles retrieving from direct solar Lyman-alpha radiation measurements
Статья научная
The resonance transition 2P-2S of the atomic hydrogen (Lyman-alpha emission) is the strongest and most conspicuous feature in the solar EUV spectrum. The Lyman-alpha radiation transfer depends on the resonance scattering from the hydrogen atoms in the atmosphere and on the 02 absorption. Since the Lyman-alpha extinction in the atmosphere is a measure for the column density of the oxygen molecules, the atmospheric 02 density and temperature profiles can be calculated thereof. A detector of solar Lyman-alpha radiation was manufactured in the Stara Zagora Department of the Solar-Terrestrial Influences Laboratory (STIL). Its basic part is an ionization camera, filled in with NO. A 60 V power supply is applied to the chamber. The produced photoelectric current from the sensor is fed to a 2 channels amplifier, providing analog signal. The characteristics of the Lyman-alpha detector were studied. It passed successfully all tests and the results showed that the so-designed instrument could be used in rocket experiments to measure the Lyman-alpha flux. From the measurements of the detector, the Lyman-alpha vertical profile can be obtained. Programs are created to compute the 02 density, atmospheric power and temperature profiles based on Lyman-alpha data. The detector design appertained to ASLAF project (Attenuation of the Solar Lyman-Alpha Flux), a scientific cooperation between STIL - Bul.Acad.Sci., Stara Zagora Department and the Atmospheric Physics Group at the Department of Meteorology (MISU), Stockholm University, Sweden. The joint project was part of the rocket experiment HotPay I, in the ALOMAR eARI Project, EU's 6th Framework Programme, And0ya Rocket Range, Andenes, Norway. The project is partly financed by the Bulgarian Ministry of Science and Education.
Бесплатно
10-антенный макет радиогелиографа на базе сибирского солнечного радиотелескопа
Статья научная
Начата модернизация Сибирского солнечного радиотелескопа - ССРТ [1, 2] - в многоволновый радиогелиограф. Создаваемый радиогелиограф будет предназначен преимущественно для измерения корональных магнитных полей, определения местоположения выделения энергии солнечных вспышек и исследования выбросов корональной массы. Такие задачи определяют весьма высокие требования к параметрам радиогелиографов следующего поколения. Требуются одновременно высокое пространственное разрешение, высокая скорость получения изображений и высокая чувствительность. Все эти параметры должны быть реализованы как можно в более широком диапазоне частот - от долей до десятков ГГц. Ожидаемые параметры будущего радиогелиографа на базе ССРТ приведены ниже: • ·пространственное разрешение 12…24′′, • ·временное разрешение 0.02…1.0 с, • диапазон частот 4…8 ГГц, • чувствительность до 100 K, • поляризация левая круговая и правая круговая, • поток данных 0.5…20 Мб/с (обычный и вспышечный режимы). В этой работе мы представляем описание широкополосных антенн, аналоговых оптических линий передачи данных и коррелятора, используемых в 10-антенном макете радиогелиографа.
Бесплатно
Alfv'en waves in the magnetosphere generated by shock wave / plasmapause interaction
Статья научная
We study Alfvén waves generated in the magnetosphere during the passage of an interplanetary shock wave. After shock wave passage, the oscillations with typical Alfvén 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 Alfvén 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 Alfvén waves.
Бесплатно
Characteristics of double sodium layer over Haikou, China (20.0° N, 110.1° E)
Статья научная
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 oEs and the virtual height h' Es of the sporadic E layer Es 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 Φ1000 mm primary mirror.
Бесплатно
Comparing simulated results of folded and unfolded log-periodic antenna used for observing the Sun
Статья научная
There are two antenna arrays located in Mingantu Spectral Radio Heliograph (MUSER). MUSER-I and MUSER-II cover the frequency band ranging from 0.4 to 2 GHz and from 2 to 15 GHz respectively. A third antenna array covering 30-240 MHz will be established in the coming years. A log-periodic antenna is one of the choices for MUSER low frequency band; it radiates structures capable of maintaining consistent impedance characteristics over a wide bandwidth. Due to the ability of achieving high gain, it is widely used in many broadband applications. In this program, folded and unfolded log-periodic antennas are simulated for the Meridian project. In order to improve its return loss, this antenna is optimized with the width of each pole and the height of the substrate. This optimized process has been implemented in the simulated software HFSS.
Бесплатно
Conditions for electric breakdown in the lower ionosphere due to a lightning discharge
Статья научная
Conditions are theoretically studied, under which a breakdown is realized in the lower ionosphere above a thunderstorm after a positive cloud-to-ground (+CG) lightning discharge. Two altitudes are seen as candidates for a breakdown initiation: (i) at which the relaxation time equals the discharge time, and (ii) at the "knee" of the conductivity profile. According to this, a criterion of a breakdown occurrence is formulated. The conductivity is the key factor for a breakdown onset (i.e. more important than the charge moment change), due to its large variability at these heights.
Бесплатно
FIP-эффект как индикатор динамических процессов в солнечной атмосфере и межпланетной среде
Статья обзорная
Представлен обзор современных наблюдательных и теоретических представлений о проявлениях FIP-эффекта, т. е. превышения содержания элементов с низким первым потенциалом ионизации (first ionization potential - FIP) (10 эВ), в различных слоях и структурных образованиях солнечной атмосферы - от фотосферы до короны и солнечного ветра в межпланетной среде. Отдельно рассмотрен вопрос о составе солнечных энергичных частиц, связанных с солнечными вспышками и корональными выбросами массы. Сделан вывод о том, что основную роль в возникновении FIP-эффекта могут играть альфвеновские волны (с возможной трансформацией в другие виды волн) и процессы пересоединения магнитных полей. Кратко отмечены проявления FIP-эффекта у звезд, близких по характеристикам Солнцу, и описаны примеры возникновения обратного FIP-эффекта у некоторых звезд. Подчеркнуто, что данные наблюдений FIP-эффекта могут быть использованы для диагностики физических процессов в коронах Солнца и звезд.
Бесплатно
Fine structure events in microwave emission during solar minimum
Статья научная
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.
Бесплатно
Localized climatic responses during the 29 march 2006 eclipse at Manavgat, Turkey
Статья научная
Changes in the physical state of the 10m ground atmospheric layer owing to a sharp drop in the direct solar radiation have been observed during the March 29, 2006 total solar eclipse (TSE). Observations were conducted near the town of Manavgat, Turkey. Temperature, humidity, barometric pressure, speed and direction of the wind were measured with a fast automatic meteorological station with high resolution specially designed for this event. In addition, temperature in the 20 cm soil layer were measured. The difference in temperature changes at different heights before, during and after the total phase was in the interval 16-17 °C. Minimum of the air temperature during the TSE was measured 2 min after the end of the total phase. Atmospheric pressure was sharply changed from 1021 hPa - at the beginning of the eclipse (09 h 38 min 28 s ) to 1028 hPa - 1 min 26 s after the end of the total phase (10 h 58 min 49 s). The relative humidity increases from 72 % up to -76 % after the total phase. Speed of the wind was measured in 5 minutes during the partial phases and in 1 min during the total phase. It decreases with 3 m/s just before the total phase and increases after the end of the total phase changing its direction from south-east to north-east, which coincides with the motion of the lunar shade on the earth.
Бесплатно
Long-term variation of strong geomagnetic storms and its effect on ionospheric and telluric currents
Статья научная
Geomagnetic storms affect ionospheric currents, which induce electric fields at the Earth surface, and finally drive telluric currents. Tong-term variation in strong geomagnetic storms is studied through the number of days per year with aa index > 80 nT, and the number of hours per year with Akasofu's epsilon parameter (ε) >1013 W. A long-term behavior consisting of the Suess cycle modulated by the Gleissberg cycle is observed. Considering that these storms involve also high frequency variations with magnetic inductive effects, and the direct relation between e and geoelectric fields, this result can be extended to ionospheric and telluric currents.
Бесплатно
MHD waves in the collisional plasma of the solar corona and terrestrial ionosphere
Статья научная
We have studied MHD waves (Alfvén and fast compressional modes) in a homogeneous collisional three-component low-β plasma. The three-component plasma consists of electrons, ions, and neutrals with arbitrary ratio between collision frequencies and wave time scales. We have derived a general dispersion equation and relationships for phase velocity and collisional damping rates for MHD modes for various limiting cases: from weak collisions to a strong collisional coupling, and for longitudinal and oblique propagation. In a weak collision limit, the MHD eigen-modes are reduced to ordinary low-damping Alfvén and fast magnetosonic waves. For a partially ionized plasma with a strong collisional coupling of neutrals and ions, velocities of magnetosonic and Alfvén waves are substantially reduced, as compared to the Alfvén velocity in the ideal MHD theory. At a very low frequency, when neutrals and ions are strongly coupled, a possibility arises of weakly damping MHD modes, called “decelerated” MHD modes. These modes can be observed in the solar corona/chromosphere and in the F layer of the terrestrial ionosphere.
Бесплатно
Статья научная
С использованием данных вертикального зондирования и измерения температуры средней атмосферы, полученных с помощью СВЧ-зонда MLS Aura, проведено исследование связи между появлениями аномально высоких ночных значений критической частоты в зимнее время и стратосферными потеплениями. Получено, что такие явления развиваются во время стратосферных потеплений на фоне усиления активности колебаний с периодами планетарных волн в атмосфере. Взаимодействие планетарных волн с суточными и полусуточными приливами может увеличить амплитуду полусуточных волн, что определяет повышение ночной ионизации в ионосфере.
Бесплатно
Статья научная
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.
Бесплатно
Possible influence of space weather changes on dynamics of traffic accidents in middle latitudes
Статья научная
We describe the results of joint studies to reveal a possible effect of space weather variations on the dynamics of traffic accidents in middle latitudes. We arrived at the conclusion that impulsive geomagnetic disturbances (storms) affect the number of traffic accidents more significantly than gradually changing background geomagnetic activity. The probable cause of this is the retarded or inadequate human brain's reaction. We also found a high correlation between cosmic ray activity (neutron flux) on the Earth's surface and the number of traffic accidents. Spectral analysis has revealed certain periodicities in the dynamics of traffic accidents, well-known in solar-terrestrial physics.
Бесплатно
Статья научная
The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September-December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer. Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals. In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.
Бесплатно
Scale sequentially Clean for mingantu spectral radioheliograph
Статья научная
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 Högbom 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.
Бесплатно
Solar uv radiation and ozone dynamics over Bulgaria
Статья научная
This paper presents an investigation of the solar UV radiation dynamics and the total ozone content (TOC) behaviour over Bulgaria in the time period 1996-2005. The data are received from measurements, using the spectrophotometer Photon, placed in Stara Zagora. We also use ozone data from satellite experiments TOMS. The data analysis shows: • ·there isn't a statistically significant TOC trend over Bulgaria in the last 10 years; • the largest TOC variations are in the winter-spring and the lowest - in the summer; • ·a strong dependence between UV-B solar radiation reaching the Earth surface and TOC is received (r = -0.62 ±0.18) at 98 % confidence level.
Бесплатно
Study of the auroral emissions and electron precipitation depending on the solar activity
Статья научная
Simultaneous observations of the OI 5577 A and 6300 A emissions, the electron precipitation, the terrestrial magnetic field and the plasma parameters, and the corresponding solar wind, Interplanetary Magnetic Field and geomagnetic activity indices data have been used in order to study the Sun-Earth interactions under various conditions. Images of 5577 A and 6300 A emissions have been obtained from the All-Sky Imager (ASI), positioned at ARR, Andenes (69.3° N, 16.03° E). The Imaging Riometer for Ionospheric Studies (IRIS), at Kilpisjarvi, Finland (69.05° N, 20.79° E) gave information about the precipitating electrons with energies in the range 10-100 keV and deposition heights centered at about 90 km. The magnetic field components have been measured by the Andenes magnetometer (69.3° N, 16.03° E). The essential ionosphere parameters have been acquired from the measurements of the Digisonde, situated at Troms0 (69.6° N, 19.2° E). A good correlation between the spatial and temporal evolutions of the optical emissions, the precipitating electron fluxes and the terrestrial magnetic field has been observed. The response of the ionosphere to the solar and geomagnetic activity changes has been studied. The study is performed under a project, part from the ALOMAR eARI Project, EU's 6th Framework Programme, Andenes, Norway.
Бесплатно
