Micrometeorological measurements in Nigeria during the total solar eclipse of 29 March, 2006

The total solar eclipse of 29 March, 2006 which was visible at Ibadan (7.55°N, 4.56°E), south-western Nigeria was utilized to document atmospheric surface-layer effects of the eclipse for the first time in Nigeria. The meteorological parameters measured are global radiation, net radiation, wind speed (at different heights), atmospheric pressure and soil temperature (5, 10 and 30 cm), moisture and heat flux and rainfall. The results revealed remarkable dynamic atmospheric effects. The observations showed that the incoming solar radiation, net radiation and air temperature were significantly affected.There was an upsurge of wind speed just before the first contact of the eclipse followed by a very sharp decrease in wind speed due to the cooling and stabilization of the atmospheric boundary layer. The atmospheric pressure lags the eclipse maximum by 1 h 30 min, while the soil temperature at 5 and 10 cm remain constant during the maximum phase of the eclipse.     

The solar corona during the eclipse of August 1, 2008

A new telescope has been created to investigate the solar corona during eclipses. One lens simultaneously forms three corona images occurring as coronal radiation passes through three polarizers with transmission directions rotated 0°, 60°, and 120° relative to the selected direction; in addition, one image is formed without the polarizer. The telescope was used for solar corona observation during the eclipse of August 1, 2008. We obtained the distributions of polarization brightness, K corona brightness, degree of K corona polarization, and total degree of polarization as well as polarization directions depending on the latitude and radius in the sky plane. Radial distributions of the electron density depending on latitude were calculated. The coronal plasma temperature was determined for different corona structures under the assumption of hydrostatic equilibrium.     

Ionospheric effects of the March 29, 2006, solar eclipse over Kazakhstan

The results of studying the ionospheric effects of the March 29, 2006, solar eclipse are presented. The results were obtained in measurements of local electron density (ED) at Alma-Ata vertical ionospheric sounding station and total electron content (TEC) at the Central Asia network of two-frequency receivers of the GPS navigation system. The ED decrease at the F-layer maximum reached approximately 28%, the delay of the minimum value of EC relative to the moment of the eclipse maximum phase was about 11 min, the relaxation time was 4 min, and the duration of the EC depression at the 0.5 level was 45 min. Dynamic interlayer formations were observed in the ionosphere near the eclipse maximum phase. A traveling ionospheric disturbance, probably generated at the shock wave front during the supersonic motion of the Moon’s shadow, was detected. The disturbance period and the horizontal projection of the velocity were about 90 min and ～680 m/s, respectively. The wave vector azimuth (145°) coincides with the model value of the normal to the shock front.     

Specific features of variations in the characteristics of VLF signals when the lunar shadow propagated along the path during the solar eclipse of March 29, 2006

The effects of the solar eclipse of March 29, 2006, in the signals of ULF radio stations, in the intensity of regular radio noise at frequencies of 0.3–10 kHz, and in the number of atmospherics received in Yakutsk mostly from the west have been considered. The observations were performed using a multichannel parallel analyzer-recorder (11 channels in the frequency band 0.47–8.7 kHz), one-point lightning direction and range finder (0.3–100 kHz), narrow-sector radio noise direction-finder (0.3–10 kHz), recorder of signals from VLF radio stations, and broadband radio noise recorder (0.3–100 kHz). A GPS clock was used to synchronize a recorder of signals from VLF radio stations. The effect was observed in radio signals, radio noise, and number of atmospherics from the direction 270° ± 20° counted off clockwise from the north during the last stage of the eclipse (～ 1100–1200 UT), when the lunar shadow approached the line of the nighttime terminator and obscured part of the signal propagation path. The effect was observed as an enhancement of the received signals by a factor of ～1.2, a factor of ～1.4 increase in the number of atmospherics, and a change in the radio station phase values.     

Effects of the solar eclipse of March 29, 2006, in the ionosphere and atmosphere

The observations of the effects of the partial (about 77%) solar eclipse (SE) of March 29, 2006, in the ionospheric plasma are presented. The experimental data were obtained using the Kharkov incoherent scatter radar. At the moment of the maximum phase of SE, a decrease in the critical frequency of the ionospheric F ₂ layer by 18%, a depletion of the density in the F ₂ layer maximum by 33%, and an increase in the maximum height z _m by 30 km were observed. The solar eclipse caused a decrease in the electron and ion temperatures by 150–300 and 100–200 K, respectively, within the height range 210–490 km. An increase in the relative density of the hydrogen ions during the maximum phase of SE by 20–25% within the height range 900–1200 km is detected. Calculations of the parameters of dynamical processes and thermal regime of the ionospheric plasma during SE are performed.     

Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August, 1999 and 9 July, 1945

Swept-frequency (1/10 MHz) ionosonde measurements were made at Helston, Cornwall (50°06N, 5°18W) during the total solar eclipse on August 11, 1999. Soundings were made every three minutes. We present a method for estimating the percentage of the ionising solar radiation which remains unobscured at any time during the eclipse by comparing the variation of the ionospheric E-layer with the behaviour of the layer during a control day. Application to the ionosonde date for 11 August, 1999, shows that the flux of solar ionising radiation fell to a minimum of 25±2% of the value before and after the eclipse. For comparison, the same technique was also applied to measurements made during the total solar eclipse of 9 July, 1945, at Sörmjöle (63°68N, 20°20E) and yielded a corresponding minimum of 16 ± 2%. Therefore the method can detect variations in the fraction of solar emissions that originate from the unobscured corona and chromosphere. We discuss the differences between these two eclipses in terms of the nature of the eclipse, short-term fluctuations, the sunspot cycle and the recently-discovered long-term change in the coronal magnetic field.     

Variations in the amplitude and phase of VLF radiowaves in the ionosphere during the August 1, 2008, solar eclipse

Time variations in the amplitude and phase of signals of the Russian telecommunication station (the frequency is 25 kHz) on the Arkhangelsk—Kharkov path with a length of about 1600 km on the day of the August 1, 2008 solar eclipse (SE) and on the adjacent days are analyzed. Two types of effects are detected. An increase of the signal amplitude by approximately 32% in comparison with the background days and the 2.1 μs time shift of the signal during 2—2.5 h is referred to the first type. Changes in the spectral composition of the quasiperiodic disturbances in the ionosphere presented the second type of the effects. For spectral analysis of the quasiperiodic variations in the amplitude and phase of the radio signal, the window Fourier transform, adaptive Fourier transform, and wavelet transformation were applied simultaneously. In the period of SE and after it, oscillations with periods of 10—15 min (according to the amplitude data) and also about 10 and 18 min (according to the phase data) were intensified. Based on radio signal characteristics, the parameters of ionospheric disturbances are estimated.     

Wave response of the ionosphere to the partial solar eclipse of August 1, 2008

Quasi-periodic variations in the Doppler shift of the HF range frequency at a vertical path and critical frequency of the F ₂ layer caused by wave disturbances in the ionosphere on the day of the partial (the magnitude was about 0.42) solar eclipse and on background days are analyzed. For the spectral analysis, the window Fourier transform, adaptive Fourier transform, and wavelet analysis were jointly used. It is shown that on the day of the eclipse and the background day, spectral characteristics of wave disturbances within the 150–200 km height range differed substantially. The changes in the spectral composition began approximately 30–35 min after the solar eclipse beginning and lasted more than 1.5 h.     

Ionospheric response to the partial solar eclipse of March 29, 2006, according to the observations at Nizhni Novgorod and Murmansk

The results of observations of the solar eclipse ionospheric effects on March 29, 2006, are presented. The observations were conducted using the partial reflection method near Nizhni Novgorod and the vertical sounding method at the automatic ionospheric station near Murmansk. It has been obtained that the electron density at altitudes of 77 and 91 km decreases by a factor of more than 4; in this case the response of the ionosphere at an altitude of 91 km lags behind the eclipse maximum phase on the Earth by approximately 20 min. It has been established that the eclipse in the E and F1 regions of the polar ionosphere causes a change in the electron density by 15–20%. The delay time of this effect varies from 12 to 24 min depending on the altitude. It has been registered that the reflection virtual altitude at altitudes of the ionospheric F region increases in Murmansk and Nizhni Novgorod.     

Observations of the dust radial velocity field in the F-corona on March 29, 2006

The results of interferometer observations of the dust radial velocity field in the F-corona during the total solar eclipse of March 29, 2006, are presented. The observations were performed in the Mugalzhar settlement, Aqtobe region, Kazakhstan. The observation results indicated that the dust orbital motion is opposite to the planetary motion and is inclined at an angle of about 105° with respect to the ecliptic plane. It is assumed that the observed dust is genetically related to Kreutz comets falling on the Sun and registered with the SOHO spacecraft on March 28 and 31, 2006.     

Comparative analysis of the distributions of brightness temperatures in the solar polar region based on observational data obtained with RATAN-600 in the microwave range during the solar eclipse of March 29, 2006

The results of microwave observations of the solar eclipse of March 29, 2006, with the RATAN-600 radiotelescope are presented. The observations were carried out using the northeastern sector of the radiotelescope in a broad wavelength range (1.03, 1.38, 2.70, 6.20, 13.00, and 30.70 cm) in the intensity channel. The aim of the present work is to conduct a comparative analysis of the distributions of brightness temperatures in the solar atmosphere at a distance (ranging from one to two solar radii) from the center of the optical solar disk. The data for the analysis come from the RATAN-600 observations of the solar eclipse of March 29, 2006, earlier observations with the RATAN-600 radiotelescope, and calculations of brightness temperatures that were carried out using the Baumbach-Allen formula which describes the electron density in the solar corona. The differences between the distributions obtained by the above-mentioned methods are discussed.     

Simultaneous observations of the natural electromagnetic emission in the ELF-VLF range at Kamchatka and in Yakutia during the solar eclipse of August 1, 2008

The effect of the solar eclipse that occurred on August 1, 2008, on the level of the natural electro-magnetic emission signals in the ELF-VLF range, simultaneously observed at Kamchatka and in Yakutsk, and the variations in the amplitude and phase of signals from the VLF radiostations, registered in Yakutsk, has been considered. The VLF radiostations in Krasnodar, Novosibirsk, and Khabarovsk successively emitted signals at frequencies of 11 905, 12 649, and 14 880 Hz. Based on the observations of the signals from these radiostations, it has been established that the signal amplitudes and phases increased by 3–5% and 30°–45° when the signals crossed the lunar shadow region. The synchronous registration of the ELF-VLF noise emission indicated that a bay-like increase and the following decrease in the emission to the background level was observed at both receiving points during the eclipse from ∼1000 to 1130 UT. This effect was registered at frequencies of 0.6–5.6 kHz in Yakutsk and at lower (30–200 Hz) and higher (2.5–11 kHz) frequencies at Kamchatka. In this case the noise emission intensity maximum was observed when the lunar shadow maximally approached the registration point. At higher frequencies, the emission maximum was observed simultaneously at both points (at 1100 UT) but with a delay relative to the maximum at lower frequencies. The possible causes of the appearance of the solar eclipse effects in the natural ELF-VLF emission are considered.     

Global Pi3 geomagnetic pulsations as a response of large variations in the solar wind and IMF during the magnetic storm of August 5, 2011

Spatial-temporal and spectral features of ground geomagnetic pulsations in the frequency range of 1–5 mHz at the initial phase of a strong magnetic storm of the 24th cycle of solar activity (August 5–6, 2011, with a Dst-variation in the storm maximum of ?110 nT) are analyzed. Large opposite in sign amplitudes of variations in IMF parameters (from ?20 to +20 nT) at a high velocity of the solar wind (～650 km/s) accompanied by intense bursts in solar-wind density (up to ～50 cm^?3) were distinctive feature of interplanetary medium conditions causing the storm. Geomagnetic Pi3 pulsations global in longitude and latitude and in-phase in the middle and equatorial latitudes were found. The onset of pulsation generation was caused by a pulse of dynamic pressure of the solar wind (～20 nPa), i.e., by a considerable compression of the magnetosphere. The maximum (2–3 mHz) in the amplitude spectrum of near-equatorial pulsations coincided with the maximum of pulsations in the daytime polar cap. After the next jump of the dynamic pressure of the solar wind (～35 nPa), an additional maximum appeared in the pulsation spectrum in the frequency band of ～3.5–4.5 mHz. Global pulsations suddenly stopped after a sharp decrease in the solar-wind dynamic pressure and corresponding extension of the magnetosphere. The obtained results are compared with the time dynamics of the position and shape of the plasmapause.     

Experimental study of the response of the midlatitude ionospheric <Emphasis Type="Italic">D</Emphasis> region to the solar eclipse of March 29, 2006

The observations of the state of the midlatitude ionospheric D region during the March 29, 2006, solar eclipse, based on the measurements of the characteristics of partially reflected HF signals and radio noise at a frequency of f = 2.31 MHz, are considered. It has been established that the characteristic processes continued for 2–4 h and were caused mainly by atmospheric gas cooling, decrease in the ionization rate, and the following decrease in the electron density. An increase in the electron density on average by 200–250% approximately 70–80 min after the eclipse beginning at altitudes of 90–93 km and approximately 240 min after the end of the solar eclipse at altitudes of 81–84 km, which lasted about 3–4 h, has been detected experimentally. This behavior of N is apparently caused by electron precipitation from the magnetosphere into the atmosphere during and after the solar eclipse. Based on this hypothesis, the fluxes of precipitating electrons (about 10⁷–10⁸ m^?2s^?1) have been estimated using the experimental data.     

Developments in solid earth geophysics volume 15: Proceedings of the Seventeenth Assembly of the European Seismological Commission Budapest, 24–29 August 1980. E. Bisztricsany and Gy. Szeidovitz (Editors). Elsevier Scientific Publishing Company,Amsterdam-Oxford-New York, 1983, XVIII + 689 pages,ISBN 0-444-99662-1.

Various methods for the prediction of secular variation are tested by applying them to data for a single element at a single station. None of them is of any use for more than a few years.