Showing papers on "Solar eclipse published in 2002"

An observational study of a magneto-acoustic wave in the solar corona

Abstract: The Solar Eclipse Corona Imaging System (SECIS) observed a strong 6-s oscillation in an active region coronal loop, during the 1999 August 11 total solar eclipse. In the present paper we show that this oscillation is associated with a fast-mode magneto-acoustic wave that travels through the loop apex with a velocity of 2100 km s−1. We use near-simultaneous SOHO observations to calculate the parameters of the loop and its surroundings such as density, temperature and their spatial variation. We find that the temporal evolution of the intensity is in agreement with the model of an impulsively generated, fast-mode wave.

Atmospheric Surface-Layer Processes During the Total Solar Eclipse Of 11 August 1999

Abstract: The central path of the total solar eclipse (TSE) of 11 August 1999 mostly passedthrough a region of active monsoon in India, with the eclipse ending around localsunset. Measurements in the surface layer (SL) were carried out close to the eclipseaxis at Akola (20°42' N, 77°2' E) in central India. The globalradiation flux reaching the surface vanishes around totality at 1803:24 (LT), followedby a small recovery before again dipping to zero at sunset. The temperatures in the SL, and subsoil at 50-mm depth, show a local minimum with a lag of about 10 min after the second contact, whereas the lag appears to vanish when the temperature series is detrended. The SL exhibits near-neutral, though generally stable, conditions from about 1500 hr itself due to heavy cloud cover followed by the eclipse-induced cooling of the surface. The wind component across the eclipse axis vanishes at totality, the wind vector aligning with the azimuth of the traversing moon shadow. The deceleration of the mean flow can be due to the combined effect of the colder surface and downward heat flux, where the locally altered horizontal temperature gradients may cause, as in this instance, the cessation of the cross flow. The oscillations in temperature and wind that show significant peaks, around 90–100 min as well as the semi-period of the eclipse near 60 min, persist for several hours past the eclipse event. A fresh analysis of the published data on the TSE of 7 March 1970 shows spectral peaks in the temperature nearly coincident with those already reported from the surface pressure records. The oscillations in the SL fields during the two TSE events are very similar implying that the source mechanism is also likely to be the same in both the cases.

Short-Period Waves That Heat the Corona Detected at the 1999 Eclipse

Abstract: As a part of a study of the cause of solar coronal heating, we searched for high-frequency (∼ 1 Hz) intensity oscillations in coronal loops in the [Fe xiv] coronal green line. We summarize results from observations made at the 11 August 1999 total solar eclipse from Râmnicu-Vâlcea, Romania, through clear skies. We discuss the image reduction and analysis through two simultaneous series of coronal CCD images digitized at 10 Hz for a total time of about 140 s. One series of images was taken through a 3.6 A filter isolating the 5303 A[Fe xiv] coronal green line and the other through a 100 A filter in the nearby K-corona continuum. Previous observations, described in Pasachoff et al. (2000), showed no evidence for oscillations in the [Fe xiv] green line at a level greater than 2% of coronal intensity. We describe several improvements made over the 1998 eclipse that led to increased image clarity and sensitivity. The corona was brighter in 1999 with the solar maximum, further improving the data. We use Fourier analysis to search in the [Fe xiv] channel for intensity oscillations in loops at the base of the corona. Such oscillations in the 1-Hz range are predicted as a result of density fluctuations from the resonant absorption of MHD waves. The dissipation of a significant amount of mechanical energy from the photosphere into the corona through this mechanism could provide sufficient energy to heat the corona. A Monte Carlo model of the data suggests the presence of enhanced power, particularly in the 0.75–1.0 Hz range, and we conclude that MHD waves remain a viable method for coronal heating.

Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

Abstract: . The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day. Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)

Gravity Anomaly During the Mohe Total Solar Eclipse and New Constraint on Gravitational Shielding Parameter

Abstract: By using a high-precision LaCoste-Romberg gravimeter, continuous and precise meas- urements were carried out during the March 9, 1997 total solar eclipse in Mohe region in Northeast China. The gravity variations were digitally recorded during the total solar eclipse so as to investigate the possible anomaly of the Sun and the Moon's gravitational fields on the Earth. After the careful processing and analysis of the observed data, no significant anomaly during the very solar eclipse was found. However, there are two 'gravity anomaly valleys' with near symmetrical decrease of about 6 ∼ 7 µgal at the first contact and the last contact. This is the anomaly phenomenon observed and reported for the first time in the literature. This paper is intended to explain the observed anomaly by conducting the tilt experiment due to the thermal stress and temperature change in the solar eclipse. A new constraint limit on gravitational shielding is thus obtained. Some analysis and discussions are presented although further studies and research are highly needed.

The J- and K-Band Brightness of the Solar F Corona Observed during the Solar Eclipse on 1998 February 26

Abstract: We analyze J- and K-band observations of the 1998 solar eclipse and derive the F-corona brightness in the K band between 3 and 7 R☉ from the center of the Sun and in the J band out to 5 R☉. The falloff in the K-band brightness from 3 to 7 R☉ is fitted with a radial power law with exponent -2.4 ± 0.1 at the solar equator and with exponent -2.9 at the solar pole. This slope is gentler than that derived from observations in 1983 but is steeper than that derived from observations for the 1991 eclipse. The radial profiles agree well with models that explain the F corona with weakly absorbing dust particles. Comparison of the J- and K-band brightness at 3 R☉ from the center of the Sun indicates a reddening of the F corona with respect to the solar spectrum. The reddening is, however, less pronounced compared to the F corona observed during the 1983 total solar eclipse. This fact may be attributed to a change in the composition of dust near the Sun. As with the radial profiles, the reddening in 1998 is better explained with models that assume weakly absorbing rather than strongly absorbing dust particles in the solar corona. Similar to recent eclipse observations, we do not detect an excess emission feature of near-solar dust in the F corona. We hence can reject the hypothesis that suggests a correlation between the detection of an emission feature and the solar activity cycle.

Geomagnetic effects due to an eclipse-induced low-conductivity ionospheric spot

Abstract: [1] The solar eclipse on 11 August 1999 was quite unique due to its totality belt coverage of the territory of central Europe where the facilities for the geophysical monitoring are most dense. Ionospheric and geomagnetic observations during the eclipse allowed us to study the eclipse-induced effects more precisely. A mathematical model based on the classical Ashour-Chapman model is considered to show that the decrease (up to 40%) of the ionospheric total electron content in the region of the totality belt leads finally to geomagnetic disturbances quantitatively dependent on the position of both the quasi-circular spot of the ionospheric conductivity decrease and given geomagnetic observatory location. The model is generalized for the anisotropic ionosphere. The theoretical estimates are compared with observational data from European geomagnetic observatories: Furstenfeldbruck, Nagycenk, Tihany, and Hurbanovo, the last one being nearby the totality belt.

Optical Response of the Atmosphere During the Caribbean Total Solar Eclipses of 26 February 1998 and of 3 February 1916 at Falcón state, Venezuela

Abstract: An investigation of the optical response of the atmosphere before, during, and afterthe total solar eclipse of 26 February 1998 at the Caribbean Peninsula of Paraguana (Falcon State) in Venezuela, was made by measuring photometrically the intensity of the sky brightness in three strategic directions: zenith, horizon anti-parallel or opposite the umbra path, and horizon perpendicular to this path. From these measurements, and by applying in an inverse way an empirical photometric model, very rough estimations of theextinction coefficient, and also of the average optical depth, were obtained in one of these particular directions. However based on meteorological measurements such as those of relative humidity and temperature, and applying a different model, a better estimation in the visual of the total global extinction coefficient of the sky (except the horizon), were made considering the contribution of each component: atmospheric aerosol, water vapour, ozone and Rayleigh scattering. It is shown that this global coefficient is mostly dependent upon aerosol extinction. In spite of the strong reduction of sky brightness photometrically observed during the totality, the results show that the sky was not dark. This is confirmed by the results obtained for the total global extinction coefficient. Additionally it is estimated that the total solar eclipse that took place also in Falcon State, Venezuela, at the beginning of the last century on 3 February 1916, was ∼30% darker that the 1998 eclipse, and that atmospheric aerosol played a relevant and similar role in the scattering of sunlight during the totality as it was for 1998's. Visual observations made during each event, which show that at length only one or two bright stars could be seen in the sky, support the results obtained for both eclipses.

Annular and Total Solar Eclipses of 2003

Abstract: On Saturday, 2003 May 31, an annular eclipse of the Sun will be visible from a broad corridor that traverses the North Atlantic. The path of the Moon's antumbral shadow begins in northern Scotland, crosses Iceland and central Greenland, and ends at sunrise in Baffin Bay (Canada). A partial eclipse will be seen within the much broader path of the Moon's penumbral shadow, which includes most of Europe, the Middle East, central and northern Asia, and northwestern North America. The trajectory of the Moon's shadow is quite unusual during this event. The shadow axis passes to the far north where it barely grazes Earth's surface. In fact, the northern edge of the antumbra actually misses Earth so that one path limit is defined by the day/night terminator rather than by the shadow's upper edge. As a result, the track of annularity has a peculiar "D" shape that is nearly 1200 kilometers wide. Since the eclipse occurs just three weeks prior to the northern summer solstice, Earth's northern axis is pointed sunwards by 22.8 deg. As seen from the Sun, the antumbral shadow actually passes between the North Pole and the terminator. As a consequence of this extraordinary geometry, the path of annularity runs from east to west rather than the more typical west to east. The event transpires near the Moon's ascending node in Taurus five degrees north of Aldebaran. Since apogee occurs three days earlier (May 28 at 13 UT), the Moon's apparent diameter (29.6 arc-minutes) is still too small to completely cover the Sun (31.6 arc-minutes) resulting in an annular eclipse.

Domonstration instrument for sun, earth and moon movement

Abstract: The utility model discloses a novel demonstration instrument for the movements of the sun, the earth and the moon, which comprises that a ball-shaped cover 3 with a collecting mirror 4 is covered outside a bulb 2 at the center of the instrument to symbolize the phenomenon that the sun, and light beams converged by the collecting mirror always illuminate an earth model 6 rotating around the ball-shaped cover to present the revolution of the earth. A small ball 5 is driven by a motor 9 to rotate aslant around the earth model to present the rotation of the moon around the earth. A motor 10 is used for changing the direction of the inclined rotating track of the small ball to present the regression of the node of the moon's path. A solar eclipse can be seen only when the small ball rotates into the light beams. The utility model has the advantages of simple structure and easy use. Besides, the utility model can reproduce the reason for the generation of the solar eclipse at any moment and can present the phenomenon of the movement of the moon shadow on the earth during the solar eclipse.

Limits on radiative decays of solar neutrinos from measurements during a total solar eclipse

Abstract: During the 1999 total solar eclipse we intended to search for photons emitted by a possible radiative decay of the heavier component of solar neutrinos, using two telescopes: an airborne one, and another at mountain altitude, in Romania(the NOTTE experiment). The weather conditions did not allow us to perform the measurements. Alternatively, we analyzed a video tape of the eclipse offered to us by a local television, obtaining some qualitative estimations on the neutrino lifetimes. We present also a first report on the observations made 21 June 2001, from Zambia.

Solar eclipse induced changes in aerosol extinction profiles: A case study of 11 Aug. 1999 solar eclipse using lidar at a tropical station Trivandrum, India

Abstract: An experiment has been conducted to understand the I I Aug. I 999 solar ec lipse induced changes in the aerosol extinction coeffic ient in the troposphere and the lower stratosphere using the multiwavclength Iidar sys tem des igned and developed in-house at a tropical stati on Trivandrum (8° 33'N, 77° E) . Results of the measure ments reveal an increase in aerosol extincti on coeffic ient in the troposphere and a decrease in the lower stratosphere compared to contro l day. Six high altitude balloon ascents with I 680 MHz radiosonde were conducted from Thumba to study the ec lipse induced variations in winds and temperature of the lower atmosphere. The study clearly reveals the cooli ng of the ent ire tropospheric layers with maximum of 5° C occurring be low 15 km altitude . The changes in the temperature and the relative hu midity during the ec lipse are the key factors contributed for the observed aerosol ext inction coefficient.

Astronomical Dating and Statistical Analysis of Ancient Eclipse Data

Abstract: All 13 Shang dynasty oracle bone eclipse records have been uniquely matched to six solar and seven lunar eclipses in the 14th to 12th centuries B.C. The King Zhong Kang fifth year autumnal (October 16, 1876 B.C.) and King Yu third year “double sunset” (September 24, 1912 B.C.) eclipses confirm the accuracy of the revised Bamboo Annals Xia dynasty chronology (Nivison and Pang, Early China 15, 1990, 87-95). The eclipse dates are plotted against the number of generations before 841 B.C. (the earliest accurate historical date), the respective kings ruled. The curve of bestfit has both the strengths of verified royal genealogy — continuity — and eclipse dating — accuracy. It is 99% accurate, and can be confidently used as a foundation for building a detailed absolute chronology for the Xia, Shang and Zhou dynasties, an important project in China’s current Five-Year Plan (Song Jian, Sci. Tech. Daily, May 17, 1996; Wehrfritz, Newsweek, July 7, 1997).

An Ancient Solar Eclipse Record ``Tian-da-yi'' in the 10th Century BC

Abstract: The ancient record ``Tian-da-yi'' (the sky darkened greatly) is identified with the solar eclipse on May 31, 976BC. This identification is demonstrated in this paper through a palaeographic, astronomical and chronological analysis. It is probably the earliest solar eclipse in Chinese history that can be so identified.

Lower polar ionosphere research by the partial radioreflections technique

Abstract: The lower polar ionosphere research are carried out by the modified measuring complex of the observatory Tumanny (69.0 degree(s)N, 35.7 degree(s)E) since 1999. It were performed an analysis of the dynamical processes caused by the neutral gas motion, preliminary investigation of statistical and spectral characteristics of the backscattered waves and, furthermore, variations of the electron density were calculated. The areas, where the electron density irregularities with scales more than 100 m at heights from 70 till 99 km were groped, were detected by the spaced sensors measurements of the backscattered waves. During the solar eclipse of 1999 August 11 for the short time the increased radioecho intensity was observed at the heights near the mesopause.

Polarization in the 530.3nm emission line and coronal magnetic field structure

Abstract: To clarify the possible influence of the coronal magnetic field on the degree of polarization p, direction of polarization , and line intensity I measured during the 11 July 1991 total solar eclipse, we have compared these quantities with dierent field parameters. The structure of the coronal mag- netic field on the eclipse day was calculated using potential approximation. The relation of p and I as measured at 1.2 R from the centre of the solar disk to the strength of the magnetic field and its dierent components is dis- cussed in detail. It is found that the points pertinent to the large-scale coronal structures of dierent morphological (physical) types (high-latitude streamers, bright equatorial regions, regions in the vicinity of coronal holes, etc.) form isolated, not overlapping clusters of points on the B - p, B - and B - logI diagrams. Two classes of objects are distinct in these diagrams. The first class comprises of high-latitude streamers in which the degree of polarization increases with decreasing B. The second class is represented by coronal conden- sations, moderately active equatorial regions, and coronal holes. In the objects of this class, the magnetic field strength is approximately three times as large as in the streamers, and the degree of polarization depends only weakly on B. It is shown that p, I and display a noticeable relationship with the indices Q1 and Q2, which we introduced to characterize the complexity (degree of in- homogeneity) of the magnetic field at any given point in the solar corona. In fact, Q1 and Q2 represent the absolute and relative deviations of B from its mean value measured in the neighbourhood of a given point. The results of our investigation suggest that we are dealing with the direct influence of the magnetic field on the generation of the polarized radiation in the 530,3 nm emission line. One can expect, therefore, that the investigation of polarization characteristics would provide a useful method for determining the magnetic field in the solar corona.

Ionospheric response to the total solar eclipse of June 21, 2001

Abstract: We discuss the measurements of the main parameters of the ionospheric response to the total solar eclipse of June 21, 2001. This study is based on using the data from three stations of the global GPS network located in the area of the totality band in Africa. This period was characterized by a low level of geomagnetic disturbance (the Dst-index varied from -6 to 22 nT), which alleviated greatly the problem of detecting the ionospheric response to eclipse. An analysis revealed a clearly pronounced effect of a decrease (depression) of the total electron content (TEC) for all GPS stations. The delay between the smallest value of the TEC with respect to eclipse totality was 9-37 min. The depth and duration of the TEC depression were 0.5-0.9 TECU and 30-67 min, respectively. The results obtained in this study are in good agreement with earlier measurements and theoretical estimations.

The Occurrence of Retinopathy in 11 Eyes After a Solar Eclipse, 1999

Abstract: To present the visual outcome of patients with solar retinopathy and evaluate the effects of treatment on the visual prognosis. One hundred and eighty-eight patients with visual disturbances applied for ophthalmic examination following the solar eclipse on August 11, 1999. All patients underwent routine ophthalmologic examination; those with fundus changes also underwent fundus fluorescein angiography, Amsler grid and computerised perimetry. Among them, nine patients (11 eyes) were evaluated as having solar retinopathy with decreased visual acuity and discernible fundus findings. Mean age was 21.5 (17-34) in this group. Five patients were given treatment, three were on oral methyl prednisolon and two were on ginkgo glycosides. Statistical analysis could not be performed because of the small number of patients in the treatment groups. The duration of exposure was 1-30 min. The mean initial visual acuity was 20/32 (min 20/100, max 20/25). All eyes aside from one revealed positive Amsler grid tests. Computerised perimetry showed central scotoma in four eyes. The mean visual acuity at final examination (3 months later) was 20/24 (min 20/50, max 20/20). Metamorphopsia persisted in five eyes, and disability at near vision persisted in one eye after 3 months. Early and late fundoscopic findings did not correlate with either duration of exposure or visual acuity. Reversible or persistant visual abnormalities may follow a solar retinal burn. Prevention seems to remain the best treatment. Corticosteroids may be beneficial in severe cases.

Short-Period Waves That Heat the Corona Detected at the 1999 Eclipse

Abstract: As a part of a study of the cause of solar coronal heating, we searched for high-frequency (~1 Hz) intensity oscillations in coronal loops in the [Fe XIV] coronal green line. We summarize results from observations made at the 11 August 1999 total solar eclipse from Ramnicu-Valcea, Romania, through clear skies. We discuss the image reduction and analysis through two simultaneous series of coronal CCD images digitized at 10 Hz for a total time of about 140 s. One series of images was taken through a 3.6 A filter isolating the 5303 A [Fe XIV] coronal green line and the other through a 100 A filter in the nearby K-corona continuum. Previous observations, described in Pasachoff et al. (2000), showed no evidence for oscillations in the [Fe XIV] green line at a level great than 2% of coronal intensity. We describe several improvements made over the 1998 eclipse that led to increased image clarity and sensitivity. The corona was brighter in 1999 with the solar maximum, further improving the data. We use Fourier analysis to search in the [Fe XIV] channel for intensity oscillations in loops at the base of the corona. Such oscillations in the 1-Hz range are predicted as a result of density fluctuations from the resonant absorption of MHD waves. The dissipation of a significant amount of mechanical energy from the photosphere into the corona through this mechanism could provide sufficient energy to hear the corona. A Monte-Carlo model of the data suggests the presence of enhanced power, particularly in the 0.75-1.0 Hz range, and we conclude that MHD waves remain a viable method for coronal heating.

Study on geomagnetic effects of the March 9, 1997 solar eclipse in Mohe area, China*

Abstract: The geomagnetic effects of the total solar eclipse in Mohe area and the partial eclipse occurred on March 9, 1997 in China are analyzed in this paper. The geomagnetic effects of the eclipse widely distributed in China are obtained, which show H component decreases obviously and is symmetric along the latitude with a center near 33°N during the eclipse time. These results of solar eclipse geomagnetic effects are the newest in recent years obtained in the largest area in China.