Showing papers on "Solar eclipse published in 1999"

Ionospheric total electron content response to solar eclipses

Abstract: On October 24, 1995, and March 9, 1997, two solar eclipse events occur. It is therefore of interest to investigate how the ionosphere responded to the eclipses. Five global positioning system (GPS) ground-based receivers are specifically designed to observe large-scale ionospheric variations over the geomagnetic equatorial, equatorial anomaly crest, and midlatitude regions. Two-dimensional images of ionospheric total electron content (TEC) during the two eclipse periods are constructed. The deviations in the TEC images on eclipse days from those on reference days show that during the eclipse days the ionosphere experienced some large-scale changes. Four features of the TEC deviations, pre-ascension (PA), major depression (MD), sunset ascension (SA), and secondary depression (SD) have been observed. A detailed study shows that in geomagnetic low latitudes, PAs are possibly related to the locations of the equatorial anomaly crest. The latitudinal location, amplitude, and occurrence time of MDs suggest that the fountain effect is essential. SAs and SDs occurring in geomagnetic equatorial and low latitudes and appearing respectively before/around and after local sunset indicate that the prereversal enhancement plays an important role.

A study of tomographically reconstructed ionospheric images during a solar eclipse

Abstract: The low-latitude ionospheric tomography network (LITN) consists of a chain of six Naval Navigation Satellite System (NNSS) receiving stations established along 121°E longitude from a geographic latitude of 14.6°N to 31°N. It is specifically designed to observe large-scale ionospheric variations over the equatorial anomaly region by using tomographic imaging techniques. Recently, the network LITN was applied to observations of the October 24, 1995, solar eclipse. Two-dimensional images of ionospheric electron density during the eclipse period were reconstructed. These images and the corresponding results from a nearby ionosonde were compared with those for a reference day. It is shown that during the eclipse day the ionosphere experienced some large-scale changes. In particular, four episodes of electron density enhancement or depression have been identified. (1) The maximum enhancement occurred before the maximum phase of the solar eclipse at approximately 7°–10°N geomagnetic latitude at the 275–300 km ionospheric height. (2) The second enhancement appeared roughly 3 1/2 hours after the maximum obscuration at 15°–22°N geomagnetic latitude and 300–325 km ionospheric height. (3) The largest electron density depression occurred roughly 2 hours after the maximum obscuration at approximately 9°–15°N geomagnetic latitude and on both the bottom and topside ionosphere. (4) The second depression occurred about 4 hours after the maximum obscuration at approximately 5.5°N geomagnetic latitude and mainly on the topside ionosphere. More detailed study suggests that the two enhancements have their origins in the ionospheric day-to-day variations, the first depression is related to the combined photochemical and the equatorial fountain effects, and the second depression may have its origin in geomagnetic coupling between conjugate ionospheres. These observations are interpreted within the framework of ionospheric dynamics in the equatorial anomaly region.

The midlatitude ionosphere during the total solar eclipse of March 9, 1997

Abstract: The total solar eclipse of March 9, 1997, was visible from some regions of China, Mongolia, and East Siberia during 0045–0130 UT. The eclipse coincided with a relatively long geomagnetically quiet period. During the total solar eclipse, the observations included oblique-incidence ionograms recording; also measurement the total electron content along specified directions to the visible Global Positioning System satellites and the Doppler sounding on various HF ray paths over the region under consideration were carried out. This paper presents results derived from studying the spatial pattern of midlatitude ionospheric response to this eclipse on the basis of a numerical simulations. Calculations have been executed using a model for ionosphere-plasmasphere coupling. Comparison of model results with data of all measurements showed a good qualitative and quantitative agreement. It is shown that by and large the behavior of the ionosphere during the eclipse manifests itself as a short-lasting (∼l-hour) rearrangement to nighttime conditions with the ion flow directed downward from the plasmasphere, as a rise of the F2 layer maximum by about 20 km, and as a twofold increase in electron density at the height of the maximum during the eclipse's totality phase. The electron temperature decreases by 200–400 K, while the ion temperature drops only slightly. It is found that changes in the spatial distribution of electron density along the HF ray paths during the eclipse give rise to variations of Doppler frequency shift with amplitudes of about 1 Hz and a duration of about 120 min. The findings reported in this paper do not validate the hypothesis that solar eclipses generate atmospheric gravity waves and associated traveling ionospheric disturbances.

Dynamics of Polar Plumes Observed at the 1998 February 26 Eclipse

Abstract: This paper presents first observations of dynamics of the white-light solar corona detected during the few minutes of totality of a solar eclipse. Perturbations of a polar plume associated with an embedded ‘jet’ structure observed simultaneously at 195 A with the EUV Imaging Telescope (EIT) aboard the SOHO spacecraft lead to estimates of the electron density fluctuations accompanying the jet: ±15%. The morphological behavior of the jet, its apparent upward propagation speed of ≈ 200 km s−1, and the inferred density perturbations suggest that the jet is led by a weak, outward-propagating shock resulting from the injection of material at high velocity at the base of the corona. Smaller perturbations of the white-light corona are apparent at many other locations, sustaining hope that propagating Alfven waves may be measurable in the solar corona. Density perturbations associated with the jet follow from empirical electron density models of the polar inter-plume and plume regions, as derived from the ground-based eclipse measurements of coronal polarization brightness. These models indicate polar plume densities 4–6 times that of the interplume low corona.

PROBABLE DETECTION OF A BRIGHT INFRARED CORONAL EMISSION LINE OF Si IX NEAR 3.93 MICRONS

Abstract: We report here the probable detection of an emission line of Si IX that was observed from an open C130 aircraft over the Pacific Ocean during the 1998 total solar eclipse. Although the IR data themselves are inconclusive because of the uncertainty in the precise central wavelengths of the narrowband filters during the eclipse, the consistency of the measured IR limb excess with simultaneous EUV emission measured by SOHO/Coronal Diagnostic Spectrometer and the EUV Imager Telescope support our detection claim. This line appears to be the brightest IR coronal line yet observed, and its existence may significantly improve future prospects for obtaining optical coronal magnetic field measurements.

Effects of a Total Solar Eclipse on the Mesoscale Atmospheric Circulation over Europe – A Model Experiment

Abstract: ¶On August the 11th, 1999 Central Europe saw a spectacular astronomical event, a total solar eclipse. We present a model study concerning the meteorological effects of this eclipse in central Europe using the state-of-the-art limited area forecast model Deutschland-Modell DM from the German Weather Service DWD. Under typical summer radiation conditions very strong anomalies in the surface energy flux and temperature in screen height are simulated. The main temperature signal in the lower troposphere is delayed by about one hour with respect to the surface. Furthermore it is connected with a well defined dynamical signal which is reminiscent to a large scale land – sea circulation. The event could be used as a test case for mesoscale atmospheric models.

Eclipse Observations of Compact Sources in the Outer Solar Corona

Abstract: We report here on high angular resolution observations of solar noise storm sources at a frequency of 75 MHz. The data for the study were obtained at the Gauribidanur Radio Observatory (long.: 77°26′12′′ E, lat.: 13°36′12′′ N) about 100 km north of Bangalore, India, during the solar eclipse of 24 October 1995. Our main conclusion is that there are structures of angular size ≤2.5 arc min in the outer solar corona.

Short-period intensity oscillations in the solar corona observed during the total solar eclipse of 26 February 1998

Abstract: Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998 Three interference filters with passbands of about 150 A and centered around 4700, 4900, and 5000 A were used The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 001–02 Hz A least-squares analysis yields 901, 252, and 69 s periods for the three prominent components which have amplitudes in the range 05–35% of the coronal brightness These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse

Ionospheric responses to a total solar eclipse deduced by the GPS beacon observations

Abstract: The total electron content (TEC) data during the total eclipse of March 9, 1997 were collected, which were observed by means of nine GPS receivers located at the eastern Asia. The responses of total TEC to the eclipse were analyzed. The results show that: 1) the eclipse led to apparent decrement in TEC that lasted for six to eight hours; 2) the maximum decrement occurred after the middle of the eclipse with time-delays varying from twenty minutes to about three hours; 3) the maximum absolute deviations of TEC on the eclipse day do not show a simple and consistent relationship to the maximum solar obscuration.

Satellite technology glimpses ionospheric response to solar eclipse

Abstract: The millennium's last solar eclipse was observed on August 11, 1999, over most of Europe, along the northeast coast of North America, and in the Near East and Middle East The eclipse was also observed by the global navigation satellite systems (GNSS), the Global Positioning System (GPS), and the Russian GNSS (GLONASS), because the transmitted signals can be used to infer the total electron content of the ionosphere Disruption of photoionization and thermospheric heating leads to numerous complex phenomena in the ionosphere Because of the supersonic speed of the Moon's cool shadow in the atmosphere, atmospheric gravity waves may be generated; these propagate upward and trace as traveling ionosphere disturbances in the ionosphere [Chimonas and Hines, 1970] Analogous to the atmospheric pressure on the Earth's surface, total electron content (TEC) can be understood as the “pressure” of the electron gas of the ionosphere, which will decrease with reduced energy input

Interpretation of the tidal residuals during the 11 July 1991 total solar eclipse

Abstract: Observations of gravity and atmospheric pressure variations during the total solar eclipse of 11 July 1991 in Mexico City are presented. An LCR-G402 gravimeter equipped with a feedback system and a digital data acquisition system scanned gravity and pressure every second around the totality. On the pressure record an oscillation, starting at the totality, with a peak to peak amplitude of 0.5 hPa and a periodicity of 40 to 50 min, can clearly be seen. This oscillation results from the thermal shock wave produced by the Moon shadow travelling at supersonic speed. At the 0.1 μGal (1 nm · s−2) level all gravity perturbations are explained by the atmospheric pressure effect.

Wind and temperature over Hyderabad during the solar eclipse of 24 Oct. 1995

Abstract: A special balloon flight was conducted jointly by National Scientific Balloon Facility of TIFR. Hyderabad, and India Meteorological Department. Hyderabad. during the solar eclipse of 24 Oct. 1995 to study the eclipse induced effects on wind and temperature profiles over Hyderabad (I7°23'N,78°29'E). The balloon went up to 37 km. Maximum cooling by almost 9-IDoC was obserVed below the tropopause at analtitude of 15.5 km (27% obscuration) and the tropopause was found to descend down by 300 m and got broadened. Changes in wind velocity were observed below the tropopause at 15.5 km.

How to protect your eyes from solar retinopathy.

Abstract: On August 11, in Belgium a solar eclipse will occur which will be total in the Southern area of the country. Although the observation of a solar eclipse is an intriguing phenomenon, inappropriate shielding from the sunlight can cause irreversible ocular lesions. Besides good absolute absorption of visible light, a blocking of ultraviolet and infrared light is equally important. In this study, four homemade sun filters were tested: a soot-blackened piece of glass, a black unexposed developed slide film, an audio-CD and a recordable CD-ROM. Also two commercially available filters were investigated: eclipse-shades and mylar foil. The soot-blackened glass and black slide film slip were highly transparent for infrared light, making them dangerous for solar observation. The recordable CD-ROM was too transparent for visible light to serve as solar filter, while the audio-CD tested absorbed enough visible, ultraviolet and infrared light to make it suitable for eclipse viewing. However, many types of audio-CD's are available making it impossible for the observer to know if a given CD is safe to use for solar viewing. Both commercially available solar filters tested had a good absolute visible light absorption, as well as an equally good absorption of ultraviolet and infrared light, making them safe for eclipse observation.

Variations in atmospheric aerosols and electrical conductivity at Roorkee during the total solar eclipse of October 1995

Abstract: Continuous measurements of some meteorological and electrical parameters in conjunction with the total solar eclipse of 24 Oct. 1995 were made from 22 to 27 Oct. 1995 at Roorkee (29 deg 52 min N, 77 deg 53 min 52 s E, 275 m above sea level). Roorkee observed 90-92 percent maximum obscurity of eclipse, as it was close to the path of totality. The event lasted from 7.10 a.m. to 9.30 a.m. IST (0140-0400 hrs GMT). Considerable increase of aerosols and positive and negative conductivities were recorded during the eclipse with respect to those made on any other day. An increase in relative humidity and a decrease in temperature were also observed during the eclipse.

Modeling study of the ionospheric effects during a total solar eclipse

Abstract: On October 24, 1995 a total solar eclipse occurred with its path cutting through the low latitude region of Asia. In this paper the ionospheric effects of this solar eclipse are investigated using a 2-D ionospheric theoretical model. The results are compared with experimental observations made by six ionosondes along the 120 degrees E meridian. Only the depression of solar EW fluxes during the eclipse has been taken into account in the calculation under the solar eclipse condition. Simulation results show that: (1) During the period of the eclipse the optical eclipse effects are quite clear at the low altitude of the ionosphere, while the responses to the eclipse are later and smaller but longer lasting at the high altitude ionosphere; (2) The lower the magnetic latitude, the stronger is the response to the solar eclipse. In low latitude region the values of f(0)F(2) on the eclipse day are lower comparing with those on the control conditions, while h(m)F(2) values are higher. (3) Near the magnetic equator there is a sharp transition in h(m)F(2) after the maximum phase, and a solar F-1.5 layer appeared; (4) After the maximum phase the effects of the eclipse lasted longer near Hainan, and a secondary depression occurred over magnetic equator. The mechanisms that may be responsible for eclipse-caused effects are discussed in the paper.

Ionospheric Responses to a Total Solar Eclipse Deduced by the GPS Beacon Observations

Abstract: The total electron content (TEC) data during the total eclipse of March 9, 1997 were collected, which were observed by means of nine GPS receivers located at the eastern Asia. The responses of total TEC to the eclipse were analyzed. The results show that: 1) the eclipse led to apparent decrement in TEC that lasted for six to eight hours; 2) the maximum decrement occurred after the middle of the eclipse with time delays varying from twenty minutes to about three hours; 3) the maximum absolute deviations of TEC on the eclipse day do not show a simple and consistent relationship to the maximum solar obscuration.

Study on “double dawn”

Abstract: The ancient record, “During the first year of King Yi, the day dawned twice at Zheng”, has provided important clues to early Chinese chronicles. The astronomical conditions and visible area distributions related to such a “double dawn” event are discussed, and the precision and current problems in the calculations of ancient astronomical phenomena are shown. On such a basis, all the solar eclipses from 1000 BC to 840 BC are calculated and their associated “double dawn” features investigated. The conclusion that the “double dawn” was a solar eclipse occurring on April 21st, 899 BC is corfirmed to be the most reasonable.

Staying safe during the eclipse. Turn your back on the sun.

Abstract: On 11 August at 11 11 am, a total solar eclipse will occur over south west England and north west France. Its path, over 100 miles wide, leads it east and south across the continent of Europe, passing from the north of France to Munich, and thence to Bucharest and the Middle East. A partial eclipse may be visible from the north of Scotland to the north of Spain and from northern Poland to southern Italy. The eclipse will occur at the height of summer, as the sun nears its zenith, over some of the most densely populated regions of the world, and thus may be followed by an even greater incidence of retinal injury than reported after other recent eclipses.1–5 There seems to be two mechanisms of retinal injury from solar radiation Viewing the sun through binoculars or telescopes produces the 10-25° temperature rise in the retina required for a …

Effect of the 1999 solar eclipse on atomic clocks

Abstract: Solar eclipses have been reported to have a strange influence on the behaviour of atomic clocks1 and pendulums2,3, which has been attributed to some unknown feature of gravity4. Here we correct this idea after being unable to detect any anomalous changes in the relative rates of three types of atomic clock, based on the ground-state hyperfine transitions of hydrogen, rubidium and caesium, during the solar eclipse of 11 August 1999 over central Europe.

Radio and the 1999 UK Total Solar Eclipse

Abstract: On the morning of the August 11th 1999, a total eclipse of the sun plunged Cornwall and parts of Devon into darkness. The event of the eclipse was bound to attract a great deal of scientific and media attention. Realizing that the differences in day-time/night-time propagation of VLF/LF/MF to HF bands would also apply during the darkness of the eclipse, the eclipse offered a rare PR opportunity to promote radio to the general public. At the same time the specific nature of the disturbance to the upper atmosphere and the effect on radio propagation could be examined in detail using scientific instruments at minimum cost since most instruments would not have to be moved. This would allow prediction models to be tested in a controlled fashion. Contained within this report are the details and results of the radio and ionospheric experiments conducted by the Rutherford Appleton Laboratory during the 1999 total solar eclipse. The promoting of the radio experiments with the general public produced nearly 60 appearances on local and national TV, newspapers and periodicals. Close to 1700 people responded to the general public medium wave experiment and 16 million people looked in on the general eclipse web site (part funded by RA) that included the details of the radio experiments. A large database of systematic observations across VLF to HF was collected from radio amateurs and from the RA Regional Offices allowing comparisons to be made with ITU estimates. There is a brief look at the scientific results and a forward look as to how the analysis of this disturbance might have impact on the use of ionospheric models for Space Weather tools in the future.