Showing papers on "Solar eclipse published in 1986"

Observations of the May 30, 1984, annular solar eclipse at Millstone Hill

Abstract: The Millstone Hill incoherent scatter radar was operated on May 30, 1984, to gather data on the effects of the annular solar eclipse on the structure and dynamics of the earth's ionosphere and thermosphere. Maximum obscuration of 86% was experienced at Millstone Hill at 1700 UT, and there was only low magnetic activity coincident with the event. The observations, which were made using both the zenith-fixed and the steerable antenna at Millstone Hill, indicated a drop of 60% in electron density shortly after peak obscuration time in the altitude region 130–250 km and a smaller decrease (15–30%) at higher altitudes. The electron temperature was found to decrease by 500–700 K in the F region during the eclipse, and relatively little variation was observed in the ion or neutral temperature. The measured three-dimensional ion drifts in the F region were synthesized in terms of a meridional wind velocity of about 25 m/s northward at eclipse time, which represents a drop of 40–50 m/s from conditions prior to the eclipse. Electric field strengths were less than 1 mV/m and showed the same general pattern as quiet time fields at Millstone Hill. Comparisons with predictions of the neutral atmospheric response made for this eclipse by the NCAR thermospheric general circulation model (TGCM) and of the ionospheric response made by the NCAR ionospheric model indicate good agreement below 250 km for the electron density and temperature; at higher altitudes the predictions and observations can be reconciled when the effects of heat and ionization flux are taken into account for the boundary condition in the ionospheric model. The predicted neutral winds are within a factor of 2 of the measurements, but it is difficult to ascertain reliably from the data the magnitude of the perturbation fields converging onto the eclipse path.

Ionospheric and thermospheric response over Millstone Hill to the May 30, 1984, annular solar eclipse

Abstract: The National Center for Atmospheric Research (NCAR) thermospheric general circulation model (TGCM) is used to calculate the time-dependent thermospheric response to the May 30, 1984, annular solar eclipse. The path of maximum obscurity begins at sunrise in the Pacific Ocean near 2°N and 135°W. It moves northeastward, passing across central Mexico, the eastern United States, and then the Atlantic before ending near 28°N and 4°E in Algeria. The area of the partial shadow is relatively large, and the total solar flux incident on the dayside of the earth is decreased by about 6% during the eclipse. The TGCM calculates the time-dependent response of the winds, temperature, and the mass mixing ratios of the major constituents throughout the thermosphere. Perturbations follow the path of the annular eclipse, with maximum deviations occurring near 1700 UT at about 300 km for the temperature and at higher altitudes for the winds and composition. The perturbation winds converge from all directions toward the shadow at speeds reaching 75 m s−1 in the upper thermosphere. The maximum temperature anomaly (−55 K) and vertical wind anomaly (−7 m s−1) occur near the center of the shadow. At a constant altitude of 300 km, both the N2 density and the O density decrease by about 10% and 6%, respectively. The path of maximum obscuration passes within 3° of latitude of the incoherent scatter radar at Millstone Hill, Massachusetts (42.6°N, 71.5°W). The station experiences a maximum solar obscuration of 86% at 1700 UT (1200 LT). A time-dependent one-dimensional numerical model of the ionosphere that uses the TGCM-calculated winds, temperature, and composition at Millstone Hill is used to calculate the electron and ion densities and temperatures and the densities of the odd-nitrogen species NO, N(4S), and N(²D) during the eclipse. The calculated electron density decreases by about factors of 2 in the F region, 4 in the F1 region, and 3 in the E region compared to a similar control run without an eclipse. The F1 region emerges during the eclipse with an increase in the NO+/O+ ratio. The calculated electron temperature decreases by 460 K during the eclipse but then increases 200 K following the eclipse because of the intense solar heating in a region of reduced electron densities. The calculated ion temperature generally follows the changes in neutral temperature. The calculated thermospheric and ionospheric responses agree well with measurements made by the Millstone Hill incoherent scatter radar.

The post flare loops observed at the total eclipse of February 16, 1980

Abstract: A post flare loop system was observed on the west limb at the total solar eclipse of February 16, 1980 in Kenya. Analyzing the monochromatic images and the flash spectra, we obtained the following results: (1) the lower part of the post flare loop system is characterized mainly by distinct cool loops of Hα and Fe x 6374. Fe x 6374 emitting plasma (T e = 1.0 × 106 K) is highly concentrated in the loops. The 6374 loops are broader in diameter and located very close to but a little higher than the corresponding Hα loops. The electron densities of the dense part in Hα and Fe x 6374 loops are 1011 cm-3 and 6 × 109cm-3, respectively; (2) the Ca xv emitting region (3.5 × 106 K) is confined to the upper part of the post flare loops. The electron density of this hot region is estimated as 8 × 109 cm-3 from the Ca xv line intensity ratio, I(λ5694)I(λ5445). These observational results led us to construct an empirical model of the post flare loop system which is consistent with the reconnection model of Kopp and Pneuman (1976).

Effect of solar eclipse on the behavior of a captive group of chimpanzees (Pan troglodytes).

Abstract: A captive group of chimpanzees, housed in an outdoor compound at the Yerkes Regional Primate Research Center, was observed during the annular solar eclipse of May 30, 1984 The behavior of each animal was recorded using an instantaneous scan-sampling technique (Altmann: Behaviour 49:227–265, 1974) Beginning 2 days prior to the eclipse and continuing through the day following the eclipse, data were collected from 1100 to 1300 hours daily At 1214 hours on the day of the eclipse, when the sky began to darken and the temperature began to decrease, solitary females and females with infants moved to the top of a climbing structure As the eclipse progressed, additional chimpanzees began to congregate on the climbing structure and to orient their bodies in the direction of the sun and moon At 1223 hours, during the period of maximum eclipse, the animals continued to orient their bodies toward the sun and moon and to turn their faces upward One juvenile stood upright and gestured in the direction of the sun and moon Sunlight began to increase at 1225 hours, and as it became brighter, the animals began to descend from the climbing structure The behaviors exhibited by the group during the period of maximum eclipse were not observed prior to or following the eclipse nor as darkness approached at normal, daily sunset These data indicate that a solar eclipse, a rare and uncommon environmental event, can influence and modulate the behavior of chimpanzees

Absorption of radio waves during a solar eclipse

Abstract: In this paper, the results of our observations on Al-method ionospheric absorption of radio waves on 1.8 and 2.2 MHz during the solar eclipse of 16 February 1980 are presented. The absorption decreased by about 41% and 46% of the normal value respectively at the above two frequencies at Ahmedabad following the maximum phase of the eclipse (about 77% of full disc) with a delay of 18 minutes. The quantityAT(f) which is a measure of eN vdh is now examined for better clarity of the influence of the changes in theE-layer. The results are discussed in relation to the observations of the ionizing radiations from the sun, changes in the electron density, recombination rate and absorption in the underlyingD andE regions.

Solar chromospheric modeling based on submillimeter limb brightness profile

Abstract: A method of modeling the solar chromosphere is developed, based on submillimeter continuum observations of the solar limb. Submillimeter radiation from the solar limb emanates from the chromosphere in local thermodynamic equilibrium, making it an important chromospheric diagnostic. Also, the use of high-resolution limb profiles allows for atmospheric modeling independent of gravitational hydrostatic equilibrium. The chromospheric model is constructed to match high-resolution solar limb profiles at 30, 50, 100, and 200 microns, determined by an occultation of the solar limb observed from the Kuiper Airborne Observatory during the total solar eclipse of July 31, 1981. This matching is achieved by 'stretching' the solar model atmosphere of Vernazza, Avrett, and Loesser (1981) vertically out of hydrostatic equilibrium, while maintainingn its vertical temperature-optical depth profile.

Millstone Hill measurements and TGCM simulation for the 30 May 1984 annular solar eclipse

Abstract: On 30 May 1984, the Millstone Hill incoherent scatter radar was operated to gather data on the effects of the annular solar eclipse on the structure and dynamics of the ionosphere and thermosphere. The eclipse path was about 3 deg. south of Millstone which experienced a maximum obscuration of 86% at about 1705 UT. Both the zenith steerable antennas at Millstone were used in the experiment to collect data on the temporal evolution of the eclipse effects. This experiment represented the first opportunity at Millstone to collect data during an eclipse in the absence of a major magnetospheric disturbance which had previously made the unravelling of eclipse effects difficult. In addition, the configuration of the experiment and analysis of the data included a detailed examination of the effects on the neutral atmosphere. A major catalyst for this study was the opportunity to compare the results with the predictions made from the Thermospheric General Circulation Model (TGCM) at NCAR, as a calibration point for the model. The Arecibo and Sondrestrom radars also participated as part of a radar chain experiment. The analysis of the data from these stations is in progress; the initial results from Millstone Hill are presented.

The effect on the geomagnetic field of the total solar eclipse in papua new guinea

Abstract: The effect on geomagnetic field of the total solar eclipse was observed at Port Moresby, PAPUA NEW GUINEA during the total solar eclipse on June 11, 1983The eclipse effect is distinct by the eliminated the normal daily variation and disturbed variation of the eclipse day The results indicate that the decrease of the horizontal intensity ( - 36 ± 12nT), the deviate eastward of the declination (06'±01'E) and the increase of the vertical intensity (50 ± 11 nT) It's confirmed the magnitude change in intensity and direction of geomagnetic field due to solar eclipse depends on the degree and the duration time of totality, the high of altitude of sun (that is the local time of the solar eclipse occurrence) and seasons

Slowly varying local solar decameter sources

Abstract: Local sources of the slowly varying component of solar radio emission have been observed at centimeter and decimeter wavelengths, and (less reliably so) in the meter-wave band. Claims have been made by several authors (Kundu et al., 1977; Sastry et al., 1983) that slowly varying decameter sources have been recorded. However, analyses of the solar radio emission data taken between l973 and l976 with the UTR-2 antenna at the Ukrainian Radiophysics Institute (and including the emissions during the solar eclipse on April 29, l976) indicated that both the emergence of the source on the sun and the rise in solar brightness temperature after the burst were not due to a slowly varying component. 6 references.

The highest geoactivity in 1981 and its source on the Sun

Abstract: On observe que des trous coronaux sporadiques, a basse latitude (observes durant l'eclipse du 31 juillet 1981) sont a l'origine d'une activite geomagnetique particulierement elevee

Coronal structure observed at the total solar eclipse of 11 june, 1983 in indonesia*

Abstract: From the photographs taken at the total solar eclipse of 11 June 1983, we derived the electron density for the north polar rays and for the thread-like fine structures above the active region, which are 108 at 1.4 solar radii and 3 × 109 at 1.15 solar radii, respectively. The brightness distributions of the corona at the polar region and above the active region, and the flattening index were also derived.

Present and future of astronomical science at Gadjah Mada University, Central Java, Indonesia

Abstract: Reasons for the growth of interest in astrophysics and astronomy are discussed. The two main reasons are firstly the solar eclipse of June 1983 and secondly publicity given to the regular N.A.S.A. shuttle flights. However, radioastronomy will develop much faster than optical astronomy because the site requirements are much less stringent than for optical astronomy and the technical infrastructure is readily available.

Analysis of an elongated narrow coronal streamer observed at the 1973 solar eclipse

Abstract: A detailed photometric analysis has been made of a narrow elongated coronal streamer observed at the 1973 total eclipse After deriving real intensity distributions, the electron density has been deduced under the assumption that the distribution is axially symmetric and that the decrease in density from the central axis follows the gaussian law The results show that the gradient of the electron density is much steeper at the lower part, nearest to the solar limb, than those reported previously for larger scale streamers