Annular Solar Eclipse Research Articles

ЭФФЕКТЫ СОЛНЕЧНОГО ЗАТМЕНИЯ 20 МАРТА 2015 Г. В ИОНОСФЕРЕ НАД ЕВРОПОЙ: РЕЗУЛЬТАТЫ ИОНОЗОНДОВЫХ НАБЛЮДЕНИЙ

ЭФФЕКТЫ СОЛНЕЧНОГО ЗАТМЕНИЯ 20 МАРТА 2015 Г. В ИОНОСФЕРЕ НАД ЕВРОПОЙ: РЕЗУЛЬТАТЫ ИОНОЗОНДОВЫХ НАБЛЮДЕНИЙ

Impact of the 15 January 2010 annular solar eclipse on the equatorial and low latitude ionosphere over the Indian region

The annular solar eclipse of 15 January 2010 over southern India was studied with a multi-instrument network consisting of magnetometer, ionosonde and GPS receivers. The presence of a counter electrojet (weakened or westward zonal electric field) during the eclipse and adjacent days suggests the strong gravitational tidal effect associated with the exceptional Sun–Moon–Earth alignment around the eclipse day. With a strong backup of magnetometer recordings on the day of eclipse, its adjacent days and the normal electrojet day, it is argued that the regular eastward electric field for the whole day at the equator was not just weakened, but actually was flipped for several hours by the influence of enhanced lunar tides. The effect of flipping the electric field was clearly seen in the equatorial ionosonde data and through the large array of GPS receivers that produced the total electron content (TEC) data. The main impact of flipping the electric field was poor feeding of equatorial ionization anomaly (EIA) due to the severely weakened fountain effect on the eclipse day, with the regular anomaly crest shifting towards the equator. The equatorial ionosonde profile was also showing an enhanced F2 region peak in spite of a reduced vertical TEC. While the plasma density depletion at the lower F region altitude over the equator was due to the temporary lack of photo-ionization, the reductions in high altitude plasma density beyond the equator were caused by the electrodynamics taking place around the eclipse. The important finding of this analysis is that the electrodynamical consequences on the low latitude ionosphere were mainly due to the combination of eclipse and lunar tides which were far more significant and influenced the EIA density rather than eclipse alone. Based on these findings, it is argued that the prevailing lunar tidal impact also needs to be taken into account while seeking to understand the electrodynamical impact of the solar eclipse on the low latitude ionosphere.

OBSERVATIONS OF THE ANNULAR ECLIPSE ON 2012 MAY 21 BY THE GENERAL PUBLIC IN JAPAN

We had a campaign of observing the annular solar eclipse on 2012 May 21 by naked eye through eclipse eyeglasses to determine the limit line of annularity. As a result, we had about 15,000 reports through our website. In addition there were many observation groups for which about 30,000 people in total participated in the observations. The overall result was that the limit we observed by naked eye through eclipse glasses coincided with a prediction that took into account the lunar limb irregularity within the error of ±500 m. This error of the limit line location corresponds to about ±200 km of the radius of the Sun.

SMILES observations of mesospheric ozone during the solar eclipse

AbstractThe Superconducting Submillimeter‐Wave Limb‐Emission Sounder (SMILES) successfully observed vertical distributions of ozone (O3) concentration in the middle atmosphere during the annular solar eclipse that occurred on 15 January 2010. In the mesosphere, where the photochemical lifetime of O3 is relatively short (approximately 100 s), altitude‐dependent changes in O3 concentration under reduced solar radiation and their temporal variations were clearly observed as a function of the eclipse obscuration. This study reports the vertical distributions of mesospheric O3 during a solar eclipse event and analyzes theoretically the eclipse‐induced changes. We show that simple analytical expressions for O3 concentration, which assume that O3 and O are in a photochemically steady state, can be used to describe the O3 concentration under reduced solar radiation. The SMILES data obtained during the eclipse provide a unique opportunity to test our current understanding of mesospheric O3 photochemistry.

Gravity wave signatures in the dip equatorial ionosphere‐thermosphere system during the annular solar eclipse of 15 January 2010

The present work pertains to the eclipse‐induced gravity wave modulations in the ionosphere‐thermosphere region over Trivandrum (8.5°N, 77°E, dip 2°N) during the annular solar eclipse of 15 January 2010. Electron density and neutral wind rocket payload measured horizontal winds and electron densities at E region altitudes, and ionosonde‐derived foF1 and foF2 parameters are used to analyze the characteristics of the eclipse‐induced gravity waves. The analysis reveals an intensification of gravity waves with periods around 30–100 min during the peak phase of the eclipse. The vertical wavelength of the prevalent wave is found to be around 2 km. The role of gravity wave‐induced winds in generating blanketing Es over the equator is also examined.

A radio determination of the time of the New Moon

Sighting and detection of the New Moon at sunset is of importance to communities based on the lunar calendar. This is traditionally undertaken with visual observations. We propose a radio method which allows a higher visibility of the Moon relative to the Sun and consequently gives us the ability to detect the Moon much closer to the Sun than is the case of visual observation. We first compare the relative brightness of the Moon and the Sun over a range of possible frequencies and find the range 5–100 GHz to be suitable. The next consideration is the atmospheric absorption/emission due to water vapour and oxygen as a function of frequency. This is particularly important since the relevant observations are near the horizon. We show that a frequency of ∼10 GHz is optimal for this programme. We have designed and constructed a telescope with a full width at half-maximum resolution of 0|$_{.}^{\circ}$|6 and low sidelobes to demonstrate the potential of this approach. At the time of the 2012 May 21 New Moon, the Sun/Moon brightness temperature ratio was 72.7 ± 2.2 in agreement with predictions from the literature when combined with the observed sunspot numbers for the day. The Moon would have been readily detectable at ∼2° from the Sun. Our observations at 16 h 36 min ut indicated that the Moon would have been at closest approach to the Sun 16 h 25 min earlier; this was the annular solar eclipse of 00 h 00 min ut on 2012 May 21.

A Case Study of How Natural Phenomena Were Justified in Medieval Science: The Situation of Annular Eclipses in Medieval Astronomy

ArgumentThe present paper is an attempt to understand how medieval astronomers working within the Ptolemaic astronomical context in which the annular eclipse is an unjustified and impossible phenomenon, could know, define, justify, and later make attempts that led to success in predicting annular solar eclipses. As a context-based study, it reviews the situation of annular eclipses with regard to the medieval hypotheses applied to the calculation of the angular diameters of the sun and the moon, which was basic for contemplating the possibility of annular eclipses. This gives the premises and the preliminary insights that were necessary to clarify the complex situation of the annular eclipse in the late medieval Islamic period and to explain the historical mechanisms leading to justifying the phenomenon during that period. This was, first due to a convincing and efficient observational evidence which, of course, was available only to a number of medieval astronomers and significantly for only a limited time period, and, second, the result of an amazing interaction amongst various astronomical traditions available to them. At a more general level, the research aims to inspect or, at least, to give some impressions of the essential conditions, i.e., identification of phenomenon, empirical evidence, and the justifying underlying tradition, under which it became possible in the tradition-based science of the `medieval period to permit a not-already-defined and tradition-opposed phenomenon to be posed and justified.

Ionospheric effects on the F region during the sunrise for the annular solar eclipse over Taiwan on 21 May 2012

Abstract. On 21 May 2012 (20:56, Universal Time; UT, on 20 May), an annular solar eclipse occurred, beginning at sunrise over southeast China and moving through Japan, sweeping across the northern Pacific Ocean, and completing its passage over the western United States at sunset on 20 May 2012 (02:49 UT, 21 May). We investigated the eclipse area in Taiwan, using an ionosonde and global positioning system (GPS) satellite measurements. The measurements of foF2, hmF2, bottomside scale height around the peak height (Hm), and slab thickness (B0) were collected at the ionosonde station at Chung-Li Observatory. In addition, we calculated the total electron content (TEC) to study the differences inside and outside the eclipse area, using 3 receivers located at Marzhu (denoted as MATZ), Hsinchu (TNML), and Henchun (HENC). The results showed that the foF2 values gradually decreased when the annularity began and reached a minimum level of approximately 2.0 MHz at 06:30 LT. The hmF2 immediately decreased and then increased during the annular eclipse period. The TEC variations also appeared to deplete in the path of the eclipse and opposite the outside passing area. Further, the rate of change of the TEC values (dTEC / dt measured for 15 min) was examined to study the wave-like fluctuations. The scale height near the F2 layer peak height (Hm) also decreased and then increased during the eclipse period. To address the effects of the annular eclipse in the topside and bottomside ionosphere, this study provides a discussion of the variations between the topside and bottomside ionospheric parameters during the eclipse period.

On Sky Brightness Variantion Caused by Annular Solar Eclipse Observed with CCD Cameras

On Sky Brightness Variantion Caused by Annular Solar Eclipse Observed with CCD Cameras

ON THE COMBINATION OF IMAGING-POLARIMETRY WITH SPECTROPOLARIMETRY OF UPPER SOLAR ATMOSPHERES DURING SOLAR ECLIPSES

We present results from imaging polarimetry (IP) of upper solar atmospheres during a total solar eclipse on 2012 November 13 and spectropolarimetry of an annular solar eclipse on 2010 January 15. This combination of techniques provides both the synoptic spatial distribution of polarization above the solar limb and spectral information on the physical mechanism producing the polarization. Using these techniques together we demonstrate that even in the transition region, the linear polarization increases with height and can exceed 20%. IP shows a relatively smooth background distribution in terms of the amplitude and direction modified by solar structures above the limb. A map of a new quantity that reflects direction departure from the background polarization supplies an effective technique to improve the contrast of this fine structure. Spectral polarimetry shows that the relative contribution to the integrated polarization over the observed passband from the spectral lines decreases with height while the contribution from the continuum increases as a general trend. We conclude that both imaging and spectral polarimetry obtained simultaneously over matched spatial and spectral domains will be fruitful for future eclipse observations.

First observational study during a solar eclipse event on variations in the horizontal winds simultaneously in the troposphere-stratosphere-mesosphere-lower-thermosphere region over the equatorial station Thumba (8.5°N, 77°E)

The longest annular solar eclipse of the millennium occurred on 15 January, 2010, and was visible over the equatorial station Thumba (8.5°N, 77°E) around noon time. A host of experiments were carried out to study the variations due to the solar eclipse event on various geophysical parameters, from the Earth’s surface to ionospheric heights. The present study focuses on the variation in the horizontal winds in the height regions of 0–65 km and 80–100 km, using GPS-sondes, rocket-sondes and meteor wind radar. The observations were made during, and after, the maximum obscuration on the day of the eclipse, as well as at the same time on a control day. The observations showed a strengthening/weakening of winds along with directional changes both in zonal and meridional winds in the selected height domains. A drastic change from easterly to westerly is observed at 98 km during, and after, the maximum phase, but, for the meridional wind, the reversal is observed only after the maximum phase. Variations due to the eclipse were also observed around the tropopause and stratopause in both wind components. However, the observed changes in winds around the tropopause and stratopause could not be attributed unambiguously to the eclipse as day-to-day wind variability is not available in these height regions. The significance of the present study lies in reporting the variations in the horizontal wind components from the ground to the 100-km height region (with a gap around 65–80 km), and the characteristics of the atmospheric waves generated due to the mid-day annular solar eclipse.

Atmospheric electric parameters and micrometeorological processes during the solar eclipse on 15 January 2010

Indian scientists got the unique opportunity to study the near‐Earth environment during a long annular solar eclipse at the end of the last long deep solar minimum, on 15 January 2010. Continuous high time resolution records of the atmospheric electric parameters and meteorological parameters were made at Tirunelveli (8.07°N, 77.08°E, 35 m Above Mean Sea Level (AMSL) and Braemore Hill (8.41°N, 76.59°E, 460 m AMSL) stations where the eclipse was during 11:07:57–15:06:52 IST with maximum obscuration (~90%) at 13:17:09 Indian Standard Time (IST). The recorded values of the parameters show marked deviations from those normally observed on control fair‐weather days. The ambient electric field underwent a large drop by up to 65% during the eclipse, and potential gradient showed epochs of enhancements during and after the eclipse until postsunset. The data also seem to reveal the long lasting paradox of conductivity enhancement during eclipse, which may be due to the eclipse induced upsurge of low winds or waves that brings high density of free space charges embedded in air parcels.

Wābkanawīʼs prediction and calculations of the annular solar eclipse of 30 January 1283

The paper presents a critical review of the iterative process used by Shams al-Dīn Muḥammad al-Wābkanawī (Iran, Maragha, ca. 1270–1320) in order to compute the annular solar eclipse of 30 January 1283 from the solar and lunar parameter values obtained by Muḥyī al-Dīn al-Maghribī (Maragha, 1260–1274). The position of this prediction in medieval astronomy will also be discussed. Wābkanawī uses an observation as evidence for the correctness of his prediction, and his results agree to a remarkable extent with modern astronomical computations of the same eclipse.

Variation of Spectral Radiance of the Zenith Sky During the Annular Eclipse on May 21, 2012

The absolute brightness of the zenith sky was measured using a simple calibrated spectrometer during the annular solar eclipse event on May 21, 2012 in Fujioka City, Japan (36.2924°N, 139.0823°E). The sensitivity of the spectrometer was calibrated as a function of wavelength between 400 and 700 nm with an integral sphere. The brightness of the sky decreased to 6 % of its usual condition at the maximum magnitude of the annular eclipse of 0.95 for all wavelengths. The curve describing the variation of sky brightness accords well with the total luminosity of the solar disk estimated by a simple model that accounts for the limb darkening effect. This study provides zenith sky radiance as a function of wavelength and solar elevation angle, which is useful for the investigation of new optical instruments for atmospheric studies.

Response of spectral characteristics of wind and temperature of atmospheric surface layer to the noontime annular solar eclipse

The influence of annular solar eclipse of 15 January 2010 on the spectral behaviour of surface layer winds and temperature has been investigated. At the peak of the eclipse, the magnitudes of spectral power of wind and the rate of dissipation of turbulent kinetic energy decreased by an order whereas, the temperature decreased by more than one order. A distinct spectral characteristic of wind components is noticed during the peak phase and for the first time, influence of surface wind speed and wind direction associated with the eclipse on the spectral characteristics of wind components has been investigated.

Drastic variation in the surface boundary layer parameters over Cochin during the annular solar eclipse: Analysis using sonic anemometer data

Atmospheric surface boundary layer parameters vary anomalously in response to the occurrence of annular solar eclipse on 15th January 2010 over Cochin. It was the longest annular solar eclipse occurred over South India with high intensity. As it occurred during the noon hours, it is considered to be much more significant because of its effects in all the regions of atmosphere including ionosphere. Since the insolation is the main driving factor responsible for the anomalous changes occurred in the surface layer due to annular solar eclipse, occurred on 15th January 2010, that played very important role in understanding dynamics of the atmosphere during the eclipse period because of its coincidence with the noon time. The Sonic anemometer is able to give data of zonal, meridional and vertical wind as well as the air temperature at a temporal resolution of 1s. Different surface boundary layer parameters and turbulent fluxes were computed by the application of eddy correlation technique using the high resolution station data. The surface boundary layer parameters that are computed using the sonic anemometer data during the period are momentum flux, sensible heat flux, turbulent kinetic energy, frictional velocity (u⁎), variance of temperature, variances of u, v and w wind. In order to compare the results, a control run has been done using the data of previous day as well as next day. It is noted that over the specified time period of annular solar eclipse, all the above stated surface boundary layer parameters vary anomalously when compared with the control run. From the observations we could note that momentum flux was 0.1Nm−2 instead of the mean value 0.2Nm-2 when there was eclipse. Sensible heat flux anomalously decreases to 50Nm−2 instead of the mean value 200Nm−2 at the time of solar eclipse. The turbulent kinetic energy decreases to 0.2m2s−2 from the mean value 1m2s−2. The frictional velocity value decreases to 0.05ms−1 instead of the mean value 0.2ms−1. The present study aimed at understanding the dynamics of surface layer in response to the annular solar eclipse over a tropical coastal station, occurred during the noon hours. Key words: annular solar eclipse, surface boundary layer, sonic anemometer

Delayed effects of annular solar eclipse of 15 January 2010 on the tropospheric and lower stratospheric winds along the eclipse path

The annular solar eclipse of 15th January 2010, which was the longest solar eclipse of the millennia, was visible at several parts of South India and China. A host of experiments were carried out at Thumba (8.5° N, 76.9°E) and Gadanki (13.51° N, 79.21° E) in India to study the effect of annular solar eclipse on various atmospheric processes taking place right from surface layer to Ionosphere as the maximum obscuration of the Sun took place during the peak noon hours. Many of the studies reported from these experiments focused on the effect of annular solar eclipse on the geophysical parameters and their variability during the maximum phase of the eclipse. However, there were no efforts to study the delayed effects of the annular solar eclipse on the geophysical parameters. In this regard, the present study discuss the delayed effect (~4hours after the maximum phase of the eclipse) of annular solar eclipse of 15th January 2010 on the troposphere and lower stratosphere winds over the eight geographical locations along the eclipse path [Thumba, Qingdao (36.06° N, 120.33°E), Zhengzhoes (34.71° N, 113.65°E), Enshi (30.28° N, 109.46°E), Chongqing (29.51° N, 106.48°E), Sheyang (33.76° N, 120.25°E), Fuyang (32.86° N, 115.73°E) and Weining (26.86° N, 104.28°E)]. The regular meteorological soundings over these eight locations at 12 UTC are utilized for the present study. The important difference between the observations over Thumba and other latitudes is the local time of occurrence of maximum phase of the eclipse. Over the Thumba the maximum phase of the annular eclipse observed in the mid-day whereas it is observed during the sunset hours over other latitudes. The analysis revealed that significant changes in zonal and meridional winds occurred only over Thumba, but not showed any significant changes over the other latitudes. The results are discussed in the light of present understanding of the eclipse induced atmospheric perturbations.

The equatorial ionospheric response over Tirunelveli to the 15 January 2010 annular solar eclipse: observations

Abstract. In this paper we present a case study of the annular solar eclipse effects on the ionization of E and F regions of equatorial ionosphere over Tirunelveli [77.8° E, 8.7° N, dip 0.4° N] by means of digital ionosonde on 15 January 2010. The maximum obscuration of the eclipse at this station was 84% and it occurred in the afternoon. The E and F1 layers of the ionosphere showed very clear decrease in their electron concentrations, whereas the F2 layer did not show appreciable changes. A reduction of 30% was observed in the foF1 during the maximum phase of the eclipse. During the beginning phase of the eclipse, an enhancement of 0.97 MHz was observed in the foF2 as compared to that of the control days. But the foF2 decreased gradually as the eclipse progressed and a decrease of 0.59 MHz was observed towards the end phase of the eclipse. Observed variations in the h'F2 and hmF2 showed lower values than the control days, although hmF2 was found to increase a bit during the eclipse. Observed variability in the E, F1 and F2 layer ionospheric parameters on the eclipse day and their departure from the control days are discussed as the combined effect of annular eclipse and presence of counter equatorial electrojet (CEEJ).

First ever VLF monitoring of the lunar occultation of a solar flare during the 2010 annular solar eclipse and its effects on the D-region electron density profile

A ground based Very Low Frequency (VLF) radio receiver of Indian Centre for Space Physics located at Khukurdaha (22°27′N, 87°45′E) monitored the VLF signal at 19.8kHz from the NWC station during a partial solar eclipse (maximum obscuration 75%) which took place on January 15, 2010. The receiver and the transmitter were on two opposite sides of the annular eclipse belt. During the same period, a solar flare also occurred and it was partly blocked by the lunar disk. Thus the resultant signal was perturbed both by the eclipse and by the flare. The deviation of the signal from the normal value was obtained by subtracting from the average diurnal signal on days bracketing the eclipse. The deviation was analysed. We compare the data from GOES-14, HINODE and RHESSI satellites during the event. We got a clear depression in the data during the period of the partial eclipse. Most interestingly, there was also a flaring activity in the sun which reached its peak (C-type) just after the time when the eclipse was near maximum. By superposing the lunar disk on the image obtained by HINODE mission, we pin-point the time frame of blocking hard and soft X-rays. We extract the time variation of the electron density profile in the D-region of the ionosphere due to occulted solar flare from the combined effect of the eclipse and the flare. We also compare the results with a normal solar flare.

Transient land breeze: Eclipse induced wind flow modifications—Observations over plant canopy

An experiment is conducted over Cassava plant canopy at a coastal station at CTCRI, Thiruvananthapuram (8°29'N, 76°59E) to study the response of meteorological parameters and land–sea breeze circulations to the annular solar eclipse on January 15, 2010. Observations reveal decrease of solar radiation to a minimum of 96Wm−2 during the peak eclipse period. Air temperature drops by 4°C and relative humidity increases by 20%. Sensible heat flux reduces to zero. Transient land breeze occurs for a few minutes with a time lag of about 1h possibly due to outflow from the umbra region or temperature gradient over land with the eclipse progressing in the eastward direction. Sea breeze is delayed by about 3h on the next day of eclipse. Spectral energy density of wind (u, v, w) and temperature attains a minimum value during totality and increases later, attributable to reduction in turbulence due to eclipse-induced stability.