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Register a new userIonospheric response to the total solar eclipse of June 21, 2001
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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.
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This paper proposes a new method for estimating the contribution from different ionospheric regions to the response of total electron content variations to the solar flare which uses the effect of partial shadowing of the atmosphere by the terrestrial globe. The study uses GPS stations located near the boundary of the shadow on the ground in the nightside hemisphere. The beams between the satellite-borne transmitter and the receiver on the ground for these stations pass partially through the atmosphere lying in the region of total shadow and partially through the illuminated atmosphere. The analysis of the ionospheric effect of a powerful solar flare of class X5.7/3B that was recorded on July 14, 2000 (10:24 UT, N22W07) in quiet geomagnetic conditions (Dst=-10 nT) has shown that about 20% of the TEC increase correspond to the ionospheric region lying below 100 km, about 5% refer to the ionospheric E-region (100-140 km), about 30% correspond to the F1-region (140-200 km), and about 30% to regions lying above 300 km.
This paper examines the predictions made by Chinese, Muslim and Jesuit astronomers of the eclipse of 21 June 1629 in Beijing, allegedly the event that determined Emperor Chongzhens resolution to reform the calendar using the Western method. In order to establish the accuracy of these predictions, as reported at the time by the Chinese scholar and convert Xu Guangqi, we have compared them with an accurate reconstruction of the eclipse made at NASA. In contrast with current opinions, we argue that the prediction made by the Jesuits was indeed the most accurate. It was in fact instrumental in dissipating Chongzhens doubts about the need to entrust Jesuit missionaries serving at the Chinese court with the task of reforming the calendar, leading to the first important scientific collaboration between Europe and China.
We report on a search for short-period intensity variations in the green-line FeXIV 530.3 nm emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United States. Our experiment was performed with a much more sensitive detection system, and with better spatial resolution, than on previous occasions (1999 and 2001 eclipses), allowing fine details of quiet coronal loops and an active-region loop system to be seen. A guided 200-mm-aperture Schmidt-Cassegrain telescope was used with a state-of-the-art CCD camera having 16-bit intensity discrimination and a field-of-view 0.43 degree x 0.43 degree that encompassed approximately one third of the visible corona. The camera pixel size was 1.55 arcseconds, while the seeing during the eclipse enabled features of approx. 2 arcseconds (1450 km on the Sun) to be resolved. A total of 429 images were recorded during a 122.9 second portion of the totality at a frame rate of 3.49 images per second. In the analysis, we searched particularly for short-period intensity oscillations and travelling waves, since theory predicts fast-mode magneto-hydrodynamic (MHD) waves with short periods may be important in quiet coronal and active-region heating. Allowing first for various instrumental and photometric effects, we used a wavelet technique to search for periodicities in some 404 000 pixels in the frequency range 0.5-1.6 Hz (periods: 2 second to 0.6 second). We also searched for travelling waves along some 65 coronal structures. However, we found no statistically significant evidence in either. This negative result considerably refines the limit that we obtained from our previous analyses, and it indicates that future searches for short-period coronal waves may be better directed towards Doppler shifts as well as intensity oscillations.
Visible coronal structure, in particular the spatial evolution of coronal streamers, provides indirect information about solar magnetic activity and the underlying solar dynamo. Their apparent absence of structure observed during the total eclipses of throughout the Maunder Minimum has been interpreted as evidence of a significant change in the solar magnetic field from that during modern cycles. Eclipse observations available from the more recent Dalton Minimum may be able to provide further information, sunspot activity being between the levels seen during recent cycles and in the Maunder Minimum. Here, we show and examine two graphical records of the total solar eclipse on 1806 June 16, during the Dalton Minimum. These records show significant rays and streamers around an inner ring. The ring is estimated to be ~ 0.44 R_S in width and the streamers in excess of 11.88 R_S in length. In combination with records of spicules or prominences, these eclipse records visually contrast the Dalton Minimum with the Maunder Minimum in terms of their coronal structure and support the existing discussions based on the sunspot observations. These eclipse records are broadly consistent with the solar cycle phase in the modelled open solar flux and the reconstructed slow solar wind at most latitudes.
Results derived from analysing the ionosphere response to faint and bright solar flares are presented. The analysis used technology of a global detection of ionospheric effects from solar flares as developed by the authors, on the basis of phase measurements of the total electron content (TEC) in the ionosphere using an international GPS network. The essence of the method is that use is made of appropriate filtering and a coherent processing of variations in the TEC which is determined from GPS data, simultaneously for the entire set of visible GPS satellites at all stations used in the analysis. This technique is useful for identifying the ionospheric response to faint solar flares (of X-ray class C) when the variation amplitude of the TEC response to separate line-on-sight to GPS satellite is comparable to the level of background fluctuations. The dependence of the TEC variation response amplitude on the flares location on the Sun is investigated.
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