# Total solar eclipse of July 22, 2009: Its impact on the total electron content and ionospheric electron density in the Indian zone (2023)

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## Journal of Atmospheric and Solar-Terrestrial Physics

Volume 72, Issue 18,

December 2010

, Pages 1387-1392

(Video) Global Positioning System (GPS) and its Application in Atmospheric (Part 1)

## Abstract

The longest total solar eclipse during the 21st century occurred in South and East Asia on July 22, 2009. Ionospheric response to this rare total solar eclipse which was observed right from the time of sunrise in the Indian zone, has been studied in terms of the total electron content (TEC) obtained from three global positioning system (GPS) receivers located at Udaipur, Hyderabad and Bengaluru, and electron density obtained using space based GPS-Radio Occultation technique. The study reveals significant reductions in the electron density and TEC that persisted up to 2h past the last contact even during early morning eclipse. These observations imply that during the early morning eclipse, the production and loss of ionization dominate over the plasma transport processes.

### Research Highlights

► Studies during rare sunrise time total solar eclipse from Indian zone presented. ► 40–50% reduction in TEC has been observed even during early morning eclipse. ► During early morning eclipse production and loss processes dominant. ► Electron density profile shows maximum reduction between 300 and 400km altitude. ► Up to 70% reduction in electron density has been observed.

## Introduction

Solar eclipse is one of the important solar terrestrial events which has a direct impact on earth’s ionosphere. During solar eclipse, the amount of solar radiation reaching the earth diminishes, which results in reduced production of plasma. Hence, compared to a normal day, the loss rate of plasma on an eclipse day dominates over the production rate. Thus, during the solar eclipse, lower electron density in the ionosphere is expected. Works by Chandra et al., 1980, Chandra et al., 1981, Chandra et al., 1997, Vyas et al. (1997) and Boitman et al. (1999) for example, show decrease in ionospheric electron density during the solar eclipses. Theoretical investigations of the effects of the eclipse on ionospheric E and F regions were made by Rishbeth (1968). Since the total electron content (TEC) is the measure of integrated electron density, major variations in electron density are expected to be reflected in the TEC. Earlier works (Yeh et al., 1997, Afraimovich et al., 1998, Huang et al., 1999, Tsai and Liu, 1999, Jakowski et al., 2008, Krankowski et al., 2008) have reported that the TEC started decreasing, after the commencement of partial eclipse and reached a minimum value, around 30min to 2h from the time of maximum obscuration. This delay has been interpreted as an indicator of the combined effect of the photochemical processes and plasma dynamics in equatorial and anomaly crest regions. Additionally, Afraimovich et al., 1998 suggested that the depression in TEC growth during the eclipse is almost independent of longitude and latitude (within the observation ranges 52°±6°N and 104°±11°E). But during the total solar eclipses of October 24, 1995 and March 9, 1997 (Tsai and Liu, 1999), it was found that the decrease in the TEC is dependent on the geomagnetic latitude and that the fountain effect plays a significant role in the low latitudes. Recently, Le et al. (2009) have also reported a detailed observational and modelling study concerning the latitudinal effect of eclipses on various ionospheric parameters including the TEC. For the annular solar eclipse of October 3, 2005, Krankowski et al. (2008) reported that the ionospheric response in terms of TEC depends upon latitude as well as longitude.

Studies concerning eclipse induced effects on the ionosphere are important mainly due to the fact that the processes that control the ionosphere are extremely complex and hence provide an opportunity to understand the behaviour of the system as a whole. Since the atmospheric system supports multiple processes and what one sees is always a resultant of the multiple forcings, investigating phenomena like solar eclipse at different times and epochs could give clues to the relative importance of the respective processes and their dependence on time and the epoch. Total solar eclipse is a rare event, with each eclipse occurring at different hours of the day, study of the impact of every eclipse on the ionosphere is desirable. In this context, the eclipse of July 22, 2009 was rarest of the rare event, as the eclipse was observable right from the sunrise in the Indian zone. In fact, it was an eclipsed sun that rose on the day. To the best of our knowledge, during the past 50 year’s period, the eclipse of July 22 is the only total solar eclipse that occurred right from the sunrise in the region. Since studies relating to the changes in TEC and electron density profile during eclipses virtually do not exist in the Indian region, such a study for the eclipse of July 22, 2009 has been undertaken. The TEC has been computed from the time delay measurements of the signals emitted by the GPS satellites which provide a wide spatial and temporal coverage, not attempted earlier in the region. These results have been supplemented by simultaneous electron density measurements made using the GPS-RO technique and are being reported for the first time during an eclipse. Hence, the main aim of this paper is to evaluate the effect of solar eclipse at three different geographic latitudes in the longitude zone (75°±4°E) having different obscuration rates. The location of ground stations and the passes of the GPS satellite enabled us to cover a vast ionospheric region in time domain as well, from geomagnetic equator to and beyond the crest of the equatorial ionization anomaly, which is known to be highly variable and is a seat of a number of ionospheric processes. Significantly, in spite of these variabilities, eclipse induced changes in the ionospheric parameters, like electron density and TEC could be detected which were discernible over and above the statistical variations. Another note worthy feature of the present studies is the assessment of the impact of eclipse on the electron density profile over a wide range of altitudes. This study would also provide crucial information on signal delays, in case of rare events like solar eclipses, used for continuous and smooth operation of satellite based navigation systems.

## Solar eclipse path over Indian zone

The total solar eclipse of July 22, 2009, occurred with its path of totality passing over India, Nepal, Bhutan, China and part of North Pacific Ocean and it ended in South Pacific Ocean. The first contact of the totality path occurred in the Arabian Sea at the west coast of Gujarat state in India, with geographic coordinates 20.35°±1°N, 70.52°±0.25°E, at 0000UT. The eclipse attained totality at about 0053UT in the Indian region. The duration of the totality was 3min 12s at the western most

## Results and discussion

Compared to the earlier total solar eclipses, the total solar eclipse of July 22, 2009 was a rare event, characterized by its time of onset. As stated earlier, the eclipse was observable right from the sunrise in the Indian zone. In fact, it was an eclipsed sun that rose on the day as could be seen from Table 1 which also gives the time of sunrise at a few Indian locations. The first contact of the solar eclipse of July 22, 2009 occurred around 0000UT in the Indian zone and its time of last

## Acknowledgements

The GSV 4004A GPS receiver at Udaipur was purchased through the grants from the University Grants Commission, New Delhi under the DRS-SAP and X plan. This work is partially supported under the ISRO-RESPOND program. Shweta Sharma is thankful to the UGC for the UGC-NET-SRF fellowship. RINEX data for HYDE, Hyderabad and IISC, Bengaluru station were downloaded from the IGS site ftp://garner.ucsd.edu. The GPS-RO data was downloaded from the site http://cosmic-io.cosmic.ucar.edu/cdaac/.

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(Video) Let's Look Behind a Real Human Liver

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## Cited by (24)

• Effect of 21 June 2020 solar eclipse on the ionosphere using VLF and GPS observations and modeling

A solar eclipse event provides a great opportunity to examine the behavioral concept of the ionospheric electron density (Ne) variability in the low latitude region. The current work presents our outcomes from the simultaneous assessment of Tweeks (radio atmospherics) and radio signals (fixed frequency of the transmitter's signal) from multifarious VLF transmitters observed at Varanasi (Geog. Lat. 25.270N, Geog. Long. 82.980 E, Geomag. Lat. 140 55′N). To find the presence of disturbances in the ionosphere Global Positioning System (GPS) data at Hyderabad (geog. lat. 170 20/ N, long. 780 30/ E) and Bangalore (geog. lat. 120 58/ N, long. 770 33/ E) is also analyzed during the period of the solar eclipse on 21 June 2020. As the Sun was eclipsed, the nighttime phenomenon of ‘Tweeks' was also observed in the daytime through the annular solar eclipse due to nighttime conditions as the solar disc was dusked. Tweek analysis shows the variation in the ionospheric reflection heights (∼8–11km) and electron density (∼3–2cm−3) in the D-region during the eclipse. The reflection height of the D-region ionosphere increases from∼84km and goes to∼95km and then decreases to∼87km. Electron concentration (electron density) decreased throughout the eclipse from 24cm−3 to 21cm−3 and then increases to 23cm−3. Eclipse-imposed modifications in VLF transmitter’s (HWU and NWC) signals displays an average change (decrease) of 2.8dB and 0.8dB in the signal strength of 18.3kHz (HWU) and 19.8kHz (NWC) transmitters respectively and a rise in virtual reference height (H′) and sharpness factor (β), as compared with normal days. The de-trended value of total electron content (DTEC) variations at both stations clearly shows the presence of travelling ionospheric disturbances (TIDs) having wave-like features. The Fast Fourier Transform (FFT) analysis shows that periodicity at both the station lies in two regimes one belongs to a period between 20 and 50min and the other belongs to 50–90min indicating such oscillation observed in the ionosphere are induced by atmospheric gravity waves (AGWs) generated during the period of the solar eclipse.

• A study on TEC reduction during the tail phase of the 21st June 2020 annular solar eclipse

Ionospheric response during the annular solar eclipse of June 21, 2020, has been examined in terms of the Total Electron Content (TEC) obtained from six Global Positioning System (GPS) receivers positioned in the Chinese-Taiwanese region. We have shown TEC variation from satellites designated by PRNs (Pseudo-Random Noise code) 2, 6, and 19. PRN wise TEC trend was observed to depend upon satellite-pass trajectory to the receiver's location during the eclipse period. A time lag of ~15–30min is also observed in maximum TEC decrement after the phase of maximum eclipse. Instead of the percentage of eclipse magnitude, a reduction in TEC is seen more for the station for which the orbital track of respective satellites was in closer view relative to receivers for more hours of eclipse window. Additionally, the eclipse day diurnal variations are compared with the pre-eclipse day TEC trend, and observed results show a clear decrease in TEC values at all chosen stations after the eclipse onset then reached the lowest value a few minutes afterward the maximum eclipse phase.

• The investigation of ionospheric response to total eclipses on 29th March, 2006 and on 20th March, 2015 based on HF oblique sounding data

2016, Journal of Atmospheric and Solar-Terrestrial Physics

Citation Excerpt :

Actually during solar eclipse phenomenon the electron density depletion in the whole thickness of the ionosphere is observed (Farges et al., 2003; Sharma et al., 2010; Singh et al., 2012); the decreasing of TEC (Sharma et al., 2010; Kumar and Singh, 2012; Vyas and Sunda, 2012), of electron temperature, changing of ion drift velocity and ion drift direction at F-layer altitude are also occurred (Farges et al., 2003). As a rule there is a delay between eclipse phase and the following ionospheric response (Farges et al., 2001; Jakowski et al., 2008; Sharma et al., 2010; Phanikumar et al., 2014). As the result of movement of the moon shadow in the Earth's atmosphere, acoustic-gravity waves and their ionospheric response (traveling ionospheric disturbances) occur (Altadill et al., 2001).

The investigation of ionosphere response to solar eclipses was carried out. Maximum observable frequencies were analyzed during two eclipses on 29th March, 2006 and on 20th March, 2015 on several oblique sounding paths which were within the range of solar flux obscuration. The model describing local changes in the ionosphere, caused by the obscuration of solar flux during eclipse, is suggested. The computer simulation of HF radiowave propagation during the eclipses was carried out on the basis of this model, while quiet ionosphere was described by IRI-2012 model. It is shown that this approach gives adequate description of HF channel during eclipses for all propagation paths under consideration while the parameters of the model were the same for all paths. As the result of computer simulation time delays of ionosperic responses during eclipses were obtained (~1800–2000s). It was found that maximum depletion of electron concentration reached 85% in D-region for both eclipses. The electron density depletions at height of F2-peak were 48% and 34% for eclipse on 29th March, 2006 and on 20th March, 2015 respectively.

(Video) Outer space

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

2015, Journal of Atmospheric and Solar-Terrestrial Physics

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.

• Time constants in the ionosphere from neural network models

Neural network (NN) models for the low latitude and the polar ionosphere from the D- to the F-region were developed which are based on incoherent scatter radar data from Arecibo and EISCAT Svalbard, respectively. The various geophysical input parameters defining the NN are not only the ones that represent the time one wants to predict, but also the geophysical conditions prior to the time of the prediction. The optimum length of these preceding periods are derived for the two models are different, but a period of 60days is a compromise acceptable for both latitudes. Furthermore from the Arecibo data time constants of electron density decay after sundown are derived which – arguably – are also relevant elsewhere, including the polar latitudes. Whereas at all altitudes the electron densities decay exponentially after sundown, below 300km there is an additional variation with solar zenith angle.

• Response of low latitude D-region ionosphere to the total solar eclipse of 22 July 2009 deduced from ELF/VLF analysis

Citation Excerpt :

Solar eclipse is one of the important events for ionospheric research because it has direct influence on the Earth’s ionosphere. During the period of solar eclipse, the amount of solar radiation reaching the Earth is reduced due to Moon’s shadow resulting in the less production of the plasma while the loss processes remains unaffected (Sharma et al., 2010). Hence loss rate of plasma on the eclipse day dominates over the production rate, in comparison to normal quiet day.

Response of the D-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (Geog. lat., 25.27° N; Geog. long., 82.98° E; Geomag. lat.=14° 55’ N) was investigated using ELF/VLF radio signal. Tweeks, a naturally occurring VLF signal and radio signals from various VLF navigational transmitters are first time used simultaneously to study the effect of total solar eclipse (TSE). Tweeks occurrence is a nighttime phenomena but the obscuration of solar disc during TSE in early morning leads to tweek occurrence. The changes in D-region ionospheric VLF reflection heights (h) and electron density (ne: 22.6–24.6cm−3) during eclipse have been estimated from tweek analysis. The reflection height increased from ∼89km from the first occurrence of tweek to about ∼93km at the totality and then decreased to ∼88km at the end of the eclipse, suggesting significant increase in tweek reflection height of about 5.5km during the eclipse. The reflection heights at the time of totality during TSE are found to be less by 2–3km as compared to the usual nighttime tweek reflection heights. This is due to partial nighttime condition created by TSE. A significant increase of 3dB in the strength of the amplitude of VLF signal of 22.2kHz transmitted from JJI-Japan is observed around the time of the total solar eclipse (TSE) as compared to a normal day. The modeled electron density height profile of the lower ionosphere depicts linear variation in the electron density with respect to solar radiation as observed by tweek analysis also. These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days.

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