Eclipse Day Research Articles

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

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.

In-situ measurements of vertical structure of ozone during the solar eclipse of 15 January 2010

Sudden blockage of the solar radiation during the eclipse leads to both prompt and delayed effects on both the stratospheric and the tropospheric ozone. In this paper we present the in-situ measurements of vertical distribution of ozone made by ozonesondes during the annular solar eclipse of January 15, 2010 from Thiruvananthapuram (8.53°N, 76.87°E). Concurrent measurement of various atmospheric parameters, columnar ozone and UV radiation were also made from ground. The column ozone showed a large decrease matching well with the maximum phase of the eclipse. A systematic decrease in the ozone concentration observed in the stratosphere. A formation of double mixed layer inversion was also observed at ∼2km on the eclipse day. The eclipse was manifested from the space and captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellites.

Effect of the annular solar eclipse of 15 January 2010 on the low latitude mesosphere

In the present study, we mainly tested two existing hypotheses linked with the solar eclipse effect on the middle atmosphere. One is on the VHF radar mesospheric echo occurrence characteristics and another on the wave generation and propagation. Significant reduction in the echo occurrence is found during the maximum epoch of the eclipse as expected. Estimations on D-region electron density during the eclipse day and on a normal day are also made. High frequency gravity waves (30min–1h) in the vicinity of the eclipse path are detected in the troposphere and mesosphere, which is not expected.

Gravity waves and spreadEsobserved during the solar eclipse of 22 July 2009

[1] During the total solar eclipse of 22 July 2009, two ground-based high-frequency radio systems were applied to observe the ionospheric variations over Wuhan, China. The ionosonde recorded ionograms every 5 min; the Wuhan Ionospheric Oblique Backscattering Sounding System recorded echo range and Doppler every 1 min. Comparing the observations of the two radio systems, we found that the periodic fluctuation on the top penetration frequency of regular Es (fEs) and on the Doppler velocity of the spread Es appeared and disappeared simultaneously on the eclipse day. Moreover, wavelet analysis results show that the fEs curve and the Doppler velocity of the spread Es contain the same period of ∼35 min. The spread Es occurred owing to the off-vertical reflections from the tilted layer at the Es latitude. Atmospheric gravity waves are considered to be generated during the solar eclipse and propagate upward to deform the Es layer and produce the moving wave-like structures in the layer. The tilted plasma concentration in the moving wave-like structures induced the off-vertical HF radiowave reflections and added the Doppler modulation of also ∼35 min period on the reflected radiowave. Furthermore, the Doppler values of regular Es indicate that the layer at lower altitude was weakly disturbed and the layer at higher altitude was deeply modulated, which is in agreement with the theory that the amplitude of gravity waves increases with height.

Effect of January 15, 2010 annular solar eclipse on meteorological parameters over Goa, India

Atmospheric perturbations due to the annular solar eclipse were monitored to understand its influence on the meteorological parameters from surface to the lower stratosphere. A strong inversion at 13 km and an abnormal warming in the upper troposphere were noticed on the eclipse day. A decrease in tropopause height associated with increase in temperature caused anomalous warming. Considerable attenuation of incoming solar radiation resulted in abrupt increase of air temperature during the next 24 h followed by sharp decrease in relative humidity. The time lag is attributed to the distance from the totality and the response time between tropopause and surface layer.

Temperature perturbations in the troposphere-stratosphere over Thumba (8.5° N, 76.9° E) during the solar eclipse 2009/2010

Abstract. Measurements of atmospheric temperature profiles in the troposphere and lower stratosphere were made over Thumba Equatorial Rocket Launching Station (TERLS) (8.5° N, 76.9° E) during a partial solar eclipse (22 July 2009) and an annular solar eclipse (15 January 2010). It was observed that during the partial solar eclipse, the temperature decreased by 2–3 °C in the vicinity of the tropopause and in the lower stratosphere the temperature increased by ~2.6 °C during the maximum phase of the partial solar eclipse. During the annular solar eclipse, a temperature reduction of ~2 °C was observed around the tropopause. This study also revealed a feature of delayed effect in the form of a very intense warming of ~8 °C at 18 km after about 4 h of the annular solar eclipse. The Cold-Point Tropopause (CPT) temperature increased slowly before the beginning of the eclipse (up to 10:00 IST) and during the maximum phase of the eclipse, the difference in CPT temperature and height was −3.5 °C and ~110 m, respectively, as that of the control day. After the four hours of the eclipse, the CPT height had decreased by ~1.7 km and the CPT temperature increased by ~4.6 °C. This is for the first time that the diurnal variation of the tropopause has been reported during a solar eclipse day. The present study, thus, provided an opportunity to investigate the temperature perturbations in the troposphere and lower stratosphere during a partial and annular solar eclipse. The highlight of the present results are (1) cooling of the entire troposphere and lower stratosphere during the maximum phase of annular solar eclipse, (2) an intense heating of the lower stratosphere by 8 °C after nearly four hours from the maximum phase of the annular eclipse, and (3) drastic variations in the diurnal evolution of the tropical tropopause characteristics. The cooling effect is attributed to the radiative response of the atmosphere to the solar eclipse, where as heating is attributed to the dynamical response of the atmosphere to the solar eclipse. These results may have important implications in understanding the response of the atmosphere to the radiative, as well as dynamical, perturbations caused by any celestial or terrestrial disturbances.

Solar eclipse induced impacts on sea/land breeze circulation over Thumba: A case study

On 15th January 2010, Thumba ( 8 . 5 ∘ N , 76 . 9 ∘ E ), witnessed one of the longest noontime Solar Eclipse centered at 13:14 LT. In the present case study, we report first observations on sensitivity of the sea breeze circulation cell to short-term obscuration in solar irradiance. Temporal evolution of surface layer windspeed segregated into right-angle components along the coastline on eclipse and normal days indicated a significant reduction in the intensity of sea breeze during the period of eclipse. Vertical thickness of the sea breeze cell was confined to 300 m on the eclipse day, whereas it was extending to about 610 m on the control day.

Vertical profiles of aerosol black carbon in the atmospheric boundary layer over a tropical coastal station: Perturbations during an annular solar eclipse

Altitude profiles of aerosol black carbon (BC) in the atmospheric boundary layer (ABL) over a tropical coastal station, Trivandrum have been examined on two days using an aethalometer attached to a tethered balloon. One of these days (15th January, 2010) coincided with a (annular) solar eclipse, the longest of this century at this location, commenced at 11:05 local time and ended by 15:05, lasting for 7min and 15s (from 13:10:42), with its maximum contact occurring at ~13:14 IST with ~92% annularity, thereby providing an opportunity to understand the eclipse induced perturbations. Concurrent measurements of the ABL parameters such as air temperature, relative humidity and pressure were also made on these days to describe the response of the ABL to the eclipse. BC profiles, in general, depicted similar features up to an altitude of ~200m on the eclipse day and control day, above which it differed conspicuously with profiles on eclipse day showing increasingly lower concentration as we moved to higher altitudes. Examination of the meteorological profiles showed that the altitude of maximum convection rapidly fell down during the eclipse period compared to that on control day indicating a rather shallow convection on eclipse day. Comparison of diurnal variations of BC at the surface level showed that the rate of decrease in BC during daytime on the eclipse day was smaller than that on the control day due to the reduced convection, shallow ABL and consequent reduction in the ventilation coefficient. Moreover the time of the nocturnal increase has advanced by ~1:30h on the eclipse day, occurred at around 19:30 IST in contrast to all the other days of January 2010, where this increase usually occur well after 20:30 IST, with a mean value of 21:00 IST. This is attributed to the weak sea-breeze penetration during the eclipse day, which led to an early onset of the land breeze.

Penentuan Tarikh Kematian Ibrahim Putera Rasulullah S.A.W. Daripada Perspektif Falak

In Islamic history, there were several accounts on the date of the Prophet Muhammad’s son death, Ibrahim, which referred to some different dates. However, it was recorded that the death of Ibrahim occurred at the same day of solar eclipse, i.e. the only sun eclipse occurred within the prophethood era of Muhammad. This fact has been unanimously agreed by Muslim historians and it is based on several sound hadiths. With the development of science and technology today, the actual date of the death of Ibrahim can be identified by reviewing the data of solar eclipse. This paper analyzes this issue and attempts at investigating the actual date of Ibrahim’s death according to the theory of solar eclipse and its datas. The datas on Ibrahim’s death were acquired by historical documentation. The datas were then analyzed by using Moon Calculator software to calculate the actual date of Ibrahim’s death. The study formulates that the year of Ibrahim’s death as narrated in the history is accurate, but the day and month are different from what are mentioned by the historical accounts. This difference is assumed to be influenced by the practice of al-nasi’ in lunar calendar which was prevalent among Arab community at that time.

Solar eclipse effects of 22 July, 2009 on the propagation of radio signals

The results of investigation of the variation of radio signal strengths during the solar eclipse on July 22, 2009 are reported in this paper. Observations of the radio signals transmitted from different radio stations at different frequencies and received at a particular observing site indicate a distinct change in signal strength around the time the eclipse umbra passes the propagation paths. The three types of variations in the eclipse day and particularly during its peak period are different from propagation under normal condition. The phenomena of signal variations, the noted “Inverted U-shape“ at one of the frequencies before the occurrence of the eclipse and 13 to 15 minutes time difference between the enhancement of the signal strength and the onset of eclipse are some interesting characteristics. The results are interpreted by ionospheric D-layer behavior at such times.

Ionosphere variations at 700 km altitude observed by the DEMETER satellite during the 29 March 2006 solar eclipse

We present an experimental and modeling study of the effects of the 29 March 2006 solar eclipse in the topside ionosphere. Measurements of the densities and temperatures of the thermal electrons and ions were provided by instruments aboard the Centre National d'Etudes Spatiales microsatellite DEMETER, which flew over Europe and Africa near the time of maximum solar obscuration. Data from several orbits, either on the same day or on days encompassing the eclipse day, were available to determine a reference state of the ionosphere along the orbit in absence of eclipse. The comparison between this latter and the actual observations along the eclipse orbit reveal a clear thermal effect with a fast drop of about 200 K of the electron and ion temperatures that follows the variations of the solar UV flux in the F region of the ionosphere conjugate to the satellite position. The plasma density decreases by about 30% but with a significant delay and is better correlated with the solar UV flux averaged over the previous 1 to 2 h in the conjugate F region. This delayed and prolonged decrease of density induces an increase of the electron temperature to be higher than the reference ionosphere. We have also performed a modeling of the ionosphere using the SAMI2 code, after having introduced adequate modifications to reproduce fairly realistic eclipse conditions. Applied to the DEMETER conditions of observation, the model reproduces the observations very well. This work shows that the plasma temperature responds very quickly along the magnetic field lines to the variations of the energy available from the photoelectrons while the plasma density variations are controlled by more complex and slower transport processes.

Ozone and NO2 variations measured during the 1 August 2008 solar eclipse above Eureka, Canada with a UV‐visible spectrometer

On 1 August 2008, a solar eclipse of 98% totality passed over the Polar Environment Atmospheric Research Laboratory at Eureka, Canada (80.05°N, 86.42°W), which is run by the Canadian Network for the Detection of Atmospheric Change. During the eclipse, a zenith‐sky UV‐visible spectrometer measured slant column densities (SCDs) and vertical column densities (VCDs) of ozone up to 82% occultation and NO2 up to 96% occultation, beyond which low light intensities and changes in the solar spectrum due to limb darkening compromised data quality. Ozone VCDs during the eclipse remained within natural variability, and this study is inconclusive regarding ozone oscillations due to limited temporal resolution and measurement errors toward eclipse maximum. Measured NO2 SCDs increased and decreased symmetrically around the eclipse maximum. NO2 SCDs were also calculated using a photochemical box model and a one‐dimensional radiative transfer model. The modeled ratio of eclipse day SCDs to the previous day's SCDs was compared to the measurements. They agreed within error bars leading up to maximum occultation, but the model ratio was systematically larger than the measured ratio for the second half of the eclipse, perhaps due to changing cloud conditions throughout the eclipse. The measured NO2 SCD ratio of 1.84−0.43+0.12 at 96% totality is larger than observed in past studies and agrees with modeled ratio of 1.91. Therefore our current understanding of stratospheric photochemistry is sufficient to predict the evolution of NOx chemistry through a solar eclipse.

Enhancement and HF Doppler observations of sporadic‐E during the solar eclipse of 22 July 2009

The sporadic E (Es) frequently emerging in midlatitude during summer is a very special layer in the ionosphere, and its formation mechanism is different to from that of other layers. The total solar eclipse of 22 July 2009 provided a very unique opportunity to study the relationship of Es and solar radiation. During the solar eclipse day and the days before and after, the vertical incidence ionosonde was located in Wuhan to record the ionograms for this event. Two oblique incidence high‐frequency radio systems were used to record the waves from Wuhan to Suzhou and from Wuhan to Huaian. The enhancement of Es during the eclipse period was observed in the vertical and oblique incidence ionograms. The quasi‐periodic fluctuations in the critical frequency and Doppler frequency shift curves indicated the possible existence of the gravity waves, which may be responsible for the Es enhancement. However, we find that the enhancement occurred earlier than the appearance of gravity waves and consider that there may be other mechanisms which contribute to the observed enhancement in the ionosphere. A hypothesis is put forward that the cooling effect of the lunar shadow induced powerful airflow from the northern and southern limits of the shadow toward its center, which accelerated the irregularities in Es to produce the large‐scale Doppler shift in the reflected waves and form the meridional windshear. Both the windshear and the gravity waves may affect the Es layer and increase the electron concentration. Many observed phenomena are in accordance with this.

Effects of the solar eclipse on 15 January 2010 on the surface O<sub>3</sub>, NO, NO<sub>2</sub>, NH<sub>3</sub>, CO mixing ratio and the meteorological parameters at Thiruvanathapuram, India

Abstract. In this paper, we present the effect of total solar eclipse on surface O3, NO, NO2, NH3, CO mixing ratio and the meteorological parameters on 15 January 2010 at Thiruvanathapuram, India. On the day of total solar eclipse (i.e., 15 January 2010), the decrease in mixing ratio of surface O3 and NO2 is observed after the beginning of the solar eclipse events (11:15 to 15:30). Decrease in surface O3 may be due to decreased efficiency of the photochemical ozone formation, whereas, mixing ratio of NO and NH3 have been changed following the night time chemistry. Surface O3 reduced to 20.3 ppb after 22 min of full phase of the eclipse. During the solar eclipse period, the ambient temperature and wind speed have decreased, whereas, relative humidity has increased as expected.

The Effects of Solar Eclipse of August 1, 2008 on Earth’s Atmospheric Parameters

Several experiments were undertaken at Kolkata (latitude: 22°34′N, longitude: 88°30′E) on the solar eclipse day of August 1, 2008 to observe the effects of the solar eclipse on Fair Weather Field (FWF) and VLF amplitude and phase. The experimental results presented here show significant deviations of the observed parameters from their normal values, as they are determined by the average of the records obtained on 5 days adjacent to the day of the solar eclipse.

Ionospheric measurements during the total solar eclipse of 11 August 1999

Abstract A number of radio experiments were conducted at Ahmedabad (23°N, 73°E) with the aim of studying the ionospheric effects of the total solar eclipse of 11 August 1999. Rapid radio soundings from the ionosonde were made on the eclipse day and on control days. A riometer was operating at 30 MHz, and field strength measurements along the three oblique incidence paths of Colombo-Ahmedabad (11905 kHz), Bombay-Ahmedabad (558 kHz) and Rajkot-Ahmedabad (810 kHz) were also made. A reduction of about 20% was observed in the minimum frequency of reflection from the ionosonde (fmin), which indicates a reduction in D-region ionization. The critical frequency of the E-layer was not measurable beyond 1600 h IST on eclipse day due to the strong blanketing sporadic-E, but there is a 20% decrease in the critical frequency of the F1-layer. Although there was no change in the minimum virtual height of the F-layer on eclipse day, there appears to have been a decrease in the height of maximum ionization (hpF2) during the eclipse, indicating a reduction in the thickness of the F-layer. The signal strength of the Colombo-Ahmedabad path shows an initial rapid increase with the start of the eclipse (indication of a decrease in ionization in the D- and lower E-regions), but subsequently decreases until the maximum of the eclipse (excessive deviative absorption because of the wave penetrating to the E-region). The field strength measurements of the Bombay-Ahmedabad path show a large fading after sunset as the sky wave also appeared. On eclipse day the fading started about an hour earlier. Riometer recordings also show a higher signal during eclipse day, which again indicates an eclipse-associated decrease in ionization.

GPS ionospheric TEC measurement during the 23rd November 2003 total solar eclipse at Scott Base Antarctica

The total solar eclipse of 23rd November 2003 over Antarctica presents a unique oportunity to investigate the influence of the sun on the earth upper ionosphere. At Scott Base station, Antarctica (GEO: −77.85°, 166.76°; CGM: −79.94°, 327.23°), the partial solar eclipse was observed with the magnitude of 0.769. This solar eclipse event was a rare event due to its mixed eclipse-storm-TID. A severe magnetic storm which lasted for three days took place on 20th November 2003 with disturbance storm time index (Dst) reading of −465 nT and the planetary indices Kp and Ap of 9 and 117, respectively, and on the day of the solar eclipse minor storm activities was detected. A strong and rapid TEC oscillation with 3–4 oscillations and ranging from 20 to 30 min, a signature of Traveling Ionospheric Disturbances (TIDs) event was observed at the onset of eclipse event. Investigation on the TEC responses during the day before and after the eclipse event, showed that the TID event exist at about the same time period of the eclipse event on these days. Several TID events were also observed on other time of the day during the major storm period. At the time of maximum eclipse (at zero time delay), sudden decrease in TEC or TEC dip of 1.7 TECU with duration of 9 min was observed and the overall TEC level decreased during the eclipse period. Comparison of TEC levels at the time window of the eclipse period on 22nd and 24th November show that the TEC levels decreased by about 17% and 30% with respect to the day before and the day after the eclipse, respectively. Measurement of TEC for each GPS satellites within the observation window of the solar eclipse on 22nd, 23rd and 24th showed some satellites experienced TEC dip of about 1.5–1.7 TECU at the maximum solar eclipse period than on the day before and after the solar eclipse. The ionosonde measurements at Scott Base station show a similar behavior. The TEC dip observed from GPS and ionosonde measurement is in good agreement. During the eclipse event, a noise was detected by SuperDARN Syowa East Radar, which confirms the existence of the TID observations at the onset of the eclipse. Results of TEC measurements at McMurdo (GEO: −77.84°, 166.95° and CGM: −79.95°, 325°, eclipse magnitude 0.769) and Davis station (GEO: −68.58°, 77.97° and CGM: −74.91°, 101.91°, eclipse magnitude 0.983) shows a significant TEC depletion of 1.5 TECU at McMurdo station and 2.2 TECU at Davis station. The observed delay and duration of eclipse at McMurdo station are 0 and 9 min while at Davis station they are 5 and 12 min, respectively. A linear relationship between the eclipse magnitude and TEC depletion was observed from the results obtained from these stations. At McMurdo station, rapid noise in the TEC measurements was observed prior to the maximum eclipse time and also on the day before and after the eclipse. The observation of the TID waves before and after the eclipse day suggested that the TID event on the eclipse period cannot be resulted from the solar eclipse, but they could be resulted from the tropospheric origin, however, further investigation is required to examine the sources behind these waves.

Tomographic study of ionospheric effects associated with a solar eclipse

This paper studies the ionospheric effects associated with the solar eclipse of October 24th, 1995 by means of Computerized Ionospheric Tomography (CIT). Since the reconstructed profiles from experimental CIT are sporadically located in time, a time domain interpolation method based on Singular Value Decomposition (SVD) technique is proposed and applied to extract the ionospheric effects. The effects can be extracted by comparison analysis between the interpolated CIT profiles of the eclipse days and that of the reference day that are time-aligned. A series of figs have been obtained showing the attenuation of photonization effect at low altitudes and the weakening of plasma’s transportation process at high altitudes, etc. The photonization effect recovered to normal level soon after the last contact. The maximum electron density diminishing is observed about 2 h after the eclipse maximum and the effects seem vanished in the hours followed. Analysis on vertical TEC’s latitudinal-temporal variation gives similar conclusions.

Impact of total solar eclipse on spectral radiance characteristics of various objects and comparison of different vegetation indices

The division of Agricultural Meteorology, Pune of I.M.D. conducted a study of anomalous radiation environment during the last total solar eclipse period at Principal Evapotranspiration Observatory (PET) Canning, W.B. The spectral radiance characteristics from various objects viz. bare soil, G.T.R. calibration plate (coated uniformly with BaSO4), rice crop at late vegetative stage and rice crop at panicle (flowering) stage were measured from 23-25 October 1995 to in blue (0.45-0.52m), green (0.52-0.59m), red (0.62-0.68m) and in the portion of near infrared (0.77-0.86m) wavelengths, by use of multi-band ground truth radiometer (G.T.R.) and different vegetation indices were computed. The minimum values of spectral radiance were observed from all the four objects between 0830 to 0930 hrs IST on the eclipse day. The proportion of drop was the maximum in the portion of near infrared (NIR) band during the eclipse period for both the rice crops. The rice crop at late vegetative stage showed sharp drop in both RVI (ratio vegetation index) and NDVI (normalized difference vegetation index) values between 0830 to 0930 hrs IST, while the other rice crop at panicle (flowering) stage showed sharp fall (in both the values) at 0830 hr IST. Both the RVI and NDVI values for the bare soil showed fluctuations on the eclipse day between 0730 to 1000 hrs IST. The MGVI (modified green vegetation index) values indicated that on the eclipse day during the period of total eclipse, quantity of radiation reflected by different objects dropped in all the four bands.

Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

Abstract. The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)