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This paper highlights the impact of intense solar events over India during 3–20 December 2006. Ionospheric effects of a major solar flare (X9) on December 5 (10:35 UT) have been investigated by using dayside and nightside magnetometer data, dayside ionosondes, and dayside GPS vTEC observations. On the next day, a stream of fast solar wind hits the magnetosphere, causing a HILDCAA (High Intensity Long Duration Continuous Auroral Activity) preceded by moderate geomagnetic storm. The origin and characteristics of a positive ionospheric storm which occurred over Tirunelveli (TIR, geomagnetic latitude: −0.18°N) in the recovery phase of storm due to simultaneous presence of enhanced O/N2 and WEJ or weakened EEJ during the HILDCAA (7th and 8th of December) is investigated. Subsequently, on December 14, the most powerful CME since the Halloween event impacts the Earth, and three SSCs are recorded on December 14, 16, and 18. The variability of the ionosphere over the Indian longitude sector due to these intense space weather fluctuations is presented by utilizing the magnetometers, ionosonde, GPS vTEC, and satellite‐based observations in the same region. This study reports the influence of prompt penetration of the magnetospheric convection electric field and the disturbance dynamo on several key ionospheric and magnetic parameters within the Indian longitude sector. Plain Language Summary: Earth's ionosphere, the ionized portion of the upper atmosphere is highly variable due to atmospheric variations and solar activity. Due to disturbances in the ionospheric electric fields and plasma densities, the ionospheric current systems and their presence on ground‐based magnetometers can undergo very complicated changes during space weather events (such as coronal mass ejections (CME), high‐speed solar wind (HSS), Co‐rotating Interaction Regions (CIRs), solar flares, etc.). In this study, a thorough multi‐instrument examination of the ionospheric fluctuations and the accompanying magnetic variations over Indian longitude regions has been done during the several geomagnetic storms between 3 and 20 December 2006 (Solar flare on 5th, CIR induced moderate storm on 6th, following HILDCAA on 7th–8th, and CME induced intense storm on 15th of December in particular). We have also been able to adequately explain the day‐to‐day fluctuations of the ionosphere over India by taking into account the storm‐produced physical events (such as PPEF, DDEF, change in composition, TID, etc.). Key Points: A detailed multi‐instrument study of magnetic and ionospheric variation due to a variety of space weather phenomenon in December 2006 over Indian longitudes is presentedThis study shows the signature of the X9 solar flare of 5 December 2006 on the SYM‐H and ASY‐H indicesThe impact of solar and geomagnetic events on the variation of the Earth's magnetic field due to the ionospheric electric currents is addressed [ABSTRACT FROM AUTHOR]

X-class solar flares, which occurred in the daytime from 2008 to 2016 during solar cycle 24, were studied for their influence on the lower ionosphere over the lowequatorial Indian region. To understand the D-region behaviour during flare events, we used the very low frequency (VLF) navigational transmitter NWC (19.8 kHz) signal recorded at Pryagraj, Uttar Pradesh, India. A total of seven parameters were estimated: (i) the magnitude of X-ray flux, (ii) VLF signal rising amplitude perturbation (SRAP), (iii) X-ray flux and NWC signal start time difference (STD), (iv) peak time difference (PTD), (v) Wait’s ionospheric parameters h′ (reference height), (vi) β (sharpness factor) and (vii) D-region electron density difference (EDD) to determine the overall effect of solar flares on the D-region. The results suggest that three parameters (X-ray flux, SRAP and h′) show a decreasing trend through the linear fit line, two parameters (β and EDD) show an increasing trend, while the remaining two parameters show a mixed trend (decrease during low activity and increase during high activity). Further, the trend line during the diurnal variation shows an increasing trend for X-ray flux, PTD and h′, and a decreasing trend for SRAP, STD, β and EDD. Deviation in the case of individual events may indicate the dependence of these parameters on the seasons as well. The present study will provide the base for more robust analysis and modelling work in the future to understand the complexity of ionospheric change during flare events, and to develop a predictive model for space weather mitigation. [ABSTRACT FROM AUTHOR]

Aditya-L1 is India's first observatory-class solar space mission to study the Sun from the Lagrange L1 point. The Solar Ultra-Violet Imaging Telescope (SUIT) is one of the payloads onboard Aditya-L1. SUIT is an off-axis Ritchey–Chrétien (RC) telescope, which images the Sun onto a 4k×4k CCD covering a field-of-view of 1.5 R⊙ with a plate scale of 0.7 ″ pixel−1. One of the primary objectives of SUIT is to study the early evolution of solar flares with high temporal cadence in the near-UV wavelengths (200 – 400 nm). The SUIT onboard intelligence was developed to achieve this objective. The complete intelligence algorithm is divided into several sub-modules, each working on a specific aspect of intelligence. These are: the HEL1OS flare-trigger module: generates flare trigger using HEL1OS hard X-ray data, the flare-localization module: locates the flare on the SUIT full-disc images, the Region of Interest (RoI) tracking module: accounts for the shift in RoI coordinates caused by rotation of the Sun, auto-exposure control module: adjusts the exposure time depending upon the flare intensity for better contrast. In this article, these onboard-intelligence modules are explained in detail. The working principles of these modules are tested using available data from various existing missions and also using synthetic data, and the obtained results are presented. The modules are implemented in hardware using an Actel RTAX 2000S FPGA and are tested using a laboratory setup. From the testing, it is found that flares are successfully localized in a mean time of 40 seconds from the GOES soft X-ray catalog start time. Also, a temporal cadence of under three seconds for a single-filter flare RoI image is achieved. [ABSTRACT FROM AUTHOR]

Abstract: A statistical study of different solar activity features (sunspot number, solar active prominences and Hα solar flares) with all India homogeneous rainfall (RF) is presented using 44 years (1963–2006) data. The correlation coefficient, significance of correlation coefficient and other statistical parameters are computed for the seasonal months of January–February (JF), March–April–May (MAM), June–July–August–September (JJAS), October–November–December (OND) and also annual. Correlation coefficient and its significance of two, four and six point moving average of RF with different solar activity features have also been calculated. A negative correlation is found between annual RF and solar activity features, and for sunspot number and solar flares with two, four and six point moving average of RF whereas moves from negative to positive for solar active prominences. Lag/lead analysis between RF and different solar activity features have also been analyzed and presented. [Copyright &y& Elsevier]

Abstract: The variation of the first Schumann resonance (SR) frequency spectra observed from the recorded data over Kolkata (22.56°N, 88.5°E) during a solar proton event (SPE) on July 14, 2000 has been presented. It shows increase in frequency during X-ray bursts and decrease during the period of occurrence of an SPE. The results from some other locations for the same event are also reported. The severe X-ray bursts recorded just before the proton event exhibit enhancement in frequency of the first mode due to enhancement of ionization in the D-region of the ionosphere. Some attempts are made to explain the observed variation during solar proton events in terms of the perturbations within the Earth–ionosphere waveguide on the basis of two-layer-model. [Copyright &y& Elsevier]

Solar X-ray Spectrometer (SOXS), the first space-borne solar astronomy experiment of India was designed to improve our current understanding of X-ray emission from the Sun in general and solar flares in particular. SOXS mission is composed of two solid state detectors, viz., Si and CZT semiconductors capable of observing the full disk Sun in X-ray energy range of 4-56 keV. The X-ray spectra of solar flares obtained by the Si detector in the 4-25 keV range show evidence of Fe and Fe/Ni line emission and multi-thermal plasma. The evolution of the break energy point that separates the thermal and non-thermal processes reveals increase with increasing flare plasma temperature. Small scale flare activities observed by both the detectors are found to be suitable to heat the active region corona; however their location appears to be in the transition region. [ABSTRACT FROM AUTHOR]

Terrestrial as well as extraterrestrial satellite data and environmental parameter records were correlated. It has been observed that some relationship exists in between the changes in environment and extraterrestrial phenomenon. The star flare changes the cosmic parameters. The nearest star of earth, the Sun, is found to be under the influence of the star flare. It has been observed that there is some relationship in between the planetary indices (Kp) Electron flux (E flux) Proton flux (P-flux) of Sun-Earth environment with the changes in thermosphere, ionosphere, atmosphere and geosphere. The tsunami of 26 December 2004, abnormal snowfall in 2004-2005, sudden hike in global temperature and erratic monsoon in India and irregular rainfall in other parts of the world in 2006-2007 followed by snowfall and torrential rain are the impact of the star-sun-earth relationship. [ABSTRACT FROM AUTHOR]

We present the first results from the low-energy detector payload of the solar X-ray spectrometer (SOXS) mission, which was launched onboard the GSAT-2 Indian spacecraft on May 08, 2003 by the GSLV-D2 rocket to study solar flares. The SOXS low-energy detector (SLD) payload was designed, developed, and fabricated by the Physical Research Laboratory (PRL) in collaboration with the Space Application Centre (SAC), Ahmedabad and the Indian Space Research Organization (ISRO) Satellite Centre (ISAC), Bangalore. The SLD payload employs state-of-the-art, solid-state detectors, viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices that operate at near room temperature (−20 °C). The energy ranges of the Si PIN and CZT detectors are 4 – 25 and 4 – 56 keV, respectively. The Si PIN provides sub-keV energy resolution, while the CZT provides ~1.7 keV energy resolution throughout the energy range. The high sensitivity and sub-keV energy resolution of the Si PIN detector allows measuring the intensity, peak energy, and the equivalent width of the Fe-line complex at approximately 6.7 keV, as a function of time in all ten M-class flares studied in this investigation. The peak energy ( E p) of the Fe-line feature varies between 6.4 and 6.7 keV with increase in temperature from 9 to 58 MK. We found that the equivalent width ( w) of the Fe-line feature increases exponentially with temperature up to 30 MK and then increases very slowly up to 40 MK. It remains between 3.5 and 4 keV in the temperature range of 30 – 45 MK. We compare our measurements of w with calculations made earlier by various investigators and propose that these measurements may improve theoretical models. We interpret the variation of both E p and w with temperature as being to the changes in the ionization and recombination conditions in the plasma during the flare, and as a consequence, the contribution from different ionic emission lines also varies. [ABSTRACT FROM AUTHOR]

The response of equatorial ionosphere–thermosphere system to the X3.8 solar flare of January 17, 2005 has been studied using the coordinated measurements of GPS-derived Total Electron Content (TEC), OI 630.0 nm dayglow and magnetic field measurements over a dip equatorial station Trivandrum (8.5° N, 77° E, dip 0.5° N), in India. It has been observed that Equatorial Electrojet (EEJ) as inferred using the ground-based magnetometers and GPS-derived TEC measurements show prompt enhancements during the peak flare, as expected. Interestingly, the temporal evolution of TEC at different latitudes revealed that the X3.8 class flare produced significant weakening of the plasma fountain and hence in the Equatorial Ionization Anomaly (EIA). Furthermore, the response of OI 630.0 nm dayglow during the flare is found to be strongly affected by the prevailing electrodynamics. The plausible physical mechanism for these effects is discussed in context of the current understanding of the neutral and electrodynamical coupling processes. [ABSTRACT FROM AUTHOR]