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In this paper, I investigate the three-dimensional evolution of solar wind density and speed distributions associated with coronal mass ejections (CMEs). The primary solar wind data used in this study has been obtained from the interplanetary scintillation (IPS) measurements made at the Ooty Radio Telescope, which is capable of measuring scintillation of a large number of radio sources per day and solar wind estimates along different cuts of the heliosphere that allow the reconstruction of three-dimensional structures of propagating transients in the inner heliosphere. The results of this study are: i ) three-dimensional IPS images possibly show evidence for the flux-rope structure associated with the CME and its radial size evolution; the overall size and features within the CME are largely determined by the magnetic energy carried by the CME. Such a magnetically energetic CME can cause an intense geomagnetic storm, even if the trailing part of the CME passes through the Earth; ii ) IPS measurements along the radial direction of a CME at ∼ 120 R ⊙ show density turbulence enhancements linked to the shock ahead of the CME and the core of the CME. The density of the core decreases with distance, suggesting the expansion of the CME. However, the density associated with the shock increases with distance from the Sun, indicating the development of a strong compression at the leading edge of the CME. The increase of stand-off distance between ∼ 120 R ⊙ and 1 AU is consistent with the deceleration of the CME and the continued outward expansion of the shock. The key point in this study is that the magnetic energy possessed by the transient determines its radial evolution.

Knowledge of the radial evolution of the coronal mass ejection (CME) is important for the understanding of its arrival at the near-Earth space and of its interaction with the disturbed/ambient solar wind in the course of its travel to 1 AU and further. In this paper, the radial evolution of 30 large CMEs (angular width > 150 super(), i.e., halo and partial halo CMEs) has been investigated between the Sun and the Earth using (i) the white-light images of the near-Sun region from the Large Angle Spectroscopic Coronagraph (LASCO) onboard SOHO mission and (ii) the interplanetary scintillation (IPS) images of the inner heliosphere obtained from the Ooty Radio Telescope (ORT). In the LASCO field of view at heliocentric distances R,30 solar radii (R sub()), these CMEs cover an order of magnitude range of initial speeds, V sub(CME)-260-2600 km s super(-1). Following results have been obtained from the speed evolution of these CMEs in the Sun-Earth distance range: (1) the speed profile of the CME shows dependence on its initial speed; (2) the propagation of the CME goes through continuous changes, which depend on the interaction of the CME with the surrounding solar wind encountered on the way; (3) the radial-speed profiles obtained by combining the LASCO and IPS images yield the factual view of the propagation of CMEs in the inner heliosphere and transit times and speeds at 1 AU computed from these profiles are in good agreement with the actual measurements; (4) the mean travel time curve for different initial speeds and the shape of the radial-speed profiles suggest that up to a distance of 80 R sub(), the internal energy of the CME (or the expansion of the CME) dominates and however, at larger distances, the CME's interaction with the solar wind controls the propagation; (5) most of the CMEs tend to attain the speed of the ambient flow at 1 AU or further out of the Earth's orbit. The results of this study are useful to quantify the drag force imposed on a CME by the interaction with the ambient solar wind and it is essential in modeling the CME propagation. This study also has a great importance in understanding the prediction of CME-associated space weather at the near-Earth environment.

Radio spectrometers of the CALLISTO type to observe solar flares have been distributed to nine locations around the globe. The instruments observe automatically, their data is collected every day via internet and stored in a central data base. A public web-interface exists through which data can be browsed and retrieved. The nine instruments form a network called e-CALLISTO. It is still growing in the number of stations, as redundancy is desirable for full 24 h coverage of the solar radio emission in the meter and low decimeter band. The e-CALLISTO system has already proven to be a valuable new tool for monitoring solar activity and for space weather research.

We report the results of a multi-instrument, multi-technique, coordinated study of the solar eruptive event of 13 May 2005. We discuss the resultant Earth-directed (halo) coronal mass ejection (CME), and the effects on the terrestrial space environment and upper Earth atmosphere. The interplanetary CME (ICME) impacted the Earth’s magnetosphere and caused the most-intense geomagnetic storm of 2005 with a Disturbed Storm Time ( Dst ) index reaching −263 nT at its peak. The terrestrial environment responded to the storm on a global scale. We have combined observations and measurements from coronal and interplanetary remote-sensing instruments, interplanetary and near-Earth in-situ measurements, remote-sensing observations and in-situ measurements of the terrestrial magnetosphere and ionosphere, along with coronal and heliospheric modelling. These analyses are used to trace the origin, development, propagation, terrestrial impact, and subsequent consequences of this event to obtain the most comprehensive view of a geo-effective solar eruption to date. This particular event is also part of a NASA-sponsored Living With a Star (LWS) study and an on-going US NSF-sponsored Solar, Heliospheric, and INterplanetary Environment (SHINE) community investigation.

Radio pulsars show remarkable clock-like stability, which make them useful astronomy tools in experiments to test equation of state of neutron stars and detecting gravitational waves using pulsar timing techniques. A brief review of relevant astrophysical experiments is provided in this paper highlighting the current state-of-the-art of these experiments. A program to monitor frequently glitching pulsars with Indian radio telescopes using high cadence observations is presented, with illustrations of glitches detected in this program, including the largest ever glitch in PSR B0531+21. An Indian initiative to discover sub-\\[\\mu \\]Hz gravitational waves, called Indian Pulsar Timing Array (InPTA), is also described briefly, where time-of-arrival uncertainties and post-fit residuals of the order of \\[\\mu \\]s are already achievable, comparable to other international pulsar timing array experiments. While timing the glitches and their recoveries are likely to provide constraints on the structure of neutron stars, InPTA will provide upper limits on sub-\\[\\mu \\]Hz gravitational waves apart from auxiliary pulsar science. Future directions for these experiments are outlined.

We report the interplanetary effects of a fast coronal mass ejection (CME) associated with the intense X2.7 flare that occurred on 05 May 2015. The near-Sun signatures of the CME at low-coronal heights [ < 2 R ⊙ ] are obtained from the EUV images at 171 Å and metric radio observations. The intensity and duration of the CME-driven radio bursts in the near-Sun and interplanetary medium indicate this CME event to be an energetic one. The interplanetary-scintillation data, along with the low-frequency radio spectrum, played a crucial role in understanding the radial evolution of the speed and expansion of the CME in the inner heliosphere as well as its interaction with a preceding slow CME. The estimation of the speed of the CME at several points along the Sun to 1 AU trajectory shows that: i) the CME went through a rapid acceleration as well as expansion up to a height of ≈ 6 R ⊙ , and ii) the CME continued to propagate at speed ≥ 800 km s − 1 between the Sun and 1 AU. These results show that the CME likely overcame the drag exerted by the ambient/background solar wind with the support of its internal magnetic energy. When the CME interacted with a slow, preceding CME, the turbulence level associated with the CME-driven disturbance increased significantly.

The power spectra of intensity fluctuations in interplanetary scintillation (IPS) observations can be used to estimate solar-wind speeds in the inner heliosphere. We obtain and then compare IPS spectra from both wavelet and Fourier analyses for 12 time series of the radio source 3C48; these observations were carried out at Japan’s Solar-Terrestrial Environment Laboratory (STEL) facility, at 327 MHz. We show that wavelet and Fourier analyses yield very similar power spectra. Thus, when fitting a model to spectra to determine solar-wind speeds, both yield comparable results. Although spectra from wavelet and Fourier closely match each other for solar-wind speed purposes, those from the wavelet analysis are slightly cleaner, which is reflected in an apparent level of intensity fluctuations that is enhanced, being ≈ 13 % higher. This is potentially useful for records that show a low signal-to-noise ratio.

In this article, we investigate the formation and disruption of a coronal sigmoid from the active region (AR) NOAA 11909 on 07 December 2013, by analyzing multi-wavelength and multi-instrument observations. Our analysis suggests that the formation of the sigmoid initiated ≈ 1 hour before its eruption through a coupling between two twisted coronal loop systems. This sigmoid can be well regarded as of ‘transient’ class due to its short lifetime as the eruptive activities started just after ≈ 20 min of its formation. A comparison between coronal and photospheric images suggests that the coronal sigmoid was formed over a simple β -type AR which also possessed dispersed magnetic field structure in the photosphere. The line-of-sight photospheric magnetograms also reveal small-scale flux cancellation events near the polarity inversion line, and overall flux cancellation during the extended pre-eruption phase which suggest the role of tether-cutting reconnection toward the build-up of the flux rope. The disruption of the sigmoid proceeded with a two-ribbon eruptive M1.2 flare (SOL2013-12-07T07:29). In radio frequencies, we observe type III and type II bursts in meter wavelengths during the impulsive phase of the flare. The successful eruption of the flux rope leads to a fast coronal mass ejection (with a linear speed of ≈ 1085 km s −1 ) in SOHO/LASCO field-of-view. During the evolution of the flare, we clearly observe typical “sigmoid-to-arcade” transformation. Prior to the onset of the impulsive phase of the flare, flux rope undergoes a slow rise (≈ 15 km s −1 ) which subsequently transitions into a fast eruption (≈ 110 km s −1 ). The two-phase evolution of the flux rope shows temporal associations with the soft X-ray precursor and impulsive phase emissions of the M-class flare, respectively, thus pointing toward a feedback relationship between magnetic reconnection and early CME dynamics.

In this study, we investigate the interplanetary consequences and travel time details of 58 coronal mass ejections (CMEs) in the Sun–Earth distance. The CMEs considered are halo and partial halo events of width > 120 °. These CMEs occurred during 2009 – 2013, in the ascending phase of the Solar Cycle 24. Moreover, they are Earth-directed events that originated close to the centre of the solar disk (within about ± 30 ° from the Sun’s centre) and propagated approximately along the Sun–Earth line. For each CME, the onset time and the initial speed have been estimated from the white-light images observed by the LASCO coronagraphs onboard the SOHO space mission. These CMEs cover an initial speed range of ∼ 260 – 2700 km s − 1 . For these CMEs, the associated interplanetary shocks (IP shocks) and interplanetary CMEs (ICMEs) at the near-Earth environment have been identified from in-situ solar wind measurements available at the OMNI data base. Most of these events have been associated with moderate to intense IP shocks. However, these events have caused only weak to moderate geomagnetic storms in the Earth’s magnetosphere. The relationship of the travel time with the initial speed of the CME has been compared with the observations made in the previous Cycle 23, during 1996 – 2004. In the present study, for a given initial speed of the CME, the travel time and the speed at 1 AU suggest that the CME was most likely not much affected by the drag caused by the slow-speed dominated heliosphere. Additionally, the weak geomagnetic storms and moderate IP shocks associated with the current set of Earth-directed CMEs indicate magnetically weak CME events of Cycle 24. The magnetic energy that is available to propagate CME and cause geomagnetic storm could be significantly low.