18-Oct-2021: Clue to mystery of solar flares & CMEs in regions on Sun with disturbed magnetic field can help improving solar weather predictions
Astronomers exploring regions on the Sun with disturbed magnetic fields or active regions that sometimes exhibit solar flares without accompanying Coronal Mass Ejection (CME) have confirmed that changing structure of the magnetic field on the Sun’s surface determined whether a flare or a CME was emitted. This understanding will be useful in improving predictions of solar weather, which can affect electrical, and communication systems in Earth and satellite systems in space.
The Sun has a complex magnetic field near its surface that is connected to its hot plasma and changes its configuration all the time as the plasma itself moves around in this field. This magnetic field can erupt out of some regions (called Active Regions) on the Sun's surface in loops, become twisted, realign its geometry, and release tremendous amounts of energy in the process, which was stored as magnetic energy till then. The light (in many wavebands) emitted in this process is called a solar flare. On the other hand, a CME is when a huge amount of hot gas, with its embedded magnetic field, is ejected at high velocities into the solar corona. It is known that some Active Regions produce flares, some produce CMEs, and some produce both. What determines this difference remained a puzzle though earlier studies indicated that the mystery lies in the magnetic field in this region.
The underlying magnetic configuration that stores energy is typically seen having twisted magnetic fields, which are quantified by a parameter known as magnetic helicity. The corona of the active region (AR) is being pumped with such twists or magnetic helicity. When helicity reaches beyond a threshold level, CME is the only way to remove the excess helicity. However, finding the threshold level of the coronal helicity budget is still a formidable problem for the prediction of a CME eruption in due course of the AR evolution.
Dr. P. Vemareddy from the Indian Institute of Astrophysics, Bengaluru, an autonomous institute of the Department of Science & Technology, Government of India, first spotted a peculiar evolution of helicity injection in the Active Region called AR 12257 without CMEs. The scientists studied this astronomical event based on the magnetic and coronal images of the Sun, taken every 12 minutes by NASA's Solar Dynamics Observatory in space, and found that the AR injected positive helicity in the first 2.5 days followed by negative helicity after that. The study showed that active regions where the sign of the helicity (or twist) reverses with time cannot produce coronal mass ejection.
The results have been published in the journal Monthly Notices of the Royal Astronomical Society.
“Surprisingly, the magnetic structure that we derived from the data did not show any twist in the core of the active region,” said Dr. Vemareddy. According to the IIA team, studies of how helicity is injected seem to be key to predict the eruptive potential of an active region, and these results are expected to shed light on magnetic field production in stars and planets as well.
21-Sep-2021: Study probes how ejections from Sun’s corona influence space weather predictions crucial for monitoring satellites
A recent study has shown how conditions and events in the solar atmosphere like coronal mass ejections influence the accuracy of space weather prediction, which is crucial for the health of our satellites. This understanding will aid the interpretation of data from the upcoming Aditya-L1, India's first solar mission.
Space weather refers to the conditions in the solar wind and near-Earth space, which can adversely affect the performance of space-borne and ground-based technological systems. The space weather near the Earth is mainly due to Coronal Mass Ejections (CMEs), which are frequent explosive expulsions of huge magnetized plasma from the Sun into its surroundings, which can blow past the Earth. Example of space weather events is the geomagnetic storm, a perturbation in the Earth’s magnetic field, which can last for few hours to few days. Understanding of how events in the solar atmosphere influence space weather is necessary for monitoring and maintaining our satellites.
In the present work, astronomers led by Dr. Wageesh Mishra of the Indian Institute of Astrophysics (IIA), Bengaluru, an autonomous institute of the Department of Science & Technology, Govt. Of India showed that plasma properties and Earth arrival times of CMEs from the Sun can vary substantially with longitudinal locations in the interplanetary space. This research is published in the Monthly Notices of the Royal Astronomy journal and is co-authored by Kunjal Dave from C.U. Shah University, Gujarat, Prof. Nandita Srivastava from Physical Research Laboratory, Udaipur, and Prof. Luca Teriaca from the Max Planck Institute of for the Solar System Research, Germany.
In this research, the team studied the Earth-directed CMEs and interplanetary counterparts of CMEs (ICMEs). With access to publicly available plasma measurements in situ at three locations in the Solar System, -- two of NASA’s STEREO spacecraft and the LASCO coronagraph onboard SOHO located near the first Lagrangian point (L1) on the Sun-Earth line, they reconstructed a 3D view of the CMEs & ICMEs. The two events that are the basis of the present study are the ICMEs of 11th March and 6th August 2011 (which is when they arrived at Earth). Using multi-point remote and in situ observations, the study investigated the differences in the dynamics, arrival time, plasma, and magnetic field parameters of ICME structures at the locations in the heliosphere where the different satellites are located.
The team explains Sun emits a continuous stream of charged particles called the Solar Wind. The two selected events were ideal for studying the effects of the CME shocks moving through the solar wind.
“We found that plasma characteristics and arrival times of a CME-driven shock, propagating in a pre-conditioned inhomogeneous medium, may be different at different longitudinal locations in the heliosphere,” said Wageesh Mishra, the lead author.
The study highlights the difficulties in connecting the local observations of an ICME from a single in situ spacecraft to its global structures and explains that accurate prediction of large CME structures at any location in the heliosphere is challenging. It emphasized that lack of information about the pre-conditioned ambient solar wind medium can severely limit the accuracy of CME arrival time and space weather prediction. This new understanding will aid the interpretation of data from space missions.
9-Sep-2021: Scientists peek into the Sun by estimating magnetic fields using radio observations
Indian Scientists, along with international collaborators, have measured the magnetic field of an eruption from the Sun's atmosphere (by observing the weak thermal radio emission associated with the erupted plasma for the first time), offering a rare peek to the interior of the Sun. The study of the phenomenon happening in the Sun's atmosphere or the solar corona provides insights into the inner workings of the Sun.
The Sun is an extremely active object, spewing out vast quantities of gas in many violent events and the corona is a region of very high temperatures, strong magnetic fields, and violent plasma eruptions. A class of such eruptions are Coronal Mass Ejections (CMEs). CMEs are the most powerful explosions happening in our solar system. When a really strong CME blows past the Earth, it can damage the electronics in our satellites and disrupt radio communication networks on Earth. Hence, astronomers regularly study these events. This field of research helps to understand Space Weather.
A team of scientists from the Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science & Technology (DST), Government of India, along with their collaborators, used data from their radio telescopes to measure the magnetic field and other physical conditions of the plasma in a CME detected on 1 May 2016. It was found with the help of radio telescopes of IIA in Gauribidanur, Karnataka, along with some space-based telescopes that observed the Sun in extreme ultraviolet and white light and was caught when the base of its activity was just behind the visible limb of the Sun. This allowed the researchers to detect a much weaker radio emission called thermal (or blackbody) radiation from the plume of gas that was ejected in the CME. They were also able to measure the polarisation of this emission, which is indicative of the direction in which the electric and magnetic components of the waves oscillate. Using this data, they then calculated the physical properties of the ejected plasma as well. The results of the study by R. Ramesh, A. Kumari, C. Kathiravan, D. Ketaki, and T. J. Wang have been published in the leading international journal Geophysical Research Letters.
“Though CMEs can occur anywhere on the Sun, it is primarily those which originate from regions near the centre of the visible solar surface (called the photosphere) like the one we studied that are important for us, since they may propagate directly towards the Earth,” said R. Ramesh, Professor at the Indian Institute of Astrophysics (IIA), Bangalore and the lead author of the paper. “These CMEs are usually studied in visible light, but because the disc of the Sun is so much brighter, we can detect and follow these CMEs only when they have travelled beyond the Sun's surface. However, radio observations of the thermal emission, like in our study, lets us study the CMEs right from the surface itself”, she added,” said A. Kumari, a co-author.
“Knowing the source region of the CMEs, the associated magnetic field, and their kinematics in the region up to seven lakh kilometer either above the solar surface or off its limb, are important to fully understand the characteristics of the CMEs in a holistic manner,” says C. Kathiravan, another co-author of the study.
