Bengaluru: After multiple days of intense solar activity and once-in-a-lifetime aurorae sightings at lower latitudes, including faintly in India, the Indian Space Research Organisation (ISRO) has given out details about the very strong coronal mass ejections from the Sun that led to intense geomagnetic storms this weekend.
ISRO Tuesday published data and readings on the geomagnetic storm as observed by the space agency from the ground, from space, and from the Moon’s orbit. The technical findings detail the kind of flares that were emitted from the Sun, the energy and flux they carried, and how the observations varied between earth and space.
Observations in the form of spectral signatures have been posted from Aditya-L1 spacecraft, the solar observation mission that is located between the Earth and the Sun in space, and Chandrayaan-2, which is currently in orbit around the moon.
According to ISRO, the agency “has mobilised all its observation platforms and systems” to record data and electromagnetic signatures of this solar event. The data captured by ISRO confirms that the ongoing solar storm was the largest since 2003, as has also been stated by other sources.
ThePrint explains the technical findings from the data posted by ISRO and the impact of the geomagnetic storm measured on spacecraft and radio communication.
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What are geomagnetic storms and coronal mass ejections?
The Sun’s immense generation of energy and charges results in magnetic field structures that make up the structure of the Sun. Once in a while, these magnetic connections stress and break, and then reconnect in the form of giant loops of material. Such events can trigger a coronal mass ejection — a large explosion of material from the Sun along these magnetic lines outwards into the solar system.
The source of the material is typically regions on the Sun that hold colder planet-sized spots called sunspots. These cooler parts of the Sun often lead to comparatively cold and therefore dense material being trapped by magnetic flux, preventing the usual flow of hot material in the Sun.
When the flux reconnects, the dense filament of colder material is either reabsorbed or ejected, travelling faster than the regular stream of charged particles from the Sun, along with a shock wave.
The material from the Sun interacts with the ionosphere (part of the Earth’s upper atmosphere) and the charged particles interact in turn with atmospheric gases, producing northern and southern lines high up above the ground.
Due to the Earth’s magnetic field lines, these interactions tend to occur closer to the poles typically, and in lower latitudes during high intensity. Such interactions with the atmosphere are called geomagnetic storms, and make up the solar or space weather.
These storms not only cause aurorae or natural light displays in the Earth’s sky, but also have the potential to knock out satellite communications and affect electronic infrastructure on the ground, depending on the intensity of the storm.
Milder versions erupt as solar flares and are not powerful enough to release enough coronal mass to cause strong geomagnetic storms on the earth.
All solar flares and coronal mass ejections release radiation across the electromagnetic spectrum in just a few minutes.
Geomagnetic storm intensities are measured on the geomagnetic storm index known as Kp. The maximum value is 9 for the strongest class of solar flares called X-class. M-class flares are less strong, C-class below them, followed by B-class and finally A-class flares.
A, B, and C-class flares have no consequences for the earth, while M-class medium-sized flares can cause radio blackouts. X-class flares are the largest and most powerful.
The active sunspot region from which material was ejected in the recent storm is named AR13664. A series of strong X-class flares were released towards the earth. Kp values this time reached 9, and very strong X-class flares were recorded. Multiple coronal mass ejection events were observed, with two main ones at 1744 hours UTC on 9 May and a stronger one on 10 May at 0631 hours UTC.
ISRO’s observations from Earth
The coronal mass ejection event occurred on 10-11 May, and charged particles reached the atmosphere above India in the early morning hours of 11 May.
The ionosphere changes in density and energy through the day as sunlight increases and decreases, and is not considered fully “formed” in the morning. Satellite observations from the National Atmospheric Research Laboratory, or NARL, at Gadanki in Andhra Pradesh showed a decrease of electron content by over half overnight on the 10th.
Subsequently, in the morning, the electron content of the ionosphere above India went up by 10 percent with large variations, indicating that this atmospheric layer was being disturbed. By evening, electron content had risen by upwards of 30 percent.
Measuring the total electron content (TEC) of the ionosphere is significant as the presence of electrons — and plasma or superheated ionised gas — directly affects the propagation of radio waves, which in turn affects satellites and the Global Positioning System (GPS).
Another observation was made at Kerala’s Thumba, a substation of the Indian Network for Space Weather Impact Monitoring. Instruments here are built for space weather study, and thus readings here are more sensitive.
A steep and drastic increase of TEC by over 100 percent was observed on 10 May compared to the previous day.
Observations from lunar orbit
Chandrayaan-2 is currently in polar orbit around the Moon and is equipped with instruments that measure space weather due to its operational environment.
The XSM instrument on board mainly monitors solar X-rays and high energy particles. ISRO says the instrument observed “many interesting phenomena” in this geomagnetic storm.
The readings from the instrument showed numerous spikes in the charged particles’ concentration around the moon over the last five days. It also showed that high-energy particles in the lunar orbit rose steadily with a steep spike on 10 May.
Observations by Aditya L1
The Aditya mission is India’s first to study and understand the sun. It orbits around an empty point at a region called L1, which lies between the earth and the sun, and moves along with the earth as it orbits the sun. The spacecraft hosts a number of instruments that have been built to study data from the sun in great detail.
The Solar Wind Ion Spectrometer (SWIS) and Supra Thermal and Energetic Particle Spectrometer (STEPS) made detailed observations about solar wind, temperature, plasma and ion flux. The SWIS instrument’s readings showed the increase of alpha particles and proton flux in the solar wind signature.
Alpha particles are those that are made up of two protons and two neutrons bound together. These are ions or positively charged particles that are missing two electrons.
When alpha particles interact with electrons in the atmosphere, they become an electrically neutral double helium atom. But because they are highly energetic, they travel at fast speeds and interact with atmospheric molecules, knocking off electrons from the atoms and ionising or charging them.
Ionisation or charging of the atmosphere by alpha particles and cosmic rays influences aerosols and cloud formation to a limited extent. Proton flux measures the amount of positively charged particles or protons that enter the atmosphere. These are also high-energy particles that are emitted from the Sun, and can ionise or charge the atmosphere, which in turn interferes with radio and satellite communication.
STEPS’ observations indicated a steady increase over the day on 10 May in the rise of energetic ions and particles in the atmosphere.
The X-ray instruments, namely SoLEXS and HEL1OS, onboard Aditya-L1 observed multiple X and M-class flares over the last few days. The magnetometer instrument also made these observations.
How ISRO monitored health of instruments
Geomagnetic storms of greater strengths are of particular danger to spacecraft and satellites that are above the earth’s atmosphere as they can be affected by the stream of charged particles from the sun. This includes space missions orbiting the earth, sun, and moon.
For ISRO, the Master Control Facility (MCF) in Karnataka closely tracks all flight readings and health of spacecraft. Due to the waves of charged particles, some spacecraft observed slight changes in their momentum. Because of the high amount of heat transferred by the solar particles to the atmosphere, higher layers heat up and expand, including downward. This then increases the density of the atmosphere where satellites orbit, leading to more drag and loss of altitude.
Some lower earth satellites displayed signs of orbital decay of up to five or six times compared to normal, but these are not substantial enough to require concern.
Otherwise, the ISRO stated, no major anomalies have been observed in any of the 30 high-altitude satellites and spacecraft so far, including all of the agency’s earth-observation satellites.
ISRO’s Navigation Centre also stated that satellites that are part of the Indian navigation satellite system, NaVIC, have seen no impact from the geomagnetic storm.
The solar activity from the active region AR13664 is ongoing, along with more, weaker solar flares. Astronomers across the globe continue to monitor space weather, which is expected to be rougher this year and the next as the sun reaches the peak activity of its 11-year solar cycle.
(Edited by Nida Fatima Siddiqui)
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