Space weather: a brief introduction

09/08/2021

The 20th century saw an unprecedented technological leap forward in space exploration, with a flood of machines and devices exploring the cosmos, and learning more and more about the Universe around us, and perhaps its most important object, the Sun. It turns out that space weather is not a phenomenon beyond our control, but a process that has an enormous impact on life on Earth, both positive and negative. We, therefore, continue to make enormous efforts to improve our understanding of the concepts involved in space weather and to make our predictions as accurate as possible.

What does space weather do?

Space weather is a branch of physics that studies the Sun, the solar wind, the magnetosphere, and the different layers of the atmosphere, in particular the ionosphere and the thermosphere. Among other things, researchers in this field are looking for answers to the question of how these factors affect life on Earth, health and our advanced satellite-based communication and navigation devices. Ultimately, the answers will focus on the emergence of extreme weather conditions that threaten the current functioning and socio-economic structure of human civilisation as a new chapter in the field of weather services.

The history of space weather

Humanity officially joined the spacefaring species in the 1950s (assuming we are not alone). It was then that we began to observe our solar system and the Sun, discovering its dynamic influence, which is invaluable to human life. Our knowledge of the climate grew with our knowledge of the outside world, and we realised that the Earth's atmosphere is made up of many parts.

Meteorology is an ancient science, but space weather has grown out of the physical sciences. Before we got out into space, three areas had long intrigued mankind and it was able to observe them: the first was the aurora borealis, the second was the sunspot and the third was the Earth's magnetic field. Cosmic radiation, an important aspect of space weather, was only later discovered in the early 20th century by Rudolf Hess using balloons for measurement. It was the mapping of the relationship between these phenomena that marked the beginning of a discipline that took off in the 1950s.

The Sun

The Sun, for thousands of years the object of worship and admiration, is just one of the 100 billion stars in the Milky Way, yet for us, this celestial body, some 4.5 billion years old, represents life itself. Its most important property is that it emits solar energy. It produces a thermonuclear reaction (nuclear fusion) in the Sun's core, where protons form helium nuclei, generating enormous energy that is released into space as heat and light energy when it reaches the Sun's surface. This is how photosynthesis is possible for plants on Earth, why we have days and tolerable temperatures on the Earth's surface, and why our planet is habitable. The Sun is a dynamically changing star with a magnetic field.

The sunspot

It has been known for centuries that darker regions can be distinguished on the Sun's surface. Two Dutch scientists, Hendrik Antoon Lorentz and Pieter Zeeman were awarded the Nobel Prize in Physics in 1902 for their description of the physical effect and further studies of the phenomenon. It turned out that these regions are less hot than their surroundings, but a thousand times stronger in terms of their magnetic fields than the nearby solar surface.

Even more interesting, many sunspot groups suddenly release energy from the Sun's photosphere. One type of phenomenon associated with strong magnetic fields is solar flares. When this happens, an incredible amount of energy reaches the surface of the Sun in a matter of minutes: temperatures of nearly 100 million degrees Celsius are much higher than the Sun's core. In proportions, this is like exploding hundreds of millions of hydrogen bombs at once.

The solar activity cycle

It has been shown that the intensity of sunspots can be understood in the context of an 11-year cycle. Over this time, the number of sunspots first increases, peaks, and then begins to decrease. Although this recurring pattern has been observed since the 1800s, it has been possible to distinguish between solar maximum and solar minimum periods in modern times. (In the former, the Sun's magnetic lines of force rotate faster along the Sun's equator than at the poles.) One such event occurred on September 1 and 2, 1859, and was called the Carrington Event. As a result, the northern light, otherwise observable by locals, was even observed in Hawaii and Cuba. But even more ominous was the serious damage to telegraph systems.

The solar corona, solar wind

As already mentioned, the Sun's magnetic field is constantly moving away from the Sun's surface, creating the phenomenon of solar wind. The solar wind causes the aurora and the magnetic storms that can already damage electrical systems on Earth.

During a total solar eclipse, the light surrounding the Sun, the corona, is visible. This is the outer part of the Sun's atmosphere, which is much more extensive than the Sun itself, with a detectable presence up to 17 million kilometres. It is not symmetrical and not equally bright in all directions, and fortunately, you no longer need a total eclipse to study it: a special telescope called a coronagraph is all you need. Particles of certain energy can escape the Sun's gravitational field and form the plasma solar wind, which is moving away from the Sun at an extraordinary speed.

The Coronal Mass Ejections

The motion and structure of the Sun's magnetic field are behind the constant variation of the corona. Sometimes, parts of the solar disk become hugely inflated and are blown out of the Sun into the so-called heliosphere, the region of space beyond the solar corona, which is the whole solar system, the interplanetary space.

This phenomenon is the coronal ejecta or coronal mass ejections, which is sometimes 1012 kg of extremely hot coronal material, and which is gaining speeds even greater than the solar wind. When this latter event occurs, a shock wave is generated and, acting as a kind of particle accelerator, it scatters large quantities of high-energy particles across the Earth's space, often causing damage to satellites.

The geomagnetic storm

As we have already seen, events in space are not without consequences for the Earth.

In April-May 2021, for example, the Sun proved to be particularly active, which could trigger geomagnetic storms in the Earth's atmosphere through coronal aberrations or high-speed solar winds. Among the storm types ranked from 1 to 5 in strength, a magnitude 3 wave hit the Earth in May, one of the causes of which was a solar wind of more than 1 000 000 km/h in April, followed by a coronal mass ejection. Why is this a constant threat to 21st-century man? The problem is our exposure to and damage to various systems. Indeed, a strong geomagnetic storm can cause problems on Earth and even in orbit: high-frequency radio communication between ship and shore, between ships and in aircraft navigation. A strong geomagnetic storm can thwart all this. Global positioning systems for precise positionings, such as GPS or the European Galileo system, are also damaged, as they give incorrect signals to their users in strong magnetic storms. In Quebec, Canada, in March 1989, the storm overloaded a transformer, causing the whole system to collapse - and six million people there were without power for nine hours. When we are at solar maximum, and the grid is already at maximum capacity due to the increased heat, the outlook is even bleaker, with more difficulty to deal with space weather events in the event of a major geomagnetic activity storm.

The space weather forecast

Humanity has already launched hundreds of satellites, and our knowledge and data processing capabilities are growing. The American spaceweather.com and the European Space Weather Service Network act as space weather forecasting websites: they report on the current status of sunspots, in addition to the current status of solar winds and solar flares. But this is just an enthusiastic amateur's site. If you want professional visualisation and data, check out the US space weather forecasting centre on the web! The SWPC continuously monitors the Earth's immediate space environment, provides accurate, reliable information on events in the Sun-Earth relationship, coordinates research and development programmes, and plays a leading role in the space weather community.

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