Space
weather

“Space weather” describes the physical state of the space surrounding the earth and planets of the solar system, which is permeated by the solar wind. This is a continuous flux of electrically charged particles (or “plasma”), which is confined by the similar “interstellar wind” within a huge bubble called heliosphere. The sun is a stable, middle-aged yellow dwarf star which is about 5 billion years old. As it rotates, it transforms the weak magnetic field produced by its internal dynamo into strong magnetic fields emitting from the solar spots. The amount of solar spots characterizes the sun’s activity cycle, on a period of about 11 years. A scarcity of solar spots indicates that the sun is in a phase of low activity. Conversely, a high number of spots tells us that the sun’s activity is very strong. This characteristic derives from the fact that solar spots can release magnetic energy during the so-called “flares” emitted by the chromosphere, accompanied by particle acceleration and by the emission of electromagnetic radiation, ranging from X-rays to radio waves. Huge “plasma bubbles” (coronal mass ejections, or CME) are accelerated towards the planets. If a planet has a magnetic field which acts as a shield against particles from space, the field is compressed and magnetic storms ensue.

On earth, polar auroras are observed, as delicate, multicolor tapestries. They shine because the atoms and molecules of the atmosphere are excited by solar particles that pass through the magnetic shield. This phenomenon occurs also on other planets of the solar system, such as Jupiter and Saturn. The perturbations in the ionosphere influence the quality of radio transmissions, and create difficulties for the use of, for example, Gps systems. In addition, intense electric currents in the ionosphere can induce strong additional currents in power lines, causing electrical blackouts. Planes flying on polar routes can be hit by dangerous amounts of ionizing radiation and experience problems with their on-board instruments. During solar storms, astronauts performing extra-vehicular activities could absorb strong amounts of radiation, and satellites can suffer temporary, or in the worst case permanent, malfunctions, caused by solar and cosmic particles (cosmic rays) that interfere with their electronic equipment.

Space weather also concerns the study, modelling, and forecast of space meteorology, using data from space and earth-bound observatories. Space meteorology is a fairly new subject, concerning the weather in the entire heliosphere, which is determined not just by the Sun star, but also from high-energy phenomena occurring throughout our galaxy, or even in external galaxies. The flux and energy distribution of cosmic rays, in fact, is related to the evolution of close and distant populations of supernovae, while gamma-ray bursts (GRB) are caused by processes such as those occurring in hypernovae stars, or in stars with exceptionally strong magnetic fields (magnetars). These phenomena require long and difficult studies, which aim to build an experimental and interpretative scenario for space climate, considered the long-term evolution of space weather.

Space weather monitoring is based on observations from earth and from space, but at present the observing network is not large enough to provide a global coverage with the required detail. This lack of a strong infrastructure also limits the development of consolidated operational models for the forecasting of perturbations. Therefore, for several phenomena instantaneous observations (nowcasting) have to suffice, while the prediction (forecasting) of the sun’s activity cycle, flares, and CME remains in the early stages of development, despite the use of sophisticated methods based on long-term observations and on artificial neural networks.