# Space Weather Effects on Satellites
## 1 Introduction  
The term'space weather' (SW) first appeared in the scientific literature in 1968; see [1] for a historical review of the relevant terminology. Nowadays, the SW concept includes a multitude of solar drivers and their environmental, technological, and biological effects via different physical mechanisms and a chain of processes. A widely-circulated definition of SW from the 1995 issue of the US National Space Weather Program, _The Strategic Plan of Space Weather_, reads as 'conditions on the Sun and in the solar wind, magnetosphere, ionosphere and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health' [2]. This multi-disciplinary sphere of research is gaining attention in both academic and commercial aspects due to its social relevance and the high economic costs of extreme SW events [3; 4; 5]. The solar drivers of SW can be summarized as electromagnetic (EM) emissions by solar flares (SFs); pressure and magnetic field interaction of the coronal mass ejections (CMEs) and fast-speed solar wind streams: co-rotating interaction regions (CIRs)/streaming interaction regions (SIRs); and radiation by solar energetic particles: protons (SEPs) and electrons (SEEs). All these solar activity drivers are known as the solar perspective of SW [6; 7; 8]. SFs are the most violent explosions in the solar system, releasing up to \(10^{25}\) J of energy, causing magnetic field line re-configurations in the corona, mass motion, and particle acceleration [9; 10]. Their EM radiation is the first to arrive at Earth (in about 8 min) and cause SW effects. In contrast, CMEs are the last to arrive (up to 3-5 days after the SF flash phase) and cause a disturbance. The CMEs are large magnetized clouds of plasma expelled from the corona into the interplanetary (IP) space. Single-spacecraft observations provide theiron-sky projected speeds which range from a few hundred to over 3000 km s\({}^{-1}\)[11, 12]. The CMEs are the drivers of the geomagnetic storms (GSs) occurring when a southward-directed IP magnetic field (termed \(B_{z}\)-component) and the day-side of the terrestrial magnetosphere undergo a process known as magnetic reconnection [13, 14]. The magnetic reconnection is the underlying process that powers the SFs as well. Nowadays, the chain of processes that takes place in the magnetosphere is well established, leading to the development of ring current systems that eventually causing a decrease in the terrestrial magnetic field. The CMEs near the Sun and their IP counterparts (ICMEs) and their link to GSs have been the topic of numerous research studies, e.g., [15, 16, 17, 18] and the references therein. Apart from the ICME arrivals, high-speed solar wind streams can cause the so-called recurrent GSs, which are usually weaker than the ICME-driven ones, e.g., [19, 20]. The intermediate, in time scale, SW effects are those from energetic particles. SEEs arrive shortly after the SF brightening (10s of minutes), whereas SEEs can take hours to be recorded at the spacecraft, usually situated at the first Lagrange point (L1), constantly facing the Sun. These in situ observed electrons, protons, and heavy ions, with keV up to hundreds of MeV energies, show a velocity dispersion in their intensity-time profiles (e.g., the high-energy particle channels peak earlier in time), which is taken as an evidence for their solar origin [21, 22]. Despite the ongoing debate in the literature, nowadays both SFs and CMEs are considered as their solar origin [23, 24]. The in situ particles can have important SW effects on technology in the IP space. For example, during strong SEP events the spacecraft optical systems can be saturated due to the impact of particles on the CCD matrix, leading to so-called snow-like effects. The images are thus highly degraded in quality, and usually the spacecraft is switched off into a safe mode.