This area is particularly important to ionospheric radio communications because this is the area where most of the absorption of radio signal energy occurs. The majority of the energy is extinguished in the extreme lower region of the ionosphere (around 50–80 km in altitude). However, during unusually strong flares, protons can be accelerated to sufficient energies to reach the Earth's magnetosphere and ionosphere around the north pole and south pole.Įnergetic protons that are guided into the polar regions collide with atmospheric constituents and release their energy through the process of ionization. Protons accelerated during an SPE normally have insufficient energy to penetrate the Earth's magnetic field. They are less intense near Earth than gradual events.Īn additional hybrid class has been identified which involves characteristics of both gradual and impulsive events. They are associated with short-duration flare emissions at low altitudes and type III radio bursts.

Impulsive SPEs are thought to involve the acceleration of particles mostly by processes associated with magnetic reconnection and wave-particle interactions at the locations of solar flares.

These events produce the highest particle intensities near Earth. They are associated with type II radio bursts and are characterized by elemental abundances, charge states, and temperatures similar to that of the ambient corona. Gradual SPEs are thought to involve the acceleration of particles by shocks driven by coronal mass ejections in the upper corona. However, SPEs can generally be divided into two classes based on their acceleration mechanisms. The physical mechanism behind the acceleration of solar energetic particles leading up to SPEs is currently debated. When solar energetic particles interact with the Earth's magnetosphere, they are guided by the Earth's magnetic field towards the north and south poles where they can penetrate into the upper atmosphere. These charged particles, referred to as solar energetic particles, can escape into interplanetary space where they follow the interplanetary magnetic field. SPEs occur when charged particles in the Sun's atmosphere are accelerated to extremely high velocities. Energetic protons are a significant radiation hazard to spacecraft and astronauts. These particles can penetrate the Earth's magnetic field and cause partial ionization of the ionosphere.

Other nuclei such as helium and HZE ions may also be accelerated during the event. In solar physics, a solar particle event ( SPE), also known as a solar energetic particle ( SEP) event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in the Sun's atmosphere during a solar flare or in interplanetary space by a coronal mass ejection shock.

Post-eruptive loops in the wake of a solar flare, image taken by the TRACE satellite (photo by NASA)

Solar energetic paeticles an astronauts