19 October 2010
Following the first in our series on space weather and solar flares (“Our Inconstant Sun: Solar activity and flares”), we now take a look at the output of solar flares and its impact on Earth.
Such phenomena have been widely studied and triggered the new scientific discipline “radioastronomy”. Indeed, with the quick development of military radars during World-War II, engineers soon discovered random interfering signals of unknown origin that regularly impeded the radar monitoring of enemy aircrafts. When they realized that this was occurring most often near sunrise and sunset, when the Sun passed through the beam of their horizon-scanning antennas, it became obvious that this was not an intended artificial jamming but a natural phenomenon, which was both unpredictable and uncontrollable. This prompted the development of a global worldwide monitoring of solar activity that has developed further until now, with the recent advent of a fully fledged discipline, now called "space weather".
Given the more and more widespread use of navigation systems in our everyday life… solar flares are more than ever the focus of human attention.
What happens, as described in the previous article, is that giant magnetic fields emerge continuously at the surface of the Sun forming huge magnetic arcades filled with plasma (electrically charged gas, primarily protons and electrons). As new magnetic fields emerge, they force their way through the pre-existing field. Those collisions cause sudden reorganizations of the magnetic fields, breaking magnetic loops connecting two polarities to form new connections with other magnetic poles.
Satellite, astronaut and flight risks
When magnetic reconnection occurs, the Sun acts as a huge particle accelerator: electrons and protons are accelerated at speeds close to the speed of light. Some of those particle beams can be directed outward and can reach the Earth in less than an hour. Those very penetrating particles can simply pass through the natural shield of the Earth magnetosphere, almost down to the Earth surface. These are satellite "killers", causing the loss of about 10 satellites per decade and damage to many others.
Considering manned missions such as the long-duration stays in the International Space Station, those particles events cause a health risk for astronauts. Solar physicists are thus attached to the manned space operations and can request delays or the cancellation of launches or of Extra Vehicular Activities (EVAs). Major flares can indeed cause enough irradiation to be deadly for astronauts.
In a more attenuated way, but with many more people involved, some of the particles can reach the typical altitude of intercontinental flights. During such events, in one flight, passengers can be exposed to a radiation dose equivalent to several chest radiographies. For flight crews, due to the long term exposure, the total cumulated dose over their career must be evaluated.
Time lapse sequence of the large flare of 16 August, 2002
(Images courtesy of USET/ROB, Brussels)
Extreme-UV image of the solar atmosphere (19.1 nm) showing the intense "flash"
produced by a moderate flare on15 July, 2002. The flare intensity exceeds the
total emission of the quiet solar surface and saturates the CCD detector, causing
the spurious horizontal bar (Image courtesy of EIT, SoHO mission, ESA/NASA)
Continued on next page...