09 December 2010
In this series on the effect of space weather and solar flares, we reviewed the energetic mechanisms of solar flares and their multiple consequences on Earth and on human technologies, and we looked at solar wind. But the storms do not just happen "up there". Some particles are so penetrating that they come “down here,” causing disruptions and posing health risks.
Particles can reach the altitude of cruising civil aircrafts following high latitude routes, like the crowded Europe-US route. During a large storm, passengers and crewmembers can be exposed to radiation doses equivalent to several chest radiographies. While not a direct health threat for occasional travelers, the exposure to this enhanced irradiation accumulates over the career of pilots and flight attendants. This is why special suitcases filled with particle detectors are flown regularly on civil aircrafts to better assess the particles fluxes in correspondence with the occurrence of solar storms.
Solar radiation alert regions based on average dose rates affecting aircrafts at the typical 35000-feet altitude of long distance flights
(Map courtesy of US Federal Aviation Administration)
When precipitating into the upper atmosphere, the solar energetic particles also induce bursts of ionization mainly in the polar ionosphere. This can cause disruptions of telecommunications (radio blackouts) during minutes for small events but up to several hours for severe storms. For the same reason, the GPS navigation system will also suffer from large losses in precision, from tens to hundreds of meters. While some services can be resilient to such disruptions by simply avoiding the stormy period if they can be predicted early enough (geodesy for oil prospecting, etc.), safety-critical applications like aviation are badly affected during such events. This is taken very seriously especially in the perspective of developing high-latitude polar routes between continents, as such shorter routes allow substantial reductions of fuel consumption and costs. The geomagnetic storms are indeed acting more vigorously near the poles (latitudes above 65°), although for large events, perturbations are experienced almost everywhere on Earth.
Sample maps showing the disturbances in the ground-satellite signal propagation of the GPS navigation system. Those disturbances are reducing the positional accuracy normally provided by GPS receivers, disrupting various applications and services (Image courtesy of CLS/SWNET, ESA)
Beside the particle "showers", another rather common physical mechanism is at work and once again at giant Earth-encompassing scales: current induction. Indeed, streams of particles accelerated by the geomagnetic storm are equivalent to huge electrical current systems, like the equatorial ring current or polar currents that circle around the Earth. Just like any current flowing along an electrical wire, this generates a varying magnetic field down to the ground level. This fluctuating magnetic field can then induce large-scale currents in any long-distance electrical conductor on Earth, like the electrical power grid or pipelines. Those geomagnetically induced currents are of course commensurable with the scale of geomagnetic storms: typical values reach tens of Amperes, even reaching about 150 Amperes for strong events.
The Earth magnetosphere is crossed by large-scale current systems shown here by the colored arrows. The equatorial ring current and the polar field-aligned currents are the main causes of intense planet-wide induced currents on the ground at the times of geomagnetic storms (Graphic courtesy of NGDC/NOAA)
Those currents have the property to neutralize the cathodic protection of pipelines and to accelerate the corrosion of buried pipelines. Therefore, maintenance plans and budgets for such infrastructure are adapted to the overall trend of solar activity that controls the frequency of occurrence of geomagnetic storms. So, as you can see, contrary to common sense, the solar presence is not simply floating above our heads. Actually, it is thus even felt down below the ground level.
The next installment
The effects of geomagnetic storms do not end here. Those induced geomagnetic currents have another much more immediate and destructive impact at ground level: large-scale disruptions and failures in the electrical power distribution, the so-called power grids. This topic will be part of the final article in this series, which will review our capacities to monitor and understand the whole chain of phenomena that can connect an apparently remote bursty magnetic reconfiguration at the solar surface and in your daily life.
About the Author
Dr. Frédéric Clette is solar physicist at the Royal Observatory of Belgium. He is an active researcher and science operator at the Solar Influences Data analysis Center (SIDC). He is also leading the development and operations of the Uccle solar patrol instruments (USET).
Other articles in the Solar Novus Today series on solar flares:
See "Real-time Image of the Sun" for a near real-time image of the sun, provided by the Extreme Utraviolet Imaging Telescope (EIT) aboard the SOHO (Solar & Heliospheric Observatory) spacecraft.
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