4. Sun-Earth Connection

    • The space outside the Eart?s atmosphere is not empty. It is filled with pieces of the Sun.

    • We are protected from the full blast of the Sunís violent activity by a dipolar magnetic field that diverts charged particles around the Earth and forms a cavity, called the magnetosphere, within the Sunís relentless winds.

    • The Earthís magnetic barrier is imperfect, and some of the tempestuous solar wind can buffet and even penetrate the magnetosphere.

    • The Sunís wind brings the solar and terrestrial magnetic fields together on the night side of the Earth, where electrons and protons can enter the magnetosphere and become accelerated within it.

    • Doughnut-shaped belts of energetic electrons and protons girdle the Earthís equator. These Van Allen belts are fed by the Sunís winds and by cosmic rays coming from interstellar space.

    • Intense, non-recurrent geomagnetic storms, accompanied by exceptionally bright auroras, occur at times of high solar activity when fast coronal mass ejections hit the Earthís magnetosphere and have the right magnetic alignment with it.

    • When the Sun is near a lull in its 11-year activity cycle, magnetic waves formed by the Sunís interacting winds strike the Earthís magnetic field and connect with it, producing moderate geomagnetic storms with a 27-day repetition period and relatively faint auroras.

    • When viewed from space, the auroras form an oval centered on each magnetic pole, where magnetic fields guide energetic electrons down into the Earthís upper atmosphere.

    • The auroras are caused by high-speed electrons that pump up oxygen and nitrogen molecules in the atmosphere, causing them to fluoresce like a cosmic neon sign.

    • High-speed protons and electrons, generated during explosive solar activity, can cripple satellites and endanger space-walking astronauts.

    • When encountering the Earth, coronal mass ejections can compress the magnetosphere below the orbits of geosynchronous satellites that hover above one place on Earth.

    • Coronal mass ejections that strike the Earth can generate power surges on transmission lines that could cause electrical power blackouts of entire cities.

    • With adequate warning, we can defend ourselves from violent space weather that is driven by the Sun and its winds. National centers and defense agencies therefore continuously monitor the Sun from ground and space to forecast threatening solar activity.

    • The total solar irradiance of the Earth, the so-called solar constant, rises and falls in step with the 11-year solar cycle, but with a total recent change of only about 0.1 percent. When sunspots cross the visible solar disk, they produce, in themselves, a brief dimming of the irradiance, amounting to a few tenths of one percent for just a few days; a brightness increase caused by faculae and plage exceeds the overall sunspot decrease at times of high solar activity.

    • Solar X-rays and extreme ultraviolet radiation both produce and significantly alter the Earthís ionosphere. The X-rays fluctuate in intensity by two orders of magnitude during the Sunís 11-year magnetic activity cycle. Near activity maximum greater amounts of X-rays produce increased ionization, greater heat, and expansion of our upper atmosphere, altering satellite orbits and disrupting communications.

    • The ozone layer in our stratosphere is both created and modulated by solar ultraviolet radiation, while also protecting us from dangerous ultraviolet sunlight.

    • An ozone hole forms above the South Pole in the local spring. The ozone is being destroyed by chlorine compounds, called chlorofluorocarbons, released into the atmosphere by past human activity. Such compounds have now been outlawed by international agreement.

    • During the past 130 years, the global sea temperature has varied in tandem with the 11-year cycle of solar magnetic activity, and the land air temperature has been correlated with the length of the solar cycle. These temperature variations might be attributed to solar-driven changes in cloud cover, caused by the Sunís 11-year modulation of the amount of cosmic rays reaching Earth.

    • The Earth is now hotter than any time during the previous 1,000 years. This global warming is attributed to carbon dioxide and other heat-trapping greenhouse gases released into the atmosphere by humans.

    • Tree ring and ice core studies respectively show rings high in radiocarbon and snow high in beryllium during the past millennium. They were precipitated over century-long periods when the Sun was inactive and the climate was cold.

    • The major ice ages, that repeat every one hundred thousand years, are caused by astronomical rhythms that alter the angles and distances from which sunlight strikes the Earth.

Copyright 2010, Professor Kenneth R. Lang, Tufts University