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Sun-weather: a new kind of connection

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Sunspots, flares, and other solar activity have long tempted climatologists to link their 11- and 22-year cycles with Earth's climate. But all such theories beg the question of what physical connection this action on the sun could have with weather on Earth.

Solar physicist Sabatino Sofia says he thinks he has a plausible answer. He and his colleagues at the NASA Goddard Space Flight Center are developing a theory of solar magnetism which suggests the sun expands and contracts during its cycles, thus significantly altering the solar energy which powers Earth's weather.

Solar cycles are rooted in the sun's magnetic activity. Sunspots, flares, and other forms of activity at the sun's surface rise to a crescendo and subside into quiescence over roughly an 11-year period. The solar magnetic field also reverses itself during this time. Thus it takes two such periods for the magnetic field to return to its original orientation--a 22-year cycle.

How the surface activity with its 11-year cycle is related to the magnetic field with its 22-year cycle is a longstanding puzzle. Sophia's theory builds on the main theory advanced to explain it.

The magnetic fields at the sun's surface are normally rather weak - about 10 times the strength of Earth's field. But near sunspots and other centers of action, they can reach strengths hundreds of thousands of times greater. Physicists attribute such strengthening to twisting and tightening of lines of magnetic force by turbulent motions in the sun's outer layer and to that layer's rotation.

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