Sunspots and Geomagnetic Disturbances

The magnetic field of the Earth, or the geomagnetic field, as measured at ground based observatories, is a combination of contributions from the main field internal to the planet, currents flowing within the Earth's crust and its liquid core, as well as electric current systems surrounding the Earth.  The main field creates a cavity in interplanetary space called the magnetosphere.  The magnetosphere is shaped somewhat like a comet in response to the dynamic pressure of the solar wind.  The magnetosphere is compressed on the side toward the sun to about 10 Earth radii and is extended tail-like on the side away from the sun to more than 100 Earth radii.

The Geomagnetic Field  Picture and description can be found at the following website: http://web.ngdc.noaa.gov/stp/ GEOMAG/geomag1.html

The strength of geomagnetic activity is measured by a number of indices, some of which have been available for many years.  The longest running series of any index is that of the AA index (a 3-hourly measure of the equivalent amplitude antipodal index).  This index is based on observations at two nearly antipodal stations (Canberra in Australia and Hartland in the United Kingdom).  This means that the index is a global index, representing world-wide magnetic activity rather than local features.  Australian observatories are particularly important in a global context and have a considerable history. They are among the few observatories in the southern hemisphere, and have achieved long records of continuous observations. The observatory set up in Hobart in 1840 by the polar explorer James Clark Ross, at the behest of the British Government, was one of the first magnetic observatories to be established anywhere in the world.

Both the sunspot number data and the AA index data are archived through the National Oceanic and Atmospheric Administration (NOAA).  As part of the NOAA, the National Geophysical Data Center (NGDC) in Boulder, Colorado manages data from the upper atmosphere, space environment, and Sun; data from the land, sea, and Earth's interior; data on ice and snow cover; and paleoclimate data.