Science
Temporal Variations Within the Coupled Solar-Terrestrial System
Frames from a global MHD simulation [courtesy of C. Goodrich and M. Wiltberger] showing the solar wind-magnetosphere interaction for a period of interest in January 1997. An interplanetary shock wave passing over the magnetosphere greatly compresses and distorts the magnetospheric cavity (as shown by the color-coded density repre-sentations in the noon-midnight plane).
Physical processes on the Sun, the Earth, and the environment in between, all vary continuously. Changing magnetic fields in the solar atmosphere, driven by an interior dynamo, cause solar variability. The resultant alterations of energy output and organization, in the form of electromagnetic and particle radiation and structure of the interplanetary magnetic field, and solar wind plasma, induce terrestrial variability, in the form of temperature, composition and particle populations at altitudes from the Earth's surface to the near-earth space environment. The figure below shows two panels displaying results from a computer model of an event in January 1997, when a shock wave in the solar wind collided with and reorganized Earth's magnetosphere, producing rapid changes.
Examples of solar terrestrial phenomena sorted by time scales.
Within and among the Earth's atmosphere, ionosphere and magnetosphere, internal oscillations and instabilities are sources of longer-term variability. Table 1 lists typical changing phenomena in different regions of the sun-earth system. Time-scales range from minutes to centuries. Terrestrial changes can result directly from the 11-year cycle modulation of the Sun's energy output (Figure 8(a): Sunspot Cycle), as well as from the cumulative effects of shorter term variations associated with eruptive events and solar rotations that occur at different rates and with different amplitudes at different phases of the activity cycle.
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