Sectors

When magnetic records from polar regions on quiet days are inspected, a special daily solar sector effect is found. Depending on the direction of the field component attending the solar wind, toward (T) or away (A) from the Sun, a corresponding field change occurs. Because the polar region field lines in space connect to the downstream magnetospheric tail boundary, there is a correspondence of the interaction of the weak tail field region with the toward or away direction of the prevailing solar wind. The sector effect is seen as a

FIGURE 3.19 ► Oscillating primary (source) currents above the Earth's surface cause secondary (induced) currents to flow within the conducting Earth. The penetration of the magnetic fields within the Earth decreases with increasing frequency of the oscillation and decreases with an increase of the Earth's conductivity.

FIGURE 3.19 ► Oscillating primary (source) currents above the Earth's surface cause secondary (induced) currents to flow within the conducting Earth. The penetration of the magnetic fields within the Earth decreases with increasing frequency of the oscillation and decreases with an increase of the Earth's conductivity.

Thüle, Greenland

Toward Sector June 8

Away Sector June 12

Universal Time

FIGURE 3.20 ► Toward and Away solar-sector effects can be observed at the north geomagnetic pole station, Thule, Greenland. There is a complete change in the phase of the sine wave that best represents the two records (light smooth curve).

a phase shift in the 100-gamma daily oscillation of quiet condition variation field at a polar cap observatory (Figure 3.20). Traces of these sector-field effects can extend down to the middle latitudes (see also Section 5.2.4, p. 130.

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