General exam question G3A13
Subelement G3, RADIO WAVE PROPAGATION· Group G3A
G3A13
What does the A-index measure?
- A.The relative position of sunspots on the surface of the Sun
- B.The amount of polarization of the Sun’s electric field
- C.The long-term stability of Earth’s geomagnetic field (correct answer)
- D.The solar radio flux at Boulder, Colorado
WhyThe A-index measures the long-term stability of Earth's geomagnetic field. The A-index summarizes geomagnetic stability over a longer period, a daily average built up from the shorter-term K-index readings, answer C. It isn't about sunspot position, solar electric field polarization (not a real measurable quantity in this context), or solar radio flux, those are unrelated or different measurements.
Published 2026-08-28 · Last updated 2026-08-28 · Question text is verbatim from the 2023-2027 NCVEC Element 3 pool (public domain); the explanation above is original writing, see our methodology.
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