Question
What is indicated by a rising A-index or K-index?
Answer Options
- A) Increasing disturbance of the geomagnetic field
- B) Decreasing disturbance of the geomagnetic field
- C) Higher levels of solar UV radiation
- D) An increase in the critical frequency
Correct Answer: A
Explanation
The A-index and K-index are two critical indicators in space weather forecasting that track the stability of the Earth’s magnetic field. The K-index is a local, short-term measure (3-hour periods) of geomagnetic activity, while the A-index is a worldwide daily average based on the K-index measurements. Both are directly related to particle activity from the Sun.
A rising A-index or K-index indicates an increasing disturbance of the geomagnetic field, typically caused by incoming charged particles from the Sun (like those released during a coronal mass ejection). High values (e.g., K=5 or higher, A=25 or higher) usually correspond to stormy geomagnetic conditions, which often cause degraded HF propagation, increased absorption, and the potential for auroral activity on VHF.
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