*Question E3C03:
Which of the following signal paths is most likely to experience high levels of absorption when the A-index or K-index is elevated?*  

*Correct Answer is  B: Through the auroral oval*  

### AI Response: (may contain errors)  

The correct answer to the question is **B: Through the auroral oval**. Here's why:

1. **Why the correct answer is correct:**
   - The auroral oval is an area around the poles where auroras occur, typically due to charged particles from the sun interacting with the Earth's magnetic field. When the A-index or K-index is elevated, it indicates increased geomagnetic activity, which can lead to higher levels of ionospheric absorption in this region. Signals passing through the auroral oval are likely to experience significant absorption, resulting in weaker signals.

2. **Why the other choices are incorrect:**
   - **A: Transequatorial**: This path typically involves signals traveling across the equator and is less affected by geomagnetic storms. While it can experience some absorption, it is not as severely impacted as signals through the auroral oval.
   - **C: Sporadic-E**: This refers to short-lived, irregular ionization in the E layer of the ionosphere. While it can enhance signals, it does not typically experience high absorption levels during elevated geomagnetic activity.
   - **D: NVIS (Near Vertical Incidence Skywave)**: NVIS is used for communication over short distances, typically under 300 miles. While it can be affected by ionospheric conditions, it is not as susceptible to absorption as signals passing through the auroral oval.

3. **Useful formulas or rules of thumb:**
   - A general rule of thumb is that higher geomagnetic activity (indicated by higher A or K indices) correlates with increased absorption in the ionosphere, particularly in polar regions. 
   - For practical purposes, when planning communications, consider the current A and K indices to assess potential signal degradation, especially for paths that may intersect the auroral oval.

In summary, signals traveling through the auroral oval are most affected by absorption during periods of elevated geomagnetic activity, making option B the correct choice.