*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)  

When studying for the FCC exam, it's important to understand how different atmospheric conditions affect radio signal propagation. The A-index and K-index are measures of geomagnetic activity, which can influence radio wave absorption.

### Explanation:

1. **Correct Answer: Through the auroral oval**

   - **Why it's correct:**  
     The auroral oval is a region around the magnetic poles where auroras occur. 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. This absorption is due to increased ionization and turbulence in the ionosphere, which can significantly attenuate radio signals passing through the auroral oval.

2. **Why the other choices are incorrect:**

   - **Transequatorial (A):**  
     Transequatorial propagation involves signals traveling across the equator. This path is less affected by geomagnetic activity and more influenced by solar activity and ionospheric conditions near the equator, making it less likely to experience high absorption due to elevated A-index or K-index.

   - **Sporadic-E (C):**  
     Sporadic-E propagation occurs when signals reflect off dense patches of ionization in the E layer of the ionosphere. This phenomenon is not directly related to geomagnetic activity and is more influenced by local ionospheric conditions, so it is less likely to be affected by elevated A-index or K-index.

   - **NVIS (D):**  
     Near Vertical Incidence Skywave (NVIS) propagation involves signals being sent nearly straight up and reflecting back down from the ionosphere. NVIS is typically used for short-range communication and is less affected by geomagnetic activity compared to paths through the auroral oval.

### Useful Rule of Thumb:

- **Geomagnetic Activity and Absorption:**  
  Elevated A-index or K-index values indicate increased geomagnetic activity, which can lead to higher absorption in polar and auroral regions. This is due to increased ionization and disturbances in the ionosphere, particularly affecting paths through the auroral oval.