*Question E3B03:
At what time of day is transequatorial propagation most likely to occur?*  

*Correct Answer is  C: Afternoon or early evening*  

### AI Response: (may contain errors)  

Transequatorial propagation (TEP) is a radio wave propagation mode that allows signals to travel over long distances across the equator. It is most effective when the ionosphere is highly ionized, which typically occurs during certain times of the day.

### Explanation:

1. **Correct Answer: Afternoon or early evening (C)**
   - **Why it's correct:** TEP is most likely to occur during the afternoon or early evening because the ionosphere is more ionized due to solar radiation. The increased ionization enhances the ability of the ionosphere to refract radio waves, making TEP more effective during these times.

2. **Why the other choices are incorrect:**
   - **Morning (A):** In the morning, the ionosphere is still recovering from the night and is not yet fully ionized. This makes TEP less likely to occur.
   - **Noon (B):** While the ionosphere is ionized at noon, TEP is more effective when the ionosphere has had more time to build up ionization, which typically happens in the afternoon.
   - **Late at night (D):** At night, the ionosphere loses ionization as there is no solar radiation to maintain it. This makes TEP unlikely to occur.

### Useful Rule of Thumb:

- **TEP Timing:** Generally, TEP is most effective when the sun is setting or has just set, as the ionosphere is still highly ionized from the day's solar activity. This typically corresponds to the afternoon or early evening hours.