*Question G3A02:
What effect does a sudden ionospheric disturbance have on the daytime ionospheric propagation?*  

*Correct Answer is  B: It disrupts signals on lower frequencies more than those on higher frequencies*  

### AI Response: (may contain errors)  

A sudden ionospheric disturbance (SID) is typically caused by solar flares, which emit a burst of X-rays and ultraviolet radiation. This radiation increases ionization in the D-layer of the ionosphere, which is the lowest layer and primarily affects HF radio waves.

1. **Correct Answer (B):**  
   - **Disruption on Lower Frequencies:** The increased ionization in the D-layer during a SID causes greater absorption of radio waves, especially at lower HF frequencies. This is because lower frequencies are more susceptible to absorption in the D-layer, leading to a significant reduction in their propagation range.
   - **Higher Frequencies Less Affected:** Higher HF frequencies are less affected because they are less absorbed by the D-layer and can often penetrate to higher layers of the ionosphere, like the F-layer, which is responsible for long-distance propagation.

2. **Why Other Choices Are Incorrect:**
   - **Choice A:** "It enhances propagation on all HF frequencies" is incorrect because SIDs generally cause absorption, not enhancement, of HF signals, especially at lower frequencies.
   - **Choice C:** "It disrupts communications via satellite more than direct communications" is incorrect because SIDs primarily affect HF propagation, not satellite communications, which typically use much higher frequencies (e.g., UHF, SHF) that are not significantly impacted by ionospheric disturbances.
   - **Choice D:** "None, because only areas on the night side of the Earth are affected" is incorrect because SIDs affect the sunlit side of the Earth, where the increased ionization occurs due to solar radiation.

3. **Useful Rule of Thumb:**
   - **D-Layer Absorption:** Lower frequencies (e.g., below 10 MHz) are more affected by D-layer absorption during the day, especially during SIDs, while higher frequencies (e.g., above 20 MHz) are less affected and may still propagate effectively.