*Question T3C08:
What causes tropospheric ducting?*  

*Correct Answer is  D: Temperature inversions in the atmosphere*  

### AI Response: (may contain errors)  

Tropospheric ducting is a phenomenon that allows radio waves to travel much farther than normal due to specific atmospheric conditions. 

### Correct Answer: D - Temperature inversions in the atmosphere

- **Explanation**: 
  - A temperature inversion occurs when a layer of warm air traps cooler air near the ground. This creates a "duct" that can reflect radio waves back towards the Earth, allowing them to travel over long distances. The warm air acts as a barrier, preventing the radio waves from dissipating into the atmosphere.

### Why the Other Choices are Incorrect:

- **A: Discharges of lightning during electrical storms**: 
  - While lightning can create radio frequency noise and affect propagation, it does not create the conditions necessary for tropospheric ducting. Lightning discharges are transient events and do not establish a stable atmospheric layer.

- **B: Sunspots and solar flares**: 
  - These solar phenomena primarily affect ionospheric propagation rather than tropospheric conditions. They can enhance or disrupt radio communications at higher frequencies but do not contribute to ducting in the troposphere.

- **C: Updrafts from hurricanes and tornadoes**: 
  - Although severe weather can influence radio wave propagation, updrafts themselves do not create the stable temperature layers required for ducting. They can cause turbulence and scattering of signals rather than enhancing long-distance propagation.

### Summary:
Tropospheric ducting is primarily caused by temperature inversions, which create a stable layer in the atmosphere that reflects radio waves. Understanding this concept is crucial for predicting radio wave behavior under various atmospheric conditions.