- D layer at 70-80 km is weakly ionised but during the day, particularly in summer, can absorb frequencies below 3-4 MHz, preventing Dx at these frequencies. The layer disappears at night
- E Layer at same altitude day and night (120 km). Intensity increases with sunlight, max at noon
- F Layer separates during daylight into F1 and F2 layers
- F Layer (night-time) height is 350 km
- F1 (day-time) height is 200 km and F2 (day-time) is 450 km