Ionosphere
Definition
The ionosphere is a region of Earth’s upper atmosphere (about 60 km to 1000 km) that contains ionized gases (free electrons and ions) created by solar radiation.
Importance:
- Radio communication
- Satellite signals
- Navigation systems
Layers of the Ionosphere
D Layer
- Height: 60–90 km
- Electron density: ~10⁸ electrons/m³
- Main gases: N₂, O₂
- Feature: Absorbs low-frequency radio waves; disappears at night
E Layer
- Height: 90–140 km
- Electron density: ~10¹⁰ electrons/m³
- Main gases: Molecular + atomic oxygen
- Feature: Reflects medium-frequency radio waves
F1 Layer
- Height: 140–250 km
- Electron density: ~10¹¹ electrons/m³
- Main gases: Atomic oxygen
- Feature: Exists only during daytime
F2 Layer
- Height: 250–400+ km
- Electron density: ~10¹² electrons/m³
- Main gases: Atomic oxygen and light ions
- Feature: Reflects high-frequency waves; exists day and night
Electron Density Summary
| Layer | Height (km) | Electron Density | Key Feature |
|---|---|---|---|
| D | 60–90 | 10⁸ /m³ | Absorption |
| E | 90–140 | 10¹⁰ /m³ | Reflection (MF) |
| F1 | 140–250 | 10¹¹ /m³ | Daytime layer |
| F2 | 250–400+ | 10¹² /m³ | HF reflection |
- Ionization is caused by solar UV and X-rays
- Electron density increases with altitude (up to F2)
- D layer disappears at night
- F1 merges with F2 at night
- F2 layer is most important for communication
Applications
- AM radio affected by D layer
- Shortwave radio uses F2 layer
- GPS signals pass through ionosphere