Question

The plasma density in the lower ionosphere has
been measured during satellite re-entry to be
about 1018 m-3 at 50km altitude, 1017 at 70 km,
and 1014 at 8km. What are the plasma frequencies
there?

Answer 1

The plasma frequencies can be expressed as

$$f=\frac{\omega}{2\pi}=\frac{e}{2\pi}\sqrt{\frac{n_e}{m_e\epsilon_0}}.$$

At 50-km altitude: $f=8.979\text{ GHz}$

At 70 km: $f=2.839\text{ GHz}$

At 8 km: $f=89.79\text{ MHz}$