---
tags: Intro to Space and Engineering, ss, ncu, Ionosphere
author: N0-Ball
GA: UA-208228992-1
---

# Ionosphere

## upper atmosphere


- Lower domain
- turbulent
- various atomic and molecular
- mixed
- molecular diffusion
- region extends from 110 to 500 km
- = ionosphere and atmosphere
- higher altitude
- long collisional mean-free-path
- particles follow ballistec trajectories
- some escape from the atmosphere
- Fluid approach in a rarefied gas
- collisions occur frequently on spatial
- time scales much smaller than those characterizing the phenomena of interest

$$
\lambda >> \lambda_c \\[1em]
\omega << v_c
$$

## Scale height


## Terrestrial ionosphere


## Plasma in Ionosphere


- Production or destruction of ionization (photochemical)
- Movement of ionization (transport)

$$
\frac{\partial n_e}{\partial t} + \nabla \cdot (n_e v_e) = P_e - L_e
$$


## Production mechanisms for electrons

### Photoionization


- absorption at least in low and mid-latitudes
- solar Extreme UltraViolet (EUV)
- X-ray
- Photons greater than about 12 eV(100nm within EUV) can ionsize the major atmospheric constituents
- Provides **heat input**
- maintain high temperatures of thermosphere
- excess energy -> kinetic energy of ion-electron pair
- transformed to heat upon recombination

### Energy sources and sinks

- EUV radiation
- particle

ex.
$$
NO_2 + hv \rightarrow NO + O
$$


## Solar spectrum


### X-rays
- wavelength range of $10 < \lambda \le 0.01nm$
- Hard X-ray
- wavelength range of $1nm > \lambda (> 1.2 keV)$
- Soft X-ray
- wavelength range of $10nm > \lambda \ge 1nm$
- XUV

### Ultraviolet
- wavelength range of $400 < \lambda \le 10nm$
- Extreme Ultraviolet
- EUV
- wavelength range of $100nm > \lambda \ge 10nm$
- Vacuum Ultraviolet
- VUV
- wavelength range of $200nm > \lambda \ge 10nm$
- Ultraviolet
- UV
- wavelength range of $400nm > \lambda \ge 100nm$

## Chapman layer


**Thereotical**

## Photoionaization

- F region
- EUV (17 - 19.1nm)
- *O* ionized by $\lambda < 91.1nm$
- $O + hv \rightarrow O^+ + e^-$
- *N~2~* ionized by $\lambda < 79.6nm$
- $N_2 + hv \rightarrow N_2^+ + e^-$
- E region
- EUV (91.1 - 102.7nm)
- *O_2* ionized by $\lambda < 102.7nm$
- $O_2 + hv \rightarrow O^+ + e^-$
- X-rays (1 - 17nm)
- D region
- EUV Ly-$\alpha$ 121.6 nm ionizes *NO*
- $NO + hv \rightarrow NO^+ + e^-$
- X-rays (0.1 - 1nm)

### Loss eactions of ions

- Ion-ion recombination
- $X^+ + Y^- \rightarrow X + Y$
- Electron-ion recombination
- $X^+ + e^- +M \rightarrow X + M$
- $X^+ + e^- \rightarrow X^* + hv$
- $\mathbf{XY^+ + e^- \rightarrow X^* + Y^*}$
- Ion-neutral (atom or molecule) interchange
- $\mathbf{X^+ + YZ \rightarrow XY^+ + Z}$
- $X^+ + YZ \rightarrow YZ^* + X$
- Collisional detachment (three body attachment)
- $X^- + M \rightleftharpoons X + e^- + M$
- $X^- + M^* \rightarrow X + e^- + M$
- Associative detachment (dissociative attachment)
- $X^- + Y \rightleftharpoons XY + e^-$
- Photo-detachment (radiative attachment)
- $X^- + hv \rightleftharpoons X + e^-$

## Topside Ionosphere

- Above F2 layer peak (atmospheric density is too low)
- chemical recombination become less important
- diffusive time constant becomes smaller than chemical time constant
- Below
- chemical recombination and transport are equally important
- Dominated by *O^+^*
- Exosphere
- Dominated by *H^+^*

## F region

- altitudes > 200km
- principal ion formed is *O^+^* By EUV (17-91.1 nm)
- $O + hv \rightarrow O^+ + e^-$
- at $\lambda < 91.1nm$
- *O^+^* loss process is **Radiative recombination**
- extremely low reaction rate
- $O^+ + e^- \rightarrow O + hv$
- $k = 3 \times 10^{-12} cm^3s^{-1}$

### ion-atom interchange

- recombination ($\beta$ loss)
- $O^+ + O_2 \rightarrow O_2^+ + O$
- k = 2x10^-11^
- $O^+ + N_2 \rightarrow NO^+ + N$
- k = 1x10^-12^
- dissociative recombination ($\alpha$ loss)
- $O_2^+ + e^- \rightarrow O + O$
- $NO^+ + e^- \rightarrow N + O$
- k=3x10^-7^

## F1 region

- altitudes 140-200 km
- principal ion formed is *O^+^* By EUV (17-91.1 nm)
- $O + hν \rightarrow O^+ + e^-$
- at $\lambda < 91.1nm$
- with some contribution from
- $N_2 + hν \rightarrow N_2^+ + e^-$
- at $\lambda < 97.6nm$

## E region

- altitudes 90-140 km
- mainly produced from *O~2~* molecules by EUV (91.1-102.7 nm)
- $O_2 + hν \rightarrow O_2^+ + e^-$
- Additional ionization of nitrogen molecules by coronal X-rays (1-17 nm)
- $N_2 + hv \rightarrow N^+ + e^-$
- $N_2^+ + O \rightarrow N + NO^+$
- $N_2^+ + O_2 \rightarrow N_2 + O_2^+$

### The distinguishing feature between E and F1 layers

- F1
- Radiative recombination is extremely low
- Must transfer their charge to molecules prior to recombination
- E
- Directly recombination
- Typically, the reaction rate is a factor of 100,000 smaller than the dissociate recombination process.