---
# System prepended metadata

title: Earth
tags: [' ss', ' ncu', Intro to Space and Engineering]

---

---
tags: Intro to Space and Engineering, ss, ncu
author: No-Ball
GA: UA-208228992-1
---

[TOC]

Earth
===

## Earth Magnetosphere

![](https://solarsystem.nasa.gov/internal_resources/1460/)
- Rigion dominiate by magnetic field
- Not a layer
- No obvious boundary with ionosphere
- View as completely free plasma
    - Most plasma come from ionosphere
    - Little come from solar wind (Hydrogen ion and Helium ion)
    - Hydrogen ion and Oxygen ion
- While facing solar wind, Earth's magnetic dipole field 
    - flat at Dayside
    - long at Nightside

### Bow Shock
- Solar wind stop because of hitting Earth's magnetic field
- Solar wind speed drop form supersonic to subsonic 
    - naturally form a bow shock
- Like bow wave at boat

### Magnetosheath
- turbulence area between magnetopause and bow shock
- plasma are from both ionosphere and solar wind

### Magnetopause
- Obvious boundary at solar wind and magnetosphere
- inner side 
    - ionosphere plasma
    - low dense, high temperature
- outer side
    - megnetosheath plasma
    - high dense, low temperature

### Polar cusp
- Trump like rigion at polar
- connect IMF and magnetic field 
    - plasma in solar wind can enter polar by magnetic field line

### Total pressure
$$
\text P_t = \rho v^2 + \rho R T + \frac{B^2}{2\mu _0}
$$
- $\rho v^2$ is dynamic pressure
- $\rho RT$ is thermal pressure
- $\frac{B^2}{2\mu _0}$ is magnetic pressure

$$
(\text P_t)_\text{solar wind} = (\text P_t)_\text{manetosheath} = (\text P_t)_\text{magnetosphere} \\[1em]
(\rho v^2 + \{\rho R T + \frac{B^2}{2\mu _0}\}\text{(small)})_\text{sw} = (\{\rho v^2 + \rho R T \}\text{(small)}+ \frac{B^2}{2\mu _0})_\text{msp} \\[1em]
\Rightarrow (\rho v^2)_\text{sw} = (\frac{B^2}{2\mu _0})_\text{msp}
$$

### Magnetotail
- Tail structure at nightside

### Plasma sheet
- At magnetotail tropic plain
- weak magnetic field, high plasma dense
- half solar wind half ionosphere 
- $E \times B$ drift 
    - bump like force 
    - push plasma at centre

### lobe
- between plasma sheet and plasma mantle
- Strong magnetic Field, low plasma dense

### Plasmasphere
- nearest part of magnetosphere to Earth
- High magnetic field, high plasma dense
- bigger as the self rotation increase

![](https://www.researchgate.net/profile/Nathan_Case2/publication/261874512/figure/fig6/AS:614175147560981@1523442174604/An-illustration-of-the-Earths-magnetosphere-the-region-of-space-dominated-by-the.png)

### Van Allen Radiation Belt

- Inner Van Allen Belt
    - at 1~2 R~E~ above
    - High energy particle trap in strong magnetic field
    - Increase while collide with other paritcle in plasmasphere
- Outer Van Allen Belt
    - at 4~5 R~E~ above
        - sometimes 3~4
        - sometimes inside plasmasphere sometimes outside
    - plasma from magnetic tail
    - Relative low energy 

#### L-shell

![](https://i.imgur.com/OsKMQo1.png)
- Van Allen radiation belt
    - L=1.5~2.5, L=4~6
- plasmapause
    - L=5
- Aurora 
    - ~L=6 
    - sometimes L=4 or L=2

#### Gradient of Plasma Cause Electric Current

$\vec{E} = (\vec{B} \times \nabla \rho)$

![](https://i.imgur.com/X2ap4md.png)

![](https://i.imgur.com/ZV4Y5K2.png)
- We can see why plasmasheet appears

## Earth's Geomagnetic
![](https://i.imgur.com/TRqrmEI.png)

### Magnetic Motion
![](https://media.nature.com/lw800/magazine-assets/d41586-019-00007-1/d41586-019-00007-1_16383826.jpg)
- Moves faster

### Disturbance Storm Time (DST) Index
- northward component disturbances of the geomagnetic field 
- low-latitude magnetic
- inirect measure of ring current

![](https://i.imgur.com/mamyRtH.png)
![](https://i.imgur.com/9xrDiqt.png)

### Magnetic Storm
- Last
    - 3 ~ 10 days
- Effect
    - mid/low-latitude area
- Process
    - initial phase
        - Dayside magnetopause move in
        - Dayside magnetopause current increase 
        - mid/lot-latitude geomagnetic field increase
    - main phase
        - plasmapause move in 
        - High Energy paricle in Van Allen Radiation Belt increase
        - ring current increase
        - mid/lot-latitude geomagnetic field decrease
    - recovery phase
        - magnetopause and plasmasphere back to normal

![](https://d3i71xaburhd42.cloudfront.net/c3be8cdf9d5873b9ac2b3dc72f265c054d949c79/27-Figure1.9-1.png)

### Kp Index
- disturbance levels int most disturbed horizontal magnetic field component

![](https://i.imgur.com/U6HyYtS.png)

### Auroral Electorjet (AE) Index
- AU, Al, AO, and AE
    - geomagnetic variations in the gorizontal component
- at auroral zone in the norhtern hemisphere

### Magnetic substorm
- Last
    - 3 hr
- Effect
    - high-latitude region
- Process
    - grow phase
        - plasma sheet flatten 
        - magnetic field pulled like magnetic tail
    - expansion phase
        - plasmas sheet grow bigger
        - magnetic field more looks like a dipole
        - Dawn-to-Dusk current forced change to magnetic tail
    - recovery phase
        - recovery to before