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

[TOC]

Earth
===

## Earth Magnetosphere

- 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


### 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

- 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

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


- We can see why plasmasheet appears

## Earth's Geomagnetic

### Magnetic Motion
- Moves faster

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


### 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


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


### 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