# Presentation: 222525

## The Earth’s Magnetosphere

**The Earth’s Magnetosphere**

- Michelle Thomsen
- LASSO Summer 2008 Workshop
- July 2008

## The Earth is a Giant Magnet...

## ... Immersed in theFlowing, Magnetized Solar Wind Plasma

## Our Magnetic Bubble: The Magnetosphere

- Solar wind plasma and magnetic field are excluded from the bubble.

## Our Magnetic Bubble: The Magnetosphere

- Blunt on sunward (“day”) side

- Long extended tail on antisunward (“night”) side

## Important Boundaries

- Magnetopause

- Bow Shock

- SOLAR WIND

- shocked solar wind

- shocked solar wind

## The Bubble Isn’t Empty

- Charged particles (plasma and high-energy particles) are trapped in the magnetospheric magnetic bottle.

## Basic Structure of the Earth’s Magnetosphere

-  Complex
-  Dynamic
-  Strongly coupled
-  Multiple populations

- MAGNETOPAUSE

## Magnetospheric Plasma Properties

- Plasmasphere
-   density = 1000 cm-3
-   temperature = 1 eV = 1 x 104 K

- Plasma Sheet
-   density = 1 cm-3
-   temperature = 5000 eV = 5 x 107 K

- Radiation Belts
-   density = 10-6 cm-3
-   “temperature” = 106 eV = 1010 K

- For comparison: Earth’s surface
-   density = 2.4 x 1019 cm-3
-   temperature = 0.0025 eV = 290 K

## Magnetospheric Parameters

## The Story of the Magnetosphere=Sources+Transport+Energization+Losses+Dynamics

## Sources:The Solar Wind(How? is actively debated.)andThe Earth’s Upper Atmosphere(Relative importance is actively debated.)

## Transport:Plasma Circulation in the Magnetosphere

- 1. Sunward Convection (driven by solar wind blowing past)

- (Equatorial Plane)

## Like Flow Behind a Cylinder

- Wake-filling flow toward object

## Transport:Plasma Circulation in the Magnetosphere

- 2. Corotation
- (caused by drag of upper atmosphere)

## Transport:Plasma Circulation in the Magnetosphere

- 1. Sunward Convection

- 2. Corotation

**Net flow**

## Transport:Plasma Circulation in the Magnetosphere

- Net flow

- Closed flow paths

- Open flow paths

- Geosynchronous orbit

## Energization:One of the most mysterious andand important aspects of the magnetosphere!

- _Source Energies:_
- Solar wind ~ 1000 eV
- Ionosphere ~ few eV

- _Magnetospheric Energies_
- Plasma sheet ~ 10,000 eV
- Radiation belts ~ millions of eV

- Temperature (K)

- Density (cm-3)

- Radiation Belts

- Plasma Sheet

- Plasmasphere

- Neutral gas at Earth's surface

- Ring Current

- Solar Wind

## Losses:What becomes of all that material entering the magnetosphere?

***Losses:***What becomes of all that material entering the magnetosphere?

- Flow out to solar wind across dayside magnetopause

## Losses:What becomes of all that material entering the magnetosphere?

**Charge-exchange** with residual neutral atmosphere

**Energetic ion (magnetically trapped)**

**Cold neutral atom**

**Energetic neutral atom (escapes)**

**Cold ion (trapped)**

## Losses:What becomes of all that material entering the magnetosphere?

***Losses:***What becomes of all that material entering the magnetosphere?

**Precipitation **along field lines into atmosphere => **Aurorae**

## Dynamics:Most fascinating aspect of all!

- The magnetosphere responds strongly to time variations in the solar wind properties.

- IMF
- Bz (nT)

- 0

- 10

- -10

- ~20-30 min

## Dynamics:

- Quiet

- Storm

## How do these factors combine to produce observed magnetospheric structure and activity?

- Sources+Transport+Energization+Losses+Dynamics

- Take a closer look...

## Solar Wind Interaction With the Magnetosphere:Circulation of plasma (and magnetic flux)

- Solar Wind

- Southward
- IMF

- Dayside
- Magnetic
- Reconnection

- Night-side
- Magnetic
- Reconnection

- convection

## Solar Wind Interaction With the Magnetosphere:Circulation of plasma (and flux tubes)

- Features:
- Creates cells (open vs closed topology)
- Allows capture of solar wind material
- Drives transport (wake filling)
- Allows loss of material to balance capture
- Converts s.w. flow energy to thermal energy
- Leads to substorms...

## Unbalanced reconnection (more at the magnetopause than in the tail) loads energy into the tail and causes it to be more and more stretched.  This strong stretching leads to the onset of new reconnection deep inside the nightside plasma sheet: A substorm onset.

- Hones, 1979

## Substorms: Particle Injections, and Aurorae

## What are the consequences of the global transport pattern + ionospheric outflow?

-  Closed drift paths => flux tubes can circulate
-     many times around the Earth.
-  Long exposure to ionospheric outflow => flux
-     tubes fill with cold plasma => **Plasmasphere**

## The Plasmasphere

## The size of the plasmasphere varies with the strength of the global convection.

- Weak

- Moderate

- Strong

## What are the consequences of the global transport pattern + solar wind entry?

- Open drift paths deliver newly-captured solar wind plasma (the **plasma sheet**) deep into the magnetosphere.

## What happens to the plasma sheet material?

-   Drifts through to dayside magnetopause
-   Precipitates into the atmosphere -> Aurorae
-   Charge exchanges with cold, neutral exosphere
- -> loss as energetic neutral atoms
-   Gets trapped and energized -> Ring Current and Radiation Belts

## Energy-Dependent Drifts

- Convection

- +

- Gradient/Curvature Drift

## Ion Drifts in the Magnetosphere

- Separatrix

## The Ring Current

- Current = Moving Charge

**J (electric current)**

## Effect of the Ring Current: Magnetic Field Perturbations

## Ground Magnetic Perturbationsfrom the Ring Current

- Ground Magnetic Perturbationsfrom the Ring Current

- (Compare to dipole field strength at equator: 3.5x104 nT)

## Magnetospheric Dynamics: Storms

- IMF is very strongly southward for an extended period...

- ...which drives very strong magnetospheric convection

## Storm-Time Ring Current

## Stormtime at Geosynchronous Orbit

- Quiet

- Storm

## Storm-Associated Radiation Belt Enhancements

## Radiation Belt Variability

- From Li et al., 1997

## Magnetospheric Dynamics:So What?

- Tune in Friday (“Space Weather”)!!

## The Magnetosphere: A Busy Place!

**The Magnetosphere: A Busy Place!**