Ionosphere, Magnetospheres & Solar Wind Interaction

• Ionosphere• Solar Atmosphere• Solar wind• Magnetosphere• Space Weather

Reference:

Planetary Sciences, I. de Pater and J. Lissauer, Cambridge University Press,2004

Ionosphere

• In the upper part of the earth atmosphere (but also on any other planet with a substantial atmopshere) radiation from the sun is causing the ionization of gas molecules.

• A shell of electrons and ions is formed as the lower part of the magnetosphere

• D layer (60 - 90km) Lyman-alpha ionizes NO, hard X-rays ionize N2 and O2.

• E layer (90 - 120km) soft X-ray and fUV ionizes O2. The shape is determined by the equilibrium of ionization and recombination.

• F layer (200 - >500km), solar radiation ionizes O

Photoionisation

Wavelength [nm] Source

>180 Photosphere

120-200 Transition Photosphere-Chromosphere

90-180 Chromosphere

10-100, Lyα(121) Transition to Corona

1-20 Quiet Corona

0.5-10 Corona active region

0.1-5 Solar Flare thermal radiation

0.001-1 Solar Flare nonthermal burst

Photoionisation

Photon flux

After integration

we can see the photon flux decrease from outside the atmosphere as result of absorption

Ion production

• Incoming photons ionise atmospheric molecules• Incoming radiation density J∞ above atmosphere decreases towards surface

depending on incidence angle χ and height z, where the absortion cross section σ leads to a ion production q

Chapman production function

• n..particle density• H..scale height

eNhN

eOhO

eOhO

22

22

Ion loss processes

• Recombination processes– Radiative recombination– Disociative recombination

YXeXY

hXeX

Diurnal and seasonal behaviour

• During night time the ionization is diminished and some layers can more or less vanish

• Winter anomaly:– The F2 layer is more ionized

during summer at mid latitudes, but seasonal atmospheric composition effects cause a higher ion loss and the net effect is a lower ionization rate. This effect may be absent for the southern hemisphere during low solar activity

• Equatiorial anomaly:– The magnetic field lines at the

magnetic equator are horizontal . Tidal oscilations and solar heating cause a plasma movement in the E layer (=electric current) which causes the ions to move up into the F layer. Thus 20° around the mag. Equator we have a higher concentration of ions

Ionosphere effects

Overview ©NASA Fountain effect

HAARP Ionogram

Ionosphere of Venus

• Venus has a dayside ionosphere at the height of 120 – 300 km

• Three layers:– v1: 120 – 130 km, O2

+

– v2: 140 – 160 km, O2+

– v3: 200 – 250 km, O+

• Maximum ion density is at ~150 km near the subsolar point

• Dayside ionization and nightside recombination cause a plasma flow towards the night/day terminator

Solar Atmosphere

• Photosphere:– Lowest and coldest part, source of solar

light, T≈5750K,– Location of sunspots (colder elements

T≈4000K, paired footprints of magnetic loops)

• Chromosphere:– Transparent to most of the visual light,

emission of H-alpha,– T heats up to 20 000K,– location of prominences (looping

structures connected to sunspots)– Transition zone: rapid increase of

temperature up to ~1 000 000K• Corona:

– Outermost part of the solar atmophere– Structured with streamers and filaments– Coronal holes: open filed lines →

source of solar wind

SOHO ESA

Solar Corona

Solar Wind

• Stream of charged particles from the sun– Electrons & Protons mostly, few

heavier ions• Originating from the corona• Ions escape through open field lines

– coronal holes – Coronal mass ejection CME:

Massive eruption and particle discharge

• Particles in corona (Plasma) have a Maxwellian energy distribution– vav ≈ 145 km/s

• At solar minima (11 year cycle)– terminal escape velocity v ≈ 400

km/s at ecliptic plane– In high latitudes v ≈ 750 – 800 km/s

• Density ~ 6 protons cm-3, T ~ 105K, Magnetic field ~10-5G @ 1 AU

Parker Spiral

• Eugene Parker calculated 1958 the speed of the solar wind assuming radial outflow carrying the “frozen in” solar magnetic field with it.

• Due to this the solar magnetic field is twisted in a spiral form.

• Interaction between the solar magnetic field and the plasma in the interplanetary medium (solar wind) is responsible for changes in the field polarity

Coronal mass ejections

• Massive bursts of solar plasma and electromagnetic radiation out of the solar corona

• Occurrence mostly at high solar activities like flares• Originating out of active regions on the sun surface (sunspots)• Cause of geomagnetic storms when earth is hit by the ejected

plasma• Can inject power in terawatt scale into the magnetosphere

• SOHO CME

Planetary Magnetospheres

• Most planets are enveloped by large magnetic structures– Created by internal magnetic

fields– In some cases interaction with the

ionised atmosphere (induced magnetosphere)

– Large scale remnant magnetic field

• Interaction with the solar wind– Shape determined by field

strength and solar wind flow– Filled with charged particles

(plasma)• Currents and large scale electric fields

are generated by charged particles– Feed back to magnetic field– Generation of radio waves

Solar wind interaction

Magnetospheric Structure

• Interaction between local solar wind plasma and planetary magnetic field• Magnetopause as boundary layer where the dynamic gas pressure ρv2 and

the magnetic pressure are in equilibrium.

• The solar wind arrives at local supersonic speed and forms a “bow shock” in front of the planet

• The “standoff” distance is empirically determined as:

• Rmp is the measured standoff distance of the magnetopause

• is the specific heat ratio and M0 the magnetosonic Mach number

• Rbs ≈ 6-15 RE

• Rmp ≈ 10-20 RE

8

22 B

v

20

20

1

211.11

M

MRR mpbs

Venus SW interaction

• Venus has no internal magnetic field

• The solar wind interacts directly with the ionised part of the atmosphere

• In this case the bow shock is formed at the equilibrium of solar wind gas pressure and the thermal gas pressure of the ionised atmosphere

• Energy exchange takes place– Ion pick up: electron exchange

of fast SW ions and neutral gas– Mass loading: UV photoionised

atmospheric gas is added as slow ions to the solar wind

Mars SW Interaction

• Due to the lower ionospheric pressure and local remnant magnetic fields an asymetric bow shock is formed, depending on the remnant field position

• The solar wind can more easily penetrate into the atmosphere and a larger mass loss is caused

MGS NASA

Jupiter Magnetosphere

• Largest structure in the solar system

• Subsolar standoff distance is ~3 million km

• Length of the magnetotail ~650 million km

• The magnetotail actually extends beyond the Saturn orbit

• Io volcanic eruptions supply plasma (S+, O+, S2+, O2+, ~103 kg/s) to a plasma torus within the Jupiter magnetosphere

• Extremely strong radiation belts• Strong radio signals at 22.2 MHz as

nonthermal radio emissions

Space Weather

• Variability's in the solar wind plasma or magnetic fields have an effect on the magnetosphere and ionosphere of an planet

• Most prominent effect is the Aurora Borealis or Australis– Charged particles are following the magnetic field and precipitate

into the atmosphere at the magnetic poles in circular shapes– At ~80km atmospheric gases are excited and emit light

• Oxygen emissions: green or brownish red, depending on the amount of absorbed energy

• Nitrogen emissions: Blue (recombination with an electron)or red (returning to ground state after excitation)

• The height in the atmosphere determines the available molecules and the excitation mechanism and there fore also the colour

Aurora

• Aurora Australis

Other effects of space weather

• Disruption of GPS and telecomunication signals• Disruption of radiao signals• Induced currents in long pipelines or power transmitting lines

causing power grid failures• Spacecraft system failure• Spacecraft orbit changes• Increased radiation doses for astronauts and long distance air travel• Navigation problems in shipping and air traffic• Disturbance of magnetic or electric resource surveys