Space Science 1

7/28/2019 Space Science 1

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18-Apr-13

IESO

Space Science

Part 1


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18-Apr-13

Solar Activity and VLF


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Outline

Solar wind

Suns magnetic topology

Transients: CIRs, CMEs, Solar flares

Earths magnetosphere/ionosphere VLF activity


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The Solar Wind

Hot plasma (106 K) from the solar corona isthe source of the solar wind

The coronal plasma is accelerated and flowsradially outward from the sun, fillinginterplanetary space

Solar wind properties at Earth (1 AU): Speed ~400 km/s

Speed range ~200-700 km/s

Number density ~ 7 cm-3

Magnetic field ~ 5 nT

Electron temperature ~ 105 K

Proton temperature ~3 x 104 K Image of solar corona takenby STEREO spacecraft inultraviolet light. (NASA)


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Suns magnetic topology

Suns magnetic topology strongly influencescharacteristics of solar wind

Slow streams at streamers (equator)

Fast streams at coronal holes (poles)

Field is well-ordered at solar minimum

Field is complicated at solar maximum

Magnetic topology causes transients that are carried bythe solar wind: CIRs, CMEs, and Solar Flares


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Co-rotating Interaction Regions (CIRs)

Suns rotation causes fast (polar) andslow (equatorial) streams to interact

Produces compression (CIRs)

CIR leading edge propagates forwardinto solar wind

CIR trailing edge propagates back toSun


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Coronal Mass Ejections (CMEs)

Large eruptions of coronal plasma

Originate from active regions in Sunassociated with solar flares

Solar minimum: ~1/week Coronal streamer belt near the solar

magnetic equator

Solar maximum: ~ 2-3 /day Active regions, latitudinal distribution is

more homogeneous.Coronal mass ejection.

Image shows the sun in

ultraviolet light. (NASA)


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Solar Flares

Solar flare is a violent explosion inSuns atmosphere

Spans EM frequencies from radio toX-ray

May be caused by release of energystored in twisted magnetic field lines

Large increase in X-ray flux can affectsatellites

Energy release accelerates protons insolar wind and cause disturbances inEarths magnetic field. An X-ray image of an intense X9 flare taken from

the GOES-13 satellite. The flare was actually

intense enough to damage the imager.


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Solar Transients Affect Earth

CMEs, CIRs, and solar flares can affect the Earthsmagnetosphereand ionosphere.

Their effects can be severe enough to cause damage tosatellites and power systems.

VLF is sensitive to changes in the ionosphere andmagnetosphere, so it is ideal for studying the effects andcharacteristics of solar phenomena.


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What is the Magnetosphere?

SolarWind

Solar wind flows past Earth and is deflectedaround Earths magnetic field.

The solar wind compresses the magnetic

field on the sun-side, creating a boundary

termed the magnetopause at ~10 RE.

On the night side, the solar wind-dipole field

interaction results in a tail up to~60 RE.

The magnetosphere is the region within the

magnetopause, from ~10 RE on the sun side to~60 RE on the night side.

Plasma within ~4 6 RE rotates with the

Eartha region called theplasmasphere.


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Magnetosphere and solar activity

Magnetosphere before, during, and after storm

Borovsky, Joseph E. et al. The calm before the storm in CIR/magnetosphere interactions.


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Solar Activity and VLF

Increases in relativistic electron fluxes in outer radiation belt areassociated with

enhanced geomagnetic activity

enhanced chorus (VLF) wave activity

They may be produced by resonant interactions with enhancedwhistler-mode chorus emissions.

Full plasmasphere less chorus less relativistic e-


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Earths Ionosphere

Atmosphere above ~70km is partially ionized by Suns radiation

Ionosphere extends up and merges with Magnetosphere

Low frequency (< 30kHz) are reflected from D region


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Solar Activity and the Ionosphere

X-ray radiation during solar flares penetrate into the lowestlayer (D-layer)

Increases D-layer ionization rate and electron density

The D-layer ionosphere and the Earths surface form a

waveguide that can propagate VLF signals over longdistances If the D-layer electron density changes along the path from a VLF

transmitter to a receiver, amplitude and phase changes can beobserved by the receiver.


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Moons Two Shadows

Shadow of the moon consists of:

1) Penumbra: Faint outer shadow

2) Umbra: Dark inner shadow

Total eclipse of Sun seen whenumbral shadow sweeps acrossEarths surface

Path of Totality: track of this shadowacross the Earth

Must be inside this path of totality to

see the total eclipse of the Sun


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Solar Eclipses and the Ionosphere

Solar eclipses cause disturbances inthe ionosphere

Effects noticed on VLF radio wavesthat propagate in Earth-ionospherewaveguide between ground and Dregion of ionosphere

Solar eclipses represent localized Dregion disturbance on propagationof these waves

Rare opportunity of getting directmeasurements of D region

characteristics

Space Science 1

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