Science Projectto study

Solar Terrestrial Physics

September – December 2010

Radio & X Ray observations of the Sun

• We will build a radio receiver that can give us information on the X Rays emitted from the Sun

• We will learn about the Physics of the Sun, interplanetary space, and the impact of X rays and the Solar Wind on the earth.

• We will set up a 24/7 observing programme and use software to analyse data

Radio & X Ray observations of the SunRadio & X Ray observations of the Sun

SolarTerrestrialEnvironmentPhysics

PROJECT STEP - Monmouth Boys School (Sept – Dec 2010)

STEP

Radio & X Ray observations of the Sun

• The project will have a number of stages:– Introduction to Solar – Terrestrial Physics– Building a suitable radio receiver– Testing & calibrating the receiver– Monitoring & analysis software– Observing & logging data– Data analysis & physical insights– Comparing with Satellite data– Setting up an observing programme

Introduction to Solar – Terrestrial Physics

• The introduction will cover:– The Solar – Terrestrial environment– The Earths Ionosphere & Magnetosphere– Effects of Solar X rays on the Ionosphere– Using Military Transmitters as probes– The electronics needed– The software required– Examples of what will be observed– Comparing with Satellite Data

Our Sun

• The Sun is a gravitationally bound nuclear reactor

• It is largely stable, but hassome variability

• There is the 11year sunspot cycle

• Strong magnetic fieldswind up around theequator as the Sun spins

• The field lines SNAP andtrapped energy is thrown into space

1865 2015year

Sun spins faster at the equator

• Field lines get twisted with differential rotation

Field lines dragged along equator

Lines get wound up like an elastic band

Eventually the lines ‘snap’ andrelease stored energy

Solar instabilities - flares

• Sun rotates once every 27 days• Flares last minutes or hours• Notice the ‘flashes’

Solar Flares

• When the flare occurs the

changing magnetic fields

propel millions of tons of charged

particles into space

• Sometimes in the direction

of the Earth

• Energetic X Rays are also emitted

& travel at the speed of light

• This ‘prompt’ radiation reaches

earth in ~ 9 minutes – particles

take several hours or days

Production of hard X rays in magnetic ‘pinch’

• Sun spot fields

make X rays

reconnection

flare loop

material ejected into space

‘pinch’ constriction

Surface of Sun

Magnetic field lines

sun spot sun spot

From Kanya Kusano JAMSTEC

Solar Flares

• The fast particles first encounter the Earths Magnetosphere at up to 10x the radius of the Earth & form a shock wave boundary

• Charged particles cannot cross field lines – they travel around & along them

Earth’s Magnetic Field

• The magnetic field of the Earth is thought to be generated in the rotating molten iron core

• Without the Solar wind it would be a Dipolar Field - like a bar magnet

Earth’s Magnetosphere

• Configuration of magnetic fields in the Magnetosphere

Magnetically neutral Polar Cusps

• Charged particles can flow into the Polar Cusps• Can flow down into the Atmosphere

Charged particles

H

H

Particles create an aurora in Polar regions

• Example of Aurora Borealis in Alaska

Aurora are almost symmetrical around poles

• Auroral Oval – Aurora Australis

11/9/2005

Magnetosphere is like a ‘jelly’

• Magnetosphere is compressed by impact of solar particles & vibrates or wobbles

Particles

Earth’s magnetic fieldHorizontal (x)

Horizontal (y)

3- 4 / 8/ 2010Solar Particles hit

BAA (RAG) 2010

X Rays from the Sun

• X rays are very energetic

photons

• Produced when electrons

are accelerated very rapidly

when solar magnetic field ‘snaps’

• Travel at light speed to Earth

9 minutes

X rays penetrate the Magnetosphere

• X rays are not charged – they can penetrate magnetic fields

• When they reach the earth

they pass through the

Magnetosphere into the

Ionosphere

• They only start to

interact with the

atmosphere when

it becomes dense

enough

• 100km altitude

Diurnal solar energy deposition in ionosphere

• UV and X rays ionise the day side ionosphere

The Ionosphere

• Consists of layers of charged particles – Plasma in bands at various heights

• Some layers disappear

at night when solar UV

energy is cut off

• These plasma layers

reflect radio waves

from surface of the earth

• Low frequency waves

cannot pass through

D Region

What is a Plasma ?

• Plasma is the name given to matter that is ionised• It is neutral in bulk but is composed of electrons & ions

and neutral atoms• The electrons can react to radio waves• The electrons take in energy and speed up• Energy is taken back by collisions with neutral atoms and

ions & released as heat

+

-

+

+

+

+

++

+

+

-

-

-

-

-

-

-

-

-

-

-

+ Positive ion

- electron

Neutral atom

Radio wave propagation

• In daytime the LW & MW signals are reflected and ABSORBED

• At night the plasma density is less and the waves are preferentially reflected

• Propagation through a plasma depends on two things:– Electron density– Collisions with neutrals

• Both vary with plasma

density & height

Radio waves & reflecting plasma layers

• Height and density of layers varies diurnally & with sunspot cycle – function of input energy from Sun

We will look in some detail at the D region

& Very Low Frequency waves

High frequencies escape – low are reflected

• Low frequency waves are reflected

Direct signal partly blockedby curvature of the earth

VLF reflection from D Region

• VLF radio waves are reflected by the

D Region

Bottom of D Region @ 90km

TransmitterReceiver

Location of Military VLF transmitters

• Used to communicate with Naval ships & submarines• Low frequencies travel around the world & penetrate

water

NAA 24kHz

GBZ 19.6kHz

ICV 20.27kHz

JXN 16.4kHz

QUFE 18.1kHz

DHO 23.4kHz

GQD 22.1kHz

HWU 18.3kHz

Frequencies of VLF Military transmitters

GBZ

DHO

GQD

NAA

UFQE

Military transmitters 15 – 24kHz

JXN

Radio Spectrum15 to 24kHz

Dependence on height of reflecting layer

• The reflection point depends on h & D

• The height ‘h’ depends on the plasma density

receiver

h

D

Using the ionosphere as a X ray detector

• The plasma density depends on the input energy – UV and Xrays

• X rays ionise the D region and increase the plasma density

• The D region gets thicker & the base moves to lower altitude

• The reflection geometry changes !

• Signals from the VLF transmitters change !

The outcome

• The Earth’s ionosphere can be used as a

SOLAR X RAY DETECTOR

There is an additional path lengthfor the sky wave

When summed with the ground wavewe get an interference pattern between the two waves that depends on ‘h’

Calculating signal strength with height of D region

Difference in path lengthbetween sky & ground waveis just L-D Giving a phase difference inRadians of :

Add in phase inversion on reflection

From eqn. 1 – 3 we can calculatereceived signal strength as afunction of height ‘H’

Work by Mark Edwards

Calculation of VLF signal Strength @ 19.6kHzS

igna

l Str

engt

h

D r

egio

n he

ight

km78km 78km

71km

calculated

Sig

nal S

tren

gth

measured

Diurnal variation of VLF signal Strength

Evidence of X ray impact - S.I.D.

• Sudden Ionospheric Disturbance (SID)

due to Solar X ray flares• Normal diurnal variation shown in blue• Two SID events just after mid day• Characteristic ‘shark fin’ shape

Measured VLF signal level

SIDs

~ I day

Practical value of monitoring Solar –Terrestrial Environment

LEO

GEO

• Solar generated Geomagnetic storms

kill sensitive satellites in Low Earth Orbit

and in Geostationary orbits

• Large scale power grids

have been overloaded

by surges on long power

lines caused by

geomagnetic storms

Building a receiver

• Requires an antenna - a loop aerial• An amplifier - high gain & wide band• A waveform digitiser - computer sound card• Spectrum analyser - Fourier software• Data logger - data file software• Graph plotter - graphing software• Data analysis - Microsoft XL

We will build a couple of receivers and set up a SID Monitoring Station in Monmouth

In future we may connect it to the internet

Basic layout of VLF receiver

Loop Antenna1m x 1m

High GainAmplifier

PC withsound card

Display

Spectrum Labsoftware

pegs to wind coil around

coil – 40 turns

central wooden support

woodenbracing arms

wooden joining plate

fixingscrews

pole in groundor fixed to tripodslips inside hole

Receiving Antenna 1m x 1m

1m

1m Approx 40 turns(~200m wire)

Terminal block

Coaxial cable

10nF

+V

-V

0V

1k

33k

CA3140

10k

100k

2 2

334 4

6 67 7 2

34

67

CA3140 CA3140

output

input

~33x GainAmplifier

~3x GainAmplifier

X1 GainBuffer

Initial VLF Receiver Amplifier (Gain ~ 333x or 50dB)

+6 to +12V

-6 to -12V

+

1000uF

1000uF

Buffered output

+

The 10k trim pot is used to adjust the offset nullThe buffer output stage is only required if using > 50m of output coaxial cable

1

5

10k

Gain=33x Gain=10x

IC1 IC2

High gain Amplifier

Amplifier construction

ground

ground

-ve rail

+ve rail

10

tri

m p

ot

IC1 IC2

notch notch

1

4 5

8 1

4 5

8

In

Output

WIRING LAYOUT OF INITIAL APMLIFIER BOARD

Output from Spectrum Lab software

Typical Spectrum of Received Signal 0 to 24kHz

Frequency Hz

Sig

na

l L

ev

el

dB

40dB orX 100

VLF Transmitting stations

general man maderadio noise (mains)

*Typical voltage from resonant antenna = 0.14mV rms

*

Time (hours)

Sig

na

l S

tre

ng

th d

B)

A plot of 10 VLF transmitter signal strengths as a function of time

Graph plotting software

SID captured on 12th June 2010

VLF Stations 12/6/2010 M Class Flare SID

-120

-110

-100

-90

-80

-70

-60

Time

Sig

nal

Str

eng

th

08:00 20:0009:00 10:00 11:00 15:0012:00 13:00 16:00 17:00 18:00 19:0014:00

HWE 18.3kHz SID record 12/6/2010

-93

-91

-89

-87

-85

-83

-81

-79

-77

-75

Time

Sig

nal

Str

eng

th

08:00 20:0009:00 10:00 11:00 15:0012:00 13:00 16:00 17:00 18:00 19:0014:00

Live Satellite data

• To confirm a true SID we need X Ray flux data• This can be obtained from the GOES satellite• Near real time download via the internet

Solar X ray burst - generates SID

• Solar X Ray burst - GOES spacecraft

STEREO satellite - multi wavelength pictures of Sun

• Two spacecraft STEREO (ahead) & STEREO (behind)

• Together give 3D data on Solar activity

Solar Dynamic Observer satellite

• SDO view of Sun on 13/7/2010

SDO Generates high definition movies

of Solar activity

Comparing our results• SID monitoring site in Italy• Enables us to compare our results• We need to collect data every day and log all results• Can give talks at Astronomical society meetings

GOES 14 X Ray Flux

Time of day

SID SID

We will have a working system by Christmas

• Massive flare on limb of Sun

Start building next time