Science Project
to 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 Sun
PROJECT STEP - Monmouth Boys School (Sept – Dec 2010)
Solar
S
Terrestrial
T
Environment
E
Physics
P
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 has
some variability
• There is the 11year
sunspot cycle
• Strong magnetic fields
wind up around the
equator as the Sun spins
• The field lines SNAP and
trapped energy is thrown
into space
1865
year
2015
Sun spins faster at the equator
• Field lines get twisted with differential rotation
Field lines dragged along equator
Eventually the lines ‘snap’ and
release stored energy
Lines get wound up like an elastic band
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
From Kanya Kusano JAMSTEC
material ejected into space
reconnection
‘pinch’ constriction
flare loop
Magnetic field lines
Surface of Sun
sun spot
sun spot
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
Earth’s magnetic field
Horizontal (x)
Horizontal (y)
Particles
Solar Particles hit
3- 4 / 8/ 2010
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
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
+
+
-
-
-
+
+
-
+
-
+
-
-
-
-
electron
+
-
+
+ Positive ion
-
+
-
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 blocked
by curvature of the earth
VLF reflection from D Region
• VLF radio waves are reflected by the
D Region
Bottom of D Region @ 90km
Transmitter
Receiver
Location of Military VLF transmitters
• Used to communicate with Naval ships & submarines
• Low frequencies travel around the world & penetrate
water
QUFE 18.1kHz
JXN 16.4kHz
GBZ 19.6kHz
GQD 22.1kHz
DHO 23.4kHz
HWU 18.3kHz
NAA 24kHz
ICV 20.27kHz
Frequencies of VLF Military transmitters
Military transmitters 15 – 24kHz
GBZ
GQD
UFQE
DHO
NAA
JXN
Radio Spectrum
15 to 24kHz
Dependence on height of reflecting layer
• The reflection point depends on h & D
h
D
receiver
• The height ‘h’ depends on the plasma density
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 length
for the sky wave
When summed with the ground wave
we get an interference pattern
between the two waves that depends
on ‘h’
Calculating signal strength with height of D region
Difference in path length
between sky & ground wave
is just L-D
Giving a phase difference in
Radians of :
Add in phase inversion on reflection
From eqn. 1 – 3 we can calculate
received signal strength as a
function of height ‘H’
Work by Mark Edwards
78km
78km
Signal Strength
71km
calculated
Signal Strength
Diurnal variation of VLF signal Strength
measured
D region height km
Calculation of VLF signal Strength @ 19.6kHz
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
• Solar generated Geomagnetic storms
kill sensitive satellites in Low Earth Orbit
and in Geostationary orbits
LEO
GEO
• Large scale power grids
have been overloaded
by surges on long power
lines caused by
geomagnetic storms
Building a receiver
•
•
•
•
•
•
•
Requires an antenna
An amplifier
A waveform digitiser
Spectrum analyser
Data logger
Graph plotter
Data analysis
-
a loop aerial
high gain & wide band
computer sound card
Fourier software
data file software
graphing software
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
Spectrum Lab
software
High Gain
Amplifier
Loop Antenna
1m x 1m
PC with
sound card
Display
Receiving Antenna 1m x 1m
pegs to wind coil around
wooden joining plate
coil – 40 turns
wooden
bracing arms
fixing
screws
central wooden support
pole in ground
or fixed to tripod
slips inside hole
High gain Amplifier
Initial VLF Receiver Amplifier (Gain ~ 333x or 50dB)
~33x Gain
Amplifier
~3x Gain
Amplifier
X1 Gain
Buffer
+6 to +12V
+V
1m
33k
10k
input
100k
+
1000uF
1
1m
7
2
5 6
CA3140
3
4
Approx 40 turns
(~200m wire)
10nF
1k
2
3
7
6
CA3140
4
2
7
CA3140
3
6
4
Buffered
output
IC2
IC1
10k
output
+
Terminal
block
Coaxial cable
-6 to -12V
-V
Gain=33x
0V
1000uF
Gain=10x
The 10k trim pot is used to adjust the offset null
The buffer output stage is only required if using > 50m of output coaxial cable
Amplifier construction
WIRING LAYOUT OF INITIAL APMLIFIER BOARD
10 trim pot
+ve rail
notch
notch
1
8
4
8
Output
IC2
IC1
In
1
5
4
5
ground
ground
-ve rail
Output from Spectrum Lab software
Typical Spectrum of Received Signal 0 to 24kHz
general man made
radio noise (mains)
VLF Transmitting
stations
*
Signal Level dB
40dB or
X 100
Frequency Hz
*Typical voltage from resonant antenna = 0.14mV rms
Graph plotting software
Signal Strength dB)
A plot of 10 VLF transmitter signal strengths as a function of time
Time (hours)
SID captured on 12th June 2010
VLF Stations 12/6/2010 M Class Flare SID
-60
-80
-90
-100
HWE 18.3kHz SID record 12/6/2010
-110
-75
-77
-120
08:00
09:00
10:00
11:00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
19:00
20:00
-79
Time
Signal Strength
Signal Strength
-70
-81
-83
-85
-87
-89
-91
-93
08:00
09:00
10:00
11:00
12:00
13:00
14:00
15:00
Time
16:00
17:00
18:00
19:00
20:00
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
SID
SID
GOES 14 X Ray Flux
Time of day
We will have a working system by Christmas
• Massive flare on limb of Sun
Start building next time