Transcript SARA Regional Conference Arecibo Radio Observatory Puerto

Conference
Arecibo Radio
Observatory
Puerto Rico
December 10-12, 2004
Application of Spectral Analysis
for Amateur Radio Astronomers:
Probing the Sun-Earth Connection
John C. Mannone
Visiting Professor of Physics and Astronomy
Tamke-Allan Observatory
&
Consulting Nuclear Chemical Safety Analyst
Duke, Cogema, Stone & Webster, Ltd
Supporting Researchers
Wanda Diaz, University of Puerto Rico, San Juan
David Fields, Director of the Tamke-Allan
Observatory
Bill Howe, Computer Consultant
Abstract
Examples of spectral analysis techniques for the
amateur astronomer are demonstrated with Excel.
Sunspot and magnetometer data (interplanetary
magnetic field (ACE satellite) and geomagnetic
field (GOES satellite)) as well as decametric
antenna signals are analyzed in context of the
Sun-Earth connection; especially ionospheric
phenomena.
A brief update on the status of plasma bubble
research is presented. This includes plans for the
construction of an inexpensive fluxgate
magnetometer as well as improved data
acquisition and computer processing.
SUN SPOT CYCLES
SOLAR OBSERVATORY OBSERVATIONS
The number of sunspots on the visible solar surface
Counted by many solar observatories
Averaged into a single standardized quantity- sunspot number, R
Daily index of sunspot activity R = k(10g +s) where
s = number of individual spots g = number of sunspot groups
k is an observatory factor (= 1 for the Zurich Observatory;
adjusted for all others to obtain approximately the same R)
Once derived at Zurich (see Wolf number) Rz; now at Brussels
RI is widely distributed smoothed sunspot number (since 1981)
This number has been determined from data back to 1620 (some
regularity since 1700 and on a strict daily basis since 1849)
11.1 years
11.1 years
85.3
9.8
85.3
9.8
51.2
8.5
51.2
8.55.4
5.4
Excel Tools
Data Analysis
Fourier Analysis
(FFT)
limited to 2N data
points (… 256, 512,
1024, 2048, or 4096)
304 annual sunspot
data points =>
require two
overlapping power
spectra
The results are
virtually identical
Spectral analysis of the Sunspot Numbers and
Meteorological Parameters
1. Classical Fast Fourier Transform (FFT)
2. Maximum entropy method (MEM)
3. Lomb-Scargle periodogram method including (optionally) a
fast evaluation scheme
4. CLEAN deconvolution method, including the possibility to
reconstruct time series from the derived spectral
components in an integrated computational step
5. Autoregressive method of the spectral analysis (ARMA)
Comparison of power spectra for different methods.
88 years
11 years
Sunspot Cycle using 160 years of Daily Sunspot Numbers
(56,900 data points from the archives of the Royal Society
of Belgium)
Note the 11-year sunspot cycle is very apparent, but solar
cycle length and the intensity variation over the long 88-yr
period (Gleissberg) are not as obvious, but are extracted
with spectral analysis
Solar Rotation Frequency
From FFT of Daily Sunspot
Numbers
Butterfly diagram show
sunspot distribution
symmetric about solar
equator +/- 35 degrees
Expect rotation period
band from sunspot
numbers time average
equatorial period close
to 25.6 days.
The 26.9 days is within
experimental and model
errors (FFT algorithm
and axis of tilt)
Solar Rotation Period and other Short Cycles
Solar Cycles found in Meteorological Indices
27, 13-14, 9, and 6-7 day
Earth’s Magnetic Field disturbances
6 and 9 day
Simulating the Mechanism of the Action of Heliophysical
Parameters on Atmospheric Processes
Geofisica Internacional,April 1997
J. Pérez-Peraza1, A. Leyva1, I. Ya. Libin2, V. Fomichev2, R. T.
Guschina2, K. Yudakhin2 and A. Jaani3
1 Instituto de Geofísica, UNAM, México.
2 IZMIRAN, Troitsk, Moscow Region, Russia.
3 Estonian Meteorological and Hydrological Institute, Tallinn,
Estonia.
Abstract: With the aim of developing prediction techniques of meteorological
and climatological phenomena we develop a simulation of the mechanisms of
influence of heliophysical parameters on atmospheric parameters. The physical
mechanism of the influence of solar and geomagnetic activities and other
cosmophysical factors on the behavior of the weather, pressure, Earth's
temperature, precipitation, atmospheric circulation, and stormicity is reviewed.
The different mechanisms of the influence of solar activity (SA) on
meteorological and climatological parameters and on the behavior of
experimental meteorological and climatological data at different cycles of the
SA are also discussed. The behavior of experimental data is compared with the
predictions of theoretical models of the influence of SA on the lower
atmosphere: our results indicate a relationship between the variations of
atmospheric parameters and variations of galactic (GCR) and solar (SCR)
cosmic rays and atmosphere transparency. The predictions of different scientific
works in the field of helioclimatology are analyzed, and it is shown that
Pudovkin's model of the influence of SA on the lower atmosphere is correct.
Finally, a method for the prediction of the different meteorological and
climatological parameters using previous data on them as well as on SA, GCR
and SCR is proposed.
WHAT THE SUNSPOT RECORD TELLS US ABOUT SPACE
CLIMATE Submitted to Solar Physics 2004/08/31 DAVID H.
HATHAWAY and ROBERT M. WILSON NASA/Marshall Space
Flight Center/NSSTC, Huntsville, AL 35812
Abstract: The records concerning the number, sizes, and positions of
sunspots provide a direct means of characterizing solar activity over
nearly 400 years. Sunspot numbers are strongly correlated with
modern measures of solar activity including: 10.7-cm radio flux,
total irradiance, x-ray flares, sunspot area, the baseline level of
geomagnetic activity, and the flux of galactic cosmic rays. The
Group Sunspot Number provides information on 27 sunspot cycles,
far more than any of the modern measures of solar activity, and
enough to provide important details about long-term variations in
solar activity or “Space Climate”
” The sunspot record shows: 1) sunspot cycles have periods of
131±14 months (10.9±1.2 yrs) with a normal distribution; 2) sunspot
cycles are asymmetric with a fast rise and slow decline; 3) the rise
time from minimum to maximum decreases with cycle amplitude; 4)
large amplitude cycles are preceded by short period cycles; 5) large
amplitude cycles are preceded by high minima; 6) although the two
hemispheres remain linked in phase, there are significant
asymmetries in the activity in each hemisphere; 7) the rate at which
the active latitudes drift toward the equator is anti-correlated with the
cycle period; 8) the rate at which the active latitudes drift toward the
equator is positively correlated with the amplitude of the cycle after
the next; 9) there has been a significant secular increase in the
amplitudes of the sunspot cycles since the end of the Maunder
Minimum (1715); and 10) there is weak evidence for a quasi-periodic
variation in the sunspot cycle amplitudes with a period of about 90
years. These characteristics indicate that the next solar cycle should
have a maximum smoothed sunspot number of about 145±30 in 2010
while the following cycle should have a maximum of about 70±30 in
2023.
INTERPLANETARY MAGNETIC FIELD
ACE MAGNETOMETER
ACE Level 2 Data Summary by Instrument
*
*
*
*
*
*
*
*
CRIS: Galactic Cosmic Ray Element Fluxes
EPAM: Solar Particle Fluxes
MAG: Interplanetary Magnetic Field Parameters
SEPICA: Solar Energetic Particle Element Fluxes
SIS: Solar Energetic Particle, Low Energy
Galactic Cosmic Ray, and Anomalous Cosmic
Ray Fluxes
SWEPAM: Solar Wind Parameters
SWICS/SWIMS: Temperatures and Speeds of
Solar Wind Ions, and Solar Wind Species Ratios
ULEIS: Solar Suprathermal and Energetic
Particle Fluxes
The MAG Instrument on ACE
The Magnetic Field Experiment (MAG) consists of twin vector fluxgate
magnetometers controlled by a common CPU. The sensors are mounted
on booms extending 4.19 meters from the center of the spacecraft at
opposite sides along the +/-Y axes of the spacecraft. The instrument
returns 6 magnetic field vector measurements each second, divided
between the two sensors, with onboard snapshot and FFT buffers to
enhance the high-frequency resolution.
Interplanetary Magnetic Field Data
MAG level 2 data is organized into 27 day time periods (Bartels
Rotations - roughly one solar rotation period). For each Bartels Rotation,
the level 2 data contains time averages of the magnetic field data over the
following time periods:
*
*
*
*
*
16 seconds
4 minutes
hourly
daily
27 days (1 Bartels rotation)
ACE Interplanetary Magnetic Field
Days 192 to 201 (mid July) 2000
North component
Quiet and Active Periods during the Sunspot Maximum
IMF is quiet during the solar maximum; FFT 4096 point Power
Spectrum is featureless- essentially a corresponding delta
function (or its approximation by the sinc function- sinx/x)
(sampling frequency corresponds to 16 seconds between
samples or 62.5 millihertz)
IMF is indicating storming during the solar maximum; FFT
4096 point Power Spectrum has features- solar waves in the
wind have periods in the order of hours (18.2, 4.6, 3.0, 1.1,
0.53) with moderate to strong amplitude (energy)
IMF is not indicating storming, but may be experiencing
some disturbance; FFT 4096 point Power Spectrum has
features- solar waves in the wind have periods in the order of
hours with one strong amplitude (1.4 hr), but the majority are
substantially weaker (energy) (4.6, 2.3, 1.1, 0.86, 0.70 hr)
IMF is not indicating storming, but may be experiencing
some disturbance; FFT 4096 point Power Spectrum has
features- solar waves in the wind have periods in the order of
hours with strong doublet amplitude (3.6, 2.6 hr), and some
weaker (energy) ones (1.8, 1.5, and 1.1)
(A sudden enhanced disturbance was noted that day)
During solar minimum the Sun's magnetic field, like Earth's, resembles that of
an iron bar magnet, with great closed loops near the equator and open field
lines near the poles. Scientists call such a field a “dipole." The Sun's dipolar
field is about as strong as a refrigerator magnet, or 50 gauss. Earth's magnetic
field is 100 times weaker.
During the years around solar maximum (2000 and 2001 are good examples)
spots pepper the face of the Sun. Sunspots are places where intense magnetic
loops -- hundreds of times stronger than the ambient dipole field -- poke
through the photosphere. Sunspot magnetic fields overwhelm the underlying
dipole; as a result, the Sun's magnetic field near the surface of the star becomes
tangled and complicated.
The Sun's magnetic field isn't confined to the immediate vicinity of our star.
The solar wind carries it throughout the solar system. Out among the planets
we call the Sun's magnetic field the "Interplanetary Magnetic Field" or “IMF."
Because the Sun rotates (once every 27 days) the IMF has a spiral shape -named the “Parker Spiral” after the scientist who first described it.
Above: Steve Suess (NASA/MSFC) prepared this figure, which shows the
Sun's spiraling magnetic field from a vantage point ~100 AU from the Sun.
Earth has a magnetic field, too. It forms a bubble around our
planet called the magnetosphere, which deflects solar wind gusts.
(Mars, which does not have a protective magnetosphere, has lost
much of its atmosphere as a result of solar wind erosion.) Earth's
magnetic field and the IMF come into contact at the
magnetopause: a place where the magnetosphere meets the solar
wind. Earth's magnetic field points north at the magnetopause. If
the IMF points south -- a condition scientists call "southward Bz"
-- then the IMF can partially cancel Earth's magnetic field at the
point of contact.
"When Bz is south, that
is, opposite Earth's
magnetic field, the two
fields link up," explains
Christopher Russell, a
Professor of
Geophysics and Space
Physics at UCLA. "You
can then follow a field
line from Earth directly
into the solar wind" -or from the solar wind
to Earth. Southpointing Bz's open a
door through which
energy from the solar
wind can reach Earth's
atmosphere!
Southward Bz's often herald widespread
auroras, triggered by solar wind gusts or
coronal mass ejections that are able to
inject energy into our planet's
magnetosphere.
TERRESTRIAL MAGNETIC FIELD
GOES MAGNETOMETER
GOES SEM Mission
SEM in the Big Picture
NOAA operates a series of meteorology observing
satellites known as Geosynchronous Operational
Environmental Satellites (GOES). Even though the
weather pictures from GOES are seen nightly in
our living rooms via the local weather broadcast,
few people know that GOES also monitors space
weather via its onboard Space Environment
Monitor (SEM) system. The three main
components of space weather monitored by GOES
at 35,000 Km altitude are: X-rays, energetic
particles, and magnetic field.
Magnetometer
A twin-fluxgate spinning sensor allows Earth's
magnetic field to be described by three mutually
perpendicular components: HP, HE and HN. HP is
parallel to the satellite spin axis, which is itself
perpendicular to the satellite's orbital plane. HE
lies parallel to the satellite-Earth center line and
points earthward. HN is perpendicular to both HP
and HE, and points westward for SMS-1, SMS-2,
GOES-1, GOES-2, GOES-3, and GOES-4, and
eastward for later spacecraft (like GOES 6 here).
HE and HN are deconvoluted from the transverse
component HT. Field strength changes as small as
0.2 nanoTesla can be measured.
Magnetometer (cont.)
The magnetometer samples the field every 0.75
seconds (1333mHz). Four of these values
constitute a frame and are sent to the ground
station together.
The data here is averaged in 60 second intervals
(16.7 mHz)
Data availability
online data plotting capabilities
1974 and the present (GOES series)
N ame
O rbit type
G O E S 6 (G O E S- F)
G E O at longitude:
*
1 3 5 ° W (2 8 /0 4 /1 9 8 3 -2 9 /0 7 /1 9 8 4 )
*
9 8 ° W (2 9 /0 7 /1 9 8 4 -1 2 /1 1 /1 9 9 4 )
O perator
NO A A
L aunc h date/time
2 8 A pril 1 9 8 3 0 2 :2 6 :0 0 U T C
I ns trument
I ns trument SE M (Spac e E nvironment M onitor)
D ata c overage
0 1 /1 9 8 6 - 1 1 /1 9 9 4
D ata res olution
5 - minute averaged
PI
E P S: H erbert H . Sauer (SE L /N O A A )
X- ray monitor: H oward A . G arc ia (N O A A )
D an Wilkins on (N G D C /S P I D R)
Sourc e
SP I D R
L - c overage 6 .5 - 7 .5 RE
D ata s et
V ariable
D es c ription
A ltitude
Fixed value: 3 5 7 9 0 km
L atitude
Fixed value: 0 °
L ongitude
I nterpolated from daily averages
M eas ured B M agnetometer data
Hp
M agnetometer data
He
M agnetometer data
Hn
M agnetometer data
Spin rate 100 RPM
or 16,667 mHz
Time Series of GOES 6 Magnetometer Data
Approaching solar
maximum; FFT 1024
point Power
Spectrum
(sampling frequency
corresponds to 60
seconds between
samples or 16.7
millihertz)
resonant frequency, mHz
power, dB
0.07
38.74
0.16
31.88
0.31
29.01
0.55
24.33
0.96
19.43
1.64
18.81
2.21
16.52
2.80
15.74
3.35
14.43
3.89
19.25
4.44
13.97
5.00
14.83
5.55
8.58
6.09
10.25
6.64
6.80
7.23
7.32
P = af-2
(f > 1 mHz)
Clearly not
random noise nor
typical of
geophysical
spectra behavior,
which follows 1/f
(according to
Kevin Kilty, but I
have not
confirmed this)
RADIO SCINTILLATION
20 MHz ANTENNA SIGNALS
Solar Bursts, Jovian Emissions, and
Galactic Noise
p = -0.65
Radio Spectra
of Various Sources
20
Frequency, MHz
Preliminary Data Reduction Sequence
-Radio Skypipe Pro software SPD files converted to TXT files
-Save data in Word document which automatically delimits the
data into 3 columns: date, time, signal strength
-Correct logging errors
(37:.94 must be changed to 37:0.94;
often jumps at the minute intervals; other errors in format or
placement)
-Copy data into Excel and format illegible data
Data Collection & Preparation
-Note that Excel truncates the Hour in Column B. Therefore, label
column as time, min:sec after the hour (e.g., after 22Z). However,
computations in Excel will treat this a fractional day.
-Compute sampling interval time (in seconds) in cell D4 type
(=(B4-B3)*24*3600)
-Plot Signal Strength vs. Time to reproduce the time series.
-Compute sampling statistics
-Load FFT capability in Excel by executing the submenu path
Tools/Add-Ins/check Analysis Toolpak/OK
-Excel algorithms require exactly 2N data points for FFT, Use 512.
1024, etc not to exceed 4096.. Truncate or pad as necessary.
Sampling Statistics
-Perform FFT (Tools/Data Analysis/Fourier Analysis/OK):
Input the range of data for the signal strength
matching 2N
points; e.g., C4:C515; direct output, e.g., F4:F515
-Decimate the frequency according to N. That is, step-wise increase the
frequency (sampling frequency/N).
-Calculate spectral power: square the magnitude of the complex number
returned by the FFT (=IMABS(F4)2); propagate to N/2 -1 points to
avoid reflection of results.
-Plot Power Spectrum: Power vs. Frequency.
-Scale the plot down by a factor of around 104 to105 to see the spectral
components above the noise.
-Plot Log Power vs. Log Frequency with close attention to the 100 to
1000 millihertz range for behavior of the noise floor.
Spectral Analysis
date
6/7/04
6/7/04
6/7/04
6/7/04
6/7/04
6/7/04
6/7/04
6/7/04
6/7/04
6/7/04
time min:sec af ter 03Z
00:01.5
00:02.5
00:03.5
00:04.5
00:05.6
00:06.6
00:07.6
00:08.6
00:09.6
00:10.6
signal strength
1193.28717
1194.124165
1160.717424
1101.4359
1098.102841
1061.301716
1025.577841
1082.086039
1092.537121
1061.860795
sample interv al, sec
1.015
1
1.015
1.016
1
1.016
1
1.015
1
Left Portion of Excel Spreadsheet Analysis
Spreadsheet Calculations
f requency , mHz
0
1.933628666
3.867257333
5.800918549
7.734579765
9.668240981
11.6019022
13.53556341
15.46922463
17.40288585
Power
6.12016E+11
12913918697
1566834437
397147700
915499695.9
22021517.12
321565561.1
193625161.7
30158076.27
198033620.1
log f
log Power
0.286373
0.587403
0.763497
0.888437
0.985347
1.064529
1.131476
1.189469
1.240621
10.11106
9.195023
8.598952
8.961658
7.342847
8.50727
8.286962
7.479404
8.296739
The frequency is stepped in about 2 mHz increments
(step = sampling frequency/N = 990 mHz/512 samples)
Right Portion of Excel Spreadsheet Analysis
Spreadsheet Calculations
GEOMAGNETIC PERTURBATIONS
PLASMA BUBBLES & SUDDEN
ENHANCEMENT DISTURBANCES
20 MHz ANTENNA SIGNALS
Significant Ionospheric Scintillation
of Radio Waves
Caused by Plasma Instabilities
Polar/Auroral Zone
Particle Precipitation
Equatorial Zone
Plasma Plumes and Bubbles
Mid Latitudes
Storm Enhanced Density (SED) from high latitudes
Sudden Storm Enhancement (SSE) from low latitudes
Plasma Plumes and Bubbles
Equatorial ionosphere illustration
Coupled Ionosphere-thermosphere forecast model
Linked to theoretical growth-rate model (left)
Linked to non-linear plasma bubble evolution (right)
Rayleigh-Taylor Instability
&
E x B Drift
Spectral index p = 5 for plasma bubbles
over San Juan, Puerto Rico
02Z
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
log power
log power
02Z
0
1
2
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
3
y = -1.1241x + 8.0911
2
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8
log f
log f
Before and After the Irregularity
log power vs. log frequency
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
log Power
log Power
04Z
0
1
2
log f(mHz)
3
04Z
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
y = -0.7906x + 7.5143
2
2.1
2.2
2.3
2.4
2.5
log f(mHz)
2.6
2.7
2.8
Time Variation of Spectral Index
June 6, 2004 6 PM
June 7, 2004 8 PM
9 PM
11 PM
6 AM
Time, hrs 6/7/04
-2
-1
0
1
2
3
4
5
6
7
8
9
10
Spectral Index (100-1000 mHz)
-0.6472
-0.1645
-0.4339
0.2937
-1.1241
-5.0300
-0.7906
-1.2000
-0.4972
-1.3139
-1.4440
-0.2128
-1.3572
June 6, 2004 sunset 6:57 PM 23Z = -01Z 6/7/04
June 7, 2004 sunrise 5:48 AM =
+10Z 6/7/04
log power
Significant change in
slope suggests
multiple phenomena
03Z
50 100
10
9
8
7
6
5
4
3
0
1
2
1000 mHz
3
log f (millihertz)
Corner frequency 316 mHz relates to the first Fresnel zone
Size and speed of irregularity can be estimated from this
03Z
7.5
7
6.5
6
5.5
5
4.5
4
log power
log power
03Z
y = -0.8337x + 8.635
2
2.1
2.2
2.3
log f
2.4
2.5
7.5
7
6.5
6
5.5
5
4.5
4
y = -5.0327x + 19.105
2.5
2.6
2.7
2.8
2.9
log f
A major change is indicated in the condition of the ionized layer
during the measurement interval.
Each linear segment is analyzed between 100 and 1000 mHz,
the correct range for scintillation observations (the “trend line”
feature in Excel is used to obtain an unbiased linear regression)
3
Diurnal Variation of Plasma Bubble Growth
Change in Spectral Index
Radio Nois e at 20 M Hz
6 PM and 6AM Local Tim e Pue rto Rico
1
0
Spectral Index
100-500 millihertz
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
-1
-2
-3
-4
-5
Radio sky background
spectral index -0.65
-6
UTC Tim e , hours June 7, 2004
Post-sunset (-01Z) and Pre-midnight (+04Z) Growth
of Suspected Plasma Bubble
Diffraction and Scattering Models p1
Scintillation caused by change in refractive index, n,
caused by diffraction on irregularities related to electron
number density fluctuations or atmospheric turbulence.
(Appleton-Hartree equation)
Irregularity size >> wavelength, wave front is disturbed,
get random phase modulation; further modulation occurs
before it reaches the antenna => complicated diffraction
pattern.
Temporal variation if source is moving relative to the
receiver.
Diffraction and Scattering Models p2
Phase screen, simplest model: irregular layer replace by
equivalent thin screen a distance z to the antenna (multiple
screen are necessary for extended medium and an
inhomogeneous background).
Fresnel Diffraction leads to power law frequency
dependence f-p where p is the spectral index.
Various types of scintillation lead to different spectral
indices: the quiet sky 0.65, typical ionospheric scintillation
8/3 (2.5), plasma bubbles range 2-8 with average 4,
tropospheric scintillation 11/3, interstellar scintillation like
ionospheric without the seasonal or geographic
restrictions.
Spectral index p = 4 for plasma bubbles
over Varanasi, India
Ionospheric Plasma by VHF Waves, R.P. Patel, et al
Pramana Journal of Physics, India Academy of Sciences, Vol 55, No. 5 & 6,
Nov/Dec 2000, pp. 699-705
SED
High TEC observed northern Florida ( July 15, 2000 Kp=9
event) and the north-central USA is more typical of premidnight SED events for Kp=5 or 6.
Snapshot of SED plume in
the post-noon sector obtained
vertical TEC from > 120
GPS receiving sites during a
15-min interval. Red contour
denotes the instantaneous
position of the SED/TEC
enhancement.
Geomagnetic coordinate treated in this page is "geomagnetic dipole
coordinate" referring to the geocentric dipole field approximating the
geomagnetic field based on International Geomagnetic Reference Field
(IGRF). The poles are the intersections of the dipole axis with the Earth's
surface at (79.5N, 71.6W) and (79.5S, 108.4E)(IGRF 2000), and move
slowly according to "secular variation of the geomagnetic field".
Geomagnetic latitude and longitude are defined as shown in the illustration.
HAARP Flux Magnetometer
"H" component positive magnetic northward
"D" component positive eastward
"Z" component positive downward
Geomagnetic storminess is usually indicated in oscillatory variations in the
earth's magnetic field. Additional detail concerning the nature and severity of
the ionospheric disturbance can be found through analysis of the three
components of the field.
MAGNETOMETER DESIGN
The fluxgate is one kind of magnetic field sensor which combines good sensitivity
with relative ease of construction. The basic principle is to compare the drive-coil
current needed to saturate the core in one direction as opposed to the opposite
direction. The difference is due to the external field. Full saturation is not
necessary; any nonlinearity will do. As the core approaches saturation, the signal
picked up in the sense coil will show the nonlinearity. For instance, if you put a
sine-wave into the drive coil, the sense coil would detect harmonics of the
fundamental frequency; increasing in strength relative to the fundamental as the
core becomes more fully saturated. You can also drive with a square wave (easier
to generate) and look at asymmetries in the sense coil output. If you are interested
in building a fluxgate yourself, I recommend the 1991 article in EW+WW [1].
I have drawn above a quick sketch of the windings of a toroidal-core, single-axis
fluxgate: that is, it responds to the magnetic field vector along the indicated axis of
sensitivity. Note that the red wire (drive coil) is wound closely around the core,
passing through the central hole on each turn. The blue wire (sense coil) is wound
around the outside and does NOT pass through the central hole at all. I have drawn
a few windings for clarity but in practice, for best sensitivity, both drive and sense
windings might have 100 turns or more. With this type of core you can get two
orthogonal axes of sensitivity for almost the price of one, just by winding another
sense coil over the first but at right angles (the wires would run horizontal in the
picture above, and the axis of sensitivity would be up-and-down.)
You can also make a single-axis with a simple rod core: in this case you wind the
sense and drive coils over each other (or side by side) and you can get only one
sensing axis (along the core) per fluxgate.
Almost any metal or ferrite will do for the core; when you want good sensitivity
then you use special high-mu materials. I happened to use a random core from
Haltek Electronics in Sunnyvale, CA (36 mm OD, 8 mm thick, partly copper-clad,
marked "2299926-2C AL729").
For those interested, I provide an outline of the circuit I used to make a fluxgate.
This is a simplified version of the article's [1] circuit with a non-optimal core; even
so, I was able to pick up fluctuations in the earth's field of 20 gammas or so. Since
the ambient field is fluctuating at least that much constantly, it's hard to determine
if you have better sensitivity unless you have an active nulled Helmholtz-coil
system to provide a more stable local field, or a magnetically-shielded room (which
I didn't have). I was able, for instance, to see clearly someone rolling a metal cart
through the hallway about three meters away.
FGM3-Sensor by Speake & Co. Ltd., UK
www.speakesensors.com Download Datasheet(MS-Word.doc)
Karsten Hansky (DL3HRT) and Dirk Langenbach (DG3DA)
devellopped this kit Trough the AKM-Forum für Polarlichter
(german) this Project became also known by the visual aurora
chasers. In the mean time the prototype (Picture 1) has been
turned into a more professional kit that can be easily build by
others. The measurements are comparable to the professional
magnetometers, especially if one takes the simplicity of the
equipment in account.
The complete electronics ( Microcontroler, real-time clock,
in- and output , two analogue outputs and keyboard-,LCDand RS-232 Interfaces) are all have their place on the
100x100 mm doublesided printed circuit board (Picture 2).
The key board is on a small
separate printed circuit board.
No exotic components or smd
techniques were used. Below a
picture of the finished
magnetometer: Picture 3
CONCLUSIONS
-spectral analysis of radio signals provides a potential probe of the
intervening media the wave propagates through
-inexpensive and extensive equipment and readily available
resources renders this favorable to amateur radio astronomy
-state of ionosphere can be examined by monitoring the radio
noise floor as a function of time in concert with space weather and
geomagnetic parameters
-major irregularities like SEDs and plasma bubbles can be
detected in midlatitudes
-June 7 decametric data clearly shows the evolution of an
irregularity that fits the characteristics of a plasma bubble over
Puerto Rico. Geomagnetic conditions were not remarkable.
Radio Poetry
John C. Mannone
Dec 8, 2004
On the Spectrum of Things About the Sun
Sunspots
Like twirling overcooked spaghetti
magnetic field lines twist and break
in hot swirling plasma
Giant hurricanes anchor the broken strands
for a while
but the constant churning, year after year
incites a riot
A heated outrage breaks out
every decade or so
like a labor union with an agenda on a time clock
or maybe it’s just an adolescent sun
that flares up when its face gets blemished by all those spots.
Sunstruck
The Sun, struck like a bell with multiple tones
each clamor to be heard
cacophony swept as static in solar wind, like sea
swoosh
Legacy of coronal tunes
echo in the surf washing on our shore
Pause
Contemplate the crests, the swirls
those that mesmerize, beckon
like ocean waves invite
to plunge the cool
of nature’s rhythms
Allow the seduction…
of the mind.
Sunwhispers
A Type II tidal wave
rushes towards Earth a million miles an hour
Sometimes the sun quakes and spits out its vaporized lava like
some angry volcano god
Thank the real God for magnetic coats that work like asbestos ones
Billions of tons of fire water crash and bend the shield
A few sneak through and burn the sky with purple shimmer
Most squeeze the field
Sending ripples down its spine
Like dominos that fall into each other
ripples wiggle into every thing, our planet
The storm transforms
to the kind that doesn’t need a metaphor
to the kind that’s wet with fury
to the kind that’s sweet with spring
I wonder what El Nino is whispering today
Whispering
In a small still voice
whispering…
Aside
Storm Enhanced Density
SED is the ionospheric signature of the erosion of the outer
plasmasphere by ring current-induced disturbance electric
fields. The low-altitude ionosphere: appearance of sunwardconvecting regions of enhanced plasma density at mid latitudes.
Millstone Hill incoherent scatter radar has observed SEDs in
the pre-midnight sub-auroral ionosphere during the early stages
of magnetic storms.
These high-TEC plumes of ionization appear at the
equatorward edge of the mid-latitude ionospheric trough and
stream sunward driven by poleward-directed electric fields at
the equatorward limit of region of sunward convection.