-
Hermanus Magnetic
Observatory
Page 1 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
HERMANUS MAGNETIC OBSERVATORY
Correlation between energetic charged particle precipitation
over the South Atlantic Magnetic Anomaly
and L-band Ionospheric
Scintillation over South Africa: Investigation in support of
SA’s
SKA bid.
Doc No: 6021-0003-709-A1
Prepared by: Drs Ben Opperman and Pierre Cilliers
Prepared for: Dr Adrian Tiplady
Date: 22/11/2010
Hermanus Magnetic Observatory P O Box 32 HERMANUS 7200
-
Hermanus Magnetic
Observatory
Page 3 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Table of Contents
Table of Contents
.............................................................................................................
3 List of Figures
...................................................................................................................
5 List of Tables
....................................................................................................................
8 1 Introduction
..............................................................................................................
9 2 Methodology and data
..............................................................................................
9 3 Background
...............................................................................................................
9 4 Ionosphere and Total Electron Content
..................................................................
13 5 Ionospheric Scintillation
.........................................................................................
14 6 Proxies for S4 amplitude scintillation
.....................................................................
15 7 Validating the S4-proxy algorithm
..........................................................................
18 8 Correlation between geomagnetic disturbance and EPP
........................................ 20
8.1 Disturbance storm time index (Dst)
...............................................................
21 9 Data challenges
.......................................................................................................
23
9.1 Non-availability of data.
.................................................................................
23 9.2 False positives associated with cycle slips.
.................................................... 24
10 DMSP SSJ/4 EPP sensor
........................................................................................
26 11 Data
processing.......................................................................................................
27
11.1 DMSP
.............................................................................................................
27 11.2 GPS
.................................................................................................................
29 11.3 Integrating SSJ/4 and S4p data
........................................................................
30
11.3.1 Visual comparison
..................................................................................
30 11.3.2 Statistical correlation of median values
..................................................
31 11.3.3 Statistical correlation of integrated values
............................................. 31
12 Results
....................................................................................................................
31 13 Discussion
...............................................................................................................
35 14 Conclusions
............................................................................................................
38 15 Key Project Participants
.........................................................................................
38
15.1.1 Dr BDL Opperman. Co-ordinator
.........................................................
38 15.1.2 Dr PJ Cilliers.
.........................................................................................
38 15.1.3 Dr LA McKinnell.
..................................................................................
38
16 Appendix A: Precipitation – Scintillation correlation
results ................................. 39 16.1 Gough
Island 2000
.........................................................................................
40 16.2 Gough Island 2001
.........................................................................................
42 16.3 Gough Island 2003
.........................................................................................
44 16.4 Gough Island 2004
.........................................................................................
46 16.5 Gough Island 2008
.........................................................................................
48 16.6 Cape Town 2000
.............................................................................................
50 16.7 Cape Town 2001
.............................................................................................
52 16.8 Cape Town 2003
.............................................................................................
54 16.9 Cape Town 2004
.............................................................................................
56 16.10 Cape Town 2008
.........................................................................................
58 16.11 Perth 2000
...................................................................................................
60 16.12 Perth 2001
...................................................................................................
62 16.13 Perth 2003
...................................................................................................
65 16.14 Perth 2004
...................................................................................................
67
-
Hermanus Magnetic
Observatory
Page 4 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
16.15 Perth 2008
...................................................................................................
69 17 References
..............................................................................................................
71 18 Web pages
..............................................................................................................
71
-
Hermanus Magnetic
Observatory
Page 5 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
List of Figures
Figure 1. Contours indicating geomagnetic field strength
illustrate the weak
magnetic field over the South Atlantic Magnetic Anomaly region.
Superimposed on the figure are the magnetic equator, equatorial
anomaly (± 15° from geomagnetic equator) and aurora oval edge.
......... 10
Figure 2. World map of the AP-8 MAX integral proton flux >10
MeV at 500 km altitude.
(www.spenvis.oma.be/help/background/traprad/traprad.html) .
11
Figure 3. World map of the AE-8 MAX integral electron flux >1
MeV at 500 km altitude (bottom).
(www.spenvis.oma.be/help/background/traprad/traprad.html)
................ 11
Figure 4. Electron particle precipitation as observed with the
DMSP SSJ4-instrument. Superimposed on the image are the geomagnetic
equator (magenta), equatorial anomaly regions (cyan) and locations
of Gough Island, Cape Town and Perth (yellow triangles).
..................................... 12
Figure 5. Proton particle precipitation as observed with the
DMSP SSJ4-instrument. Superimposed on the image are the geomagnetic
equator (magenta), equatorial anomaly regions (cyan) and locations
of Gough Island, Cape Town and Perth (yellow triangles).
..................................... 12
Figure 6. Auroral oval footprint shifting with Kp index. During
Geomagnetically disturbed conditions, aurora-associated particle
precipitation is observed in the auroral oval. With increased Kp
values, associated with high disturbance, auroral observations
extend northwards (in Southern hemisphere) as indicated by the
Kp-lines. www.swpc.noaa.gov/Aurora/globeSE.html. Note that Southern
Africa and the South Atlantic Magnetic Anomaly are not affected by
auroral particle precipitation during disturbed conditions.
................................... 13
Figure 7. Elevation weighting coefficient (β) of Du et al. used
to relate ROTI to the S4-proxy S4p
.........................................................................................
17
Figure 8. ROTI as S4p-proxy calculated from Gough Island GPS
data on 28 October 2003 (day 301). The increased ROTI values around
11:00 UT are indicative of scintillation events observed by five
satellites. Severe geomagnetic storm (Kp = 9, Dst = -475 nT) was
experienced on this day.
................................................................................................
17
Figure 9. Geographic location of ROTI- S4p-proxy occurrences
(red circles) superimposed on GPS satellite IPP ground trace (green
dots), as observed from Gough Island on 28 Oct 2003. Large blue
circles represent different satellite elevation angles. The
relative high elevation occurrence of ROTI illustrates that
observations are not associated with (low elevation) multipath
effects. These ROTI occurrences were observed around the same time
around 11:00 UT by five different satellites.
.............................................................................
18
Figure 10. Comparison of S4 and ROTI and other related
parameters from GPS observations at Ascension Island, (JASTM 61
(1999) pp 1219-1226 ) ... 19
Figure 11. Comparison of GISTM-observed S4 scintillation with
elevation weighted S4 proxy (S4p,) as observed respectively by a
Novatel
-
Hermanus Magnetic
Observatory
Page 6 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
GSV4004B GISTM and conventional Ashtech dual frequency GPS
receiver installed on Gough Island. Observations were done along
the ray path from satellite PRN10. The S4p were determined at
5-minute intervals from GPS data sampled at 30s intervals, the ROTI
values were determined at 30 second intervals while the S4 values
were recorded at 1 minute intervals. The top panel in the diagram
shows the elevation (Elv) of satellite PRN10 on the same time scale
to indicate that the observed event occurred at an elevation of
about 50 ⁰, well above the horizon, and thus not due to multipath
effects. Panel 2 shows the normalised power on the L1-signal (CNo)
recorded at a sampling rate of 50 samples per second with the GISTM
to illustrate the power dip that is associated with the S4-event.
The TEC shown in panel 5 depicts the small but rapid increase in
the TEC which is associated with the dip in the power, which seems
to indicate that the S4-event was caused by the ray path traversing
a region of increased electron density, which increased the
absorption of the signal. The slope of the TEC curve is shown as
the Rate of Change of TEC (ROT) in panel 6. Panel 7 shows the Rate
of Change of TEC Index, which is standard deviation of the ROT,
with averaging done over a 5-minute period.
.......................................................................................................
19
Figure 12. Comparison of GISTM-observed S4 scintillation with
elevation weighted S4 proxy (S4p,) as observed respectively by a
Novatel GSV4004B GISTM and conventional Ashtech dual frequency GPS
receiver installed on Gough Island. Observations were done along
the ray path from satellite PRN18.
.................................................................
20
Figure 13. Year 2000 Proton flux values at various energy levels
(top) compared to Dst values (bottom)
..............................................................................
22
Figure 14 Year 2004 Proton flux values at various energy levels
(top) compared to Dst values (bottom)
..................................................................................
22
Figure 15. Example of false positive ROTI caused by cycle slips
not associated with sustained perturbed ionospheric phase
observation. For satellite PRN13, observed from Perth on 12 June
2008, cycle slips are observed in L1 and L2 phase as phase jumps
(top), abrupt jumps in slant TEC with ~2 TECU (middle) and
associated ROTI (bottom). Note the relative high ROTI values
associated with these cycle slips. Such ROTI calculations typically
are associated with false positive scintillation events.
...................................................................................
25
Figure 16. Example of false positive ROTI scintillation events
associated with cycle slips observed on all GPS receiver channels
for 12 June 2008 at Perth. Scrutiny revealed this day’s raw data
was too suspicious to use and was subsequently ignored.
.................................................................
26
Figure 17. Geographic windows of 10˚ centred on the key
locations ......................... 28 Figure 18 SSJ4 Electron
and ion flux and energy levels observed at South Atlantic
Anomaly region around 2001-03-16-06:41 UTC . The red line
indicates the geographic latitude of the Gough Island GPS receiver
used for the ionospheric scintillation calculations. Note that
particle precipitation values are an order of magnitude larger than
for Cape Town.
........................................................................................................
28
-
Hermanus Magnetic
Observatory
Page 7 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 19. SSJ4 Electron and ion flux and energy levels observed
at South Africa around 2001-03-16-03:17UTC. The red line indicates
the geographic latitude of the Cape Town GPS receiver used for the
ionospheric scintillation calculations.
.......................................................
29
Figure 20. SSJ4 Electron and ion flux and energy levels observed
over Australia around 2001-03-16-08:2UTC. The red line indicates
the geographic latitude of the Perth GPS receiver used for the
ionospheric scintillation calculations.
..............................................................................................
29
Figure 21. Year 2003 Gough Island electron (Ne) and ion (Ni)
flux (panes 1-2), 5-minute median S4p (ROTI), pane 3) and Dst
(bottom). Note the large S4p values around day 319 which appears to
coincide with a large Dst value and apparent increased electron and
ion flux. ................................. 32
Figure 22. Year 2003 statistical correlation of Gough Island
electron (Ne) and ion (Ni) flux with 5-minute median S4p (ROTI)
............................................. 33
Figure 23. Year 2003 Statistical correlation between,
respectively, daily integrated electron flux (top) and ion flux
(bottom) and S4p ..................................... 33
Figure 24. Year 2001 days 88-94 illustrate Cape Town and Perth
observations of proton flux (black crosses) compared with S4p
scintillation (blue dots). No GPS data was available for Gough
Island for this period, but proton flux is illustrated for
completeness. ..............................................
36
Figure 25. Year 2003 days 303-307 illustrate Cape Town, Perth
and Gough island observations of proton flux (black crosses)
compared with S4p scintillation (blue dots). Minimum Dst on day 303
was -383 nT ............. 37
-
Hermanus Magnetic
Observatory
Page 8 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
List of Tables
Table 1. Geomagnetic field parameters at selected locations on
June 2010. ............ 10 Table 2. Archived GPS data
availability, in days, with percentage days available
for a specific year given in brackets
().....................................................
23 Table 3 Geographic and Geomagnetic Coordinates of key
locations used in the
study together with the GISTM data availability.
.................................... 27 Table 4. Correlation
coefficients between S4p and EPP. (∫S4p represents integrated
S4p)
............................................................................................................
34
-
Hermanus Magnetic
Observatory
Page 9 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
1 Introduction The objective of the study is to investigate the
possible effect(s) of energetic particle precipitation (EPP),
observed over the South Atlantic Magnetic Anomaly (SAMA) region, on
ionospheric scintillation over Southern Africa and Australia. This
study was conducted in support of the Square Kilometre Array (SKA)
bid for identifying a suitable host location based on the stability
of the ionosphere so as to minimize modulation of trans-ionospheric
radio astronomy signals. Theoretical studies (Figure 2 and 3) and
satellite X-ray and energetic proton and electron measurements
(Figure 4 and 5) have indicated that the eastern limb of the SAMA
extends to the southern tip of Africa. This phenomenon begs the
question as to what extent SAMA EPP influences the South African
ionosphere. Although studies by Gledhill (1976), Haggard (2004) and
Abdu et al. (2005) identified EPP as a possible source of increased
ionospheric ionization observed over the SAMA, a study by Sibanda
(2006) concluded that it was not possible to establish a direct
connection between EPP events and ionospheric disturbances over the
South African region. By extending the data sets used by Sibanda
(2006) and extending the observation period and regional coverage,
this study set out to specifically investigate the relation between
SAMA EPP and ionospheric scintillation over South Africa and
Australia.
2 Methodology and data EPP was expressed in terms of energetic
electron and proton flux as well as particle energy measurements by
the Defence Meteorological Satellite Programme (DMSP). DMSP
measurements over SAMA were compared to ionospheric scintillation
indices calculated from GPS measurements observed at Gough Island
(South Atlantic), Cape Town (South Africa) and Perth (Australia)
and statistics were derived to quantify EPP-scintillation
correlations. To cover a representative range of geomagnetic and
solar conditions, this study was conducted for geomagnetic quiet
and disturbed conditions using observations over an almost complete
solar cycle for the years 2000, 2001, 2003, 2004 and 2008. Solar
cycle 23 reached its peak in 2001 and significant solar
disturbances, with accompanying geomagnetic/ionospheric
disturbances, were observed around solar maximum with major events
also occurring in 2003 and 2004.
3 Background The South Atlantic Magnetic Anomaly (SAMA, See
Figure 1) is a region located between Southeast Brazil and South
Africa, where the magnetic field strength is particularly low due
to the eccentric nature of the Earth's magnetic dipole. The minimum
value of the total geomagnetic field of roughly 22575 nT is found
within the SAMA at about 26° South and 54° West. Energetic Particle
Precipitation (EPP) is primarily observed in the aurora regions and
over the SAMA. EPP involves the deposition of energetic particles
from the Van Allen radiation belts
-
Hermanus Magnetic
Observatory
Page 10 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
into the ionosphere, which would result in an increase in
ionization and conductivity of the upper atmosphere. The
precipitation mechanism proceeds by energetic electrons being
scattered into the loss cone and subsequently interacting with
atmospheric neutrals. The altitude at which the electrons are
deposited depends on their energy and pitch angle as well as the
strength of the magnetic field. Lower magnetic field strengths,
such as those found within the SAMA, are thus conducive to EPP.
Figure 1. Contours indicating geomagnetic field strength
illustrate the weak magnetic field over the South Atlantic Magnetic
Anomaly region. Superimposed on the figure are the magnetic
equator, equatorial anomaly (± 15° from geomagnetic equator) and
aurora oval edge.
Table 1. Geomagnetic field parameters at selected locations on
June 2010.
Location Magnetic Latitude
Inclination Total Field strength (nT)
Approximate weakest field position over SAMA (26⁰S, 54⁰W)
-17.8 -32° 04’ 22 575
Gough Island (40°21'S, 9°52'W)
-42.5 -63° 44’ 24 658
Cape Town (34°11'S, 18°26'E)
-36.7 -65° 59’ 25792
Perth (31°48'S, 115°53'E) -25.22 -66°15’ 58 284 Note: Total
Field Strength and Inclination calculated by means of the IGRF11
model (www.ngdc.noaa.gov/geomag/magfield.shtml). Magnetic Latitude
calculated by the on-line CGM model
(omniweb.gsfc.nasa.gov/vitmo/cgm_vitmo.html)
-
Hermanus Magnetic
Observatory
Page 11 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 2. World map of the AP-8 MAX integral proton flux >10
MeV at 500 km altitude.
(www.spenvis.oma.be/help/background/traprad/traprad.html)
Figure 3. World map of the AE-8 MAX integral electron flux >1
MeV at 500 km altitude (bottom).
(www.spenvis.oma.be/help/background/traprad/traprad.html)
-
Hermanus Magnetic
Observatory
Page 12 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 4. Electron particle precipitation as observed with the
DMSP SSJ4-instrument. Superimposed on the image are the geomagnetic
equator (magenta), equatorial anomaly regions (cyan) and locations
of Gough Island, Cape Town and Perth (yellow triangles).
Figure 5. Proton particle precipitation as observed with the
DMSP SSJ4-instrument. Superimposed on the image are the geomagnetic
equator (magenta), equatorial anomaly regions (cyan) and locations
of Gough Island, Cape Town and Perth (yellow triangles).
Electron particle flux from DSP ssj4 sensor day 001 of 2000
-180 -120 -60 0 60 120 180-90
-60
-30
0
30
60
90
0.5
1
1.5
2
2.5
3
x 108
Ion particle flux for day 001 of 2000
-180 -120 -60 0 60 120 180-90
-60
-30
0
30
60
90
0.5
1
1.5
2
x 107
-
Hermanus Magnetic
Observatory
Page 13 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 6. Auroral oval footprint shifting with Kp index. During
Geomagnetically disturbed conditions, aurora-associated particle
precipitation is observed in the auroral oval. With increased Kp
values, associated with high disturbance, auroral observations
extend northwards (in Southern hemisphere) as indicated by the
Kp-lines. www.swpc.noaa.gov/Aurora/globeSE.html. Note that Southern
Africa and the South Atlantic Magnetic Anomaly are not affected by
auroral particle precipitation during disturbed conditions.
4 Ionosphere and Total Electron Content The ionosphere is the
portion of the atmosphere that lies between about 50 km and about
2000 km in which the density of free electrons formed by
photo-ionization is large enough to have an appreciable effect on
the propagation of radio waves. The ionosphere is divided into D, E
and F-layers. The D-layer is the innermost layer ranging from 60 km
to 90 km; the E-layer ranges from 90 km to 120 km and the F-layer,
in which the peak electron density occurs, extends from about 200
km to more than 500 km above the surface of Earth. The Total
Electron Content (TEC) is defined as the integral of electron
density along a cylindrical column centred on a ray path between a
radio receiver and a transmitting satellite through the atmosphere.
Faraday rotation, a left-handed elliptical polarisation rotation of
EM rays propagating through electrically-conducting plasma in the
presence of a magnetic field, is directly proportional to TEC
(which includes contributions from the interstellar medium) and has
relevance in radio astronomy signals. In the context of GPS
satellites orbiting at 20 200 km, TEC is derived from a linear
combination of the phase observations on the L1 (1.5754 GHz) and L2
(1.2276 GHz) carrier waves and given in TEC Units (TECU) with 1
TECU = 1016 electrons.m-2 (Schaer, 1999):
1
2 2 1 12 21 2
1 1 [ ]TEC TECUf f
where
α : 40.28x1017 m.s-2.TECU-1 φ1, φ2 : Phase observed on L1, L2
carrier waves f1, f2 : L1, L2 frequencies (Hz) λ1, λ2: L1, L2
wavelengths (m)
-
Hermanus Magnetic
Observatory
Page 14 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
5 Ionospheric Scintillation Ionospheric scintillations are rapid
variations (1-10 Hz) in the electron density of the ionosphere,
particularly near the F2 layer, that cause rapid fading on HF Radio
(3-30 MHz) communications, deterioration of the accuracy of GPS
navigation, and fluctuations in the polarization, amplitude and
phase of radio-astronomy signals from cosmic sources. As an EM
waves pass through the ionosphere, the phase velocity is advanced
and the group velocity delayed by an amount proportional to the
TEC. Ionospheric scintillation manifests as rapid amplitude fading
and phase shifts which occur when the ray path of a
trans-ionospheric signal traverses ionospheric irregularities in
the form of small scale F-region field aligned patches of increased
electron density or bubbles of decreased electron density Field
aligned patches are more common at auroral latitudes while bubbles
more frequently occur near the equator. At mid-latitudes, both can
occasionally occur. The severity of amplitude scintillation is
expressed in terms of the S4 index, defined as the normalised
second central moment of the signal intensity i.e.
22
4 ,I I
SI
where I is the intensity of the signal measured at the receiver,
expressed as the square of the amplitude. Values of 4S below 0.3
are called weak scintillations, which have minimal effect, while
values above 0.3 are strong scintillations. For weak scintillation,
4S is proportional to the variance of the electron density
variations 2N . Phase scintillation is defined in terms of the
phase scintillation index, or the standard deviation of phase
fluctuations defined as
22 , where is the received phase. With dedicated L-band
ionospheric scintillation monitors such as the GSV4004B GPS
Ionospheric Scintillation and TEC Monitor (GISTM) installed on
Gough Island, the amplitude and phase is sampled at 50 Hz, and
averaged over 1 minute. The scale of the irregularities determines
its effect. If the scale of the irregularities is much larger than
the Fresnel radius ,fz r amplitude variation is minimal. Here is
the wavelength and r is the distance from the irregularities to the
receiver. At or below fz amplitude variations on signals traversing
the irregularities are significant. At typical ionospheric heights
(~400 km for the F2-layer peak) and assuming vertical propagation,
fz is of the order of 276 m at the GPS L1 frequency. Ionospheric
scintillation depends on solar activity, geomagnetic activity,
season, time of day, geographical location and frequency.
Scintillations occur predominantly in the equatorial band that
extends from about 20⁰S to 20⁰N of the magnetic equator, and in the
auroral and polar cap regions. The processes that produce
scintillations in these two regions are quite different, leading to
significant differences in the characteristics of the resulting
scintillations. In the equatorial regions, ionospheric
scintillations predominantly occur during the period between dusk
and local midnight, when the upward E B drift creates low density
structures
-
Hermanus Magnetic
Observatory
Page 15 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
moving upward through the F-layer of the ionosphere, an effect
known as the Equatorial Fountain. Equatorial scintillations
increase during the equinoxes and during solar maximum. In the high
latitudes, ionospheric scintillation is association with field
aligned patches of increased electron density and are peaked in the
period centred on midnight magnetic local time (MLT). In the
mid-latitudes, scintillations may result from equatorial
irregularities and high latitude irregularities moving towards the
mid-latitudes, as well as from the precipitation of energetic
particles into the ionosphere. Other mechanisms for high and
mid-latitude scintillations show a strong dependence of the
direction of the component of the interplanetary magnetic field
(IMF) which is aligned with the Earth’s axis (Bz). During
northward-directed Bz the cause of scintillations is bursty bulk
flow irregularities of unknown origin, while during
southward-directed Bz, the scintillations are caused by the
electric field associated with field-line mapped movement of plasma
in the magnetosphere. Ionospheric scintillation has been noted to
occur in regions of large temporal and spatial gradients of the
total electron content (TEC). Scintillations can also occur during
daylight hours and at mid-latitudes when Sporadic-E is present in
the E-layer. Sporadic-E layers are thin layers of highly dense
plasma at heights of about 100 km in which large density gradients
can exist. However, scintillations produced by Sporadic-E are much
less common and less predictable than those produced by the F-layer
processes described above. An index derived from the rate of change
of TEC, the so-called Rate of change of TEC index (ROTI), is often
used as a proxy for 4S . In this analysis of the effects of
precipitation on ionospheric scintillation, ROTI is primarily used
to express the intensity of scintillation, since high sampling rate
ionospheric scintillation monitors were not available at the
locations of interest during the previous solar minimum and solar
maximum.
For weak scintillations, 4 2.51S
f where f is the carrier frequency. This means that
scintillation is stronger at lower frequencies. At the
geomagnetic equator 4S does not depend on geomagnetic activity,
whereas high-latitude scintillation is frequently observed during
disturbed magnetic conditions and is thought to be associated with
an influx of high energy electrons that gain entry into the Earth’s
polar cap regions when the solar wind IMF couples with the Earth’s
magnetic field. A similar situation occurs in the South Atlantic
Magnetic Anomaly (SAMA) due to the increased precipitation of high
energy electrons in the atmosphere over the SAMA. Existing models
to predict ionospheric scintillation are best developed for
equatorial regions, but are inadequate for mid-latitude
regions.
6 Proxies for S4 amplitude scintillation In the absence of
measured L-band 4S scintillation values at the GPS stations of
which the data was used in this study, a number of proxies for the
amplitude scintillation index
4S can be used. The rate of change of TEC index (ROTI), defined
as the standard deviation,
22ROTI ROT ROT
-
Hermanus Magnetic
Observatory
Page 16 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
of the rate-of-change of TEC (ROT) with the averaging done over
a 5-minute period from 30 second sampled GPS data has been proposed
(Pi et al.,1997), Studies by (Pi et al.,1997); (Basu et al.,1999)
and (Beach and Kintner, 1999) concluded that ROTI could be used as
a proxy for assessing the presence of ionospheric scintillation.
Beach and Kintner (Beach and Kintner, 1999) concluded that ROTI
roughly proportional to measures of TEC fluctuation for weak
scintillation with ROTI (2 5)S4 rendering good expressions for
their measurements. Similarly, Basu et al.found ROTI (2 )S4 using
their dataset. The quantitative relationship between ROTI and S4
varies considerably due to variations of the ionospheric projection
of the satellite velocity and the ionospheric irregularity drift.
The study by (Basu et al, 1999) indicated that ROTI is selective of
Fresnel scale structures of 400 m at GPS frequencies. In this study
the approach of (Du et al 2000) was followed in quantifying a proxy
scintillation index (S4p) related to ROTI by an elevation-weighted
coefficient . The coefficient is calculated from a function of
satellite’s motion relative to the ionosphere, which is assumed to
be concentrated on an imaginary thin shell 400 km above earth (the
phase screen):
4 pS ROTI where
2
36.2135 10 vs
2 2 2 22 cos cosp I p Iv v v v v i s
pe s
v r hv
R r
cos( )cos
r hs
1 cossin rr h
Parameters and relevant values used in the calculation:
Re: Earth radius (6378 km) h: Assumed ionospheric height (400
km) θ: Satellite elevation angle i: GPS orbital plane inclination
(55o) vI: Ion drift velocity (120 m.s-1) vp: Velocity of the
ionospheric pierce point moving at h vs: Satellite orbital speed
(3874 m.s-1) rs: Satellite orbital altitude (20 000 km)
The elevation-weighted coefficient (β) shown in Figure 7
selectively suppresses low elevation ROTI compared to high
elevation ROTI. An example illustrating S4p proxy, calculated from
ROTI for Gough Island, is illustrated in Figure 8 for 28 October
2003 during which a severe geomagnetic storm occurred.
-
Hermanus Magnetic
Observatory
Page 17 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 9 shows the geographic location of the S4p occurrences
(red circles) superimposed on GPS satellite IPP ground trace (green
dots), as observed from Gough Island on 28 Oct 2003.
Figure 7. Elevation weighting coefficient (β) of Du et al. used
to relate ROTI to the S4-proxy S4p
Figure 8. ROTI as S4p-proxy calculated from Gough Island GPS
data on 28 October 2003 (day 301). The increased ROTI values around
11:00 UT are indicative of scintillation events observed by five
satellites. Severe geomagnetic storm (Kp = 9, Dst = -475 nT) was
experienced on this day.
0 3 6 9 12 15 18 21 240
5
10
15
20
25
30
Time [UTC hours]
S 4p
Gough Island S4p scintillation proxy calculated from ROTI. 28
October 2003 (day 301)
-
Hermanus Magnetic
Observatory
Page 18 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 9. Geographic location of ROTI- S4p-proxy occurrences
(red circles) superimposed on GPS satellite IPP ground trace (green
dots), as observed from Gough Island on 28 Oct 2003. Large blue
circles represent different satellite elevation angles. The
relative high elevation occurrence of ROTI illustrates that
observations are not associated with (low elevation) multipath
effects. These ROTI occurrences were observed around the same time
around 11:00 UT by five different satellites.
7 Validating the S4-proxy algorithm Several studies (Pi et al.
1997, Beach & Kintner 199, Du et al. 2000) have shown
correlation between S4 amplitude scintillation and ROTI and
confirmed the theory for the proxy ROTI-S4 use. To establish
confidence in the S4-proxy algorithm the GPS-derived elevation
weighted S4-proxy, S4p and the ROTI from which it is derived were
compared with actual GISTM S4- scintillation results obtained from
the GISTM installed on Gough Island in September 2008(Table 3).
Because of the prolonged solar minimum period towards the end of
solar cycle 23, very few significantly geomagnetic disturbed
periods were observed. A moderate geomagnetic storm observed on 3
August 2010 (Kp = 5) rendered significant S4 counts for Gough
Island which were however not matched by any concomitant
scintillations observed in Hermanus. Figure 10 shows a comparison
of S4 with ROTI for data from the equatorial GPS station at
Ascension. Figure 11 and Figure 12 show some examples using data
from Gough Island obtained during the geomagnetic storm on 3 August
2010. The parameters Co/N (signal-to-noise-ratio) and S4 were
obtained from the Novatel GISTM receiver, while the remaining
parameters were from the Ashtech standard GPS receiver. These
comparisons, combined with exhaustive hand-checking of results,
supplied the necessary confidence in the algorithms and
software.
344 346 348 350 352 354 356-45
-44
-43
-42
-41
-40
-39
-38
-37
-36
Longitude [Degrees]
Latit
ude
Gough Island ROTI scintillation on 28 Oct 2003
80o
60o
40o
-
Hermanus Magnetic
Observatory
Page 19 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 10. Comparison of S4 and ROTI and other related
parameters from GPS observations at Ascension Island, (JASTM 61
(1999) pp 1219-1226 )
Figure 11. Comparison of GISTM-observed S4 scintillation with
elevation weighted S4 proxy (S4p,) as observed respectively by a
Novatel GSV4004B GISTM and conventional Ashtech dual frequency GPS
receiver installed on Gough Island. Observations were done along
the ray path from satellite PRN10. The S4p were determined at
5-minute intervals from GPS data sampled at 30s intervals, the ROTI
values were determined at 30 second intervals while the S4 values
were recorded at 1 minute intervals. The top panel
-
Hermanus Magnetic
Observatory
Page 20 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
in the diagram shows the elevation (Elv) of satellite PRN10 on
the same time scale to indicate that the observed event occurred at
an elevation of about 50 ⁰, well above the horizon, and thus not
due to multipath effects. Panel 2 shows the normalised power on the
L1-signal (CNo) recorded at a sampling rate of 50 samples per
second with the GISTM to illustrate the power dip that is
associated with the S4-event. The TEC shown in panel 5 depicts the
small but rapid increase in the TEC which is associated with the
dip in the power, which seems to indicate that the S4-event was
caused by the ray path traversing a region of increased electron
density, which increased the absorption of the signal. The slope of
the TEC curve is shown as the Rate of Change of TEC (ROT) in panel
6. Panel 7 shows the Rate of Change of TEC Index, which is standard
deviation of the ROT, with averaging done over a 5-minute
period.
Figure 12. Comparison of GISTM-observed S4 scintillation with
elevation weighted S4 proxy (S4p,) as observed respectively by a
Novatel GSV4004B GISTM and conventional Ashtech dual frequency GPS
receiver installed on Gough Island. Observations were done along
the ray path from satellite PRN18.
8 Correlation between geomagnetic disturbance and EPP
The most extreme conditions for observing particle precipitation
occurs during geomagnetic disturbed conditions associated with
increased solar activity as manifested in solar flares, X-ray
flares or coronal mass ejections (CMEs). During such events the
Earth’s geomagnetic field is severely disturbed because of the
Interplanetary Magnetic
-
Hermanus Magnetic
Observatory
Page 21 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Field (IMF)-magnetosphere coupling and enhanced equatorial ring
currents. Apart from increased particle precipitation, the
ionosphere is significantly disturbed on a global scale, making it
difficult to distinguish between enhanced ionization due “normal”
geomagnetic response or to particle precipitation. To facilitate
the identification of particle precipitation occurrences during and
outside storm-time days, disturbed days were identified by the
Disturbance storm time index (Dst).
8.1 Disturbance storm time index (Dst) The Dst is an index of
magnetic activity and is derived from a network of near-equatorial
geomagnetic INTERMAGNET observatories that measure the intensity of
the globally symmetrical equatorial ring current. These
observatories are located at San Juan (Puerto Rico), Honolulu
(Hawaii), Hermanus (South Africa) and Kakioka (Japan). Severe
geomagnetic storms result in large negative Dst values. The Oct
2003 and Nov 2004 geomagnetic storms (Kp = 9) e.g. resulted in Dst
values of up to -475 nT. Moderate storms (Kp = 5) have Dst values
of about -50 nT. To illustrate the correlation between geomagnetic
activity and EPP, hourly global proton flux measurements in the
> 1, 2, 4, 10, 30 and 60 MeV range from the OMNI2 data sets were
compared to disturbance storm time (Dst) values and are presented
for the years 2000 (Figure 13) and 2004 (The OMNI2 proton flux
values were obtained from the IMP-7 and IMP-8 satellites recorded
during the Charged Particle Measurement Experiment (CPME) &
Energetic Particle Experiment (EPE) from 1973-2005.
[sd-www.jhuapl.edu/IMP/imp_index.html]. The correlation between
increased EPP with associated large negative Dst values is clear
from the figures. From these results it’s evident that increased
EPP is observed during geomagnetically disturbed periods.
-
Hermanus Magnetic
Observatory
Page 22 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 13. Year 2000 Proton flux values at various energy levels
(top) compared to Dst values (bottom)
Figure 14 Year 2004 Proton flux values at various energy levels
(top) compared to Dst values (bottom)
30 60 90 120 150 180 210 240 270 300 330 3600
0.5
1
1.5
2
2.5
3x 104 2000 Proton flux at various energy levels (OMNI data)
Day of year
Pro
ton
flux
[1/(c
m2
sec
ster
)]
> 1 MeV> 2 MeV> 4 MeV> 10 MeV> 30 MeV> 60
MeV
0 30 60 90 120 150 180 210 240 270 300 330 360-400
-300
-200
-100
0
Dst: 2000
Dst
[nT]
Local time [day-of-year]
30 60 90 120 150 180 210 240 270 300 330 3600
0.5
1
1.5
2
2.5
3x 10
4 2004 Proton flux at various energy levels (OMNI data)
Day of year
Pro
ton
flux
[1/(c
m2
sec
ster
)]
> 1 MeV> 2 MeV> 4 MeV> 10 MeV> 30 MeV> 60
MeV
0 30 60 90 120 150 180 210 240 270 300 330 360-400
-300
-200
-100
0
Dst: 2004
Dst
[nT]
Local time [day-of-year]
-
Hermanus Magnetic
Observatory
Page 23 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
9 Data challenges
9.1 Non-availability of data. The availability of relevant GPS
data used in the study is summarized in Table 2
For some years GPS data was very sparse. Gough Island data
availability varied between 67-83% over the period. No
supplementary data was available due to the isolation of the
island lack of receiver redundancy on the island.
Cape Town (South Africa) data availability varied between
21-100% with data in 2003-2004 being particularly sparse. Where
possible gaps in the Cape Town data were supplemented from the
Simonstown and Hermanus GPS receivers, both within 100 km from Cape
Town. Prior to 2005 Hermanus data was only recorded from (06:00 –
20:00 LT) daily due to CDSM surveying policy at the time. No
night-time ROTI measurements were subsequently possible when
Hermanus data prior to 2005 was used.
Perth data availability was mostly above 85%, except for one
year (63%). Perth data was supplemented by Dongara Data for the 130
day period during 2001when Perth data was not available.
Table 2. Archived GPS data availability, in days, with
percentage days available for a specific year given in brackets ().
Year Receiver
2000
2001 2003 2004 2008
Gough Island (GOUG) 09:52:51.3W, 40.:20:55.2S
286 (78) 255 (70) 245 (67) 261 (72) 305 (83)
Cape Town (CTWN) 18:28:06.1E, 33:57:04.8S
336 (91) 304 (83) 126 (34) 76 (21) 365 (100)
Hermanus (HNUS) 19:13:22.3E, 34: 25:28.2S
- - 239 325 -
Simonstown (SIMO) 18:26:22.4E, 34: 11:16.4S
- - 266 57 -
Combined (CTWN, SIMO, HNUS)
336 (91) 304 (83) 334 (92) 340 (93) 365 (100)
Perth (PERT) 115:53:06.9E, 31:48:07.1S
314(86) 229 (63) 325 (89) 354 (97) 349 (95)
Dongara (YAR1) 115:20:49.1E, 29:02:47.6S
- 130 - - -
Combined (PERT,YAR1)
314(86) 359 (98) 325 (89) 354 (97) 349 (95)
-
Hermanus Magnetic
Observatory
Page 24 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
9.2 False positives associated with cycle slips. The biggest
challenge in processing the GPS data was eliminating false positive
scintillation events associated with cycle slips observed in the
GPS L1-L2 phase data. A cycle slip is attributed to a momentarily
signal loss-of-lock by the GPS receiver with an associate unknown
integer ambiguity offset added to the measured L1 and L2 phase. The
difference between consecutive TEC values calculated across a cycle
slip may subsequently vary from a few to several thousand TECUs,
leading to very large rate-of change of TEC (ROT) values across a
cycle slip and subsequent large ROTI (scintillation S4 proxy)
values. Cycle slips (or phase jumps) are often associated with
disturbed ionospheric conditions and are indications of a
scintillation event, but in this study it was found the majority
cycle slips occurred randomly during non-disturbed conditions. It
was also evident that, in the event of an ionospheric disturbance,
the magnitude of the phase jump is not necessarily related to the
severity of the event/disturbance. Large ROTI values associated
with large cycle slips subsequently do not necessarily represent
large ionospheric scintillations and might be misleading when
interpreting results. In the initial ROTI analysis false positives
constituted about 40% of the results and a general methodology had
to be developed to correct for cycle slips and eliminate false
positives without affecting true scintillation observations. The
method was developed over several iterations as cycle slips
presented it in various forms. To find a general methodology proved
difficult because of the various ways cycle slips represented
themselves. At times relative small cycle slips (~0.25 - 2 TECU)
could occur during disturbed conditions, but such slip-values might
be smaller than valid epoch-to-epoch TEC differences or disturbance
amplitude (Figure 15). In such cases cycle slip correction may
smooth out valid scintillation observations. At other times, very
steep, but valid consecutive TEC differences (> 10 TECU) were
observed during disturbed conditions, but no cycle slips occurred
and care had to be taken not to eliminate valid such scintillation
events. To eliminate false scintillation observations, cycle slips
were identified by checking for time-gaps and large TEC differences
over continuous data arcs. On identifying a cycle slip in a
continuous data arc, it was corrected by adding a relevant offset.
Cycle slip correction reduced the number of false positives to
-
Hermanus Magnetic
Observatory
Page 25 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 15. Example of false positive ROTI caused by cycle slips
not associated with sustained perturbed ionospheric phase
observation. For satellite PRN13, observed from Perth on 12 June
2008, cycle slips are observed in L1 and L2 phase as phase jumps
(top), abrupt jumps in slant TEC with ~2 TECU (middle) and
associated ROTI (bottom). Note the relative high ROTI values
associated with these cycle slips. Such ROTI calculations typically
are associated with false positive scintillation events.
14 15 16 17 180.85
0.9
0.95
1
1.05
1.1
1.15
1.2x 108
Pha
se
Phase observed for PRN 13 on 12 June 2008 (day 164) from PERTH
IGS GPS Receiver
L1L2
14 15 16 17 1828
29
30
31
32
33Phase-derived Slant TEC observed for PRN 13 on 12 June 2008
(day 164) from PERTH IGS GPS Receiver
TEC
[TE
CU
]
14 14.5 15 15.5 16 16.5 17 17.5 1828
30
32
TEC
[TE
CU
]
14 15 16 17 180
5
10
RO
TI
Time [UTC hours]
ROTI and Phase-derived Slant TEC observed for PRN 13 on 12 June
2008 (day 164) from PERTH IGS GPS Receiver
-
Hermanus Magnetic
Observatory
Page 26 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 16. Example of false positive ROTI scintillation events
associated with cycle slips observed on all GPS receiver channels
for 12 June 2008 at Perth. Scrutiny revealed this day’s raw data
was too suspicious to use and was subsequently ignored.
10 DMSP SSJ/4 EPP sensor The SSJ/4 sensor, a precipitating
Electron and Ion Spectrometer, was built by the United States Air
Force (USAF) Research Lab and Space Vehicles Directorate. It was
designed to measure the flux of charged particles as they enter the
Earth’s upper atmosphere from the near-Earth space environment. The
SSJ/4 sensor has flown on board the Defence Meteorological
Satellite Programme (DMSP) satellites. DMSP satellites are in a
sun-synchronous, low altitude polar orbit. The orbital period is
101 minutes and the nominal altitude is 830 km. The DMSP satellites
are three axes stabilised with particle detectors configured to
point toward local zenith (Hardy et al., 1985). The DMSP SSJ/4
particle precipitation sensor data provide a complete energy
spectrum of the low energy particles that cause the aurora and
other high latitude phenomena. The data set consists of integrated
electron and ion particle fluxes between 30 eV and 30 KeV and
satellite ephemeris and magnetic coordinates where the particles
are likely to be absorbed by the atmosphere. The differential
number flux is the number of particles crossing a unit area from a
unit solid angle per second at each energy level. The parameters
relevant for this project are the number flux and the energy flux
and are stored in 15 second intervals along with relevant satellite
coordinates at observation epochs. The number flux (Nf) is derived
by integrating the differential number flux across all energies. It
is a measure of intensity and is independent of the energy, i.e.
the number of particles crossing a unit area from a unit solid
angle per second regardless of the energy. Similarly, the
differential energy flux is the amount of energy crossing
0 3 6 9 12 15 18 21 240
5
10
15
20
25
30
35
40ROTI associated with cycle slips obsereved on 12 June 2008
(day 164) from PERTH IGS GPS Receiver
Time [UTC hours]
RO
TI
-
Hermanus Magnetic
Observatory
Page 27 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
the same unit area from a unit solid angle per second at each
energy level, which when integrated across all energy levels, gives
the energy flux (Ef), i.e. Ef is the total energy crossing a unit
area from a unit solid angle per second. Dividing the energy flux
by the number flux gives the average energy of the particles i.e.
< E > = Ef/Nf The detectors also record high energy ions that
penetrate both the satellite and the instrument. This is most
noticeable in the South Atlantic Anomaly and at the "horns" of the
radiation belts.
Table 3 Geographic and Geomagnetic Coordinates of key locations
used in the study together with the GISTM data availability.
Location Geographic Coordinates of antenna
Geomagnetic coordinates CGM
Date since which 1 minute scintillation parameters logged
Date since which 50 Hz raw data logged
Hermanus Magnetic Observatory (HMO)
34°25'24.87"S, 19°13'24.36"E
42.27°S 83.22°E L 1.86
2010/06/01 2010/06/01
Gough Island 40°20'58.11"S, 9°52'49.17"W
42.29°S 51.09°E L 1.86
2008/09/21 2008/09/21
Note: Corrected Geomagnetic Coordinates were calculated using
the on-line calculator at
omniweb.gsfc.nasa.gov/cgi/vitmo/vitmo_model.cgi
11 Data processing
11.1 DMSP SSJ4 data for DMSP satellite F13 were obtained from
NOAA for years 2000, 2001, 2003, 2004 and 2008. Relevant Matlab ®
scripts were developed to read the ASCII orbit files to extract
energetic particle flux/energy measurements and corresponding
geographic (and magnetic) coordinates. Relevant close overpasses of
the F13 satellite over the three locations (Gough Island, Cape
Town, and Perth) were identified by a geographic window of 10˚x 10˚
(Figure 17) in longitude and latitude centred on each location.
Using this window, electron and ion flux and energy values were
extracted to represent particle precipitation measurements over the
respective locations. All EPP values were checked for outliers and
the cleaned results stored separately for each of the three
locations for later comparison and correlation with GPS
scintillation measurements. Examples of EPP measurements along a
DMSP F13 satellite overpass are illustrated in Figure 18 to Figure
20 It was assumed that the 15-second sampled EPP data observed
during the transit of each 10˚ geographic window represented EPP
flux and energy over the whole 10˚ window. It was also
-
Hermanus Magnetic
Observatory
Page 28 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
assumed that EPP continues over the geographic window at similar
flux and energy levels for some time (Δτ) after the satellite has
passed through the window and can no longer take measurements of
that geographic region. This period, Δτ, is assumed to be
sufficiently long to permit EPP flux and energy levels observed
over each window to be considered concurrent with the closest
(5-minute interval) S4p calculation.
Figure 17. Geographic windows of 10˚ centred on the key
locations
Figure 18 SSJ4 Electron and ion flux and energy levels observed
at South Atlantic Anomaly region around 2001-03-16-06:41 UTC . The
red line indicates the geographic latitude of the Gough Island GPS
receiver used for the ionospheric scintillation calculations. Note
that particle precipitation values are an order of magnitude larger
than for Cape Town.
-150 -100 -50 0 50 100 150
-80
-60
-40
-20
0
20
40
60
80
Longitude [Deg]
Latit
ude
[Deg
]
Geographic windows around key locations
Gough Island
Cape Town
Perth
-60 -40 -20 00
2
4
6x 107 SAA Ne flux
-60 -40 -20 00
2
4
6
8x 108SAA Electron energy flux
-60 -40 -20 010
15
20
25SAA Electron EAVE
-60 -40 -20 00
1
2
3x 107 SAA Ni flux
Latitude-60 -40 -20 00
1
2
3x 108 SAA ION energy flux
Latitude-60 -40 -20 05
10
15SAA ION EAVE
Latitude
-
Hermanus Magnetic
Observatory
Page 29 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 19. SSJ4 Electron and ion flux and energy levels observed
at South Africa around 2001-03-16-03:17UTC. The red line indicates
the geographic latitude of the Cape Town GPS receiver used for the
ionospheric scintillation calculations.
Figure 20. SSJ4 Electron and ion flux and energy levels observed
over Australia around 2001-03-16-08:2UTC. The red line indicates
the geographic latitude of the Perth GPS receiver used for the
ionospheric scintillation calculations.
11.2 GPS Dual frequency GPS data in the form of Receiver
Independent Exchange (RINEX) observation files were obtained for
Gough Island, Simonstown, Perth and Dongara from the International
GNSS Service [IGS] for the years under investigation. RINEX data
for Cape Town and Hermanus GPS receivers were sourced from the
South African Chief Directorate Surveys and Mapping [CDSM]. At the
time none of the South African receivers contributed data towards
IGS and were subsequently not available in the IGS network. All
RINEX data were pre-
-50 -40 -30 -20 -10 00
1
2
3x 106 RSA Ne flux
-50 -40 -30 -20 -10 00
2
4
6x 107 RSA Electron energy flux
-50 -40 -30 -20 -10 05
10
15
20
25RSA Electron EAVE
-50 -40 -30 -20 -10 00
5
10
15x 105 RSA Ni flux
Latitude-50 -40 -30 -20 -10 00
5
10
15x 106 RSA ION energy flux
Latitude-50 -40 -30 -20 -10 00
5
10
15RSA ION EAVE
Latitude
-60 -40 -20 01
2
3
4
5x 105 AUS Ne flux
-60 -40 -20 00
5
10x 106AUS Electron energy flux
-50 -40 -30 -20 -10 010
15
20
25AUS Electron EAVE
-60 -40 -20 00
1
2
3x 107 AUS Ni flux
Latitude-60 -40 -20 01
2
3
4
5x 106 AUS ION energy flux
Latitude-50 -40 -30 -20 -10 05
10
15
20AUS ION EAVE
Latitude
-
Hermanus Magnetic
Observatory
Page 30 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
processed to remove any GLONASS data and only maintain
GPS-observed L1, L2 phase and C1 and P2 code (pseudo range) data.
Erroneous or corrupted data files were deleted. Orbital (sp3)
position files for GPS satellites were obtained from [IGS]. RINEX
and sp3 files were ordered in relevant directory structures for
algorithmic batch data processing. Batch processing involved:
Reading RINEX and sp3 files Calculating phase slant TEC along
signal paths (up to 32 GPS satellites are visible
daily) Calculating satellite azimuth and elevation angles as
observed from the receiver
position Limiting slant TEC values to elevations > 40o to
eliminate multipath effects Calculating ROTI values from standard
deviation of 5-minute windowed ROT values Calculating proxy-S4
values from ROTI Storing the results in Matlab binary files
HMO-developed Matlab® scripts were used to conduct the batch
processing. All GPS receivers used in this study are permanently
installed, dual frequency, geodetic grade receivers operating with
pillar-mounted choke ring antennas to minimize the effect of
multipath signal scattering. The major applications of these
receivers are space geodesy, global ionospheric monitoring and
surveying. Typical receivers used to register data used in his
study include the Turbo Rogue SNR-8100, Ashtech Z-XII3, Ashtech
UZ-12 (micro Z-12), Ashtech Z-FX, Trimble 4000SSI and Trimble
NetR5. Depending on the GPS constellation geometry, at any given
time 3-12 satellites are visible above the local horizon and each
of these receivers can simultaneously record observables of up to
twelve GPS satellites. It is subsequently possible to have up to 12
S4p proxy values per receiver at each 5-minute epoch, supplying
sufficient redundancy in the observation data.
11.3 Integrating SSJ/4 and S4p data The DMSP F13 satellite
orbits transits the selected geographic windows twice daily, in the
morning and evening. Because of the satellite’s relative high
ground velocity, typically fewer than 20 data points are registered
during each window transit. To meaningfully compare and correlate
the sparse 15-second sampled EPP observations with up to 12 S4p
(ROTI) calculations for each 5 minute epoch, three approaches were
followed: visual comparison, statistical correlation of median
values and statistical correlation of daily integrated values.
11.3.1 Visual comparison For each 5-minute S4p (ROTI) data
epoch, all available S4p (ROTI) values were binned into the median
S4p value for that 5 minutes. This gave a representative
scintillation value for each epoch and served as a non-linear
filter to eliminate spurious outliers. For each year, the SSJ/4 Ne
and Ni flux, S4p (ROTI) and Dst were then plotted on a four-pane
graph (e.g. Figure 21). At this point all available EPP
observations were included in the comparison. This visual
comparison permitted an immediate overview of possible correlations
and proved valuable in
-
Hermanus Magnetic
Observatory
Page 31 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
identifying outliers and interesting events and for
investigating and remedying suspicious S4p (ROTI) values.
11.3.2 Statistical correlation of median values To
quantitatively correlate EPP and scintillation values for each
relevant geographic key point, it was required to first identify
the median S4p epochs (at 5-minte intervals) which closely matched
EPP observation epochs during each window transit. F13 satellite
total window transit times were typically less than two minutes
with data sampled at 15-second intervals during this period. It was
subsequently necessary to derive a single representative EPP value
for the transit period which would then be correlated with the
closest S4p 5-minute spaced value. For each year, this single EPP
value was obtained by taking the median value for each of the
electron and ion flux and energy values for each relevant key point
window transit period in that year. Corresponding times in the
median S4p values for that year were then identified. A Linear
regression analysis was conducted using the median EPP and median
S4p data sets for each year. Using the regression coefficients, a
regression line was fitted to the data and a correlation
coefficient calculated. An example result is illustrated in Figure
22
11.3.3 Statistical correlation of integrated values Because of
the limited temporal daily coverage of F13 over each key position,
the daily integrated EPP flux was also statistically correlated
with the daily integrated 5-minute median S4p (∫S4p) values for
each key point, as a measure to provide for possible
miss-correlation between S4p and EPP. Regression analysis was
conducted and correlation coefficient calculate to quantify the
correlation between, respectively, the daily integrated median S4p
and the daily integrated electron flux (Ne), and the daily
integrated median S4p and daily integrated EPP ion flux (Ni). An
example result of correlations of daily integrated values is
illustrated in Figure 21
12 Results All the figures illustrating the visual and
statistical comparison and correlation between EPP and S4p
scintillation proxy are given in Appendix A. The correlation
coefficients calculated between EPP and S4p for all three locations
for the years under consideration, are given in Table 4
-
Hermanus Magnetic
Observatory
Page 32 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 21. Year 2003 Gough Island electron (Ne) and ion (Ni)
flux (panes 1-2), 5-minute median S4p (ROTI), pane 3) and Dst
(bottom). Note the large S4p values around day 319 which appears to
coincide with a large Dst value and apparent increased electron and
ion flux.
0 30 60 90 120 150 180 210 240 270 300 330 3600
1
2x 107 Gough annual Ne flux: 2003
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
0 30 60 90 120 150 180 210 240 270 300 330 3600
1
2x 107 Gough annual Ni flux: 2003
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
30 60 90 120 150 180 210 240 270 300 330 3600
10
20
30Gough annual ROTI binned in median of 5-minute intervals :
2003
RO
TI
0 30 60 90 120 150 180 210 240 270 300 330 360-400
-200
0
Dst: 2003
Dst
[nT]
Local time [day-of-year]
-
Hermanus Magnetic
Observatory
Page 33 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 22. Year 2003 statistical correlation of Gough Island
electron (Ne) and ion (Ni) flux with 5-minute median S4p (ROTI)
Figure 23. Year 2003 Statistical correlation between,
respectively, daily integrated electron flux (top) and ion flux
(bottom) and S4p
0 1 2 3 40
2
4
6
8
10x 10
6 Gough Ne flux - ROTI correlation. 2003
median ROTI
med
ian
Ne
flux
y = 147411.6353x + 1593755.4189Corr. Coeff = 0.026011
0 1 2 3 40
5
10
15x 10
7
Gough Ne Energy - ROTI correlation. 2003
median ROTI
med
ian
Ne
Ene
rgy
y = 3479779.1814x + 10172061.302
Corr. Coeff = 0.049723
0 1 2 3 40
2
4
6
8
10
12x 10
6 Gough Ni flux - ROTI correlation. 2003
median ROTI
med
ian
Ni f
lux
y = 2967304.0588x + -55086.4871
Corr. Coeff = 0.21385
0 1 2 3 40
2
4
6
8
10x 10
7 Gough Ni Energy - ROTI correlation. 2003
median ROTI
med
ian
Ni E
nerg
y
y = 10213721.9427x + 2754569.6791
Corr. Coeff = 0.13463
0 20 40 60 80 100 120 140 160 180 2000
1
2
3
4
5
6x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ne
flux
Gough Daily integrated Ne flux - ROTI correlation. 2003
y = 3680.8355x + 17060364.9888
Corr. Coeff = 0.0087891
0 20 40 60 80 100 120 140 160 180 2000
2
4
6
8x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ni f
lux
Gough Daily integrated Ni flux - ROTI correlation. 2003
y = 65153.1734x + 3967880.0369
Corr. Coeff = 0.13119
-
Hermanus Magnetic
Observatory
Page 34 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Table 4. Correlation coefficients between S4p and EPP. (∫S4p
represents integrated S4p) S4p
2000 ∫S4p 2000
S4p 2001
∫S4p 2001
S4p 2003
∫S4p 2003
S4p 2004
∫S4p 2004
S4p 2008
∫S4p 2008
GOUG Ne Flux
-0.06 -0.14 0.01 -0.04 .02 .01 .04 .06 -0.04 0.06
GOUG Ne Energy
-0.07 x 0.08 x .05 x .00 x -0.05 x
GOUG Ni Flux
-0.07 -0.13 0.21 0.23 .21 .13 .05 .10 -0.03 0.04
GOUG Ni Energy
-0.08 x 0.11 x .13 x .03 x -0.03 x
CTWN Ne Flux
-0.04 -0.11 -0.14 0.01 -0.11 -0.17 0.11 -0.04 0.07 0.17
CTWN Ne Energy
-0.05 x -0.13 x -0.04 x 0.03 x 0.08 x
CTWN Ni Flux
-0.06 -0.13 -0.07 0.05 0.29 0.19 -0.07 -0.07 0.04 0.16
CTWN Ni Energy
-0.07 x -0.13 x 0.03 x 0.00 x 0.06 x
PERT Ne Flux
0.20 0.27 0.01 0.07 -0.05 0.11 0.08 0.00 0.08 0.08
PERT Ne Energy
0.07 x -0.05 x 0.00 x -0.01 x 0.08 x
PERT Ni Flux
0.22 0.13 -0.10 -0.09 0.07 0.44 0.10 -0.06 0.06 0.11
PERT Ni Energy
0.01 x 0.02 x 0.29 x 0.09 x 0.05 x
-
Hermanus Magnetic
Observatory
Page 35 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
13 Discussion The results in Table 4 suggest that statistical
correlation coefficients between the observed EPP flux and energy
measurements and scintillations in this study are generally very
low. The highest correlation coefficient is 0.44 (Perth 2003,
integrated ion flux-scintillation) and all other ion-scintillation
correlations below 0.3. The largest ion-scintillation correlation
coefficients (> 0.2) were observed close to solar maximum (Gough
2001, 2003; Cape Town 2003; Perth 2000, 2003). The largest electron
– scintillation correlation value was 0.27 (Perth (2000, integrated
electron flux).
A number of days with interesting scintillation and
precipitation events were identified in the visual comparison.
Results for two events in respectively 2001 (Figure 24) and 2003
(Figure 25) illustrate that scintillation and precipitation
observations were not correlated with scintillation typically
occurring before precipitation: On day 90 of 2001 a severe
geomagnetic disturbance was observed (Dst = -387 nT). Visual
analysis of EPP and S4p for days 88-94 (Figure 24) revealed that
though significant scintillations were observed at Cape Town for
this day, no increased EPP was observed. Conversely, when increased
EPP was observed on day 94, no scintillations of significance were
observed. No EPP data was available for Perth on day 90 when
scintillations were observed, but on days 93 and 94, when increased
EPP was observed, as for Cape Town, no associated scintillations
were observed. Additional days with similar results (included in
the Appendix) are also mentioned. This list is ordered by year, but
is not exhaustive. Cape Town 2000 Day 329: Increased S4p, but no
noticeable EPP increase. Relatively small Dst decrease (-50 nT).
Dst only decreased on the following day. Cape Town 2001 Day 116,
S4p increased, but EPP only increased on day 117. Day 257 seems to
show simultaneous S4p and PP, however day 263 shows increased EPP,
but no increased S4p. Day 302 has increased S4p, but no increase in
EPP. Gough 2001 Day 255: Increased EPP, but no increased S4p. Day
348-365, increased EPP, but no increased S4p Perth 2001 Day 249.
Increased EPP, but no increased S4p Day 255. Increased EPP, but no
increased S4p.
-
Hermanus Magnetic
Observatory
Page 36 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 24. Year 2001 days 88-94 illustrate Cape Town and Perth
observations of proton flux (black crosses) compared with S4p
scintillation (blue dots). No GPS data was available for Gough
Island for this period, but proton flux is illustrated for
completeness.
Cape Town 2003 Day 94: Increase in EPP, no S4p, increase Day
301: S4p, increase, but EPP only increases on day 307 (Figure 25)
Cape Town 2004 Day 313: Both EPP and S4p increases (S4p only
nominally). Dst -286 nT. Day 319: EPP increase rapidly, no S4p
increase
88 89 90 91 92 93 94 950
0.5
1
1.5
2
2.5
3Cape Town Ni flux and S4p: 2001
5-m
inut
e m
edia
n S
4p
88 89 90 91 92 93 94 950
0.5
1
1.5
2
2.5
3x 107
Pro
ton
flux
[1/(c
m2
sec
ster
)]
88 89 90 91 92 93 94 950
5
10Perth Ni flux and S4p: 2001
5-m
inut
e m
edia
n S
4p
88 89 90 91 92 93 94 950
1
2x 107
Pro
ton
flux
[1/(c
m2
sec
ster
)]
88 89 90 91 92 93 94 950
0.5
1Gough Island Ni flux and S4p: 2001
Day of year [Local time]88 89 90 91 92 93 94 95
0
5
10x 107
Pro
ton
flux
[1/(c
m2
sec
ster
)]
-
Hermanus Magnetic
Observatory
Page 37 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
Figure 25. Year 2003 days 303-307 illustrate Cape Town, Perth
and Gough island observations of proton flux (black crosses)
compared with S4p scintillation (blue dots). Minimum Dst on day 303
was -383 nT
Gough Island 2004 Day 209: Dst decreased to min of -197 nT, and
S4p noticeably increased to a maximum of 1.2. EPP, however,
remained nominal on this day and only started increasing from day
212-214, during recovery phase, i.e. 3 days after the Dst minimum.
Day 313: Dst decreased to -370 nT and Ni-EPP increased as well.
Unfortunately no GPS data was available for this day. However, from
day 316-319, 3 days after Dst minimum, there was a rapid increase
in PP, but no significant S4p increase. Cape Town 2008 A few S4p
events, but no associated EPP increase Gough 2008 No significant
S4p or EPP events Perth 2008 Day 60. Increase in S4p, no EPP
increase Day 87: Increase in S4p, no EPP increase
303 303.5 304 304.5 305 305.5 306 306.5 3070
1
2
3
4
5Cape Town Ni flux and S4p: 2003
5-m
inut
e m
edia
n S
4p
303 303.5 304 304.5 305 305.5 306 306.5 3070
1
2
3
4x 106
Pro
ton
flux
[1/(c
m2
sec
ster
)]
303 303.5 304 304.5 305 305.5 306 306.5 3070
1
2
3
4
5Perth Ni flux and S4p: 2003
5-m
inut
e m
edia
n S
4p
303 303.5 304 304.5 305 305.5 306 306.5 3070
0.5
1
1.5
2
2.5
3x 108
Pro
ton
flux
[1/(c
m2
sec
ster
)]
303 303.5 304 304.5 305 305.5 306 306.50
1
2
3
4
5Gough Ni flux and S4p: 2003
5-m
inut
e m
edia
n S
4p
Day of year [Local time]303 303.5 304 304.5 305 305.5 306
306.5
0
5
10x 106
Pro
ton
flux
[1/(c
m2
sec
ster
)]
-
Hermanus Magnetic
Observatory
Page 38 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
14 Conclusions During the period 2000-2008 several events with
increased EPP were identified. There were also a number of
occasions with L-band scintillation, but the scintillation events
were not in general correlated with the increased EPP. The
correlation between the 5-minute median S4p and EPP as well as
between the daily integrated scintillation and EPP was investigated
by means of time series plotted on the same time scale and scatter
plots of concurrent events. The magnitude of the correlation
coefficients derived from the scatter plots were less than 0.1 for
most of the locations and years for both electron and proton
precipitation. The low correlation derived from the scatter plots,
together with the lack of synchronicity of EPP and precipitation in
the time-series analysis, is taken to indicate very little or no
correlation between EPP over the SAMA and L-band scintillation
observed at each of the three locations: Gough Island, Cape Town,
and Perth.
15 Key Project Participants The following three key participants
were responsible for executing the project..
15.1.1 Dr BDL Opperman. Co-ordinator Ionospheric Research
Physicist. Hermanus Magnetic Observatory.
PhD in Ionospheric Physics (Rhodes University). Competencies.
Computational Physics, Ionospheric Physics, GPS, Orbital mechanics,
Digital signal processing.
15.1.2 Dr PJ Cilliers. Co-author Ionospheric Research Physicist.
Hermanus Magnetic Observatory : Competencies. Computational
Electromagnetics, Ionospheric Physics, GPS, Digital signal
processing.
15.1.3 Dr LA McKinnell. Managing Director, Ionospheric Research
Physicist. Hermanus Magnetic Observatory.
Research Associate. Department of Physics and Electronics,
Rhodes University.
Key competencies. Ionospheric physics, neural networks,
Ionosondes, computational physics.
-
Hermanus Magnetic
Observatory
Page 39 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
16 Appendix A: Precipitation – Scintillation correlation
results
Appendix A presents all the results obtained in this study in
the following formats for each of the three locations, Cape Town,
Gough Island and Perth: 1. Time series of EPP flux plotted on the
same time scale as the L-band scintillation index (S4p) and the
geomagnetic storm index Dst. 2. Scatter plots of median EPP against
median S4p. 3. Scatter plots of daily time-integrated EPP against
daily time-integrated median S4p. Note: In all the figures in
appendix A, the values labelled ROTI are actually the
elevation-weighted S4-proxy, S4p, derived from ROTI. See Figure 11
and Figure 12 and the preceding text for the relation between S4p
and ROTI.
-
Hermanus Magnetic
Observatory
Page 40 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
16.1 Gough Island 2000
0 30 60 90 120 150 180 210 240 270 300 330 3600
2
4
6x 10
6 Gough annual Ne flux: 2000N
f [cm
-2.s
-1.s
r-1.e
V-1
]
0 30 60 90 120 150 180 210 240 270 300 330 3600
1
2
3x 10
6 Gough annual Ni flux: 2000
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
30 60 90 120 150 180 210 240 270 300 330 3600
2
4Gough annual ROTI binned in median of 5-minute intervals :
2000
RO
TI
0 30 60 90 120 150 180 210 240 270 300 330 360-400
-200
0
Dst: 2000
Dst
[nT]
Local time [day-of-year]
-
Hermanus Magnetic
Observatory
Page 41 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
0 0.2 0.4 0.6 0.8 10
1
2
3
4x 106Gough Ne flux - ROTI correlation. 2000
median ROTI
med
ian
Ne
flux
y = -511154.299x + 919320.4745Corr. Coeff = -0.060973
0 0.2 0.4 0.6 0.8 10
1
2
3
4
5x 107Gough Ne Energy - ROTI correlation. 2000
median ROTI
med
ian
Ne
Ene
rgy
y = -8670742.1719x + 14049386.1293
Corr. Coeff = -0.071507
0 0.2 0.4 0.6 0.8 10
0.5
1
1.5
2
2.5x 106Gough Ni flux - ROTI correlation. 2000
median ROTI
med
ian
Ni f
lux
y = -357842.4184x + 703616.0548
Corr. Coeff = -0.074687
0 0.2 0.4 0.6 0.8 10
0.5
1
1.5
2
2.5x 107Gough Ni Energy - ROTI correlation. 2000
median ROTI
med
ian
Ni E
nerg
y
y = -3331196.3771x + 6634053.5432
Corr. Coeff = -0.076414
30 40 50 60 70 80 90 100 1100
0.5
1
1.5
2
2.5x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ne
flux
Gough Daily integrated Ne flux - ROTI correlation. 2000
y = -83370.5258x + 14137079.4383
Corr. Coeff = -0.14124
30 40 50 60 70 80 90 100 1100
0.5
1
1.5
2x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ni f
lux
Gough Daily integrated Ni flux - ROTI correlation. 2000
y = -48809.0907x + 9748510.6989
Corr. Coeff = -0.12841
-
Hermanus Magnetic
Observatory
Page 42 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
16.2 Gough Island 2001
0 30 60 90 120 150 180 210 240 270 300 330 3600
2
4
6x 106 Gough annual Ne flux: 2001
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
0 30 60 90 120 150 180 210 240 270 300 330 3600
1
2x 107 Gough annual Ni flux: 2001
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
30 60 90 120 150 180 210 240 270 300 330 3600
10
20Gough annual ROTI binned in median of 5-minute intervals :
2001
RO
TI
0 30 60 90 120 150 180 210 240 270 300 330 360-400
-200
0
Dst: 2001
Dst
[nT]
Local time [day-of-year]
-
Hermanus Magnetic
Observatory
Page 43 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
0 0.5 1 1.5 2 2.50
1
2
3
4
5
6x 106 Gough Ne flux - ROTI correlation. 2001
median ROTI
med
ian
Ne
flux
y = 29558.6754x + 2049026.7314
Corr. Coeff = 0.0050904
0 0.5 1 1.5 2 2.50
1
2
3
4
5
6x 107Gough Ne Energy - ROTI correlation. 2001
median ROTI
med
ian
Ne
Ene
rgy
y = 4633617.8032x + 9370337.5821
Corr. Coeff = 0.083008
0 0.5 1 1.5 2 2.50
0.5
1
1.5
2x 107
Gough Ni flux - ROTI correlation. 2001
median ROTI
med
ian
Ni f
lux y = 3638630.9801x + 554585.3299
Corr. Coeff = 0.20907
0 0.5 1 1.5 2 2.50
0.5
1
1.5
2
2.5x 107
Gough Ni Energy - ROTI correlation. 2001
median ROTI
med
ian
Ni E
nerg
y
y = 2422707.5205x + 5057671.7948
Corr. Coeff = 0.10976
0 50 100 1500
1
2
3
4
5x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ne
flux
Gough Daily integrated Ne flux - ROTI correlation. 2001
y = -16435.4629x + 23536793.375Corr. Coeff = -0.041848
0 50 100 1500
2
4
6
8
10x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ni f
lux
Gough Daily integrated Ni flux - ROTI correlation. 2001
y = 142239.4246x + 3051745.4063Corr. Coeff = 0.2294
-
Hermanus Magnetic
Observatory
Page 44 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
16.3 Gough Island 2003
0 30 60 90 120 150 180 210 240 270 300 330 3600
1
2x 107 Gough annual Ne flux: 2003
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
0 30 60 90 120 150 180 210 240 270 300 330 3600
1
2x 107 Gough annual Ni flux: 2003
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
30 60 90 120 150 180 210 240 270 300 330 3600
10
20
30Gough annual ROTI binned in median of 5-minute intervals :
2003
RO
TI
0 30 60 90 120 150 180 210 240 270 300 330 360-400
-200
0
Dst: 2003
Dst
[nT]
Local time [day-of-year]
-
Hermanus Magnetic
Observatory
Page 45 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
0 1 2 3 40
2
4
6
8
10x 106 Gough Ne flux - ROTI correlation. 2003
median ROTI
med
ian
Ne
flux
y = 147411.6353x + 1593755.4189Corr. Coeff = 0.026011
0 1 2 3 40
5
10
15x 107
Gough Ne Energy - ROTI correlation. 2003
median ROTI
med
ian
Ne
Ene
rgy
y = 3479779.1814x + 10172061.302
Corr. Coeff = 0.049723
0 1 2 3 40
2
4
6
8
10
12x 106 Gough Ni flux - ROTI correlation. 2003
median ROTI
med
ian
Ni f
lux
y = 2967304.0588x + -55086.4871
Corr. Coeff = 0.21385
0 1 2 3 40
2
4
6
8
10x 107 Gough Ni Energy - ROTI correlation. 2003
median ROTI
med
ian
Ni E
nerg
y
y = 10213721.9427x + 2754569.6791
Corr. Coeff = 0.13463
0 20 40 60 80 100 120 140 160 180 2000
1
2
3
4
5
6x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ne
flux
Gough Daily integrated Ne flux - ROTI correlation. 2003
y = 3680.8355x + 17060364.9888
Corr. Coeff = 0.0087891
0 20 40 60 80 100 120 140 160 180 2000
2
4
6
8x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ni f
lux
Gough Daily integrated Ni flux - ROTI correlation. 2003
y = 65153.1734x + 3967880.0369
Corr. Coeff = 0.13119
-
Hermanus Magnetic
Observatory
Page 46 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
16.4 Gough Island 2004
0 30 60 90 120 150 180 210 240 270 300 330 3600
5
10x 106 Gough annual Ne flux: 2004
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
0 30 60 90 120 150 180 210 240 270 300 330 3600
5
10
15x 106 Gough annual Ni flux: 2004
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
30 60 90 120 150 180 210 240 270 300 330 3600
5
10Gough annual ROTI binned in median of 5-minute intervals :
2004
RO
TI
0 30 60 90 120 150 180 210 240 270 300 330 360-400
-200
0
Dst: 2004
Dst
[nT]
Local time [day-of-year]
-
Hermanus Magnetic
Observatory
Page 47 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
0 0.2 0.4 0.6 0.8 1 1.20
2
4
6
8x 106
Gough Ne flux - ROTI correlation. 2004
median ROTI
med
ian
Ne
flux
y = 399770.2873x + 638473.422Corr. Coeff = 0.042179
0 0.2 0.4 0.6 0.8 1 1.20
2
4
6
8
10x 107
Gough Ne Energy - ROTI correlation. 2004
median ROTI
med
ian
Ne
Ene
rgy
y = 644995.131x + 8295946.0217Corr. Coeff = 0.0048725
0 0.2 0.4 0.6 0.8 1 1.20
2
4
6
8x 106
Gough Ni flux - ROTI correlation. 2004
median ROTI
med
ian
Ni f
lux
y = 439088.1419x + 450877.7436Corr. Coeff = 0.047116
0 0.2 0.4 0.6 0.8 1 1.20
2
4
6
8x 107
Gough Ni Energy - ROTI correlation. 2004
median ROTI
med
ian
Ni E
nerg
y
y = 1943211.1991x + 4742072.0354Corr. Coeff = 0.022909
0 20 40 60 80 100 120 140 1600
2
4
6
8x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ne
flux
Gough Daily integrated Ne flux - ROTI correlation. 2004
y = 16065.9x + 6566501.6309
Corr. Coeff = 0.060845
0 20 40 60 80 100 120 140 1600
2
4
6
8x 107
Daily integrated median ROTI
Dai
ly in
tegr
ated
Ni f
lux
Gough Daily integrated Ni flux - ROTI correlation. 2004
y = 26731.0789x + 3395421.204
Corr. Coeff = 0.10386
-
Hermanus Magnetic
Observatory
Page 48 of 71
Classification: CONFIDENTIAL
Classification: CONFIDENTIAL DOC: 6021-0003-709-A1
16.5 Gough Island 2008
0 30 60 90 120 150 180 210 240 270 300 330 3600
1
2
3x 106 Gough annual Ne flux: 2008
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
0 30 60 90 120 150 180 210 240 270 300 330 3600
5
10x 106 Gough annual Ni flux: 2008
Nf [
cm-2
.s-1
.sr-1
.eV
-1]
30 60 90 120 150 180 210 240 270 300 330 3600
1
2Gough annual ROTI binned in median