D53-3 Propagation project 53 Report
SPACE WEATHER IMPACT ON COMMUNICATIONS AT SOLAR MAXIMUM
Lj.R. Cander
1. Introduction
This report deals with the impact of the space weather effects on radio communication, systems supporting
space-based navigation, and surveillance. It will examine space weather events in the current solar cycle 23
(Fig. 1) which are significant for continuing improvement of ionosphere/plasmasphere real-time
specification, short-term and long-term forecasting relevant for all aspects of radio-wave propagation in and
through the Earth’s ionosphere. In general the propagation prediction methods, usually expressed in terms of
more or less complex numerical procedures, are required for ionospheric propagation in bands from ELF to
VHF. Those for predicting sky-wave propagation at LF, MF and HF play an important role in frequency
planning while currently MF and HF ionospheric propagation prediction methods focus on the effects on
digitally modulated transmissions. Propagation through the ionosphere/plasmasphere at VHF and UHF
frequencies is of serious concern for navigation satellite systems as well as the increasing use of low-Earth
orbits satellite systems. For Earth-space paths, ionosphere/plasmasphere specification and short-term
forecasting are essential. As any kind of prediction relies on adequate data sets, ionosphere/plasmasphere
measurements, particularly those in real-time and near real-time, during the space weather events are
important part of the whole issue.
Space weather refers to conditions in Sun-solar wind-magnetosphere-ionosphere-termosphere system that can
influence the environment where space-vulnerable systems operate (Fig. 2) [1]. Accordingly space weather is
Fig. 1. Solar cycle 23 sunspot number.
Fig. 2. Space environment.
often being viewed as applied science. During the past decade, numerous international, US national and
European Space Agency investigations of space weather impact on environmental have concentrated on
particular aspects such as those seen in Fig. 3. As space environment observational and modelling tools
become more sophisticated and numerous, the prospect for significant improvement of space weather
understanding is better. However, the ability to measure, model and forecast the global space weather events
lags significantly behind current capabilities to model and forecast global tropospheric weather. Therefore,
NASA has initiated in 2001 a new program “Living with a STAR” (LWS) with emphasis on system-wide
data gathering and modelling. Just recently a new four years EU COST724 Action on “Developing the
scientific basis for monitoring, modelling and predicting space weather” has been approved and it is expected
to start by the end of 2002. The impact of LWS and COST724 Action on space weather research and
application could be enormous. Current COST271 Action on “Effects of the Upper Atmosphere on Terrestrial
and Earth Space Communications” is a program that stresses a number of space weather issues [2].
Fig. 3. The most common space weather effects on technical systems that are deployed on the Earth’s surface
and in space with their signals propagating through the space environment [1].
2. Space weather effects on radio communications
Main space weather phenomenon are: (i) Geomagnetic storms - disturbances in the geomagnetic field caused
by gusts in the solar wind that blows by Earth; (b) Solar radiation storms - elevated levels of radiation that
occur when the numbers of energetic particles increase; and (c) Radio blackouts - disturbances of the
ionosphere caused by X-ray emissions from the Sun [3]. Table 1 schematically illustrates these effects.
Table 1. Space weather (geomagnetic, solar radiation and radio blackouts) effects [3].
Descriptor
Effect
Average
Frequency (1
cycle=11 years)
Number of
GEOMAGNETIC STORMS
events; (number
of storm days)
HF radio propagation impossible in many areas for one 4 per cycle (4
Extreme
to two days, satellite navigation for days, lowdays per cycle)
frequency radio navigation out for hours, and the
aurora seen as low as equator.
HF radio propagation sporadic, satellite navigation
100 per cycle
Severe
degraded for hours, low-frequency radio navigation
(60 days per
disrupted, and the aurora seen as low as the tropics.
cycle)
Intermittent satellite navigation and low-frequency
200 per cycle
Strong
radio navigation problems, HF radio propagation
(130 days per
intermittent, and the aurora seen as low as midcycle)
latitudes.
HF radio propagation fades at higher latitudes, and the 600 per cycle
Moderate
aurora seen as low as 50 degrees.
(360 days per
2
Minor
The aurora seen as high latitudes (60 degrees);
migratory animals begin to be affected.
SOLAR RADIATION STORMS
Extreme
Severe
Strong
Moderate
Minor
Extreme
Severe
Strong
Moderate
HF communications impossible in polar regions, and
position errors make navigation operations extremely
difficult.
Blackout of HF radio communications through the
polar cap and increased navigation errors over several
days.
Blackout of HF radio propagation through the polar
cap and navigation position errors.
Small effects on HF radio propagation through the
polar cap and navigation at the polar cap impacted.
Minor impact on HF radio in the polar regions.
RADIO BLACKOUTS
HF Radio: Complete high frequency radio blackout on
the entire sunlit side of the Earth lasting for a number
of hours. No HF radio contact with mariners or en
route aviators.
Navigation: Low-frequency navigation signals used by
maritime and general aviation systems experience
outages on the sunlit side of the Earth for many hours,
causing loss in positioning. Increases satellite
navigation errors in positioning for several hours on
the sunlit side of the Earth, which may spread into the
night side.
HF Radio: HF radio communication blackout for one
to two hours on most of the sunlit side of the Earth, HF
radio contact lost during this time for mariners and en
route aviators.
Navigation: Outages of low-frequency navigation
signals cause increased error in positioning for
mariners and general aviators for one to two hours.
Minor disruptions of satellite navigation possible on
the sunlit side of Earth.
HF Radio: Wide area blackout of HF radio
communication signals, loss of radio contact for
mariners and en route aviators for about an hour on
sunlit side of Earth.
Navigation: Low-frequency navigation signals
degraded for about an hour, affecting maritime and
general aviation positioning.
HF Radio: Limited blackout of HF radio
communication signals, loss of radio contact for tens
of minutes for mariners and en route aviators.
Navigation: Degradation of low-frequency navigation
3
cycle)
1700 per cycle
(900 days per
cycle)
Number of
events; (number
of storm days**)
Fewer than 1 per
cycle
3 per cycle
10 per cycle
25 per cycle
50 per cycle
Number of
events; (number
of storm days)
Fewer than 1 per
cycle
(1 cycle=11
years)
8 per cycle (8
days per cycle)
175 per cycle
(140 days per
cycle)
350 per cycle
(300 days per
cycle)
Minor
signals for tens of minutes affecting maritime and
general aviation positioning.
HF Radio: Weak or minor degradation of HF radio
communication signals, on sunlit side, occasional loss
of radio contact for mariners and en route aviators.
Navigation: Low-frequency navigation signals
degraded for brief intervals affecting maritime and
general aviation positioning.
2000 per cycle
(950 days per
cycle)
As it is clear from Table 1 that storms (left panel in Fig. 4) represent an extreme form of space weather with
important effects on increasingly sophisticated ground-and space-based technological systems.
Fig. 4. Daily variations of the geomagnetic Dst index and corresponding foF2 variations during the space
weather event in the solar maximum of the 22 cycle.
Fig. 5. Daily MUF and LUF variations during the November 1989 space weather event
These phenomena are driven by highly variable solar and magnetospheric energy inputs to the Earth’s upper
atmosphere. Consequently the ionospheric characteristic as the critical frequency of the F region (right panel
in Fig. 4) and propagation parameters LOF and FMOF (Fig. 5) at a given altitude and location are subject to
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sudden and profound changes lasting from a few hours to several days. These changes can be both positive
and negative deviations from the norm following a storm commencement. Realistic simulations of these
features, particularly through periods of intense space weather activity, require continue monitoring and
modelling [4].
Figure 6 gives another example of ionospheric storm’s highly disruptive effect on propagation below 30
MHz. The storm results in a total blackout of HF communications between the UK and Norway by the 4th day
[5].
Fig. 6. Ionospheric storm effect as seen from oblique ionospheric sounding measurements.
An example of the range error as the first order vertical ionospheric plasma influence on the main GPS signal
(f=1575.42 MHz) is given in Fig. 7. It is the error "seen" by a single frequency user for overhead GPS
satellites. Slant range error can be higher by a factor of up to 5, depending on zenith angle and on TEC
gradients while without gradients the factor is up to 3.
Fig. 7. The range errors over European area on storm day of 12 March (left) and quiet day of 14 March (right)
1989 at 1200UT.
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The range errors within the marked rectangle are the errors calculated with the RAL short-term ionospheric
forecasting maps of foF2 and M(3000)F2. The rectangle is surrounded by a buffer zone. Outside the buffer
zone the data have been calculated from the ITU-R maps for foF2 and M(3000)F2 and therefore there is no
difference between the two days. At 2000 UT the artificial positive storm effect over the US East Coast sector
was present. The differential range errors calculated between 2 days, one storm day on 12 March and one
quiet day on 14 March 1989 is shown in Fig. 8. These significant differences are of major concern for
navigation satellite systems [6].
Fig. 8. The differential range errors over European area on storm day of 12 March (left) and quiet day of 14
March (right) 1989 at 1200UT and 2000 UT.
3. Space weather storms in 23 solar cycle maximum
The geomagnetic storm, as a main source of the ionospheric/plasmaspheric disturbances, is a world-wide
disturbance of the Earth's magnetic field, distinct from regular diurnal variations. The Dst index is an index of
geomagnetic activity derived from a network of near-equatorial Observatories that measures the intensity of
the globally symmetrical equatorial electrojet (the "ring current"). Peaks Dst values are between –20 and 20
nT during quiet geomagnetic condition and decrease to below –100 nT during highly disturbed periods. In the
case of severe storms, Dst values are below –250 nT while Dst values below –300 are observed in extreme
cases. The selection of all the significant geomagnetic storms in Table 2 is based on the Solar-Terrestrial data
published by NOAA, Boulder, USA.
Table 2. List of storms in the period September 1999 –November 2001.
Ri
Dst (nT)
START DAY
MAIN DAY
64
-149
22 September 1999
23 September 1999
87
-231
21 October 1999
22 October 1999
114
-169
11 February 2000
12 February 2000
108
-321
06 April 2000
07 April 2000
148
-317
15 July 2000
16 July 2000
170
-235
12 August 2000
13 August 2000
124
-201
17 September 2000
18 September 2000
150
-182
4 October 2000
5 October 2000
205
-358
31 March-3 April 2001
1, 2 and 3 April 2000
115
-256
11 April 2001
12 April 2001
140
-275
6 November 2001
6 and 7 November 2001
73
-213
25 November 2001
26 November 2001
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Table 3. Daily geomagnetic A and K indices at different latitudes for 31 March 2001 event.
160
16
March 2001 Chilton
15
31 March 2001
median values
140
14
130
13
120
12
110
11
100
10
foF2 (MHz)
foF2 (0.1 MHz)
150
90
80
70
29 - 31 March 2001 Chilton
9
8
7
6
60
5
50
4
40
3
30
2
measured values
1
median values
20
10
0
0
0:00
0
2
4
6
8
10
12
14
16
18
20
0:00
0:00
22
time (hours UT)
time (hours in UT)
Fig. 9. Time variations of foF2 at Chilton ionosonde station for each day in March 2001 (left panel) and foF2
measured between 29 and 31 March 2001.
Changes in the daily hourly foF2 values for all the March 2001 data are shown in Fig. 9 (left panel).
Evidently there is a part of scatter in this figure that can be only attributed to very high level of space weather
activity (see Tables 2 and 3). Fig. 9 (right panel) shows that the last day of March 2001 was a severe
geomagnetically active period with very strong negative phase in foF2 (more than –150%). These ionosonde
measurements are then compared to GPS data obtained from the nearby GPS receiver’s site at Hailsham (0.3
E, 50.9 N).
100.0
March 2001 Hailsham
90.0
80.0
TEC (TECU)
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
00:05 02:05 04:05 06:05 08:05 10:05 12:05 14:05 16:05 18:05 20:05 22:05
time (minutes UT)
Fig. 10. Time variations of TEC at Hailsham for each day in March 2001.
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Results of 31 days of TEC measurements at Hailsham taken during March 2001are shown grouped together
in Fig. 10. Again black and red solid lines represent median and storm day TEC variations. The negative
phase of TEC is detected in early morning hours after 05 UT of 31 March. The severe depletions of about –
80% relative to the median TEC values are observed. However, some of the TEC enhancements in the
nighttime, not seen in foF2 data, persist into the evening sector. The daily variations of TEC in March 2001
monitored by the GPS receivers at addition three sites are shown in Figure 11, demonstrating clearly extreme
storm effects.
90.0
Graz - March 2001
80.0
70.0
TEC (TECU)
60.0
50.0
40.0
30.0
20.0
10.0
00
:0
5
00
:5
5
01
:4
5
02
:3
5
03
:2
5
04
:1
5
05
:0
5
05
:5
5
06
:4
5
07
:3
5
08
:2
5
09
:1
5
10
:0
5
10
:5
5
11
:4
5
12
:3
5
13
:2
5
14
:1
5
15
:0
5
15
:5
5
16
:4
5
17
:3
5
18
:2
5
19
:1
5
20
:0
5
20
:5
5
21
:4
5
22
:3
5
23
:2
5
0.0
Minutes (UT)
March 1st
March 2nd
March 3rd
March 4th
March 5th
March 6th
March 7th
March 8th
March 9th
March 10th
March 11th
March 12th
March 13th
March 14th
March 15th
March 16th
March 17th
March 18th
March 19th
March 20th
March 21st
March 22nd
March 23rd
March 24th
March 25th
March 26tb
March 27th
March 28th
March 29th
March 30th
March 31st
Median
Fig. 11. Time variations of TEC at Tromsoe, Graz and Ankara for each day in March 2001.
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As expected 31 March storm at Tromsoe shows a large negative phase during daytime and the enhancement
as the first indication of the storm onset. The storm at Graz consists of both initial positive (TEC increases >
+40%) and negative (TEC decreases <-50%) phases. A relatively short positive phase (about 3 hours) is
follow by the negative daytime phase and then again positive phase in the evening and night-time sectors.
The 31 March storm does not have an obvious negative phase in TEC variations at Ankara. In fact, the whole
behaviour is the final signature of positive storm. All in all it can easily be seen that the total ionospheric
content was highly disturbed both in time and space over European area during the extreme space weather
event of 31 March 2001. More importantly the common storm pattern is far from obvious.
Indeed, there is considerable spatial/temporal structure to be seen at the archive maps generated as a part of
24-hour forecasting service at Rutherford Appleton Laboratory (http://ionosphere.rcru.rl.ac.uk/). Thus, it is
obvious that such a structure in the ionospheric/plasmaspheric ionisation during space weather storms at solar
maximum creates the great difficulty in matching the rapid foF2 and TEC variations in propagation
forecasting models and data as storms develop. The factors that lead to such a complex behaviour even at
such a limited area as Europe are beyond the scope of this report.
4. Conclusions
The literature on space weather storms and their impact on communication are now so extensive that a
comprehensive review is practically impossible. Instead only few special examples closely related to the their
prediction and forecasting have been selected for discussion. As studies continue to search for the actual
physical mechanisms that explain the spatial and temporal morphologies over various space weather events
and to test forecasting algorithms for practical applications, it would be useful to have well defined pattern of
mid-latitude ionosphere/plasmasphere storm and a technique to forecast it. Significant contribution in that
direction is given by updating climatological model predictions of ionospheric/plasmasphere and propagation
parameters. However, for quite some time, the ionospheric community has been aware of the fact that the
International Global Positioning System (GPS) Service for Geodynamics (IGS) with a global ground station
network offers a new multi-point opportunity to observe directly the terrestrial ionosphere/plasmasphere
system and use that information in prediction purposes. The development of a GPS short-term forecasting
ionospheric/plasmaspheric model may be seen as a long-term goal. In order to accomplish this goal, a
procedure of the ionospheric TEC specification over Europe has been developed [7]. The combination of
ionosonde and ground GPS monitoring, e.g. Chilton ionosonde and Hailsham GPS site, allows the near-real
time data evaluation and application of appropriate forecasting technique for a few hours ahead.
With (1) the service for solar monitoring (http://sidc.oma.be) already available; (2) multi-point observing
capabilities of GNSS ionosphere; and (3) shared international real-time ionospheric/plasmaspheric data
resources as those in COST271 Action, an operational short-term ionospheric storm forecasting (STISF) tool
for the European region available on the World Wide Web for interactive use is only a matter of time. This
facility could provide a useful tool to radio system’s users who need up-to-date information on
ionospheric/plasmaspheric conditions over Europe to meet their operational requirements. Its applications
will include frequency management, retrospective space weather event studies and input to OHD sensors.
References
[1] Song, P., H.J. Singer and G.L. Siscoe (Editors), Space Weather, Geophysical Monograph 125, American
Geophysical Union, Washington, DC, 2001.
[2] Zolesi, B. and Lj.R. Cander, Effects of the Upper Atmosphere on Terrestrial and Earth Space
Communications: The new COST271 action of the European scientific community, Advance in Space
Research, Vol. 29(6), pp. 1017-1020, 2002.
[3] Poppe, B., New scales help public, technicians understand space weather, EOS Transactions, Vol. 81, No.
29, July 18, 2000.
[4] Cander, Lj. R., Toward forecasting and mapping ionospheric space weather under the COST actions”,
Advance in Space Research, in press, 2002.
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[5] Bamford, R., Oblique ionospheric sounding, RA Project Report No. D-42, October 2000.
[6] Leitinger, R., Private communications, 2002.
[7] Cander, Lj.R. and L. Ciraolo, First step towards specification of plasmaspheric-ionospheric conditions
over Europe on-line, Acta Geod. Geoph. Hung., Vol. 37(2-3), pp. 153-161, 2002.
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