AST 301 Living with the Sun - F. Walter April 2021
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AST 301
Living with the Sun
F. Walter
April 2021
210606 HMI
Sunspot #: 11
210406
SDO
For current conditions: https://spaceweather.com https://umbra.nascom.nasa.gov/index.html/ https://solarmonitor.org/ http://www.lmsal.com/solarsoft/last_events/
Maunder Minimum
The Solar Magnetic Field
The Solar Magnetic Field
Magnetic Reconnection
https://www.youtube.com/watch?v=MNsSQjSzLv0
The Magnetic Cycle Spot cycle ~11 years Magnetic cycle ~22 yrs
Coronal Cycle
The Magnetic Cycle The Butterfly Diagram
Magnetic Butterfly Diagram
What’s Expected?
Source: NOAASolar Irradiance
Solar Irradiance?
So much for the spectacle… • Are solar flares dangerous? • Are CMEs dangerous? • Life has survived until now The terrestrial atmosphere protects us
Aside: Types of Radiation Particulate •Alpha particles •Beta particles •Neutrons •Fission Fragments Electromagnetic •Ionizing •Non-ionizing
Particulate Radiation Alpha particles •Helium nuclei •penetrate < 10 cm in air, 60 µm in tissue •stopped by paper Beta particles •Electrons •Penetrate a few mm into tissue Neutrons Fission Fragments
Electro-Magnetic Radiation
Penetrating
radiation:
•X-rays
•g raysParticulate Radiation Sources
• Radioactive decay
• High energy collisions
• Particle acceleration
• Astrophysical processes
Cosmic Rays
• Particles originating in space
• Accelerated by astrophysical processes
• Generally charged; deflected by magnetic fields
• Energies to 300 EeV (= KE of 100 mph baseball)Definitions
1 Becquerel (Bq) = 1 disintegration/second (dps)
1 Curie = 3.7 x 1010 dps
1 Röntgen = amount of ionizing radiation that
produces 1 esu/cm3 in dry air
1 rad (Röntgen absorbed dose) = 100 erg/gm
1 Gray (Gy) = 100 rads = 1 Joule/kg
Dose = 0.869 f R
f = mass absorption coefficient/air
Rem (biological equivalent dose) = rads x QF
QF (quality factor) » # ion pairs / cm
1 Sievert (Sv) = 100 rem = 1 J/kg in tissue
1 Banana Equivalent Dose (BED) = 0.1 µSvHalf Life
Time for half the original sample to decay
N = N0 e-0.693 T1/2 t
After 1 half life: ½ parent; ½ daughter
After 2 half lives: ¼ parent, ¾ daughter
After 3 half lives: 1/8 parent, 7/8 daughterHow Radiation Kills Ionizing/penetrating radiation breaks chemical bonds Particles/ionizing radiation deposits energy Lethal dose: 500 rad kills half a human population
Can You Avoid Radiation?
No!
- http://www.nsc.org/learn/safety-
knowledge/Pages/injury-facts-chart.aspx,
-
http://www.riskcomm.com/visualaids/riskscale/
datasources.php
- http://www.flmnh.ufl.edu/fish/isaf/what-are-
odds/risks-comparison/risk-deathMedical Radiation Risks • Earliest Onset of Radiation Sickness:75,000 mrad 75 rad • Onset of hematopoietic syndrome: 300,000 mrad • Onset of gastrointestinal syndrome: 1,000,000 mrad • Onset of cerebro-vacular syndrome: 10,000,000 mrad • Threshold for cataracts (dose to the eye): 200,000 mrad • Expected 50% death without medical attention: 3 – 5 x105 mrem ~ 500 rad • Doubling dose for genetic effects: 100,000 mrad • Doubling dose for cancer: 500,000 mrad • Dose for increase cancer risk of 1 in 1,000: 1,250 mrem (0.08 Sv) • Consideration of therapeutic abortion threshold: 10,000 mrem (in utero) • SL1 Reactor Accident (1961) highest dose to survivor: 27,000 mrem • Chernobyl within 30 km evacuation zone: 20-1000 mSv (
Solar Flares • No significant consequence on Earth – g-rays, X-rays absorbed in atmosphere – UV absorbed by ozone • Important for unshielded astronauts
Solar Flares come with • Solar Proton Events (SPE) • Coronal Mass Ejections (CME)
When Solar Energetic Particles Reach Earth • .
Coronal Mass Ejections • Contain high energy protons and electrons, which can be dangerous • Drag magnetic fields, which can deflect cosmic rays (Forbush Decrease) • Deflected by terrestrial magnetic field
Terrestrial Complicity
• The terrestrial magnetic field is weakening
• The field reverses on average every 3x105 years
• Last reversal:
780,000 BCE
Source: http://news.spaceweather.com/earths-magnetic-field-is-changing/How Solar Storms Affect Earth • Geomagnetically Induced Currents (GIC) • Charged particles in upper atmosphere cause varying magnetic fields • Ampere’s law: changing B -> induces electric fields. • Electric potentials (20V/km) drive currents in ground • Current strength depends on conductivity • Current flow in power lines can overload the grid.
31 Aug 2012
The 1 Sept 1859 Event
• 9/1: Carrington observed white-light flare
• 9/2: Brilliant auroras seen
(as far south as the Caribbean)
• Telegraphs functioned w/o batteries
• Telegraph operators shocked
• First solar flare recorded
• Strongest in ~500 years
• Today it would
– Bring down the electrical grid
– Fry satellitesThe 23 July 2012 Flare • At least as energetic as the 1859 Carrington event • 2 CMEs recorded • Missed Earth by about 1 week
The 23 July 2012 Flare • At least as energetic as the 1859 Carrington event • Missed by about 1 week
And if it had hit? Charged particles generate electric and magnetic fields
And if it had hit?
And if it had hit? Geomagnetically-induced currents (GIC): • Drive DC currents in power lines – Potentials up to 20V/km; Currents >106 amperes
Geomagnetically Induced Currents
• .
Source: WikipediaGeomagnetically Induced Currents
(GIC)
• Charged particles in upper atmosphere cause varying
magnetic fields (Faraday’s Law)
• Ampere’s law: changing B -> induces electric fields
• Electric potentials drive currents in ground
• DC current flow in power lines can overload the grid
(DC currents saturate AC systems)•
Aside: CME vs EMP
Estimated Economic Impact
of a 23 July 2012 Strength Flare
• Over 130 million in North America lose power
• Over 350 million heavy-duty transformers threatened
• $2 trillion – 20 x greater than hurricane Katrina
• Full recovery: 4-10 years
See:
http://science.nasa.gov/
science-news/science-
at-
nasa/2014/23jul_supers
torm/
Transformer damage
13 March 1989 storm
Salem NJ nuclear plantTransformer Damage From 2013 Lloyds report “Solar Storm Risk to the North American Electric Grid”
The 13 March 1989 Hydro Quebec
Collapse
See http://www.spaceweather.gc.ca/tech/se-pow-en.phpThe 13 March 1989 Hydro Quebec
Collapse
Strongest geo-magnetic storm since 1932
(~-500 nT/min; DST =-589 nT)
• Hydro-Quebec grid down for 9 hours
• Affected 6 million people
• Three transformers damaged (1 in NJ)
• Cost: CDN $ 13.2 million
• Strongest 7 hours later, over northern Europe
Nearly brought down North American grid
(~200 “anomalies”)
See http://www.spaceweather.gc.ca/tech/se-pow-en.phpKnown Solar Super Storms
• 660 BC: large proton event
• 774/5 AD: 14C, 10Be enhancements
• 993/994 AD: 14C, 10Be enhancements
• 1770 AD: strong equatorial aurorae
• Sept 1859: Carrington event. Dst estimated to be -1700 nT
• May 1921: New York Railroad Superstorm
– Maximum Dst -901 ± 132 nT, comparable to Carrington event
• August 1972: Geomagnetic storm sets off mines in Haiphong
harbor
– Fast CME: 14.6 hours to Earth
• March 1989: strongest storm since IGY
– Maximum Dst -589 nT
• October 2003: Halloween storm
– 2000 km/s CME
– 4th largest known proton storm
Dst: Disturbance storm time = intensity of the globally symmetrical equatorial
electrojetWho is vulnerable? • .
Geological Considerations
High tension power lines
High impedance -> high voltages and GICs
Source: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019SW0023295.4 Line Length and Rating Even a transformer whose winding hot spot
remained below the critical temperature threshold
will sustain insulation damage, and this reduces
The total resistance along each transmission lineofisthemade
the lifetime up ofThis
transformer. three comp
additional
This is a New York Issue
loss-of-life in years is incorporated
resistance, transformer internal resistance and transformer grounding resist into the model.
while the former increases with distance. The current carried by the line also
therefore the total risk increases with the total path length.
• Close to north Transformer
geomagnetic pole
core type is also significant for risk. Certain types are more vul
others. There are broad relationships of core type with kV and MVA rating; i
500 kV are single phase, while below this they are predominately three-pha
• Granite is conductive
single-phase transformers are more vulnerable to internal heating than thre
same level of geomagnetically induced current. The higher voltage lines als
therefore larger currents flow relative to lower voltage lines when exposed t
• High population density
Solar storm risk to the north American electric grid
6.6 Outage Scenarios
5.2 Ground Conductivity 5.5 Relative Risk by Coun
These risk factors can be com
The same magnetic field time-series does not result in the
same surface electric field in all regions of the globe. It
and then summarised to estim
depends on the profile of local ground conductivity. Figure The scale of relative risk rang
3 shows the relative risk due to ground conductivity model 4). This means that for some
29
variations in continental US and Canada. The risk is average transformer experien
determined from an average of surface electric field induced current is more than 1
strengths derived from many different historical magnetic
30
field time series . risk county. The regions with t
corridor between Washington
high-risk regions are the Midw
Coast.
Figures: Lloyds “Solar storm
10 risk to the north American electric grid”
5.3 Coast EffectThe Odds 12% per decade (Carrington-level) Riley, P. 2012, Space Weather, 10, s0212 Carrington event: 0.7%/yr (DST~-850) Extreme storm: 4% /yr (DST>-500) Severe storm: 28% /yr (DST>-250) Chapman, S.C. et al. 2020, GRL, accepted doi: 10.1029GRL086524
Estimated Recurrence times
Carrington-level event: 100-200 years
Quebec 1989 event: 35-70 years
Methodology: historical auroral records
Lloyd’s/AER report, 2013Current Economic Impact Insurance claims, 2000-2010 • Claims increase with geomagnetic activity • ~4% of US power grid disturbances due to geomagnetic storms and GICs – 59% caused by “electrical surges” – Implies about 500 disturbances/year • Estimated losses $118-188 Billion/year Reference: Schrijver, C.J. et al., Space Weather, 12, 487 (2014)
Insurers are Concerned • From Lloyds “Solar storm risk to the north American electric grid” (2013) • The total U.S. population at risk of extended power outage from a Carrington-level storm is between 20-40 million, with durations of 16 days to 1-2 years. The duration of outages will depend largely on the availability of spare replacement transformers. If new transformers need to be ordered, the lead- time is likely to be a minimum of five months. The total economic cost for such a scenario is estimated at $0.6-2.6 trillion USD. • Storms weaker than Carrington-level could result in a small number of damaged transformers (around 10-20), but the potential damage to densely populated regions along the Atlantic coast is significant. The total number of damaged transformers is less relevant for prolonged power outage than their concentration. The failure of a small number of transformers serving a highly populated area is enough to create a situation of prolonged outage.
Revisited Economic Impact Costs of a full blackout: • Economic cost in North America $20B- $40B/day • Cost to New York economy >$3B/day • Time to recover >6 months Reference: Oughton, E.J. et al., 2017, Space Weather, 15, 65
• Objectives:
• I. Enhance the Protection of
National Security, Homeland
Security, and Commercial Assets
and Operations against the
Effects of Space Weather
• II. Develop and Disseminate
Accurate and Timely Space
Weather Characterization and
Forecasts
NATIONAL SPACE WEATHER • III. Establish Plans and
Procedures for Responding to
STRATEGY AND ACTION PLAN and Recovering from Space
Weather Events
• Conclusion: Space weather
Product of the poses a constant threat to
SPACE WEATHER OPERATIONS, RESEARCH, and MITIGATION the Nation’s critical
WORKING GROUP
SPACE WEATHER, SECURITY, and HAZARDS SUBCOMMITTEE
infrastructure, our satellites
in orbit, and our crewed and
COMMITTEE ON HOMELAND and NATIONAL SECURITY
uncrewed space activities.
of the
NATIONAL SCIENCE & TECHNOLOGY COUNCIL
Extreme space weather
events can cause substantial
harm to our Nation’s security
March 2019 and economic vitality.Space Weather • Geomagnetic Storms: G (1-5) • Solar Radiation Storms: S (1-5) • Radio Blackouts: R (1-5) • http://spaceweather.com/ • https://www.swpc.noaa.gov/
NOAA Space Weather Scales
Category Effect Physical Average Frequency
measure (1 cycle = 11 years)
Scale Descriptor Duration of event will influence severity of effects
Kp values* Number of storm events
Geomagnetic Storms determined
every 3 hours
when Kp level was met;
(number of storm days)
Power systems: widespread voltage control problems and protective system problems can occur, some grid Kp=9 4 per cycle
systems may experience complete collapse or blackouts. Transformers may experience damage. (4 days per cycle)
Spacecraft operations: may experience extensive surface charging, problems with orientation, uplink/downlink
and tracking satellites.
G5 Extreme
Other systems: pipeline currents can reach hundreds of amps, HF (high frequency) radio propagation may be
impossible in many areas for one to two days, satellite navigation may be degraded for days, low-frequency radio
navigation can be out for hours, and aurora has been seen as low as Florida and southern Texas (typically 40°
geomagnetic lat.).**
Power systems: possible widespread voltage control problems and some protective systems will mistakenly trip Kp=8 100 per cycle
out key assets from the grid. (60 days per cycle)
Spacecraft operations: may experience surface charging and tracking problems, corrections may be needed for
G4 Severe orientation problems.
Other systems: induced pipeline currents affect preventive measures, HF radio propagation sporadic, satellite
navigation degraded for hours, low-frequency radio navigation disrupted, and aurora has been seen as low as
Alabama and northern California (typically 45° geomagnetic lat.).**
Power systems: voltage corrections may be required, false alarms triggered on some protection devices. Kp=7 200 per cycle
Spacecraft operations: surface charging may occur on satellite components, drag may increase on low-Earth-orbit (130 days per cycle)
satellites, and corrections may be needed for orientation problems.
G3 Strong
Other systems: intermittent satellite navigation and low-frequency radio navigation problems may occur, HF
radio may be intermittent, and aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic
lat.).**
Power systems: high-latitude power systems may experience voltage alarms, long-duration storms may cause Kp=6 600 per cycle
transformer damage. (360 days per cycle)
Spacecraft operations: corrective actions to orientation may be required by ground control; possible changes in
G2 Moderate
drag affect orbit predictions.
Other systems: HF radio propagation can fade at higher latitudes, and aurora has been seen as low as New York
and Idaho (typically 55° geomagnetic lat.).**
Power systems: weak power grid fluctuations can occur. Kp=5 1700 per cycle
Spacecraft operations: minor impact on satellite operations possible. (900 days per cycle)
G1 Minor
Other systems: migratory animals are affected at this and higher levels; aurora is commonly visible at high
latitudes (northern Michigan and Maine).**
* Based on this measure, but other physical measures are also considered.
** For specific locations around the globe, use geomagnetic latitude to determine likely sightings (see www.swpc.noaa.gov/Aurora)
Flux level of > Number of events when
Solar Radiation Storms 10 MeV
particles (ions)*
flux level was met**
5Spacecraft operations: corrective actions to orientation may be required by ground control; possible changes in
G2 Moderate
drag affect orbit predictions.
Other systems: HF radio propagation can fade at higher latitudes, and aurora has been seen as low as New York
and Idaho (typically 55° geomagnetic lat.).**
Power systems: weak power grid fluctuations can occur. Kp=5 1700 per cycle
Spacecraft operations: minor impact on satellite operations possible. (900 days per cycle)
G1 Minor
Other systems: migratory animals are affected at this and higher levels; aurora is commonly visible at high
latitudes (northern Michigan and Maine).**
* Based on this measure, but other physical measures are also considered.
** For specific locations around the globe, use geomagnetic latitude to determine likely sightings (see www.swpc.noaa.gov/Aurora)
Flux level of > Number of events when
Solar Radiation Storms 10 MeV
particles (ions)*
flux level was met**
Biological: unavoidable high radiation hazard to astronauts on EVA (extra-vehicular activity); passengers and 105 Fewer than 1 per cycle
crew in high-flying aircraft at high latitudes may be exposed to radiation risk. ***
Satellite operations: satellites may be rendered useless, memory impacts can cause loss of control, may cause
S5 Extreme serious noise in image data, star-trackers may be unable to locate sources; permanent damage to solar panels
possible.
Other systems: complete blackout of HF (high frequency) communications possible through the polar regions,
and position errors make navigation operations extremely difficult.
Biological: unavoidable radiation hazard to astronauts on EVA; passengers and crew in high-flying aircraft at 104 3 per cycle
high latitudes may be exposed to radiation risk.***
Satellite operations: may experience memory device problems and noise on imaging systems; star-tracker
S4 Severe
problems may cause orientation problems, and solar panel efficiency can be degraded.
Other systems: blackout of HF radio communications through the polar regions and increased navigation errors
over several days are likely.
Biological: radiation hazard avoidance recommended for astronauts on EVA; passengers and crew in high-flying 103 10 per cycle
aircraft at high latitudes may be exposed to radiation risk.***
S3 Strong Satellite operations: single-event upsets, noise in imaging systems, and slight reduction of efficiency in solar
panel are likely.
Other systems: degraded HF radio propagation through the polar regions and navigation position errors likely.
Biological: passengers and crew in high-flying aircraft at high latitudes may be exposed to elevated radiation 102 25 per cycle
risk.***
S2 Moderate Satellite operations: infrequent single-event upsets possible.
Other systems: effects on HF propagation through the polar regions, and navigation at polar cap locations
possibly affected.
Biological: none. 10 50 per cycle
S1 Minor Satellite operations: none.
Other systems: minor impacts on HF radio in the polar regions.
* Flux levels are 5 minute averages. Flux in particles·s-1·ster-1·cm-2 Based on this measure, but other physical measures are also considered.
** These events can last more than one day.
*** High energy particle (>100 MeV) are a better indicator of radiation risk to passenger and crews. Pregnant women are particularly susceptible.
GOES X-ray Number of events when
Radio Blackouts peak brightness
by class and by
flux level was met;
(number of storm days)
flux*
HF Radio: Complete HF (high frequency**) radio blackout on the entire sunlit side of the Earth lasting for a X20 Fewer than 1 per cycle
number of hours. This results in no HF radio contact with mariners and en route aviators in this sector. (2x10-3)
R5 Extreme 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. Increased satellite navigation errors in
positioning for several hours on the sunlit side of Earth, which may spread into the night side.
HF Radio: HF radio communication blackout on most of the sunlit side of Earth for one to two hours. HF radio X10 8 per cycle
-3panel are likely.
Other systems: degraded HF radio propagation through the polar regions and navigation position errors likely.
Biological: passengers and crew in high-flying aircraft at high latitudes may be exposed to elevated radiation 102 25 per cycle
risk.***
S2 Moderate Satellite operations: infrequent single-event upsets possible.
Other systems: effects on HF propagation through the polar regions, and navigation at polar cap locations
possibly affected.
Biological: none. 10 50 per cycle
S1 Minor Satellite operations: none.
Other systems: minor impacts on HF radio in the polar regions.
* Flux levels are 5 minute averages. Flux in particles·s-1·ster-1·cm-2 Based on this measure, but other physical measures are also considered.
** These events can last more than one day.
*** High energy particle (>100 MeV) are a better indicator of radiation risk to passenger and crews. Pregnant women are particularly susceptible.
GOES X-ray Number of events when
Radio Blackouts peak brightness
by class and by
flux level was met;
(number of storm days)
flux*
HF Radio: Complete HF (high frequency**) radio blackout on the entire sunlit side of the Earth lasting for a X20 Fewer than 1 per cycle
number of hours. This results in no HF radio contact with mariners and en route aviators in this sector. (2x10-3)
R5 Extreme 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. Increased satellite navigation errors in
positioning for several hours on the sunlit side of Earth, which may spread into the night side.
HF Radio: HF radio communication blackout on most of the sunlit side of Earth for one to two hours. HF radio X10 8 per cycle
contact lost during this time. (10-3) (8 days per cycle)
R4 Severe
Navigation: Outages of low-frequency navigation signals cause increased error in positioning 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, loss of radio contact for about an hour on sunlit side X1 175 per cycle
R3 Strong of Earth. (10-4) (140 days per cycle)
Navigation: Low-frequency navigation signals degraded for about an hour.
HF Radio: Limited blackout of HF radio communication on sunlit side of the Earth, loss of radio contact for tens M5 350 per cycle
R2 Moderate of minutes. (5x10-5) (300 days per cycle)
Navigation: Degradation of low-frequency navigation signals for tens of minutes.
HF Radio: Weak or minor degradation of HF radio communication on sunlit side of the Earth, occasional loss of M1 2000 per cycle
R1 Minor radio contact. (10-5) (950 days per cycle)
Navigation: Low-frequency navigation signals degraded for brief intervals.
* Flux, measured in the 0.1-0.8 nm range, in W·m-2. Based on this measure, but other physical measures are also considered.
** Other frequencies may also be affected by these conditions.
URL: www.swpc.noaa.gov/NOAAscales April 7, 2011Mitigation Strategies • Education – Raise awareness of vulnerability to solar events • Science – Develop better predictive ability – Better understanding of large event rates • Engineering – Better grounding/isolation from possible GICs – Locating transformers in areas less prone to GICs – Rapid sensing of saturated transformers
Cost of Protecting Against EMP & CME
Events
l EMP Commission estimated cost to harden 2000 critical
nodes (large and medium sized transformers) against EMP
and CME: ~ $2 BillionCost of Not Protecting Against EMP &
CME Events
l EMP Commission estimated loss of life from EMP event that
would drop electrical grid for 1 year:
60 to 90% of US population
Note: CMEs can have a similar effectEarly Warning ? Spacecraft at L1 provide: • Up to 4 days warning for CMEs • ~30 min warning for fast flare protons • No warning for photons L1 = the inner Lagrangian point • where terrestrial and solar gravities balance • about 1 million miles towards the Sun
All Copacetic?
All Copacetic? Not so fast.
The Relation Between Flares and CMEs • Not 1:1 • Not all flares produce CMEs • Most strong flares produce a CME
Superflares • Solar flares: – dN/dE ~ E-1.7+/- 0.2 – Brightest observed ~ 1032 erg • Schaefer et al. (2000) reported 9 larger flares on solar-like stars • Maehara et al. (2012) analyzed Kepler database for superflares (E>1033 erg)
Superflares
• Brightest ¤ flare observed ~ 1032 erg
• Maehara et al. (2012) found:
– dN/dE = E-2.3+/- 0.3
– 365 superflares on 148 solar-like stars
– 14 superflares on 10
old or inactive stars
• Conclusion:
– A 1035 erg solar flare
can be expected
every 5000 yearsSuperflares Okamoto et al. 2021 ApJ 906, 72 • Analysis of full Kepler primary mission data • 265 Solar-like stars: 2341 superflares – 5600-6000K; 5d
Okamoto et al Figure 10b
Superflares Okamoto et al. predictions: • Sun can produce – X700 (7 x 1033 ergs) flare every 3000 years – X1000 (1034 ergs) flare every 6000 years • Empirical predictions are consistent with solar flare power law distribution
Be Afraid. Be Very Afraid.
More Pictures and References
Solar Data Analysis Center (SDAC): http://umbra.nascom.nasa.gov/
includes links to SOHO, SDO, HINODE, and YOHKOH
Other Solar Missions:
– STEREO: http://www.nasa.gov/mission_pages/stereo/main/index.html
– TRACE: http://trace.lmsal.com/
Solar Storms
– https://medium.com/starts-with-a-bang/the-truth-about-solar-storms-
1ab160203da4
A future Space Weather catastrophe : a disturbing possibility
https://www.wunderground.com/blog/JeffMasters/a-future-space-weather-
catastrophe--a-disturbing-possibility.htmlOther References • “The 23rd Cycle”, Odenwald, S.F. 2001, Columbia University Press • “Solar Storm Risk to the North American Electrical Grid” https://www.lloyds.com/Solar Storm Risk to the North American Electric Grid.pdf • “Geomagnetic Storms and their Impacts on the U.S. Power Grid” https://fas.org/irp/eprint/geomag.pdf • “Solar Storm Threat Analysis” http://www.breadandbutterscience.com/Solar_Storm_Threat_Analysis.pd f
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