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Journal Club Week 6 Answers

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D. J. Knipp et al., The May 1967 great storm and radio disruption event: Extreme space weather and extraordinary responses, Space Weather, 14, 614–633

Below are a selection of the best student answers that we received over the past couple of weeks. Well done to all those who sent things in! The rest of the answers can be downloaded as a PDF or can be seen below.


Describe how radio communication works.

Radio communication operates by creating an EM wave in a transmitter in the range from 3Hz to 3000GHz. This is done using an alternating current to create a changing magnetic and electric field, which can convey information by changing the frequency or amplitude of the wave. For example, speech would be converted to a radio wave by recording the frequency of the speech, copying it and inverting it to create a symmetrical sine wave which can be mapped onto a wave of one frequency by modulating the amplitude (in an AM source) When this is received by an antenna, the wave is converted back to its original form by converting the EM wave back into electrical signals using a coil, and using a diode to essential halve the signal to get back to the original wave. The quality of the wave received depends on the sensitivity of the antenna and the level of background signals, as well as the frequency of the wave and the distance to the transmitter.


In the case of space weather, why are science and politics often intertwined?

Radio communications are very important for communications in general, but they also play a critical role in the military for missile detection and other warning systems. Any interference with these systems is a major cause of concern for the government as issues with these military systems could be misinterpreted as foreign interference or even an act of war. As a result, space weather forecasting has become an important part of the military system, in order to identify the causes of different radio interference events. Outside of the military, our increasingly technologically reliant world would be severely impacted by a major solar storm so the prediction and responses to these storms are of political importance. When organising a response to such an event it is crucial that both the scientists and politicians work together so that it can be effective and attainable.


How might the modern world be affected by significant solar weather effects?

The modern world would certainly be affected by significant solar weather effects as we now rely on radio communication technologies more than ever. For example, the modern world boasts around 4987 satellites orbiting earth, so damage to a significant number of them would cause huge economic impact as the price of making and sending satellites to space is very large. However, the doctrine of mutually assured destruction is no longer as prominent in the modern world, the pointing of nuclear weapons at one another has died down since the downfall of the Soviet Union. Therefore, although the economic impact today would be greater than ever before, the diplomatic impact should not be as concerning. In addition, the forecasting of space weather has also significantly improved since its early days in the 60s. Scientists at the U.S. Geological survey have recently developed a 3D modelling system, a great leap from the 1D models of possible infrastructure damage from solar weather events. Although the economic impact from solar weather effects would be greater than ever, the facilities to forecast such an impact have never been better.


Why does the aurora borealis (northern lights) occur?

The northern lights (aurora borealis) are a result of matter and radiation from the sun interacting with the atoms and molecules that make up our atmosphere. Much like the Earth, the sun has a magnetic field of its own, which is continually twisting and warping, creating irregularities. These irregularities cause a build up of magnetic energy in the outermost layer of the sun (the corona) which leads to ejections of electromagnetic radiation called solar flares. Alongside theses solar flares, charged particles, like electrons and protons, can be released as a superheated gas (called a plasma) in an event known as a coronal mass ejection. When the plasma reaches the Earth, it penetrates its magnetic field at the poles and collides with matter in the air, creating the northern and southern (aurora australis) lights. Picture an atom in the atmosphere as a tiny ball (the nucleus) orbited by electrons in shell. If a particle or wave emitted from a solar event collides with this atom, it will transfer energy to the orbiting electrons, meaning they are able to move to a shell further away from the nucleus. However, these electrons will eventually return to their original shell, and will therefore release energy in the form of a photon (a packet of light). These photons are what creates the auroras. The different colours of light correspond to the amount of energy released by the electron. Oxygen will often produce green or red light, whereas nitrogen gives off pink and purple.



Coronal Mass Ejection

It is a phenomenon where a giant cloud of solar plasma erupts from the sun and the shock wave of travelling mass can cause geomagnetic storms and disrupts the Earth’s magnetosphere. These eruptions mainly consist of protons and electrons with high amounts of energy.


Geomagnetically induced currents

Currents that are a sign at ground level of space weather phenomena, which are induced by variations in electric currents in the ionosphere.


Geomagnetic storm

A temporary disturbance in the Earth’s magnetosphere caused by ‘solar wind’ or other clouds of magnetic field that interact with the earth’s magnetic field (e.g. coronal mass ejection). This can lead to GIC mentioned above, and the northern lights being seen at lower latitudes than usual.


Ionospheric storm

A storm caused by the distribution of the earth’s
ionosphere, which can disrupt radio communications
and GPS. The ionosphere is the part of the earth’s
atmosphere which is ionised by high energy electrons
from the sun.



It is a region of space surrounding an astronomical object by which charged particles are affected by that magnetic field. The earth’s magnetosphere stops most of the particles from the sun, carried in solar wind, from hitting the Earth.


Plasma eruptions

Plasma eruptions are strands of plasma that erupt and create prominences formed of cooler clouds of gases suspended by often unstable magnetic forces.


Solar cycle

The Sun’s magnetic field goes through a cycle - every 11 years, the north and south poles switch places. The solar cycle affects the number of sunspots there are: the beginning/end of the cycle is solar minimum (the fewest sunspots) and the middle of the cycle is solar maximum (the most sunspots).

Yen Li

Solar flare

This is a sudden burst of increased brightness in the sun, although they are mostly not visible due to the general intensity of light from the sun.


Solar radio burst

Intense solar radio emission related to a solar flare and one of the extreme space weather events.



This is a temporary point on the sun's surface that is dark in colour and cooler than the surrounding areas. They are caused by the concentration of magnetic flux which stops convection. They usually come in pairs with opposite magnetic polarity.



Below is an alphabetised list of the acronyms and initialisms in this paper to refer to if you forget what they mean (I used this all the time – I don’t expect you to remember these). NOTE ON PEDANTRY: an acronym is a series of initials from a phrase that can be pronounced as a word e.g. LASER and NASA, an initialism is a similar abbreviation, but isn’t pronounced as its own word e.g. FBI and DVD.


Fourth Weather Wing


Air Force


Air Force Base


Air Force Global Weather Central


Active Region


Air Weather Service


Ballistic Missile Early Warning System


Coronal Mass Ejection


Defense Meteorological Satellite Program


Department of Defense


Environmental Science Services Administration


Extreme Ultraviolet


Geomagnetically Induced Currents


Global Navigation Satellite Systems


Global Positioning System


High frequency


Intercontinental Ballistic Missiles


National Oceanic and Atmospheric Administration


North American Air Defense


Polar Cap Absorption


Radio Frequency Interference


Strategic Air Command


Space Disturbances Forecast Center


Space Disturbances Laboratory


Solar Electro-Optical Network


Space Environment Support System


Sudden Ionospheric Disturbance


Solar Observing and Forecasting Network


Solar Proton Event


Solar Radio Bursts


Sudden Storm Commencements


Space Weather Prediction Center


United States Air Force




Analyse the phrase “intense fluxes of ionizing solar X-rays” word-by-word to understand its meaning.

Intense: extreme strength

Flux: outward flow

Ionising: has the ability to ionise (in this case remove electrons) from an atom

Solar: pertaining to the sun

X-rays: a high energy part of the electromagnetic spectrum


In total: a significant amount of high energy electromagnetic radiation was emitted from the sun with the ability to ionise material that it interacted with.

What positive outcomes were there from the “Great Storm” of May 1967?

An increased focus on understanding and predicting space weather. The American Department of Defence began to support scientists in forecasting space weather.

Summarise the abstract in two sentences.



1.1 Intersection of Nature and Politics

What happens during a ‘rise’ in a solar cycle?

There is an increase in solar activity – an increased number of sunspots and an increased number of solar flares.

What is the hydrogen-alpha line?

A spectral line corresponding to one of the transitions for an electron within Hydrogen. Specifically it’s from the third lowest to the second lowest energy level.

Why is the hydrogen-alpha line important to astronomers?

Given that stars (including our sun) contain a significant amount of hydrogen (their fuel for nuclear fusion), the hydrogen-alpha line can be used to look at features in the sun’s atmosphere.

How do astronomers obtain an image of the sun in the hydrogen-alpha region of the spectrum?

Using a filter centred on the wavelength of light (656.28nm) that corresponds to the hydrogen-alpha transition.

What is the interplanetary medium? What does it contain?

The interplanetary medium is the material within the region in between planets. Whilst we tend to think of this region as a vacuum, it actually contains interplanetary dust, cosmic rays and hot plasma from the sun as well as electromagnetic radiation and magnetic fields.

Considering the quote at the bottom of page 1, why is it crucial for space weather information to be widely shared?

Because the impact of space weather has significant effects on communication. These communication channels





1.2 Cold War and Military Background

Describe how radio communication works. This will be one of our SUMMARY QUESTIONS but try to answer this now. You may find this video helpful


What is the doctrine of ‘mutually assured destruction’?

When two (or more) nations are armed with nuclear weapons, and the knowledge that they both have them, a state of equilibrium is reached. The strategy is a form of Nash equilibrium in which, once armed, neither side has any incentive to initiate a conflict or to disarm as their destruction is guaranteed either way.

Why would radio disruptions significantly affect Strategic Air Command (SAC) communications?

Because SAC communications were conducted extensively in the radio range

What does the frequency of a wave tell us?

How many cycles occur per second. A 1Hz wave has 1 complete cycle per second. A 1MHz wave has 1million cycles per second.

What frequency band do Strategic Air Command (SAC) communications use? What part of the electromagnetic spectrum is this in?

6-30MHz. The radiowave part of the EM spectrum

What frequency does the Ballistic Missile Early Warning System (BMEWS) use? What part of the electromagnetic spectrum is this in?

440MHz. This is at the top of the radio or bottom of the microwave part of the EM spectrum (microwaves start around 330MHz).

“NORAD and SAC operations were inextricably linked as they shared early warning data; however, decisions related to the data could result in independent actions” What does this tell you about how people handle data?

That the interpretation in your particular context may lead you to take very different actions.

What motivated the setup of space weather observations leading up to 1967?

The end of World War II and the need to ensure strong radio communication channels.

Why did NORAD, and specifically its radars, need the support of solar weather understanding?

Because the radars would experience solar and auroral interference.


1.3 A Brief Guide to Solar and Geomagnetic Disturbances With Emphasis on Radio Effects

Look carefully at figure 2, what are the two events that occur within the sun that cause this ‘myriad of space weather radio effects’?

Solar flares and coronal mass ejection

In figure 2, which space weather disturbance takes the longest to affect earth?

Magneto/Ionospheric storms

In figure 2, which space weather disturbance lasts for the shortest amount of time (be careful and remember it’s a log scale).

X-ray emission

In the figure caption there is an example description of one of the events – it begins ‘as an example, energetic protons…’ Read this and understand how they’ve written this from the information in the figure. Write one of your own for a different solar weather disturbance in the figure.


What are Active Regions (ARs)?

Regions with multiple solar emissions in or above sunspots. Here the magnetic field is very strong and has a twisted shape.

“ When energy density in AR magnetic fields reaches a tipping point, the fields reconfigure, producing bursts of electromagnetic energy (flares) across a broad spectrum of wavelengths: X-ray, extreme ultraviolet (EUV), UV, visible, and radio emissions. Some very strong flares produce gamma ray and intense white-light emissions”. Using the video at this link, explain briefly the process of magnetic reconnection that is being discussed here.


At what speed do the electromagnetic waves emitted by the sun travel?


What are the two ways that radio communications can be affected by the influx of electromagnetic radiation? (HINT: These come under the category of sudden ionospheric disturbances).

They can be directly affected by interference from the radio emissions of the sun.

They can be indirectly affected as the x-ray and extreme ultraviolet emissions change the ionisation energies of elements in the earth’s upper atmosphere, limiting the propagation of radio waves and actually causing absorption of the higher frequencies.

What is plasma?

Ionised gas – it contains the ions that have had some of their electrons removed and the free electrons.

What are supersonic speeds?

Speeds higher than the speed of sound in air.

Why can’t the coronal mass ejection (CME) travel at the speed of light?

Because the CME contains particles with mass and these cannot reach the speed of light.

How do coronal mass ejections (CMEs) lead to an increased amount of radio transmission?

As they travel through the outer atmosphere of the sun, the CME interacts with the plasma it encounters, causing the emission of further radio waves. Imagine this from the perspective of the particles within the plasma: the ion cores can still be excited (given energy) so that electrons move up energy levels and then drop down, emitting photons.

If a CME takes 2-4days to reach earth, on average, then lets assume it takes 3days. At what speed has the CME travelled?

Distance from sun to earth is ~150million km (1.5×1011m). 3days=259200s.

This is a speed of ~5.8×105ms-1

What are solar energetic particle events?

Highly energetic protons and electrons ejected from the sun at the site of a flare or at the front of a coronal mass ejection.

Why are solar energetic particle events normally called solar proton events?

Since protons have a much larger mass than electrons, they carry more momentum?

Why can solar energetic particle events travel faster than a CME?

Since, on average, the particles (protons and electrons) in solar energetic particle events are lighter than the particles (ion cores and electrons) in CMEs, they can travel faster.

How can radio communication be affected by solar energetic particle (or solar proton) events?

Long lasting solar energetic particle events are called radiation storms. In the polar regions of the earth, these radiation storms can lead to changes in the gasses in the atmosphere that give rise to the absorption of high frequency radio signals (Polar Cap Absorption events).

Why do the equatorial latitudes experience these radio interferences “primarily from dusk to dawn”.

Because this is when those regions are facing the sun and are the target for the radiation that is travelling towards the earth.


Now, section 2 (May 1967 Solar-Geophysical Background and Details— What We Know Now) is a bit on the heavy side. I’d encourage you to read it to see if what you’ve researched so far makes this section more understandable, but we’re not going to have questions on this section as it’s quite dense. The section gives all of the detail about the storm of May 1967 – the timings of events and the types of solar events that happened and whereabouts on the sun. We’re going to dip back into questions at the end, section 2.4

2.4 How Severe Were the May 1967 Storms?

What is a solar flux unit?

A unit of power per metre squared to quantify the average flux per frequency of radiation from the sun received on earth.

1solar flux unit = 1 Wm-2Hz-1

Why is it difficult to list which solar storms are ‘worst’?

Because each different event is measured differently, and different parts of the earth experience it differently. Quantifying the disruption to radio signals is essentially impossible

If this storm is not top of all of the quantifiable lists, and would actually seem to be a not uncommonly large storm by many metrics, what made it so bad?

The timing of the storm on earth in relation to the political tensions that were occurring meant it could have been catastrophic for humans.




  1. Discussion: Storm Impacts and Legacies

3.1. May 1967 Storm Impacts: Radio Frequency Interference and Space Weather Support

What is military jamming?

Intentionally sending out radio signals to interfere with RADAR and other communication devices by overwhelming them with false signals.

Why would a solar radio burst be misinterpreted as jamming?

Because the measured signals would look very similar – intense bursts of radio. And if you were in a political situation where you might expect ‘the enemy’ to be using such measures, then that’s what you’d immediately conclude.

What role did NORAD play in calming the tensions?

Through their analysis and the communication of it, they concluded that the BMEWS (Ballistic Missile Early Warning System) and similar technologies should expect to see large radio bursts, and that they shouldn’t necessarily be interpreted as military jamming.

If military bombers has been launched, why might it have been difficult to recall them had the NORAD message come through later?

Due to the radio interference effects of the solar radio bursts, the communication channels between the command station and the bombers would be expected to be disrupted. The bombers are trained to carry out their orders unless they hear otherwise, so everything hinged on the radio communication.


3.2. Legacy: U.S. Air Force Space Environment Support System

What data can optical instruments give us about solar weather?

Sunspots, flares, filaments, and magnetic field configuration.

What data can radio instruments give us about solar weather?

Radio sites monitor the radio interference and emissions at discrete frequencies. Additionally, radio spectrographs sweep their observations to search for signals of moving transients in the solar atmosphere.

Why is it valuable to have staff trained across several areas e.g. Air Weather Service staff being trained in space weather.

To allow people to understand all possibly causes of signals in their data/observations. To give additional/different perspectives on topics.



One consequence of space weather on earth that is less catastrophic is the aurora borealis or northern lights. One of our summary questions this week will be to explain this phenomenon in relation to space weather. Here are a few links to get you started:


NASA have a lot of pages dedicated to space weather:

This WIRED article looks at some of the extreme effects of space weather

This BBC World Service piece discusses space weather and its effects


Remember, reading a paper isn't like reading a piece of fiction or a newspaper article. Don't get frustrated if it doesn't immediately make sense - you might need to do a little research of your own to understand some of the ideas. This article gives you an idea of how scientists read differently.

Each question refers to a specific part of the paper e.g. Page 2, Column 3 is written as (P2, C3).

Next week, we'll publish solutions to the questions and the best submitted summaries from students across the country.


As it's (a very unusual) half term for a lot of you, we won't be running Journal Club in the usual way. We're keen to ensure you all take a well-earned break so there'll be no official Journal Club. However, if you are looking for something to do, why not use the skills you've developed so far by helping us out with a future Young Person's Journal Club. We'd like you to find some more popular science writing, aimed at a more general audience, and have a go at writing the sorts of questions for it that we've been providing for you each week. More details can be found here.