Arctic Weather and Space Weather 22&23

Chapter 23

Space Weather

The Sun

The sun is the dominant source of the conditions commonly described as space weather.
The term space weather is used to designate processes occurring on the sun and in Earth’s magnetosphere, ionosphere, and thermosphere, which have the potential to affect the near-Earth environment.

The Sun

Emissions from the sun are:
continuous
Solar luminescence and
Solar wind
Eruptive
Coronal mass ejections (CME)
Flares
These solar eruptions may cause radio blackouts, magnetic storms, ionospheric storms, and radiation storms at Earth

Galactic Cosmic Rays

Galactic Cosmic Rays (GCR) are charged particles that originate in more distant supernovae and contribute to the space weather conditions near Earth.
Essentially, these charged particles comprise a steady drizzle of radiation at Earth.

Radiation

The sum of the solar and nonsolar components equal the full extent of the potential radiation dose received.
The size of the GCR flux varies inversely with the sunspot cycle;
During sunspot minimums when the interplanetary environment near Earth is laminar and steady, the GCR component is large due to its easier access to the near-Earth environment.
At sunspot maximum, the turbulence and energetics associated with solar eruptions reduce GCR access to the vicinity of the Earth.

Sunspots and the Solar Cycle

Because space weather activity varies with sunspot activity, they are often used as a proxy index for changing space weather conditions. This is because
Sunspots, by their very nature, exist due to strong local magnetic fields.
When these fields erupt, severe space weather can occur.
While sunspots are easily seen, other events such as GCR, CMEs, and increased solar wind are more difficult to observe

Solar Wind

The solar wind is the continuous flow away from the sun of charged particles and magnetic field, called plasma.
The solar wind carries the energy from most solar eruptions that affect the near-Earth environment.
The solar wind may be fast and energetic if an eruption occurs, or can gradually increase due to a coronal-hole structure which allows unimpeded high-speed solar wind to escape from the corona
As seen from the Earth, the sun rotates on approximately a 27-day period.

Solar Eruptive Activity

Most solar eruptions originate in areas that have strong magnetic fields.
Usually marked with sunspots, these areas are commonly called active regions.
Active regions are numerous and common during solar maximum and scarce during solar minimum.

Flares and CME’s

Flares are characterized by a very bright flash phase which may last for a few minutes to a few hours during the largest flares.
Flares can emit at all frequencies across the electromagnetic emission spectrum, from gamma rays to radio.

Flares and CME’s

CMEs, in contrast to solar flares, are difficult to detect, not particularly bright, and may take hours to fully erupt from the sun.
CMEs literally are an eruption of a large volume of the solar outer atmosphere, the corona.
Prior to the satellite era, they were very difficult to observe.
The energy released in a large solar flare is on par with that released in a CME, however CMEs are far more effective in perturbing Earth’s magnetic field and are known to cause the strongest magnetic storms.

Flares and CME’s

A typical travel time for a CME from the sun to Earth may range from less than 1 day to more than 4 days.
The travel time of the electromagnetic emission produced during flares, by comparison, is at the speed of light.
The frequency of solar flares and CMEs tracks with the solar cycle.
As many as 25 solar flares may occur per day during the maximum phase of the solar cycle.
At solar minimum, it may take 6 months or more for 25 flares to occur.
CME frequency varies from about 5 per day near solar maximum to one per week or longer at solar minimum

Geospace

Geospace is the volume of space that surrounds Earth, influenced by the Earth’s magnetic field in the solar wind.
If Earth did not have a magnetic field, the solar wind would blow past unimpeded, affected only by the mass of Earth and its atmosphere.
Earth’s magnetic field extends outward in all directions.
This forms a cocoon for the planet, protecting it from the flow of the solar wind. The cocoon is called the magnetosphere.

Magnetosphere

The magnetosphere typically extends towards the sun about 10 Earth radii on the dayside and stretches away from the sun many times more on the night side.
The shape is similar to a comet tail with it being extended during strong solar wind conditions and less so during more quiet times.
On its flanks, the magnetosphere extends outward roughly 20 Earth radii in the dawn and dusk sectors.

Magnetosphere

The magnetosphere deflects most of the energy carried by the solar wind, while making a fraction of it available to be absorbed by the near-Earth system.
When the sun is active and CMEs interact with Earth, the additional energy disrupts the magnetosphere, resulting in a magnetic storm.
Then, over time, the magnetosphere adjusts through various processes and once more returns to normal.

The Aurora

The most visible manifestation of the energy being absorbed from the solar wind into the magnetosphere is the aurora.
The aurora occurs when accelerated electrons from the sun follow the magnetic field of Earth down to the polar regions, where they collide with oxygen and nitrogen atoms and molecules in Earth’s upper atmosphere.

The Aurora

In these collisions, the electrons transfer their energy to the atmosphere, thus exciting the atoms and molecules to higher energy states.
When they relax to lower energy states, they release their energy in the form of light.

Ionosphere

The ionosphere is a shell of weak plasma, where electrons and ions exist embedded in the neutral atmosphere.
The ionosphere begins at roughly 80 kilometers in altitude and extends out many Earth radii, at the topside.
Extreme Ultraviolet (EUV) solar emissions create the ionosphere by ionizing the neutral atmosphere.
The electrons and ions created by this process then engage in chemical reactions that progress faster in the lower ionosphere.
The ionosphere changes significantly from day to night.
An important point is that the energy that comes from the sun in the solar wind makes its way to the ionosphere

Galactic Cosmic Radiation

Galactic Cosmic Radiation, more commonly known as Galactic Cosmic Rays (GCR), are a consequence of distant supernovae raining charged particles, heavy ions, protons, and electrons onto the inner heliosphere.
The abundance of GCR is inversely rated to the solar cycle.
At solar maximum, when the solar wind flow is turbulent and strong, the GCR flux is inhibited and therefore low.
At solar minimum, the GCR flux increases by about 30 percent in the near-Earth environment.

Geomagnetic Storms

Geomagnetic storms are strong disturbances to Earth’s magnetic field (Magnetosphere) interacting with the solar wind.
They are caused by:
Coronal Mass Ejections
Flares
Galactic Cosmic Rays
Geomagnetic storms tend to brighten auroras and allow them to move equatorward.
The duration of geomagnetic storms is usually on the order of days. The strongest storms may persist for almost 1 week.
Typically, the most intense storms occur near solar maximum, with weaker storms occurring during the declining phase.

Solar Radiation Storms

Solar radiation storms occur when large quantities of charged particles, primarily protons, are accelerated by processes at or near the sun, then bathe the near-Earth environment with these charged particles.
The polar regions on Earth are most open to these charged particles.
The magnetic field lines at the poles extend vertically downwards, intersecting Earth’s surface.
This allows the particles to spiral down the field lines and penetrate into the atmosphere and increase the ionization.

Solar Radiation Storms

A significant factor related to the criticality of the radiation increase at Earth is the energy distribution of the solar protons.
High-energy protons cause radiation dose increases that are of concern to human beings.
Lower energy protons have little effect on humans, but have a severe impact on the polar ionosphere.
For events that are of a large magnitude but low energy, the duration may last for 1 week.
Events that are of high energy may last for only a few hours.

Ionospheric Storms

Ionospheric storms arise from large influxes of solar particle and electromagnetic radiation.
There is a strong coupling between the ionosphere and the magnetosphere, which means both regimes can be disturbed concurrently.

Ionospheric Storms

The symptoms of an ionospheric storm include enhanced currents, turbulence and wave activity, and a nonhomogeneous distribution of free electrons.
This clustering of electrons, which leads to scintillation of signals passing through the cluster, is particularly problematic for the Global Navigation Satellite System (GNSS).

Ionospheric Storms

The frequency of occurrence of ionospheric storms is also similar to geomagnetic storms with one important caveat.
The near-equatorial ionosphere, a band extending approximately ± 10° in latitude on either side of the magnetic equator, can be very disturbed in the post-sunset to near-midnight hours, even in the absence of a geomagnetic storm.

Solar Flare Radio Blackouts

Radio blackouts primarily affect high frequency (HF) (3-30 megahertz (MHz))
Detrimental effects may spill over to very high frequency (VHF) (30-300 MHz) and beyond, resulting in fading and diminished ability for reception.
The blackouts are a consequence of enhanced electron densities caused by the emissions from solar flares that ionize the sunlit side of Earth.
The duration of dayside solar flare radio blackouts closely follows the duration of the solar flares that cause them beginning with the arrival of the x ray and EUV photons, and abate with their diminution.
Usually, the radio blackouts last for several minutes, but they can last for hours.

Communications

HF communications at low- to mid-latitudes are used by aircraft during transoceanic flights .
HF enables a skip mode to send a signal around the curvature of Earth.
HF communications on the dayside can be adversely affected when a solar flare occurs and its photons rapidly alter the electron density of the lower altitudes of the ionosphere, causing fading, noise, or a total blackout.
Usually these disruptions are short-lived (tens of minutes to a few hours), so the outage ends fairly quickly

Communication

Satellite communication signals pass through the bulk of the ionosphere and are a popular means of communicating over a wide area.
When the ionosphere is turbulent and nonhomogeneous, an effect called scintillation, a twinkling in both amplitude and phase, is imposed upon the transmitted signal.
Scintillations can result in loss-of-lock and inability for the receiver to track a Doppler-shifted radio wave.
Navigation and Global Positioning System (GPS/GNSS)
Space weather adversely affects GPS in three ways:
it increases the error of the computed position
it causes a loss-of-lock for receivers
it overwhelms the transmitted signal with solar radio noise.

Radiation Exposure to Flightcrews and Passengers

Solar radiation storms occurring under particular circumstances cause an increase in radiation dose to flightcrews and passengers.
As high polar latitudes and high altitudes have the least shielding from the particles, the threat is the greatest for higher altitude polar flights.
The increased dose is much less of an issue for low- and mid-latitude flights.

Radiation Effects on Avionics

The electronic components of aircraft avionic systems are susceptible to damage from the highly ionizing interactions of cosmic rays, solar particles, and the secondary particles generated in the atmosphere.
As these components become increasingly smaller, and therefore more susceptible, the risk of damage also increases.

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