Space Weather & Space Operations

Space Weather Effects – Image Credit: European Space Agency

Space Weather is one half of the major concerns for space operators, Space Debris being the other, and both have the ability to cause catastrophic failure & orbital destabilization with our space infrastructure.

Space Weather describes the variations in the space environment between the sun and Earth. In particular Space Weather describes the phenomena that impact systems and technologies in orbit and on Earth. Space weather can occur anywhere from the surface of the sun to the surface of Earth. As a space weather storm leaves the sun, it passes through the corona and into the solar wind. When it reaches Earth, it energizes Earth’s magnetosphere and accelerates electrons and protons down to Earth’s magnetic field lines where they collide with the atmosphere and ionosphere, particularly at high latitudes. Each component of space weather impacts a different technology.

In addition, increased radiation due to space weather may lead to increased health risks for astronauts, both today on board the International Space Station in low orbit and in the future on voyages to the Moon or Mars.

Most spacecraft in Earth orbit operate partly or entirely within the radiation belts. During periods of intense space weather, the density of particles within the belts increases, making it more likely that sensitive electronics will be hit by a charged particle.

For satellites in orbit, the effects of space weather can be seen in the degradation of communications, performance, reliability and overall lifetime. For example, the solar panels that convert sunlight to electrical power on most spacecraft will steadily generate less power over the course of a mission, and this degradation must be taken into account in designing the satellite.

Another significant influence of solar activity is seen with disturbances in satellite navigation services, like GPS & Galileo, due to space weather effects on the upper atmosphere. Ions striking satellites can overwhelm sensors, damage solar cells, and degrade wiring and other equipment. When conditions get especially rough in the radiation belts, satellites often switch to a safe mode to protect their systems. This in turn can affect aviation, road transport, shipping and any other activities that depend on precise positioning.

Communication from the ground to satellites is affected by space weather as a result of perturbations of the ionosphere, which can reflect, refract, or absorb radio waves. This includes radio signals from satellites. Space weather can change the density structure of the ionosphere by creating areas of enhanced density. This modification of the ionosphere makes Navigation Sats less accurate and can even lead to a complete loss of the signal because the ionosphere can act as a lens or a mirror to radio waves traveling through it. Because the ionosphere has a different refractive index from the layers above and below it, radio waves are “bent” (refracted) as they pass from one layer to another. Under certain conditions and broadcast frequencies, the radio waves can be absorbed or even completely reflected. Sharp and localized differences (or gradients) in the density of the ionosphere also contribute significantly to the effects of space weather on satellite communication and navigation. These gradients become most pronounced during geomagnetic storms.

Different types of space weather can affect different technologies on Earth. Solar flares can produce strong x-rays that degrade or block high-frequency radio waves used for radio communication during events known as Radio Blackout Storms. Solar Energetic Particles (energetic protons) can penetrate satellite electronics and cause electrical failure. These energetic particles also block radio communications at high latitudes during Solar Radiation Storms.

Coronal Mass Ejections (CMEs) can cause Geomagnetic Storms on Earth and induce extra currents in the ground that can degrade power grid operations.

Geomagnetic storms can modify radio signals, and disrupt frequency signals as they travel between satellites and ground stations, from radio navigation systems (GPS and GNSS) causing degraded accuracy. Those disrupted signals can also affect your satellite televisions and car radios. Space weather will impact people who depend on these technologies. Geomagnetic storms can also produce aurora, and can cause plasma bubbles (regions of dense ionized gas) to form in the atmosphere, which disrupt signals passing through them.

It can change the shape of the Earth’s atmosphere so that it moves into the path of satellites that normally fly above it. The increased drag on the satellite slows the spacecraft and changes its orbit, which will need to be corrected for or it could lead to a collision with another satellite.

Space Weather Phenomena – Image Credit: NASA

Space Weather Events

Aurora

The Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights) are the result of electrons colliding with the upper reaches of Earth’s atmosphere. (Protons cause faint and diffuse aurora, usually not easily visible to the human eye.) The electrons are energized through acceleration processes in the downwind tail (night side) of the magnetosphere and at lower altitudes along auroral field lines. The accelerated electrons 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. In these collisions, the electrons transfer their energy to the atmosphere thus exciting the atoms and molecules to higher energy states. When they relax back down to lower energy states, they release their energy in the form of light. This is similar to how a neon light works. The aurora typically forms 80 to 500 km above Earth’s surface.

Earth’s magnetic field guides the electrons such that the aurora forms two ovals approximately centered at the magnetic poles. During major geomagnetic storms these ovals expand away from the poles such that aurora can be seen over most of the United States. Aurora comes in several different shapes. Often the auroral forms are made of many tall rays that look much like a curtain made of folds of cloth. During the evening, these rays can form arcs that stretch from horizon to horizon. Late in the evening, near midnight, the arcs often begin to twist and sway, just as if a wind were blowing on the curtains of light. At some point, the arcs may expand to fill the whole sky, moving rapidly and becoming very bright. This is the peak of what is called an auroral substorm.

Then in the early morning the auroral forms can take on a more cloud-like appearance. These diffuse patches often blink on and off repeatedly for hours, then they disappear as the sun rises in the east. The best place to observe the aurora is under an oval shaped region between the north and south latitudes of about 60 and 75 degrees. At these polar latitudes, the aurora can be observed more than half of the nights of a given year.

When space weather activity increases and more frequent and larger storms and substorms occur, the aurora extends equatorward. During large events, the aurora can be observed as far south as the US, Europe, and Asia. During very large events, the aurora can be observed even farther from the poles. (Tips on viewing the aurora and maps of the typical extent of the aurora). Of course, to observe the aurora, the skies must be clear and free of clouds. It must also be dark so during the summer months at auroral latitudes, the midnight sun prevents auroral observations.

Coronal Holes – Image Credit: NASA SDO

Coronal holes appear as dark areas in the solar corona in extreme ultraviolet (EUV) and soft x-ray solar images. They appear dark because they are cooler, less dense regions than the surrounding plasma and are regions of open, unipolar magnetic fields. This open, magnetic field line structure allows the solar wind to escape more readily into space, resulting in streams of relatively fast solar wind and is often referred to as a high speed stream in the context of analysis of structures in interplanetary space.

Coronal holes can develop at any time and location on the Sun, but are more common and persistent during the years around solar minimum. The more persistent coronal holes can sometimes last through several solar rotations (27-day periods). Coronal holes are most prevalent and stable at the solar north and south poles; but these polar holes can grow and expand to lower solar latitudes. It is also possible for coronal holes to develop in isolation from the polar holes; or for an extension of a polar hole to split off and become an isolated structure. Persistent coronal holes are long-lasting sources for high speed solar wind streams. As the high speed stream interacts with the relatively slower ambient solar wind, a compression region forms, known as a co-rotating interaction region (CIR). From the perspective of a fixed observer in interplanetary space, the CIR will be seen to lead the coronal hole high speed stream (CH HSS).

The CIR can result in particle density enhancement and interplanetary magnetic field (IMF) strength increases preceding onset of the CH HSS. As the CH HSS begins to arrive at Earth, solar wind speed and temperature increase, while particle density begins to decrease. After passage of the CIR and upon transition into the CH HSS flow, the overall IMF strength will normally begin to slowly weaken.

Generally, coronal holes located at or near the solar equator are most likely to result in any CIR passage and/or higher solar wind speeds at Earth. Strong CIRs and the faster CH HSS can impact Earth’s magnetosphere enough to cause periods of geomagnetic storming to the G1-G2 (Minor to Moderate) levels; although rarer cases of stronger storming may also occur. Geomagnetic storms are classified using a five-level NOAA Space Weather Scale. The larger and more expansive coronal holes can often be a source for high solar wind speeds that buffet Earth for many days.

Because of their potential for escalated geomagnetic activity and possible storming (G1 or higher), forecasters analyze coronal holes closely and also note them on the daily synoptic drawing. SWPC forecasters take into account any possible effects of CIR and CH HSS activity when forecasting the anticipated levels of overall planetary geomagnetic response for each 3-hour synoptic period over the next three days; as detailed in the 3-day forecast. Additionally, any predicted CIR or CH HSS influences are explained in more detail in the forecast discussion.

Coronal Mass Ejections (CME) – Image Credit: NASA SOHO & STEREO

Coronal Mass Ejections (CMEs) are large expulsions of plasma and magnetic field from the Sun’s corona. They can eject billions of tons of coronal material and carry an embedded magnetic field (frozen in flux) that is stronger than the background solar wind interplanetary magnetic field (IMF) strength. CMEs travel outward from the Sun at speeds ranging from slower than 250 kilometers per second (km/s) to as fast as near 3000 km/s. The fastest Earth-directed CMEs can reach our planet in as little as 15-18 hours. Slower CMEs can take several days to arrive. They expand in size as they propagate away from the Sun and larger CMEs can reach a size comprising nearly a quarter of the space between Earth and the Sun by the time it reaches our planet.

The more explosive CMEs generally begin when highly twisted magnetic field structures (flux ropes) contained in the Sun’s lower corona become too stressed and realign into a less tense configuration – a process called magnetic reconnection. This can result in the sudden release of electromagnetic energy in the form of a solar flare; which typically accompanies the explosive acceleration of plasma away from the Sun – the CME. These types of CMEs usually take place from areas of the Sun with localized fields of strong and stressed magnetic flux; such as active regions associated with sunspot groups. CMEs can also occur from locations where relatively cool and denser plasma is trapped and suspended by magnetic flux extending up to the inner corona – filaments and prominences. When these flux ropes reconfigure, the denser filament or prominence can collapse back to the solar surface and be quietly reabsorbed, or a CME may result. CMEs travelling faster than the background solar wind speed can generate a shock wave. These shock waves can accelerate charged particles ahead of them – causing increased radiation storm potential or intensity.

Important CME parameters used in analysis are size, speed, and direction. These properties are inferred from orbital satellites’ coronagraph imagery by SWPC forecasters to determine any Earth-impact likelihood. The NASA Solar and Heliospheric Observatory (SOHO) carries a coronagraph – known as the Large Angle and Spectrometric Coronagraph (LASCO). This instrument has two ranges for optical imaging of the Sun’s corona: C2 (covers distance range of 1.5 to 6 solar radii) and C3 (range of 3 to 32 solar radii). The LASCO instrument is currently the primary means used by forecasters to analyze and categorize CMEs; however another coronagraph is on the NASA STEREO-A spacecraft as an additional source.

Imminent CME arrival is first observed by the Deep Space Climate Observatory (DSCOVR) satellite, located at the L1 orbital area. Sudden increases in density, total interplanetary magnetic field (IMF) strength, and solar wind speed at the DSCOVR spacecraft indicate arrival of the CME-associated interplanetary shock ahead of the magnetic cloud. This can often provide 15 to 60 minutes advanced warning of shock arrival at Earth – and any possible sudden impulse or sudden storm commencement; as registered by Earth-based magnetometers.

Important aspects of an arriving CME and its likelihood for causing more intense geomagnetic storming include the strength and direction of the IMF beginning with shock arrival, followed by arrival and passage of the plasma cloud and frozen-in-flux magnetic field. More intense levels of geomagnetic storming are favored when the CME enhanced IMF becomes more pronounced and prolonged in a south-directed orientation. Some CMEs show predominantly one direction of the magnetic field during its passage, while most exhibit changing field directions as the CME passes over Earth. Generally, CMEs that impact Earth’s magnetosphere will at some point have an IMF orientation that favors generation of geomagnetic storming. Geomagnetic storms are classified using a five-level NOAA Space Weather Scale. SWPC forecasters discuss analysis and geomagnetic storm potential of CMEs in the forecast discussion and predict levels of geomagnetic storming in the 3-day forecast.

Earth’s Magnetosphere

The magnetosphere is the region of space surrounding Earth where the dominant magnetic field is the magnetic field of Earth, rather than the magnetic field of interplanetary space. The magnetosphere is formed by the interaction of the solar wind with Earth’s magnetic field. This figure illustrates the shape and size of Earth’s magnetic field that is continually changing as it is buffeted by the solar wind.

It has been several thousand years since the Chinese discovered that certain magnetic minerals, called lodestones, would align in roughly the north-south direction. The reason for this effect wasn’t understood, though, until 1600, when William Gilbert published De Magnete and demonstrated that our Earth behaved like a giant magnet and loadstones were aligning with Earth’s magnetic field.

After several more centuries of investigation, it is now known that Earth’s magnetic field is quite complex, but still, to a great extent, can be viewed as a dipole, with north and south poles like a simple bar magnet. Earth’s magnetic axis, the dipole, is inclined at about 11 degrees to Earth’s spin axis. If space were a vacuum, Earth’s magnetic field would extend to infinity, getting weaker with distance, but in 1951, while studying why comet tails always point away from the sun, Ludwig Biermann discovered that the sun emits what we now call the solar wind. This continuous flow of plasma, comprised of mostly electrons and protons, with an embedded magnetic field, interacts with Earth and other objects in the solar system.

The pressure of the solar wind on Earth’s magnetic field compresses the field on the dayside of Earth and stretches the field into a long tail on the nightside. The shape of the resulting distorted field has been compared to the appearance of water flowing around a rock in a stream. On the dayside of Earth, rather than extending to infinity, the magnetic field is confined to within about 10 Earth radii from the center of Earth and on the nightside, the field is stretched out to hundreds of Earth radii, well beyond the orbit of the moon at 60 Earth radii.

The boundary between the solar wind and Earth’s magnetic field is called the magnetopause. The boundary is constantly in motion as Earth is buffeted by the ever-changing solar wind. While the magnetopause shields us to some extent from the solar wind, it is far from impenetrable, and energy, mass, and momentum are transferred from the solar wind to regions inside Earth’s magnetosphere. The interaction between the solar wind and Earth’s magnetic field, and the influence of the underlying atmosphere and ionosphere, creates various regions of fields, plasmas, and currents inside the magnetosphere such as the plasmasphere, the ring current, and radiation belts. The consequence is that conditions inside the magnetosphere are highly dynamic and create what we call “space weather” that can affect technological systems and human activities. For example, the radiation belts can have impacts on the operations of satellites, and particles and currents from the magnetosphere can heat the upper atmosphere and result in satellite drag that can affect the orbits of low-altitude Earth orbiting satellites. Influences from the magnetosphere on the ionosphere can also affect communication and navigations systems. All of these effects are discussed elsewhere in more detail.

F10.7 cm Radio Emissions

The solar radio flux at 10.7 cm (2800 MHz) is an excellent indicator of solar activity. Often called the F10.7 index, it is one of the longest running records of solar activity. The F10.7 radio emissions originates high in the chromosphere and low in the corona of the solar atmosphere. The F10.7 correlates well with the sunspot number, as well as a number of UltraViolet (UV) and visible solar irradiance records. The F10.7 has been measured consistently in Canada since 1947, first at Ottawa, Ontario; and then at the Penticton Radio Observatory in British Columbia, Canada. Unlike many solar indices, the F10.7 radio flux can easily be measured reliably on a day-to-day basis from the Earth’s surface, in all types of weather. Reported in “solar flux units”, (s.f.u.), the F10.7 can vary from below 50 s.f.u., to above 300 s.f.u., over the course of a solar cycle. These F10.7 measurements are provided courtesy of the National Research Council Canada in partnership with the Natural Resources Canada.

The F10.7 Index has proven very valuable in specifying and forecasting space weather. Because it is a long record, it provides climatology of solar activity over six solar cycles. Because it comes from the chromosphere and corona of the sun, it tracks other important emissions that form in the same regions of the solar atmosphere. The Extreme UltraViolet (EUV) emissions that impact the ionosphere and modify the upper atmosphere track well with the F10.7 index. Many Ultra-Violet emissions that affect the stratosphere and ozone also correlate with the F10.7 index. And because this measurement can be made reliably and accurately from the ground in all weather conditions, it is a very robust data set with few gaps or calibration issues.

Galactic Cosmic Rays

Galactic Cosmic Rays (GCR) are the slowly varying, highly energetic background source of energetic particles that constantly bombard Earth. GCR originate outside the solar system and are likely formed by explosive events such as supernova. These highly energetic particles consist of essentially every element ranging from hydrogen, accounting for approximately 89% of the GCR spectrum, to uranium, which is found in trace amounts only. These nuclei are fully ionized, meaning all electrons have been stripped from these atoms. Because of this, these particles interact with and are influenced by magnetic fields. The strong magnetic fields of the Sun modulate the GCR flux and spectrum at Earth.

Over the course of a solar cycle the solar wind modulates the fraction of the lower-energy GCR particles such that a majority cannot penetrate to Earth near solar maximum. Near solar minimum, in the absence of many coronal mass ejections and their corresponding magnetic fields, GCR particles have easier access to Earth. Just as the solar cycle follows a roughly 11-year cycle, so does the GCR, with its maximum, however, coming near solar minimum. But unlike the solar cycle, where bursts of activity can change the environment quickly, the GCR spectrum remains relatively constant in energy and composition, varying only slowly with time.

These charged particles are traveling at large fractions of the speed of light and have tremendous energy. When these particles hit the atmosphere, large showers of secondary particles are created with some even reaching the ground. These particles pose little threat to humans and systems on the ground, but they can be measured with sensitive instruments. The Earth’s own magnetic field also works to protect Earth from these particles largely deflecting them away from the equatorial regions but providing little-to-no protection near the polar regions or above roughly 55 degrees magnetic latitude (magnetic latitude and geographic latitude differ due to the tilt and offset of the Earth’s magnetic field from its geographic center). This constant shower of GCR particles at high latitudes can result in increased radiation exposures for aircrew and passengers at high latitudes and altitudes. Additionally, these particles can easily pass through or stop in satellite systems, sometimes depositing enough energy to result in errors or damage in spacecraft electronics and systems.

Geomagnetic Storms

A geomagnetic storm is a major disturbance of Earth’s magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind into the space environment surrounding Earth. These storms result from variations in the solar wind that produces major changes in the currents, plasmas, and fields in Earth’s magnetosphere. The solar wind conditions that are effective for creating geomagnetic storms are sustained (for several to many hours) periods of high-speed solar wind, and most importantly, a southward directed solar wind magnetic field (opposite the direction of Earth’s field) at the dayside of the magnetosphere. This condition is effective for transferring energy from the solar wind into Earth’s magnetosphere.

The largest storms that result from these conditions are associated with solar coronal mass ejections (CMEs) where a billion tons or so of plasma from the sun, with its embedded magnetic field, arrives at Earth. CMEs typically take several days to arrive at Earth, but have been observed, for some of the most intense storms, to arrive in as short as 18 hours. Another solar wind disturbance that creates conditions favorable to geomagnetic storms is a high-speed solar wind stream (HSS). HSSs plow into the slower solar wind in front and create co-rotating interaction regions, or CIRs. These regions are often related to geomagnetic storms that while less intense than CME storms, often can deposit more energy in Earth’s magnetosphere over a longer interval.

Storms also result in intense currents in the magnetosphere, changes in the radiation belts, and changes in the ionosphere, including heating the ionosphere and upper atmosphere region called the thermosphere. In space, a ring of westward current around Earth produces magnetic disturbances on the ground. A measure of this current, the disturbance storm time (Dst) index, has been used historically to characterize the size of a geomagnetic storm. In addition, there are currents produced in the magnetosphere that follow the magnetic field, called field-aligned currents, and these connect to intense currents in the auroral ionosphere. These auroral currents, called the auroral electrojets, also produce large magnetic disturbances. Together, all of these currents, and the magnetic deviations they produce on the ground, are used to generate a planetary geomagnetic disturbance index called Kp. This index is the basis for one of the three NOAA Space Weather Scales, the Geomagnetic Storm, or G-Scale, that is used to describe space weather that can disrupt systems on Earth.

During storms, the currents in the ionosphere, as well as the energetic particles that precipitate into the ionosphere add energy in the form of heat that can increase the density and distribution of density in the upper atmosphere, causing extra drag on satellites in low-earth orbit. The local heating also creates strong horizontal variations in the ionospheric density that can modify the path of radio signals and create errors in the positioning information provided by GPS. While the storms create beautiful aurora, they also can disrupt navigation systems such as the Global Navigation Satellite System (GNSS) and create harmful geomagnetic induced currents (GICs) in the power grid and pipelines.

Ionosphere

The Ionosphere is part of Earth’s upper atmosphere, between 80 and about 600 km where Extreme UltraViolet (EUV) and x-ray solar radiation ionizes the atoms and molecules thus creating a layer of electrons. the ionosphere is important because it reflects and modifies radio waves used for communication and navigation. Other phenomena such as energetic charged particles and cosmic rays also have an ionizing effect and can contribute to the ionosphere.

The atmospheric atoms and molecules are impacted by the high energy the EUV and X-ray photons from the sun. The amount of energy (photon flux) at EUV and x-ray wavelengths varies by nearly a factor of ten over the 11 year solar cycle. The density of the ionosphere changes accordingly. Due to spectral variability of the solar radiation and the density of various constituents in the atmosphere, there are layers are created within the ionosphere, called the D, E, and F-layers. Other solar phenomena, such as flares, and changes in the solar wind and geomagnetic storms also effect the charging of the ionosphere. Since the largest amount of ionization is caused by solar irradiance, the night-side of the earth, and the pole pointed away from the sun (depending on the season) have much less ionization than the day-side of the earth, and the pole pointing towards the sun.

Ionospheric Scintillation – Image Credit: Geospace Research Center, Nagoya University

Ionospheric scintillation is the rapid modification of radio waves caused by small scale structures in the ionosphere. Severe scintillation conditions can prevent a GPS receiver from locking on to the signal and can make it impossible to calculate a position. Less severe scintillation conditions can reduce the accuracy and the confidence of positioning results.

Scintillation of radio waves impacts the power and phase of the radio signal. Scintillation is caused by small-scale (tens of meters to tens of km) structure in the ionospheric electron density along the signal path and is the result of interference of refracted and/or diffracted (scattered) waves. Scintillation is usually quantified by two indexes: S4 for amplitude scintillation and σφ (sigma-phi) for phase scintillation. The indexes reflect the variability of the signal over a period of time, usually one minute. Scintillation is more prevalent at low and high latitudes, but mid-latitudes, such as the United States, experience scintillation much less frequently. Scintillation is a strong function of local time, season, geomagnetic activity, and solar cycle, but it also influenced by waves propagating from the lower atmosphere.

Radiation Belts – Image Credit: R.V. Hilmer, Air Force Research Laboratory

Radiation belts are regions of enhanced populations of energetic electrons and protons surrounding the Earth in space. These belts are highly dynamic, increasing and decreasing on time scales of minutes to years. The high levels of radiation caused by the energetic electrons and protons makes this a very harsh region for satellites.

Earth’s radiation belts, discovered shortly after the launch of the first US satellite in 1958, were one of the earliest discoveries of the space age. Since that time, while many satellites have made observations as they pass through the belts, much is still not understood about the processes that cause the energization, transport and loss of radiation belt particles.

There is a good understanding of the typical properties of the radiation belts, though, including their location and some of the processes that control the radiation belt intensity and variability. Radiation belt particle motion and dynamics are controlled to a great extent by the magnetic and electric fields in space and how these fields vary as a result of the interaction between the solar wind and the Earth’s magnetic and plasma environment. Electrons with typical energies above 0.1 Million electron volts (MeV) are found in both an inner belt (from about 1.5 to 3 Re (earth radii) above Earth’s center in the equatorial plane), and an outer belt (from about 3-10 Re). The so-called “slot region” forms between the two electron belts as a result of losses due to electron interactions with electromagnetic waves called whistlers. The radial location and intensity of the electron radiation belts are extremely variable, and predicting this variability is one of the major challenges for space weather forecasters. High-energy protons, with typical energies greater than 10 MeV, form one belt that extends from about 1.1 to 3 Earth radii.

The energetic particles that comprise the radiation belts can be hazardous for satellites and astronauts in space and can also have effects on Earth’s ionosphere and upper atmosphere. For example, high energy radiation belt protons, and even higher energy galactic cosmic rays, can alter the electronic state of sensitive electronic devices on satellites, resulting in computer errors or failures. In the case of high-energy electrons, they can cause serious damage to satellite cables and computer chips through a process called deep dielectric charging that culminates in harmful discharges. When MeV electrons precipitate into Earth’s upper atmosphere, they can deplete ozone and affect chemical processes in the atmosphere.

Solar EUV Irradiance

Solar Extreme Ultraviolet (EUV) is solar radiation that covers the wavelengths 10 – 120 nm of the electromagnetic spectrum. It is highly energetic and it is absorbed in the upper atmosphere, which not only heats the upper atmosphere but also ionizes it, creating the ionosphere. Solar EUV radiation changes by a factor of ten over the course of a typical solar cycle. This variability produces similar variations in the ionosphere and upper atmosphere. Solar EUV variations are one of the three primary drivers of ionospheric variability.

Solar Extreme-Ultraviolet (EUV) radiation originates in the corona and chromosphere of the Sun’s atmosphere. The solar EUV spectrum, between 1 and 120 nm, is dominated by spectral lines from hydrogen (H), helium (He), oxygen (O), sodium (Na), magnesium (Mg), silicon (Si), and iron (Fe). The EUV photons reach Earth and are completely absorbed in the upper atmosphere above 80 km. The thermosphere of the earth, 80 to 600 km in altitude, is heated predominantly by solar EUV radiation. The EUV photons also ionize the atmosphere creating electrons, which form the ionosphere. Solar EUV irradiance varies by as much as an order of magnitude on time scales of minutes to hours (solar flares), days to months (solar rotation), and years to decades (solar cycle). The highly varying EUV radiation causes the thermosphere and ionosphere to vary over similar magnitudes and time scales.

Because solar EUV radiation is absorbed by the upper atmosphere, it is impossible to measure from the ground. Thus, measurements must be made from rockets and satellites. It is difficult to build and maintain sensors that can measure the solar EUV radiation, so for many years people relied on proxies for solar EUV such as the Sunspot Number or the F10.7 cm radio flux.

Solar Flares (Radio Blackouts)

Solar flares are large eruptions of electromagnetic radiation from the Sun lasting from minutes to hours. The sudden outburst of electromagnetic energy travels at the speed of light, therefore any effect upon the sunlit side of Earth’s exposed outer atmosphere occurs at the same time the event is observed. The increased level of X-ray and extreme ultraviolet (EUV) radiation results in ionization in the lower layers of the ionosphere on the sunlit side of Earth. Under normal conditions, high frequency (HF) radio waves are able to support communication over long distances by refraction via the upper layers of the ionosphere. When a strong enough solar flare occurs, ionization is produced in the lower, more dense layers of the ionosphere (the D-layer), and radio waves that interact with electrons in layers lose energy due to the more frequent collisions that occur in the higher density environment of the D-layer. This can cause HF radio signals to become degraded or completely absorbed. This results in a radio blackout – the absence of HF communication, primarily impacting the 3 to 30 MHz band. The D-RAP (D-Region Absorption Prediction) product correlates flare intensity to D-layer absorption strength and spread.

Solar flares usually take place in active regions, which are areas on the Sun marked by the presence of strong magnetic fields; typically associated with sunspot groups. As these magnetic fields evolve, they can reach a point of instability and release energy in a variety of forms. These include electromagnetic radiation, which are observed as solar flares.

Solar flare intensities cover a large range and are classified in terms of peak emission in the 0.1 – 0.8 nm spectral band (soft x-rays) of the NOAA/GOES XRS. The X-ray flux levels start with the “A” level (nominally starting at 10-8 W/m2). The next level, ten times higher, is the “B” level (≥ 10-7 W/m2); followed by “C” flares (10-6 W/m2), “M” flares (10-5 W/m2), and finally “X” flares (10-4 W/m2).

Radio blackouts are classified using a five-level NOAA Space Weather Scale, directly related to the flare’s max peak in soft X-rays reached or expected. SWPC currently forecasts the probability of C, M, and X-class flares and relates it to the probability of an R1-R2, and R3 or greater events as part of our 3-day forecast and forecast discussion products. SWPC also issues an alert when an M5 (R2) flare occurs.

The following table provides the correlation between radio blackouts, solar flares, nominal energy flux (watts per square meter), and the designated severity event descriptor:

Radio Blackout….. X-ray Flare….. Flux (W/m2)….. Severity Descriptor

R1                            M1                   0.00001               Minor

R2                            M5                   0.00005               Moderate

R3                            X1                     0.0001                 Strong

R4                            X10                   0.001                   Severe

R5                            X20                   0.002                   Extreme

Solar Radiation Storm

Solar radiation storms occur when a large-scale magnetic eruption, often causing a coronal mass ejection and associated solar flare, accelerates charged particles in the solar atmosphere to very high velocities. The most important particles are protons which can get accelerated to large fractions of the speed of light. At these velocities, the protons can traverse the 150 million km from sun to Earth in just 10’s of minutes or less. When they reach Earth, the fast moving protons penetrate the magnetosphere that shields Earth from lower energy charged particles. Once inside the magnetosphere, the particles are guided down the magnetic field lines and penetrate into the atmosphere near the north and south poles.

NOAA categorizes Solar Radiation Storms using the NOAA Space Weather Scale on a scale from S1 – S5. The scale is based on measurements of energetic protons taken by the GOES satellite in geosynchronous orbit. The start of a Solar Radiation Storm is defined as the time when the flux of protons at energies ≥ 10 MeV equals or exceeds 10 proton flux units (1 pfu = 1 particle*cm-2*s-1*ster-1). The end of a Solar Radiation Storm is defined as the last time when the flux of ≥ 10 MeV protons is measured at or above 10 pfu. This definition allows multiple injections from flares and interplanetary shocks to be encompassed by a single Solar Radiation Storm. A Solar Radiation Storm can persist for time periods ranging from hours to days.

Solar Radiation Storms cause several impacts near Earth. When energetic protons collide with satellites or humans in space, they can penetrate deep into the object that they collide with and cause damage to electronic circuits or biological DNA. During the more extreme Solar Radiation Storms, passengers and crew in high flying aircraft at high latitudes may be exposed to radiation risk. Also, when the energetic protons collide with the atmosphere, they ionize the atoms and molecules thus creating free electrons. These electrons create a layer near the bottom of the ionosphere that can absorb High Frequency (HF) radio waves making radio communication difficult or impossible.

SWPC currently forecasts the probability of S1 (Minor Radiation Storm) occurrence as part of our 3-day forecast and forecast discussion products and issues a warning for an expected S1 or higher event; as well as a warning for when the 100 MeV proton level is expected to reach 1 pfu. Additionally, SWPC issues alerts for when each NOAA Space Weather Scale Radiation Storm level is reached (S1-S5) and/or when the 100 MeV protons reach 1 pfu.

Solar Wind – Image Credit: NASA

The solar wind continuously flows outward from the Sun and consists mainly of protons and electrons in a state known as a plasma. Solar magnetic field is embedded in the plasma and flows outward with the solar wind.

Different regions on the Sun produce solar wind of different speeds and densities. Coronal holes produce solar wind of high speed, ranging from 500 to 800 kilometers per second. The north and south poles of the Sun have large, persistent coronal holes, so high latitudes are filled with fast solar wind. In the equatorial plane, where the Earth and the other planets orbit, the most common state of the solar wind is the slow speed wind, with speeds of about 400 kilometers per second. This portion of the solar wind forms the equatorial current sheet.

During quiet periods, the current sheet can be nearly flat. As solar activity increases, the solar surface fills with active regions, coronal holes, and other complex structures, which modify the solar wind and current sheet. Because the Sun rotates every 27 days, the solar wind becomes a complex spiral of high and low speeds and high and low densities that looks like the skirt of a twirling ballerina. When high speed solar overtakes slow speed wind, it creates something known as a corotating interaction region. These interaction regions consist of solar wind with very high densities and strong magnetic fields. Above the current sheet, the higher speed solar wind typically has a dominant magnetic polarity in one direction and below the current sheet, the polarity is in the opposite direction. As the Earth moves through this evolving ballerina skirt, it is sometimes within the heliospheric current sheet, sometimes above it and sometime below it. When the magnetic field of the solar wind switches polarity, it is a strong indication that Earth has crossed the current sheet. The location of the Earth with respect to the current sheet is important because space weather impacts are highly dependent on the solar wind speed, the solar wind density, and the direction of the magnetic field embedded in the solar wind.

Each of the elements mentioned above play a role in space weather. High speed winds bring geomagnetic storms, while slow speed winds bring calm space weather. Corotating interaction regions and to a lesser extent, current sheet crossings, can also cause geomagnetic disturbances. Thus specifying and forecasting the solar wind is critical to developing forecasts of space weather and its impacts at Earth.

Sunspots

Sunspots are dark areas that become apparent at the Sun’s photosphere as a result of intense magnetic flux pushing up from further within the solar interior. Areas along this magnetic flux in the upper photosphere and chromosphere heat up, and usually become visible as faculae and plage – often times termed active regions. This causes cooler (3871o C), less dense and darker areas at the heart of these magnetic fields than in the surrounding photosphere (5537o C) – seen as sunspots. Active regions associated with sunspot groups are usually visible as bright enhancements in the corona at EUV and X-ray wavelengths. Rapid changes in the magnetic field alignment of sunspot groups associated active regions are the most likely sources of significant space weather events such as solar flares, CMEs, radiations storms, and radio bursts.

Sunspots appear in a wide variety of shapes and forms. The darkest area of a sunspot (also the first to be observed) is called the umbrae. As the sunspot matures (becomes more intense), a less dark, outlying area of well-defined fibril-like structure develops around the umbrae – called penumbra. Sunspots can grow from an individual unipolar spot into more organized bipolar spot groups; or even evolve into immense, very complex sunspot groups with mixed magnetic polarities throughout the group. The largest sunspot groups can cover large swaths of the Sun’s surface and be many times the size of Earth.

Sunspot groups that are clearly visible and observed by designated ground-based observatories, are assigned a NOAA/SWPC 4-digit region number to officially record and track the sunspot group as it rotates across the visible solar disk. Sunspot groups are analyzed and characterized based on their size and complexity by SWPC forecasters each day using the modified Zurich classification scale and Mount Wilson magnetic classification system. This daily sunspot analysis and classification is submitted at the end of each UTC-day as the Solar Region Summary report.

Sunspots can change continuously and may last for only a few hours to days; or even months for the more intense groups. The total number of sunspots has long been known to vary with an approximately 11-year repetition known as the solar cycle. The peak of sunspot activity is known as solar maximum and the lull is known as solar minimum. Solar cycles started being assigned consecutive numbers. This number assignment began with solar cycle 1 in 1755 and the most recent being cycle 24 – which began in December, 2008 and is now nearing solar minimum. A new solar cycle is considered to have begun when sunspot groups emerge at higher latitudes with the magnetic polarities of the leading spots opposite that of the previous cycle. A plot of sunspot number progression for the previous and current solar cycle, and that compares the observed and smoothed values with the official sunspot number forecast provided by the Solar Cycle Prediction Panel representing NOAA, the International Space Environmental Services (ISES), and NASA is available to view on our SWPC webpage at solar cycle progression.

The official daily and monthly sunspot numbers are determined by the World Data Center – Sunspot Index and Long-term Solar Observations (WDC-SILSO) at the Royal Observatory of Belgium. Generally, sunspot reports from observatories calculate sunspot numbers whereby each sunspot group counts as 10, and every umbra within each spot group is individually considered as 1. Therefore, no sunspots on the visible Sun would be considered as zero; while the next possible number can only be 11 or higher.

Total Electron Content

The Total Electron Content (TEC) is the total number of electrons present along a path between a radio transmitter and receiver. Radio waves are affected by the presence of electrons. The more electrons in the path of the radio wave, the more the radio signal will be affected. For ground to satellite communication and satellite navigation, TEC is a good parameter to monitor for possible space weather impacts.

TEC is measured in electrons per square meter. By convention, 1 TEC Unit TECU = 10^16 electrons/m². Vertical TEC values in Earth’s ionosphere can range from a few to several hundred TECU.

The TEC in the ionosphere is modified by changing solar Extreme Ultra-Violet radiation, geomagnetic storms, and the atmospheric waves that propagate up from the lower atmosphere. The TEC will therefore depend on local time, latitude, longitude, season, geomagnetic conditions, solar cycle and activity, and troposphere conditions. The propagation of radio waves is affected by the ionosphere. The velocity of radio waves changes when the signal passes through the electrons in the ionosphere. The total delay suffered by a radio wave propagating through the ionosphere depends both on the frequency of the radio wave and the TEC between the transmitter and the receiver. At some frequencies the radio waves pass through the ionosphere. At other frequencies, the waves are reflected by the ionosphere.

The change in the path and velocity of radio waves in the ionosphere has a big impact on the accuracy of satellite navigation systems such as GPS/GNSS. Neglecting changes in the ionosphere TEC can introduce tens of meters of error in the position calculations. The Global Positioning System (GPS), the US part of GNSS, uses an empirical model of the ionosphere, the Klobuchar model, to calculate and remove part of the positioning error caused by the ionosphere when single frequency GPS receivers are used. When conditions deviate from those predicted by the Klobuchar model, GPS/GNSS systems will have larger positioning errors.

Solar & Space Weather Observation Spacecraft

Parker Solar Probe

NASA’s Parker Solar Probe is on a mission to “touch the Sun.” The spacecraft is flying closer to the Sun’s surface than any spacecraft before it. The mission will revolutionize our understanding of the Sun.

Parker will fly more than seven times closer to the Sun than any spacecraft.

Over seven years, the spacecraft will complete 24 orbits around the Sun.

At its closest approach, the spacecraft will come within about 3.9 million miles (6.2 million kilometers) of the Sun.

Parker Solar Probe is designed to swoop within about 4 million miles (6.5 million kilometers) of the Sun’s surface to trace the flow of energy, to study the heating of the solar corona, and to explore what accelerates the solar wind.

During its journey, the mission will provide answers to long-standing questions that have puzzled scientists for more than 60 years: Why is the corona much hotter than the Sun’s surface (the photosphere)? How does the solar wind accelerate? What are the sources of high-energy solar particles?

We live in the Sun’s atmosphere and this mission will help scientists better understand the Sun’s impact on Earth. Data from Parker will be key to understanding and, perhaps, forecasting space weather. Space weather can change the orbits of satellites, shorten their lifetimes, or interfere with onboard electronics.

Parker can survive the Sun’s harsh conditions because cutting-edge thermal engineering advances protect the spacecraft during its dangerous journey.

The probe has four instrument suites designed to study magnetic fields, plasma, and energetic particles, and image the solar wind.

The mission is named for Dr. Eugene N. Parker, who pioneered our modern understanding of the Sun.

ESA-NASA SOHO

SOHO is the longest-lived Sun-watching satellite to date. Numerous mission extensions have enabled the spacecraft to observe two 11-year solar cycles and to discover thousands of comets.

SOHO is a cooperative international project between ESA and NASA. NASA contributed three instruments and launch services. ESA leads the mission.

During its pioneering career, SOHO has returned a wealth of new information about the Sun—from its core to its outer atmosphere and the solar wind.

SOHO monitors the effects of space weather on our planet, and it plays a vital role in forecasting potentially dangerous solar storms.

SOHO is the most prolific discoverer of comets in astronomical history, with more than 3,000 tracked during encounters with the Sun.

The ESA-sponsored Solar and Heliospheric Observatory (SOHO) carries 12 scientific instruments to study the solar atmosphere, helioseismology and the solar wind. Information from the mission has allowed scientists to learn more about the Sun’s internal structure and dynamics, the chromosphere, the corona and solar particles.

The SOHO and Cluster missions, part of ESA’s Solar Terrestrial Science Programme (STSP), are ESA’s contributions to the International Solar Terrestrial Physics (ISTP) program, which has involved the work of other spacecraft such as Wind and ACE, which, like SOHO, operate in the vicinity of the Sun-Earth L1 point.

NASA contributed three instruments to SOHO as well as launch and flight operations support.

About two months after launch, on Feb. 14, 1996, SOHO was placed at a distance of 932,000 miles (1.5 million kilometers) from Earth in an elliptical Lissajous orbit around the L1 libration point where it takes approximately six months to orbit L1 (while the L1 itself orbits the Sun every 12 months).

The spacecraft returned its first image Dec. 19, 1995, and was fully commissioned for operations by April 16, 1996. SOHO finished its planned two-year study of the Sun’s atmosphere, surface and interior in April 1998.

SOHO’s original lifetime was three years (to 1998), but in 1997, ESA and NASA jointly decided to prolong the mission to 2003, thus enabling the spacecraft to compare the Sun’s behavior during low dark sunspot activity (1996) to the peak (around 2000).

One of SOHO’s most important discoveries has been locating the origin of the fast solar wind at the corners of honeycomb-shaped magnetic fields surrounding the edges of large bubbling cells located near the Sun’s poles.

Another has been its discovery, as of September 2015, of over 3,000 comets (more than one-half of all known comets), by over 70 people representing 18 different nations. These discoveries were made possible because of the LASCO instrument that blocks out the Sun’s glare, rendering comets visible.

In December 2015, SOHO marked 20 years of continuous operation, having fundamentally changed our conception of the Sun “from a picture of a static, unchanging object in the sky to the dynamic beast it is,” in the words of Bernhard Fleck, the ESA project scientist for SOHO.

The longevity of the mission has allowed SOHO to cover two entire 11-year solar cycles. One of the highpoints of the mission was SOHO’s observation of a bright comet plunging toward the Sun on Aug. 3-4, 2016, at a velocity of nearly 1.3 million miles per hour (2.1 million kilometers per hour).

STEREO (Solar Terrestrial Relations Observatory)

Is a solar observation mission. Two nearly identical spacecraft were launched in 2006 into orbits around the Sun that cause them to respectively pull farther ahead of and fall gradually behind the Earth. This enabled stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.

Contact with STEREO-B was lost in 2014 after entering an uncontrolled spin preventing its solar panels from generating enough power, but STEREO-A is still operational.

The principal benefit of the mission was stereoscopic images of the Sun. In other words, because the satellites are at different points along the Earth’s orbit, but distant from the Earth, they can photograph parts of the Sun that are not visible from the Earth. This permits NASA scientists to directly monitor the far side of the Sun, instead of inferring the activity on the far side from data that can be gleaned from Earth’s view of the Sun. The STEREO satellites principally monitor the far side for coronal mass ejections — massive bursts of solar wind, solar plasma, and magnetic fields that are sometimes ejected into space.

Since the radiation from coronal mass ejections, or CMEs, can disrupt Earth’s communications, airlines, power grids, and satellites, more accurate forecasting of CMEs has the potential to provide greater warning to operators of these services. Before STEREO, the detection of the sunspots that are associated with CMEs on the far side of the Sun was only possible using helioseismology, which only provides low-resolution maps of the activity on the far side of the Sun. Since the Sun rotates every 25 days, detail on the far side was invisible to Earth for days at a time before STEREO. The period that the Sun’s far side was previously invisible was a principal reason for the STEREO mission.

STEREO’s observations are incorporated into forecasts of solar activity for airlines, power companies, satellite operators, and others.

STEREO has also been used to discover 122 eclipsing binaries and study hundreds more variable stars. STEREO can look at the same star for up to 20 days.

On July 23, 2012, STEREO-A was in the path of the CME of the solar storm of 2012. This CME, if it were to have collided with Earth’s magnetosphere, was estimated to have caused a geomagnetic storm of similar strength to the Carrington Event, the most intense geomagnetic storm in recorded history. STEREO-A’s instrumentation was able to collect and relay a significant amount of data about the event without being harmed.

SDO (Solar Dynamics Observatory)

The Solar Dynamics Observatory (SDO) is a NASA mission which has been observing the Sun since 2010. Launched on 11 February 2010, the observatory is part of the Living With a Star (LWS) program.

The goal of the LWS program is to develop the scientific understanding necessary to effectively address those aspects of the connected Sun–Earth system directly affecting life and society. The goal of the SDO is to understand the influence of the Sun on the Earth and near-Earth space by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously. SDO has been investigating how the Sun’s magnetic field is generated and structured, how this stored magnetic energy is converted and released into the heliosphere and geospace in the form of solar wind, energetic particles, and variations in the solar irradiance.

The SDO spacecraft was developed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and launched on 11 February 2010, from Cape Canaveral Air Force Station (CCAFS). The primary mission lasted five years and three months, with expendables expected to last at least ten years. Some consider SDO to be a follow-on mission to the Solar and Heliospheric Observatory (SOHO).

SDO is a three-axis stabilized spacecraft, with two solar arrays, and two high-gain antennas, in an inclined geosynchronous orbit around Earth.

The spacecraft includes three instruments:

The Extreme Ultraviolet Variability Experiment (EVE) built in partnership with the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics (LASP),

The Helioseismic and Magnetic Imager (HMI) built in partnership with Stanford University.

The Atmospheric Imaging Assembly (AIA) built in partnership with the Lockheed Martin Solar and Astrophysics Laboratory (LMSAL).

SDO is expected to remain operational until 2030.

GOES (Geostationary Operational Environmental Satellite)

The Geostationary Operational Environmental Satellite (GOES), operated by the United States’ National Oceanic and Atmospheric Administration (NOAA)’s National Environmental Satellite, Data, and Information Service division, supports weather forecasting, severe storm tracking, and meteorology research. Spacecraft and ground-based elements of the system work together to provide a continuous stream of environmental data. The National Weather Service (NWS) and the Meteorological Service of Canada use the GOES system for their North American weather monitoring and forecasting operations, and scientific researchers use the data to better understand land, atmosphere, ocean, and climate dynamics.

The GOES system uses geosynchronous equatorial satellites that have been a basic element of U.S. weather monitoring and forecasting.

The procurement, design, and manufacture of GOES satellites is overseen by NASA.

NOAA is the official provider of both GOES terrestrial data and GOES space weather data. Data can also be accessed using the SPEDAS software.

Designed to operate in geostationary orbit 35,790 kilometres (22,240 mi) above the Earth, the GOES spacecraft continuously view the continental United States, the Pacific and Atlantic Oceans, Central America, South America, and southern Canada. The three-axis, body-stabilized design enables the sensors to “stare” at the Earth and thus more frequently image clouds, monitor the Earth’s surface temperature and water vapour fields, and sound the atmosphere for its vertical thermal and vapor structures. The evolution of atmospheric phenomena can be followed, ensuring real-time coverage of meteorological events such as severe local storms and tropical cyclones. The importance of this capability was proven during hurricanes Hugo (1989) and Andrew (1992).

The GOES spacecraft also enhance operational services and improve support for atmospheric science research, numerical weather prediction models, and environmental sensor design and development.

Satellite data is broadcast on the L-band, and received at the NOAA Command and Data Acquisition ground station at Wallops Island, Virginia from which it is disseminated to users. Additionally, anyone may receive data directly from the satellites by utilizing a small dish, and processing the data with special software.

The GOES satellites are controlled from the Satellite Operations Control Center in Suitland, Maryland. During significant weather or other events, the normal schedules can be altered to provide the coverage requested by the NWS and other agencies.

GOES-12 and above also have provided a platform for the Solar X-Ray Imager (SXI) and space environment monitoring (SEM) instruments.

The SXI provides high-cadence monitoring of large scale solar structures to support the Space Environment Services Center’s (SESC) mission. The SXI unit on GOES-13, however, was damaged by a solar flare in 2006. The SESC, as the nation’s “space weather” service, receives, monitors, and interprets a wide variety of solar-terrestrial data. It also issues reports, alerts, and forecasts for special events such as solar flares or geomagnetic storms. This information is important to the operation of military and civilian radio wave and satellite communication and navigation systems. The information also is important to electric power networks, the missions of geophysical explorers, Space Station astronauts, high-altitude aviators, and scientific researchers.

The SEM measures the effect of the Sun on the near-Earth solar-terrestrial electromagnetic environment, providing real-time data.

DSCOVR (Deep Space Climate Observatory)

Deep Space Climate Observatory (DSCOVR) is a National Oceanic and Atmospheric Administration (NOAA) space weather, space climate, and Earth observation satellite. It was launched by SpaceX on a Falcon 9 v1.1 launch vehicle on 11 February 2015, from Cape Canaveral. This is NOAA’s first operational deep space satellite and became its primary system of warning Earth in the event of solar magnetic storms.

DSCOVR was originally proposed as an Earth observation spacecraft positioned at the Sun-Earth L1 Lagrange point, providing live video of the sunlit side of the planet through the Internet as well as scientific instruments to study climate change. Political changes in the United States resulted in the mission’s cancellation, and in 2001 the spacecraft was placed into storage.

Proponents of the mission continued to push for its reinstatement, and a change in presidential administration in 2009 resulted in DSCOVR being taken out of storage and refurbished, and its mission was refocused to solar observation and early warning of coronal mass ejections while still providing Earth observation and climate monitoring. It launched aboard a SpaceX Falcon 9 launch vehicle on 11 February 2015, and reached L1 on 8 June 2015.

NOAA operates DSCOVR from its Satellite and Product Operations Facility in Suitland, Maryland. The acquired space data that allows for accurate weather forecasts are carried out in the Space Weather Prediction Center in Boulder, Colorado. Archival records are held by the National Centers for Environmental Information, and processing of Earth sensor data is carried out by NASA.

DSCOVR is built on the SMEX-Lite spacecraft bus and has a launch mass of approximately 570 kg (1,260 lb). The main science instrument sets are the Sun-observing Plasma Magnetometer (PlasMag) and the Earth-observing NIST Advanced Radiometer (NISTAR) and Earth Polychromatic Imaging Camera (EPIC). DSCOVR has two deployable solar arrays, a propulsion module, boom, and antenna.

From its vantage point, DSCOVR monitors variable solar wind conditions, provides early warning of approaching coronal mass ejections and observes phenomena on Earth, including changes in ozone, aerosols, dust and volcanic ash, cloud height, vegetation cover and climate. At its Sun-Earth L1 location it has a continuous view of the Sun and of the sunlit side of the Earth. After the spacecraft arrived on-site and entered its operational phase, NASA began releasing near-real-time images of Earth through the EPIC instrument’s website. DSCOVR takes full-Earth pictures about every two hours and is able to process them faster than other Earth observation satellites.

The spacecraft is in a looping halo orbit around the Sun-Earth Lagrange point L1 in a six-month period, with a spacecraft–Earth–Sun angle varying from 4° to 15°.

Van Allen Probes

The Van Allen Probes (VAP), formerly known as the Radiation Belt Storm Probes (RBSP), were two robotic spacecraft that were used to study the Van Allen radiation belts that surround Earth. NASA conducted the Van Allen Probes mission as part of the Living With a Star program. Understanding the radiation belt environment and its variability has practical applications in the areas of spacecraft operations, spacecraft system design, mission planning and astronaut safety. The probes were launched on 30 August 2012 and operated for seven years. Both spacecraft were deactivated in 2019 when they ran out of fuel. They are expected to deorbit during the 2030s.

NASA’s Goddard Space Flight Center manages the overall Living With a Star program of which the Van Allen Probes is a project, along with Solar Dynamics Observatory (SDO). The Johns Hopkins University Applied Physics Laboratory (APL) was responsible for the overall implementation and instrument management for RBSP. The primary mission was scheduled to last 2 years, with expendables expected to last for 4 years. The primary mission was planned to last only 2 years because there was great concern as to whether the satellite’s electronics would survive the hostile radiation environment in the radiation belts for a long period of time. When after 7 years the mission ended, it was not because of electronics failure but because of running out of fuel. This proved the resiliency of the spacecraft’s electronics. The spacecraft’s longevity in the radiation belts was considered a record-breaking performance for satellites in terms of radiation resiliency.

The spacecraft worked in close collaboration with the Balloon Array for RBSP Relativistic Electron Losses (BARREL), which can measure particles that break out of the belts and make it all the way to Earth’s atmosphere.

The Applied Physics Laboratory managed, built, and operated the Van Allen Probes for NASA.

The probes are named after James Van Allen, the discoverer of the radiation belts they studied.

Solar Orbiter (SolO)

The Solar Orbiter (SolO) is a Sun-observing satellite developed by the European Space Agency (ESA). SolO, designed to obtain detailed measurements of the inner heliosphere and the nascent solar wind, will also perform close observations of the polar regions of the Sun which is difficult to do from Earth. These observations are important in investigating how the Sun creates and controls its heliosphere.

SolO makes observations of the Sun from an eccentric orbit moving as close as ≈60 solar radii (RS), or 0.284 astronomical units (au), placing it inside Mercury’s perihelion of 0.3075 au. During the mission the orbital inclination will be raised to about 24°. The total mission cost is US $1.5 billion, counting both ESA and NASA contributions.

SolO was launched on 10 February 2020. The mission is planned to last seven years.

The Solar Orbiter spacecraft is a Sun-pointed, three-axis stabilised platform with a dedicated heat shield to provide protection from the high levels of solar flux near perihelion. The spacecraft provides a stable platform to accommodate the combination of remote-sensing and in situ instrumentation in an electromagnetically clean environment. The 21 sensors were configured on the spacecraft to allow each to conduct its in situ or remote-sensing experiments with both access to and protection from the solar environment. Solar Orbiter has inherited technology from previous missions, such as the solar arrays from the BepiColombo Mercury Planetary Orbiter (MPO). The solar arrays can be rotated about their longitudinal axis to avoid overheating when close to the Sun. A battery pack provides supplementary power at other points in the mission such as eclipse periods encountered during planetary flybys.

The Telemetry, Tracking and Command Subsystem provides the communication link capability with the Earth in X-band. The subsystem supports telemetry, telecommand and ranging. Low-Gain Antennas are used for Launch and Early Orbit Phase (LEOP) and now function as a back-up during the mission phase when steerable Medium- and High-Gain Antennas are in use. The High-Temperature High-Gain Antenna needs to point to a wide range of positions to achieve a link with the ground station and to be able to downlink sufficient volumes of data. Its design was adapted from the BepiColombo mission. The antenna can be folded in to gain protection from Solar Orbiter’s heat shield if necessary. Most data will therefore initially be stored in on-board memory and sent back to Earth at the earliest possible opportunity.

The spacecraft makes a close approach to the Sun every six months. The closest approach will be positioned to allow a repeated study of the same region of the solar atmosphere. Solar Orbiter will be able to observe the magnetic activity building up in the atmosphere that can lead to powerful solar flares or eruptions.

Researchers will also have the chance to coordinate observations with NASA’s Parker Solar Probe mission (2018-2025) which is performing measurements of the Sun’s extended corona.

The objective of the mission is to perform close-up, high-resolution studies of the Sun and its inner heliosphere. The new understanding will help answer these questions:

How and where do the solar wind plasma and magnetic field originate in the corona.

How do solar transients drive heliospheric variability.

How do solar eruptions produce energetic particle radiation that fills the heliosphere.

How does the solar dynamo work and drive connections between the Sun and the heliosphere.

A fantastic website for Space Weather observation and real time data is Space Weather Live