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What are the conditions for an ionosphere to form on a given planet?
Factors I could think of are
- Class and age of the star the planet orbits
- Distance to said star
- Density and composition of the planet's atmosphere
According to the paper "Simultaneous ionospheric variability on Earth and Mars" (Mendillo et al. 2003), the overall structure of any ionised region of a planetary atmosphere depends on
a blend of in situ production and loss processes, plus effects of transport of ionization into or out of the local region of interest
Specifically, according to Mendillo et al., the only significant influence is from the photon flux from the parent star - so, the further the planet is from the star, the less the incoming photon flux. The other mechanisms are suggested to be planetary-based, including (from the article):
planetary rotation rate
which both also affect the photon flux reaching that particular part of the planetary atmosphere. Other mechanisms are to do with the planetary atmospheres themselves, with factors including:
the thermal structure, chemistry and dynamics of the planetary 'neutral' atmosphere itself.
by how much energetic particles (from the stellar wind and/or magnetosphere) affects the planetary atmosphere.
diffusion and electrodynamics from coupling from above the layer; and tides, waves and electrodynamics from coupling with below the layer.
A further study in the paper "Ionospheric photoelectrons: Comparing Venus, Earth, Mars and Titan" (Coates et al. 2011) compared the sunlit portion of planetary ionospheres, which is sustained by photoionization of primarily neutral atmospheric constituents by solar EUV (Extreme UV), a process originally identified for Earth, but recently:
the Mars Express, Venus Express and Cassini-Huygens missions have revealed the importance of this process at Mars, Venus and Titan, respectively.
It should be noted, that for planets without magnetic fields (Venus and Mars for example), the Max Planck Institute for Solar System Research page "Research about the planetary plasma environment",
The ionosphere is assumed to display two distinct states, "magnetized" and "unmagnetized", depending on the penetration depth of the solar wind magnetic field.
One more factor is suggested - dust, theorised from observations reported in the paper "On the role of dust in the lunar ionosphere" (Stubbs et al. 2011). According to the NASA page summarising the paper "Mystery of the Lunar Ionosphere", ubiquitous grains of dust from the Lunar surface may be the source of the Lunar ionosphere. The research from Stubbs et al. is summarised as:
UV rays from the sun hit the grains and ionize them. According to their calculations, this process produces enough charge (positive grains surrounded by negative electrons) to create the observed ionosphere.
The process with the lunar ionosphere is illustrated below (from the NASA page linked):
@Hackworth has also asked this question on the Geosciences SX site (link to question), where I provided an answer (link to my answer). I'm including a link to my answer there from here in case it proves useful to somebody.
Connection Found Between the Earth and Space Weather
Researchers have found a connection between weather here on Earth, and the weather in space. The connection comes from the ionosphere, a high-altitude region of the Earth’s atmosphere formed by solar X-rays and ultraviolet light. NASA satellites found that regions of the ionosphere become more dense above areas of thunderstorm activity in the lower atmosphere. This is a surprising discovery because the ionosphere and the lower atmosphere are separated by hundreds of kilometres.
Weather on Earth has a surprising connection to space weather occurring high in the electrically-charged upper atmosphere, known as the ionosphere, according to new results from NASA satellites.
“This discovery will help improve forecasts of turbulence in the ionosphere, which can disrupt radio transmissions and the reception of signals from the Global Positioning System,” said Thomas Immel of the University of California, Berkeley, lead author of a paper on the research published August 11 in Geophysical Research Letters.
Researchers discovered that tides of air generated by intense thunderstorm activity over South America, Africa and Southeast Asia were altering the structure of the ionosphere.
The ionosphere is formed by solar X-rays and ultraviolet light, which break apart atoms and molecules in the upper atmosphere, creating a layer of electrically-charged gas known as plasma. The densest part of the ionosphere forms two bands of plasma close to the equator at a height of almost 250 miles. From March 20 to April 20, 2002, sensors on board NASA’s Imager for Magnetopause to Aurora Global Exploration (IMAGE) satellite recorded these bands, which glow in ultraviolet light.
Using pictures from IMAGE, the team discovered four pairs of bright regions where the ionosphere was almost twice as dense as the average. Three of the bright pairs were located over tropical rainforests with lots of thunderstorm activity — the Amazon Basin in South America, the Congo Basin in Africa, and Indonesia. A fourth pair appeared over the Pacific Ocean. Researchers confirmed that the thunderstorms over the three tropical rainforest regions produce tides of air in our atmosphere using a computer simulation developed by the National Center for Atmospheric Research, Boulder, Colo., called the Global Scale Wave Model.
The connection to plasma bands in the ionosphere surprised scientists at first because these tides from the thunderstorms can not affect the ionosphere directly. The gas in the ionosphere is simply too thin. Earth’s gravity keeps most of the atmosphere close to the surface. Thunderstorms develop in the lower atmosphere, or troposphere, which extends almost 10 miles above the equator. The gas in the plasma bands is about 10 billion times less dense than in the troposphere. The tide needs to collide with atoms in the atmosphere above to propagate, but the ionosphere where the plasma bands form is so thin, atoms rarely collide there.
However, the researchers discovered the tides could affect the plasma bands indirectly by modifying a layer of the atmosphere below the bands that shapes them. Below the plasma bands, a layer of the ionosphere called the E-layer becomes partially electrified during the day. This region creates the plasma bands above it when high-altitude winds blow plasma in the E-layer across the Earth’s magnetic field. Since plasma is electrically charged, its motion across the Earth’s magnetic field acts like a generator, creating an electric field. This electric field shapes the plasma above into the two bands. Anything that would change the motion of the E-layer plasma would also change the electric fields they generate, which would then reshape the plasma bands above.
The Global Scale Wave Model indicated the tides should dump their energy about 62 to 75 miles above the Earth in the E-layer. This disrupts the plasma currents there, which alters the electric fields and creates dense, bright zones in the plasma bands above.
“The single pair of bright zones over the Pacific Ocean that is not associated with strong thunderstorm activity shows the disruption is propagating around the Earth, making this the first global effect on space weather from surface weather that’s been identified,” said Immel. “We now know that accurate predictions of ionospheric disturbances have to incorporate this effect from tropical weather.”
“This discovery has immediate implications for space weather, identifying four sectors on the Earth where space storms may produce greater ionospheric disturbances. North America is in one of these sectors, which may help explain why the U.S. suffers uniquely extreme ionospheric conditions during space weather events,” Immel said.
Measurements made by NASA’s Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite from March 20 to April 20, 2002, have confirmed that the dense zones exist in the plasma bands. Researchers now want to understand whether the effect changes with seasons or large events, like hurricanes.
The research was funded by NASA. The National Center for Atmospheric Research is sponsored by the National Science Foundation, Arlington, Va.
The team includes Immel, Scott England, Stephen Mende, and Harald Frey of the University of California, Berkeley Eiichi Sagawa of the National Institute of Information and Communications Technology, Tokyo, Japan Sid Henderson and Charles Swenson of Utah State University, Logan, Utah Maura Hagan of the National Center for Atmospheric Research High Altitude Observatory, Boulder, Colo. and Larry Paxton of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
Nightside radio could help reveal exoplanet details
Rice University scientists have enhanced models that could detect magnetosphere activity on exoplanets. The models add data from nightside activity that could increase signals by at least an order of magnitude. In this illustration, the planet's star is at top left, and the rainbow patches are the radio emission intensities, most coming from the nightside. The white lines are magnetic field lines. Credit: Anthony Sciola/Rice University
We can't detect them yet, but radio signals from distant solar systems could provide valuable information about the characteristics of their planets.
A paper by Rice University scientists describes a way to better determine which exoplanets are most likely to produce detectable signals based on magnetosphere activity on exoplanets' previously discounted nightsides.
The study by Rice alumnus Anthony Sciola, who earned his Ph.D. this spring and was mentored by co-author and space plasma physicist Frank Toffoletto, shows that while radio emissions from the daysides of exoplanets appear to max out during high solar activity, those that emerge from the nightside are likely to add significantly to the signal.
This interests the exoplanet community because the strength of a given planet's magnetosphere indicates how well it would be protected from the solar wind that radiates from its star, the same way Earth's magnetic field protects us.
Planets that orbit within a star's Goldilocks zone, where conditions may otherwise give rise to life, could be deemed uninhabitable without evidence of a strong enough magnetosphere. Magnetic field strength data would also help to model planetary interiors and understand how planets form, Sciola said.
The study appears in The Astrophysical Journal.
Earth's magnetosphere isn't exactly a sphere it's a comet-shaped set of field lines that compress against the planet's day side and tail off into space on the night side, leaving eddies in their wake, especially during solar events like coronal mass ejections. The magnetosphere around every planet emits what we interpret as radio waves, and the closer to the sun a planet orbits, the stronger the emissions.
Astrophysicists have a pretty good understanding of our own system's planetary magnetospheres based on the Radiometric Bode's Law, an analytical tool used to establish a linear relationship between the solar wind and radio emissions from the planets in its path. In recent years, researchers have attempted to apply the law to exoplanetary systems with limited success.
"The community has used these rule-of-thumb empirical models based on what we know about the solar system, but it's kind of averaged and smoothed out," Toffoletto said. "A dynamic model that includes all this spiky behavior could imply the signal is actually much larger than these old models suggest. Anthony is taking this and pushing it to its limits to understand how signals from exoplanets could be detected."Rice University graduate student Anthony Sciola, pictured at Kaldidalur (The Cold Valley) in Iceland, has developed a numerical model to enhance the analysis of radio signals from exoplanets. Though the instruments to obtain such data are not yet available, they could help determine what planets have protective magnetospheres. Credit: Anthony Sciola/Rice University
Sciola said the current analytic model relies primarily on emissions expected to emerge from an exoplanet's polar region, what we see on Earth as an aurora. The new study appends a numerical model to those that estimate polar region emissions to provide a more complete picture of emissions around an entire exoplanet.
"We're adding in features that only show up in lower regions during really high solar activity," he said.
It turns out, he said, that nightside emissions don't necessarily come from one large spot, like auroras around the north pole, but from various parts of the magnetosphere. In the presence of strong solar activity, the sum of these nightside spots could raise the planet's total emissions by at least an order of magnitude.
"They're very small-scale and occur sporadically, but when you sum them all up, they can have a great effect," said Sciola, who is continuing the work at Johns Hopkins University's Applied Physics Laboratory. "You need a numerical model to resolve those events. For this study, Sciola used the Multiscale Atmosphere Geospace Environment (MAGE) developed by the Center for Geospace Storms (CGS) based at the Applied Physics Laboratory in collaboration which the Rice space plasma physics group.
"We're essentially confirming the analytic model for more extreme exoplanet simulations, but adding extra detail," he said. "The takeaway is that we're bringing further attention to the current model's limiting factors but saying that under certain situations, you can get more emissions than that limiting factor suggests."
He noted the new model works best on exoplanetary systems. "You need to be really far away to see the effect," he said. It's hard to tell what's going on at the global scale on Earth it's like trying to watch a movie by sitting right next to the screen. You're only getting a little patch of it."
Also, radio signals from an Earth-like exoplanet may never be detectable from Earth's surface, Sciola said. "Earth's ionosphere blocks them," he said. "That means we can't even see Earth's own radio emission from the ground, even though it's so close."
Detection of signals from exoplanets will require either a complex of satellites or an installation on the far side of the moon. "That would be a nice, quiet place to make an array that won't be limited by Earth's ionosphere and atmosphere," Sciola said.
He said the observer's position in relation to the exoplanet is also important. "The emission is 'beamed,'" Sciola said. "It's like a lighthouse: You can see the light if you are in line with the beam, but not if you are directly above the lighthouse. So having a better understanding of the expected angle of the signal will help observers determine if they are in line to observe it for a particular exoplanet."
Modern navigational systems that use radio-wave signals reflecting from or propagating through the ionosphere as a means of determining range, or distance, are vulnerable to a variety of effects that can degrade performance. In particular, systems such as the GNSS , that use constellations of earth-orbiting satellites, are affected by space weather phenomena. See Space Weather Effects on GPS. For a map of GNSS receivers see the Canadian Active Control System of Natural Resources Canada.
If the electron density along a signal path from a satellite to a receiver changes very rapidly, as a result of space weather disturbances, the resulting rapid change in the phase of the radio wave may cause difficulties for the GPS receiver, in the form of loss of lock. Temporary loss of lock results in cycle slip, a discontinuity in the phase of the signal. Very rapid variations (less than about 15 seconds) in the signal's strength and phase are known as ionospheric scintillations. Scintillations can be particularly troublesome for receivers that are making carrier-phase measurements and may result in inaccurate or no position information.
Natural Resources Canada collaborates with the CHAIN of the University of New Brunswick to collect information on GNSS scintillations. See the CHAIN Real-time Scintillation Map for current scintillation information. For more information please contact Dr. David Boteler.
- Computational Mechanics
- Condensed Matter Physics
- Mechanics of Materials
- Physics and Astronomy(all)
- Fluid Flow and Transfer Processes
In: Physics of Fluids B , Vol. 4, No. 4, 1992, p. 1012-1016.
Research output : Contribution to journal › Article › peer-review
T1 - Criteria for excitation of parametric instability in the ionosphere by an obliquely incident high-frequency heater
N2 - Parametric excitation of lower-hybrid decay mode together with upper-hybrid sideband in the ionosphere by an obliquely incident high-frequency pump is studied. The conditions for the instability, including the frequency range, the elevation angle, and the threshold field intensity of the pump are determined.
AB - Parametric excitation of lower-hybrid decay mode together with upper-hybrid sideband in the ionosphere by an obliquely incident high-frequency pump is studied. The conditions for the instability, including the frequency range, the elevation angle, and the threshold field intensity of the pump are determined.
Revolutions in understanding the ionosphere, Earth's interface to space
The ionosphere is a layer of charged particles in Earth's atmosphere that extends from about 50 to 360 miles above the surface of Earth. Processes in the ionosphere also create bright swaths of color in the sky, known as airglow. Credit: NASA
Scientists from NASA and three universities have presented new discoveries about the way heat and energy move and manifest in the ionosphere, a region of Earth's atmosphere that reacts to changes from both space above and Earth below.
Far above Earth's surface, within the tenuous upper atmosphere, is a sea of particles that have been split into positive and negative ions by the sun's harsh ultraviolet radiation. Called the ionosphere, this is Earth's interface to space, the area where Earth's neutral atmosphere and terrestrial weather give way to the space environment that dominates most of the rest of the universe - an environment that hosts charged particles and a complex system of electric and magnetic fields. The ionosphere is both shaped by waves from the atmosphere below and uniquely responsive to the changing conditions in space, conveying such space weather into observable, Earth-effective phenomena - creating the aurora, disrupting communications signals, and sometimes causing satellite problems.
Many of these effects are not well-understood, leaving the ionosphere, for the most part, a region of mystery. Scientists from NASA's Goddard Space Flight Center in Greenbelt, Maryland, the Catholic University of America in Washington, D.C., the University of Colorado Boulder, and the University of California, Berkeley, presented new results on the ionosphere at the fall meeting of the American Geophysical Union on Dec. 14, 2016, in San Francisco.
One researcher explained how the interaction between the ionosphere and another layer in the atmosphere, the thermosphere, counteract heating in the thermosphere - heating that leads to expansion of the upper atmosphere, which can cause premature orbital decay. Another researcher described how energy outside the ionosphere accumulates until it discharges - not unlike lightning - offering an explanation for how energy from space weather crosses over into the ionosphere. A third scientist discussed two upcoming NASA missions that will provide key observations of this region, helping us better understand how the ionosphere reacts both to space weather and to terrestrial weather.
Changes in the ionosphere are primarily driven by the sun's activity. Though it may appear unchanging to us on the ground, our sun is, in fact, a very dynamic, active star. Watching the sun in ultraviolet wavelengths of light from space - above our UV light-blocking atmosphere - reveals constant activity, including bursts of light, particles, and magnetic fields.
Occasionally, the sun releases huge clouds of particles and magnetic fields that explode out from the sun at more than a million miles per hour. These are called coronal mass ejections, or CMEs. When a CME reaches Earth, its embedded magnetic fields can interact with Earth's natural magnetic field - called the magnetosphere - sometimes compressing it or even causing parts of it to realign.
It is this realignment that transfers energy into Earth's atmospheric system, by setting off a chain reaction of shifting electric and magnetic fields that can send the particles already trapped near Earth skittering in all directions. These particles can then create one of the most recognizable and awe-inspiring space weather events - the aurora, otherwise known as the Northern Lights.
But the transfer of energy into the atmosphere isn't always so innocuous. It can also heat the upper atmosphere - where low-Earth satellites orbit - causing it to expand like a hot-air balloon.
"This swelling means there's more stuff at higher altitudes than we would otherwise expect," said Delores Knipp, a space scientist at the University of Colorado Boulder. "That extra stuff can drag on satellites, disrupting their orbits and making them harder to track."
This phenomenon is called satellite drag. New research shows that this understanding of the upper atmosphere's response to solar storms - and the resulting satellite drag - may not always hold true.
"Our basic understanding has been that geomagnetic storms put energy into the Earth system, which leads to swelling of the thermosphere, which can pull satellites down into lower orbits," said Knipp, lead researcher on these new results. "But that isn't always the case."The swelling of Earth's upper atmosphere during geomagnetic storms can alter the orbits of satellites, bringing them lower and lower. Credit: NASA
Sometimes, the energy from solar storms can trigger a chemical reaction that produces a compound called nitric oxide in the upper atmosphere. Nitric oxide acts as a cooling agent at very high altitudes, promoting energy loss to space, so a significant increase in this compound can cause a phenomenon called overcooling.
"Overcooling causes the atmosphere to quickly shed energy from the geomagnetic storm much quicker than anticipated," said Knipp. "It's like the thermostat for the upper atmosphere got stuck on the 'cool' setting."
That quick loss of energy counteracts the previous expansion, causing the upper atmosphere to collapse back down - sometimes to an even smaller state than it started in, leaving satellites traveling through lower-density regions than anticipated.
A new analysis by Knipp and her team classifies the types of storms that are likely to lead to this overcooling and rapid upper atmosphere collapse. By comparing over a decade of measurements from Department of Defense satellites and NASA's Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics, or TIMED, mission, the researchers were able to spot patterns in energy moving throughout the upper atmosphere.
"Overcooling is most likely to happen when very fast and magnetically-organized ejecta from the sun rattle Earth's magnetic field," said Knipp. "Slow clouds or poorly-organized clouds just don't have the same effect."
This means that, counterintuitively, the most energetic solar storms are likely to provide a net cooling and shrinking effect on the upper atmosphere, rather than heating and expanding it as had been previously understood.
Competing with this cooling process is the heating that caused by solar storm energy making its way into Earth's atmosphere. Though scientists have known that solar wind energy eventually reaches the ionosphere, they have understood little about where, when and how this transfer takes place. New observations show that the process is localized and impulsive, and partly dependent on the state of the ionosphere itself.
Traditionally, scientists have thought that the way energy moves throughout Earth's magnetosphere and atmosphere is determined by the characteristics of the incoming particles and magnetic fields of the solar wind - for instance, a long, steady stream of solar particles would produce different effects than a faster, less consistent stream. However, new data shows that the way energy moves is much more closely tied to the mechanisms by which the magnetosphere and ionosphere are linked.
"The energy transfer process turns out to be very similar to the way lightning forms during a thunderstorm," said Bob Robinson, a space scientist at NASA Goddard and the Catholic University of America.
During a thunderstorm, a buildup of electric potential difference - called voltage - between a cloud and the ground leads to a sudden, violent discharge of that electric energy in the form of lightning. This discharge can only happen if there's an electrically conducting pathway between the cloud and the ground, called a leader.
Similarly, the solar wind striking the magnetosphere can build up a voltage difference between different regions of the ionosphere and the magnetosphere. Electric currents can form between these regions, creating the conducting pathway needed for that built-up electric energy to discharge into the ionosphere as a kind of lightning.
"Terrestrial lightning takes several milliseconds to occur, while this magnetosphere-ionosphere 'lightning' lasts for several hours - and the amount of energy transferred is hundreds to thousands of times greater," said Robinson, lead researcher on these new results. These results are based on data from the global Iridium satellite communications constellation.
Because solar storms enhance the electric currents that let this magnetosphere-ionosphere lightning take place, this type of energy transfer is much more likely when Earth's magnetic field is jostled by a solar event.
The huge energy transfer from this magnetosphere-ionosphere lightning is associated with heating of the ionosphere and upper atmosphere, as well as increased aurora.
Though scientists are making progress in understanding the key processes that drive changes in the ionosphere and, in turn, on Earth, there is still much to be understood. In 2017, NASA is launching two missions to investigate this dynamic region: the Ionospheric Connection Explorer, or ICON, and Global Observations of the Limb and Disk, or GOLD.
"The ionosphere doesn't only react to energy input by solar storms," said Scott England, a space scientist at the University of California, Berkeley, who works on both the ICON and GOLD missions. "Terrestrial weather, like hurricanes and wind patterns, can shape the atmosphere and ionosphere, changing how they react to space weather."
ICON will simultaneously measure the characteristics of charged particles in the ionosphere and neutral particles in the atmosphere - including those shaped by terrestrial weather - to understand how they interact. GOLD will take many of the same measurements, but from geostationary orbit, which gives a global view of how the ionosphere changes.
Both ICON and GOLD will take advantage of a phenomenon called airglow - the light emitted by gas that is excited or ionized by solar radiation - to study the ionosphere. By measuring the light from airglow, scientists can track the changing composition, density, and even temperature of particles in the ionosphere and neutral atmosphere.
ICON's position 350 miles above Earth will enable it to study the atmosphere in profile, giving scientists an unprecedented look at the state of the ionosphere at a range of altitudes. Meanwhile, GOLD's position 22,000 miles above Earth will give it the chance to track changes in the ionosphere as they move across the globe, similar to how a weather satellite tracks a storm.
"We will be using these two missions together to understand how dynamic weather systems are reflected in the upper atmosphere, and how these changes impact the ionosphere," said England.
Ephemeral ionospheric perturbations
X-rays: sudden ionospheric disturbances (SID)
When the Sun is active, strong solar flares can occur that hit the sunlit side of Earth with hard X-rays. The X-rays penetrate to the D-region, releasing electrons that rapidly increase absorption, causing a high frequency (3–30 MHz) radio blackout. During this time very low frequency (3–30 kHz) signals will be reflected by the D layer instead of the E layer, where the increased atmospheric density will usually increase the absorption of the wave and thus dampen it. As soon as the X-rays end, the sudden ionospheric disturbance (SID) or radio black-out ends as the electrons in the D-region recombine rapidly and signal strengths return to normal.
Protons: polar cap absorption (PCA)
Associated with solar flares is a release of high-energy protons. These particles can hit the Earth within 15 minutes to 2 hours of the solar flare. The protons spiral around and down the magnetic field lines of the Earth and penetrate into the atmosphere near the magnetic poles increasing the ionization of the D and E layers. PCA's typically last anywhere from about an hour to several days, with an average of around 24 to 36 hours. Coronal mass ejections can also release energetic protons that enhance D-region absorption in the polar regions.
A geomagnetic storm is a temporary intense disturbance of the Earth's magnetosphere.
- During a geomagnetic storm the F₂ layer will become unstable, fragment, and may even disappear completely.
- In the Northern and Southern pole regions of the Earth aurorae will be observable in the sky.
Lightning can cause ionospheric perturbations in the D-region in one of two ways. The first is through VLF (very low frequency) radio waves launched into the magnetosphere. These so-called "whistler" mode waves can interact with radiation belt particles and cause them to precipitate onto the ionosphere, adding ionization to the D-region. These disturbances are called "lightning-induced electron precipitation" (LEP) events.
Additional ionization can also occur from direct heating/ionization as a result of huge motions of charge in lightning strikes. These events are called early/fast.
In 1925, C. T. R. Wilson proposed a mechanism by which electrical discharge from lightning storms could propagate upwards from clouds to the ionosphere. Around the same time, Robert Watson-Watt, working at the Radio Research Station in Slough, UK, suggested that the ionospheric sporadic E layer (Es) appeared to be enhanced as a result of lightning but that more work was needed. In 2005, C. Davis and C. Johnson, working at the Rutherford Appleton Laboratory in Oxfordshire, UK, demonstrated that the Es layer was indeed enhanced as a result of lightning activity. Their subsequent research has focused on the mechanism by which this process can occur.
Software to analyse data from the MAVEN Particles and Fields package is available through the MAVEN Science Data Center (https://lasp.colorado.edu/maven/sdc/public/), and through the University of California at Berkeley’s Space Science Laboratory TPLOT package (http://sprg.ssl.berkeley.edu/data/maven/misc/socware/).
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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.
Radio Navigation (GPS)