Terms and Definitions|
The aurora is a bright glow observed in the night sky, usually in the polar zone. For this reason some scientists call it a "polar aurora" (or "aurora polaris"). In northern latitudes it is known as the aurora borealis, which is named after the Roman goddess of the dawn, Aurora, and the Greek name for north wind, Boreas, since in Europe especially it often appears as a reddish glow on the northern horizon as if the sun were rising from an unusual direction. The aurora borealis is also called the northern lights since it is only visible in the North sky from the Northern Hemisphere. The aurora borealis most often occurs from September to October and from March to April. Its southern counterpart, aurora australis, has similar properties.
Auroras are now known to be caused by the collision of charged particles (e.g. electrons), found in the Sun's Solar wind, with atoms in the Earth's upper atmosphere (at altitudes above 80 km). These charged particles are typically energized to levels between 1 thousand and 15 thousand electronvolts and, as they collide with atoms of gases in the atmosphere, the atoms become energized. Shortly afterwards, the atoms emit their gained energy as light.
The sun has a magnetic field which the solar wind can carry throughout the solar system. This is called the Interplanetary Magnetic Field (IMF). Earth also has a magnetic field which forms a bubble around our planet. This is called the Magnetosphere. This bubble deflects the solar wind.
Earth's magnetic field comes into contact with the sun's magnetic field in a place called the magnetopause. Here is the catch. Earth's magnetic field points north. When the sun's magnetic field points south, also known as southward Bz.. it may cancel Earth's magnetic field at point of contact. When the Bz is south the 2 fields link up. This basically opens up a door that may allow energy from the solar wind to reach Earth's atmosphere.
More detailed information and illustrations found at .. http://www.spaceweather.com/glossary/imf.html
CCD Bakeout -
Sometimes solar images taken by the SOHO aircraft are unavailable due to whats called a CCD Bakeout. To fully understand what this is, click on the below link for a great explanation.
The layer of the Sun above the photosphere where the temperature begins to rise with height.
The layer of the Sun above the chromosphere which is hotter than the Sun's surface and where many solar events can be seen.
Coronal Hole -
A hole in the Sun's atmosphere, which show up as a dark area. Holes are associated with open magnetic field lines. High-speed solar winds originate in these holes.
Coronal Mass Ejection (CME) -
A coronal mass ejection (CME) is an ejection of material from the solar corona, observed with a white-light coronagraph.
The material consists of plasma consisting primarily of electrons and protons (in addition to small quantities of heavier elements such as helium, oxygen, and iron), plus the entrained coronal magnetic field. When the solar cloud reaches the Earth as an ICME (Interplanetary CME), it may disrupt the Earth's magnetosphere, compressing it on the dayside and extending the nightside tail. When the magnetosphere reconnects on the nightside, it creates trillions of watts of power which is directed back towards the Earth's upper atmosphere. This process can cause particularly strong aurora also known as the Northern Lights(in the Northern Hemisphere) and the Southern Lights(in the Southern Hemisphere). CME events, along with solar flares, can disrupt radio transmissions, cause power outages (blackouts), and cause damage to satellites and electrical transmission lines.
VIDEO ANIMATION OF A CME AND EARTH IMPACT (4 mb file)
A mass of gas that appears as dark lines suspended over the photosphere by magnetic fields.
Geomagnetic Storm -
When unusually strong surges of solar wind (charged particles from the Sun) hit the Earth. This effect causes variations in the magnetic field which surrounds the Earth. The result are visible aurora (Northern and Southern lights).
G5 - Extreme
G4 - Severe
G3 - Strong
G2 - Moderate
G1 - Minor
Detailed Geomagnetic Storm Class information and effects can be found here http://www.swpc.noaa.gov/NOAAscales/index.html#GeomagneticStorms
Interplanetary Magnetic Field (IMF) -
IMF stands for Interplanetary Magnetic Field. It is another name for the Sun's magnetic field.
The Sun's magnetic field is huge! It goes beyond any of the planets. The Sun's magnetic field got its name because of that. We call the Sun's magnetic field the Interplanetary Magnetic Field meaning it has all of the planets within it.
The magnetic field of the Sun is carried by the solar wind which comes out from the Sun. The solar wind and magnetic field are twisted into a spiral by the Sun's rotation.
Bright cloud-like features found around sunspots that represent regions of higher temperature and density within the chromosphere. Sometimes before an actual sunspot is visible, plage regions can be signs of a forming spot and can also have a magnetic signature.
The layer of the Sun above the convective zone where light is emitted.
Polar Cap Absorption Event (PCA) -
A PCA is almost always produced by an intense solar proton flare. PCAs are the result of copious quantities of high-energy solar protons penetrating the Earths atmosphere to levels of the order of 50 km, producing intense ionospheric ionization. The result is a complete (or near-complete) radio blackout over polar latitudes.
A typical PCA lasts from 1 to 5 days and can severely effect the propagation of radio signals near or through polar regions. In intense, long-lasting events, direct entry of the high-energy solar protons to the upper atmosphere can extend equatorward as far as about 50 degrees geomagnetic latitude. They occur almost coincident with satellite-level proton events, maximize in intensity within a few hours and then begin a slow decay that can last up to 10 days for intense events.
A PCA is often followed within 48 hours by a SSC and a subsequent Minor to Major geomagnetic storm about 3 to 8 hours later.
Radio Blackout -
Disturbances of the ionosphere caused by X-ray emissions from the Sun. When moderate to strong solar flares take place, certain frequency ranges in the HF spectrum may be degraded while a flare is in progress on the sunlit side of the earth.
Radio Blackout Class
R5 - Extreme
R4 - Severe
R3 - Strong
R2 - Moderate
R1 - Minor
Detailed Radio Blackout Class information and effects can be found here http://www.swpc.noaa.gov/NOAAscales/#RadioBlackouts
Satellite Proton Event -
Proton events are almost always associated with energetic solar activity such as major flares. They are periods of increased proton bombardments at satellite altitudes. They can affect satellite transmission/reception if intense enough and can cause other satellite anomalies.
Proton events may affect the ability of a HAM operator to establish contact with a satellite, and may affect the quality of television signals received by satellite (ie. cable tv may be affected). Satellite proton events occur within a few hours of a major proton flare.
Solar Activity Description -
Solar activity as seen in the Space Weather Prediction Center (SWPC) daily reports is described (also applicable on WWV and WWVH) according to the number of flares which occur during the day. Activity is basically classified as follows:
Very Low : X-ray events less than class C.
Low : C-class x-ray events.
Moderate : Isolated (one to 4) M-class x-ray events.
High : Several (5 or more) M-class x-ray events or isolated (1 to 4) M5 or greater x-ray events.
Very High : Several M5 or greater x-ray events.
Solar Cycle -
The solar cycle or Schwabe-Wolf cycle is the eleven-year cycle of solar activity of the sun.
At periods of highest activity, known as solar maximum or solar max, sunspots appear. Periods of lowest activity are known as solar minimum. The last solar maximum was in 2001. The solar cycle is not strictly 11 years; it has been as short as 9 years and as long as 14 years in recent years.
Solar Flare -
A solar flare is a violent explosion in the Sun's atmosphere with an energy equivalent to tens of millions of hydrogen bombs. Solar flares take place in the solar corona and chromosphere, heating plasma to tens of millions of kelvins and accelerating the resulting electrons, protons and heavier ions to near the speed of light. They produce electromagnetic radiation across the electromagnetic spectrum at all wavelengths from long-wave radio to the shortest wavelength Gamma rays. Most flares occur around sunspots, where intense magnetic fields emerge from the Sun's surface into the corona. The energy efficiency associated with solar flares may take several hours or even days to build up, but most flares take only a matter of minutes to release their energy.
Solar flares are classified as A, B, C, M or X according to the peak flux (in watts per square meter, W/m2) of 100 to 800 picometer X-rays near Earth, as measured on the GOES spacecraft. Each class has a peak flux ten times greater than the preceding one, with X class flares having a peak flux of order 10-4 W/m2. Within a class there is a linear scale from 1 to 9, so an X2 flare is twice as powerful as an X1 flare, and is four times more powerful than an M5 flare. The more powerful M and X class flares are often associated with a variety of effects on the near-Earth space environment. Although the GOES classification is commonly used to indicate the size of a flare, it is only one measure.
VIDEO OF SOLAR FLARE CAPTURED BY JAPANESE HINODE SPACECRAFT (2.9 mb file)
Solar Flux -
The 10.7 cm (2800 MHz) radio flux is the amount of solar noise (light) that is emitted by the sun at 10.7 cm wavelengths. The solar flux is measured and reported at approximately 1700 UT daily by the Penticton Radio Observatory in British Columbia, Canada. Values are not corrected for variations resulting from the eccentric orbit of the Earth around the Sun.
The solar flux is used as a basic indicator of solar activity. It can vary from values below 50 to values in excess of 300 (representing very low solar activity and high to very high solar activity respectively). Values in excess of 200 occur typical during the peak of the solar cycles.
The solar flux is closely related to the amount of ionization taking place at F2 layer heights (heights sensitive to long-distance radio communication). High solar flux values generally provide good ionization for long-distance communications at higher than normal frequencies. Low solar flux values can restrict the band of frequencies which are usable for long distance communications. The solar flux is measured in "solar flux units" (s.f.u.). One s.f.u. is equivalent to 10^-22 Wm^-2 Hz^-1.
Solar Radiation Storm -
A solar radiation storm happens when an explosion (CME) on the sun accelerates solar protons toward Earth. These protons stream past our planet where they are (mostly) deflected by Earth's protected magnetic field.
S5 - Extreme
S4 - Severe
S3 - Strong
S2 - Moderate
S1 - Minor
Detailed Radiation Storm Class information and effects can be found here http://www.swpc.noaa.gov/NOAAscales/index.html#SolarRadiationStorms
Solar Wind -
A solar wind is a stream of charged particles which are ejected from the upper atmosphere of the sun. It consists mostly of high-energy electrons and protons that are able to escape the sun's gravity in part because of the high temperature of the corona and the high kinetic energy particles gain through a process that is not well understood at this time.
Sudden Storm Commencement (SSC) -
An SSC is the magnetic signature of an interplanetary shockwave most often produced by solar flares. It is always a precursor to increased geomagnetic activity, most often followed within 3 to 8 hours by a Minor to Major geomagnetic storm. It appears on the H (horizontal) trace of magnetometers.
This phenomenon is detectable at almost all magnetic observatories world-wide within 4 minutes of eachother.
Sudden Impulse (SI) -
A sudden magnetic impulse is similar to an SSC. It represents a rapid momentary fluctuation of the geomagnetic field over a period of only a few minutes. It is generally associated with interplanetary shockwaves produced by energetic solar events and can (but need not always) be followed by increased geomagnetic activity.
A sunspot is a region on the Sun's surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. Although they are blindingly bright, at temperatures of roughly 5000 K, the contrast with the surrounding material at some 6000 K leaves them clearly visible as dark spots. Interestingly, if they were isolated from the surrounding photosphere they would be brighter than an electric arc.
Sunspot Magnetic Class -
The magnetic class of sunspots is important in determining how potentially volatile particular active regions may be. Sunspots are regularly observed using instruments capable of determining the magnetic polarity of sunspots and active regions. By also applying laws which have been formulated over the years, visual observations can also be used to establish the magnetic polarity and complexity of spot groups. There are basically 7 magnetic types of sunspots that are classified. They are described as follows:
A - Alpha (single polarity spot).
B - Beta (bipolar spot configuration).
G - Gamma (atypical mixture of polarities).
BG - Beta-Gamma (mixture of polarities in a dominantly bipolar configuration).
D - Delta (opposite polarity umbrae within single penumbra).
BD - Beta with a Delta configuration.
BGD - Beta-Gamma with a Delta configuration.
Example: A region labelled as having a magnetic classification of BG indicates that the sunspot region contains a mixture of magnetic polarities, but the dominant polarity of the group is bipolar. Potentially very powerful and potent regions are those which have classifications of BG, BD and BGD. As magnetic complexity increases, the ability of an active region to spawn major energetic events likewise increases.
Sunspot Number -
This term is basically self-explanatory. It represents the number of observed sunspots and sunspot groups on the solar surface. It is computed according to the Wolf Sunspot Number formula: R = k (10g + s), where 'g' is the number of sunspot groups (regions), s is the total number of individual spots in all the groups, and k is a scaling factor that corrects for seeing conditions at various observatories.
Sunspot number varies in phase with the solar flux. Sunspot numbers can vary between zero (for sunspot minimum periods) to values in excess of 350 or 400 (in the very active "solar max" period of the suns 11 year cycle). Solar flux is related to the sunspot number, since sunspots produce radio emissions at 10.7 cm wavelengths (as well as at other wavelengths).
Sweep Frequency Events (Type II, III, IV and V events) -
Energetic solar events often produce characteristic radio "bursts". These bursts are generated by solar material plunging through the solar corona. Type III and type V events are caused by particles being ejected from the solar environment at near relativistic speeds. Type II and IV events are caused by slower-moving solar material propagating outward at speeds varying between approximately 800 and 1600 kilometers per second. Type II and IV radio bursts are of particular importance.
These sweep frequency radio events are signatures of potentially dense solar material which has been ejected from the solar surface. If the region responsible for these events is well positioned, the expelled solar material may succeed in impacting with the Earth. Such an impact often causes an SSC followed by Minor to Major geomagnetic storm conditions and significantly degraded radio propagation conditions. It is therefore interesting to pay attention to events which cause Type II and/or IV radio sweep events, since they may indicate the potential for increased magnetic activity (and decreased propagation quality) within 48 hours. It should be noted, however, that predicting degraded terrestrial conditions is significantly more complex than simply observing whether the energetic event had an associated Type II or IV radio sweep. Flare position, proton spectra, flare size, event duration, event intensity and a host of other variables must be analyzed before a qualitative judgement can be made.
It should also be noted that sweep frequency radio events are capable of producing Short Wave Fades (SWFs) and Sudden Ionospheric Disturbances (SIDs). Depending on the severity of the event, the duration of SWFs and SIDs may last in excess of several hours with typical values being approximately 30 minutes. SWFs and SIDs cause absorption of radio signals (due to intense ionization) at frequencies up to and well in excess of 500 MHz. Microwave continuum bursts can affect frequencies up to 30 GHz. Frequencies in the HF region can be completely blacked out for a period of time during intense energetic events.
A tenflare is associated with optical and x-ray flares. Solar flares emit radiation over a very wide range of frequencies. One of the more significant frequencies observed is the 10.7 cm wavelength band (2695 MHz). When a solar flare erupts, "noise" from the flare is received over this very wide range of frequencies.
When the noise received on the 10.7 cm wavelength band surpasses 100% of the background noise level during a solar flare, a Tenflare is said to be in progress. The more intense solar flares are associated with tenflares. Almost all major flares are associated with tenflares.
Generally, the greater the intensity of the burst of noise observed at the 10.7 cm wavelength band, the more significant the flare is said to be. The duration of the tenflare can also be used to determine the severity of the flare.