Proton Fluence:This term is seldom be referenced within solar reports. Proton fluence is the total proton particle flux measured by the GOES spacecraft at geosynchronous altitudes for protons of energies >1 Million electron Volts (MeV), >10 MeV and >100 MeV.The higher the proton fluence, the more intense proton bombardments are. It can be used to estimate the approximate amount of ionization occurring in the upper atmosphere, as well as the proton penetration level into the atmosphere, and possible satellite anomalies (caused by the solar proton bombardments). Fluence for particles are given in the units: particles cm-2 steradian-1 day-1. Electron Fluence:This term will seldom be referenced within solar reports. It is analagous to "proton fluence" but is measured for electrons with energies >2 MeV. Electron Fluence measurements are the same as those for proton fluence.Magnetic A-IndexThe geomagnetic A-Index represents the severity of magnetic fluctuations occurring at local magnetic observatories. During magnetic storms, the A-index may reach levels as high as 100. During severe storms, the A-index may exceed 200. Great "rogue" storms may succeed in producing index values in excess of 300, although storms associated with indices this high are very rare indeed.The A-index varies from observatory to observatory, since magnetic fluctuations can be very local in nature. The A-index for Boulder Colorado (the same value reported on WWV and WWVH) will be the one referenced most often within the reports. Occasionally, the A-index for higher latitude stations may also be referenced for purposes of comparison. Magnetic fluctuations monitored locally here at Solar Terrestrial Dispatch will also be referenced, particularly during storm periods for descriptive purposes. Magnetic K-IndexThe geomagnetic K-Index is related to the A-index. K-indices are scaled by comparing the H and D magnetometer traces (representing the horizontal and declination magnetic components) to assumed "quiet-day curves" for H and D. Each UT day is divided into 8 three-hour intervals, starting at 0000 UT.In each 3-hour period, the maximum deviation from the quiet day curve is measured for both (H and D) traces, and the largest deviation (the most disturbed trace) is selected. It is then input into a quasi-logarithmic transfer function to yield the K-index for the period. The K-index ranges from 0 to 9 and is a dimensionless number. It is assigned to the end of the 3 hour period. The K-Index is useful in determining the state of the geomagnetic field, the quality of radio signal propagation and the condition of the ionosphere. Generally, K index values of 0 and 1 represent Quiet magnetic conditions and imply good radio signal propagation conditions. Values between 2 and 4 represent Unsettled to Active magnetic conditions and generally correspond to less-impressive radio propagation conditions. K-index values of 5 represent Minor Storm conditions and are usually associated with Fair to Poor propagation on many HF paths. K-index values of 6 generally represent Major Storm conditions and are almost always associated with Poor radio propagation conditions. K-index values of 7 represent Severe Storm conditions and are often accompanied by "radio blackout" conditions (particularly over higher latitudes). K-indices of 8 or 9 represent Very Severe Storm conditions and are rarely encountered (except during exceptional periods of solar activity). K-indices this high most often produce radio blackouts for periods lasting in excess of 6 to 10 hours (depending upon the intensity of the event). Sudden Storm Commencement or 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 each other. Sudden Impulse or SIA 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.Satellite Proton EventProton 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. They are also often followed by a PCA event (see below). Polar Cap Absorption Event or PCAA 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. |