Near-Real-Time HF Radio Propagation Data
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What The Data Means
Summary
This summary, courtesy of Paul Herrman at hamqsl.com, contains the basic data you need to know to understand what the bands are doing at the moment and why. The data in it is updated every three hours.
The most important number is the solar flux. This is a measure of the intensity of solar radiation at 2800 Mhz. Along with X-rays, this is the primary determinant of how heavily ionized the F2 layer is, and it is the layer of the ionosphere that gives us most of our DX on 20 meters and up. The higher the number, the greater the level of ionization is. The lowest number that is theoretically possible is 62.5, and it will typically be around 65 or so during a sunspot minimum. At a sunspot maximum, it can rise to the hundreds, depending on how strong the maximum is.
The SSN, or Smoothed Sunspot Number is the oldest and most widely watched indicator of how well the bands should be doing, but only because it correlates reasonably well with the solar flux index as well as actual observed propagation. Solar flux, however, is actually a better gauge of how radio conditions will be, and the 304a index is even better. The number shown here is the actual "measured" sunspot number from the Space Weather Prediction Center, vs. the "calculated" number that takes into account the difference in the radio flux data, and it is the calculated number that is most often seen (including the SSN seen on the MUF map to the left). A sunspot number of zero is common during or near sunspot minimums, but can rise to the hundreds at the peak of the 11-year cycle. The number does not indicate the actual number of sunspots present; the first digit is the number of sunspot groups, and the second and third (if present) indicate the "effective" number of sunspots - determined in part by how much of the sun's visible surface is occupied by sunspots.
The A and K indexes are measures of the level of instability in the geomagnetic field. That is the earth's magnetic field that shuttles charged particles (protons and electrons) from the solar wind toward the earth's magnetic poles, and air molecules that have been ionized by solar radiation, into the layers of the ionosphere that give us radio propagation. The primary indicator is the K index, which tells us what the magnetic field is doing currently, and the A index is a measure of how unstable the K index has been over the last day. When both are elevated, it means that the geomagnetic field is unstable, and that means signals are prone to sudden fades, and some paths may close while others open up abruptly and with little warning. An elevated K index, in the absence of an elevated A index, indicates a sudden, abrupt disturbance in the geomagnetic field, which can cause an intense but brief disruption in HF propagation. An index number of one or two means the field is stable, greater than five indicates a significant disturbance. The most violent disturbances in the K index are caused by ions in ejected coronal masses passing through the earth's magnetosphere, and causing it to rapidly and violently distort.
The intensity of the interplanetary geomagnetic field itself is shown as the number after the slant-bar on the K index line, and is shown in nanoteslas, a measure of the strength of magnetic fields. The higher the number, the more intense the interplanetary magnetic field, and the more influence it will have on propagation on earth. A typical background number is about 5 or so. When it is very high, and the Bz component, listed in the dials above, is strongly positive, protons from the sun are funneled onto the earth's ionosphere, enhancing propagation, and electrons are also funneled into the ionosphere, causing blackouts, as they cancel the ionization. Which predominates is a function of whether there is an abnormally large flux at the moment. You can keep an eye on the numbers in the chart to get a feel for what they are at background during the current part of the solar cycle.
The X-ray flux indicator of importance is the letter - it indicates the order of magnitude of the X-ray flux as detected at geosynchronous orbit where it is measured. There are five letters, proceeding from weakest "A" levels, rising by order of magnitude each, through B, C, M and X. "A" indicates a low, background level of X-rays at about 1/10 microwatt per square cm., rising to the most severe at about 1 milliwatt or more per square cm., during the strongest "X" class events. When a flare occurs, the letter in the summary box indicates the order of magnitude, and the number the scalar value within that order of magnitude.
X-ray flux is responsible for some F2 but mostly D-layer ionization, the latter causing higher absorption towards the lower part of the HF spectrum (160m through about 30m). If a flare is severe enough, the D-layer absorption will become so severe that HF propagation can completely disappear for a time. So, in effect, the "solar flux" number and the "X-ray index" are duking it out to affect propagation - the former brings better conditions when the number is higher, and the latter means weaker signals when it is higher, though a modestly elevated level can enhance F2-layer ionization, resulting in improved conditions on the higher bands at the expense of propagation on the lower bands.
The 304A Index is the relative strength of total solar radiation at a wavelength of 304 angstroms, emitted primarily by ionized helium in the sun's photosphere. This index is of importance to hams, because it is radiation in this frequency band that is responsible for about half of all the ionization of the F2 layer, the ionosphere layer of greatest significance to us (the other half is due to solar wind electrons and protons, and X-ray radiation in about equal measure. The solar wind proton and electron inflow is how F2 propagation on the upper bands - 20m-10m - may remain open at night on occasion). This index is taken from the observations of the SOHO, the orbiting Solar Heliospheric Observatory. Watching this number and observing the trend will tell you whether the upper frequency band conditions - mostly 30m through 10m - will be improving or degrading, particularly during daylight hours. The time given is the time (in GMT) at which the measurement was made, and it is updated frequently because such things as solar flares and coronal mass ejections can affect the number.
Proton and Electron Fluxes are indexes of the density of charged particles in the solar wind. The higher the numbers, the more the solar wind is affecting the ionosphere. The numbers are an "order of magnitude" number, with the number on the right side of the "+" or "-" mark indicating the order of magnitude, and it refers to the number of particles in each cubic centimeter of space near the satellite.
The effects of proton and electron flux are somewhat complex, depending on a lot of parameters, but in a nutshell it is this: low levels of protons, when the magnetic field is quiet, help "charge up" the ionosphere, improving band conditions, especially on 160m through 40m at night, where these protons are the primary source for ionization of the E-layer that supports night-time propagation on those bands. But too many (more than roughly 1.00+01 on the chart) can lead to unstable F2-layer band conditions, particularly over the poles, where a "polar cap absorption" event may occur as a result of the earth's magnetic field lines funneling large numbers of solar protons onto the polar regions. Coronal mass ejections will accelerate large numbers of protons well ahead of the coronal mass itself, and these can arrive at earth within hours of the flare's occurence. When this happens, a polar cap absorption event will almost surely take place, leading to a "watery" sound in SSB signals propagating via polar paths, particularly those on the sunlit side, going through the auroral zones. Lower frequency bands, especially 80m. and 40m., experience higher noise levels, particularly as the coronal mass is passing earth.
After the proton event, and the passage of the coronal mass itself (which will cause wildly fluctuating magnetic field numbers and very unstable band conditions), the next wave is the electrons, which may last for many hours up to several days. When the electron flux rises high enough (greater than about 1.00+03 on the chart), and the Bz component is strongly negative at the same time, the solar electrons tend to replace protons and other ions in the ionosphere and lead to improved, if rather strange band conditions. Under these conditions, in which the "F3 layer" is said to be ionized, 10m through 30m can open to the entire sunlit half of the world and remain open for several hours after sunset (with 30m and 20m remaining open throughout the night), and with north-south (transequatorial) paths particularly strong, but at the same time, 40m through 80m will experience weak signals with rapid and deep QSB, and a lot of "frying pan" noise - as much as S6 or more. 6m and 10m Transequatorial openings frequently occur under these conditions as a result of the F3 layer ionization. These conditions are often accompanied by polar cap absorption events if the electron flux is high enough. These "electron storms" often follow in the wake of coronal mass ejections, so watch the space weather news for information about recent coronal mass ejections that may cause these unusual conditions several days after the ejection event, and then begin watching for this electron flux number to rise. When it does, start checking the bands for these unusual conditions. You may be the only person on the wide-open band working some rare DX!
The Bz Component is the strength and direction of the interplanetary magnetic field. It is determined by solar conditions, and will vary between positive (same direction as the earth's magnetic field), and negative (opposite magnetic polarity). When it is strongly negative, the earth's magnetic field tends to be cancelled out, at the same time that the field lines are strongly connected to the interplanetary field, which helps solar particles bombard the earth's ionosphere. This is the same parameter seen in the Solar Wind Dials. See "Solar Wind Dials" below for a more complete description.
The Solar Wind number is the speed, in kilometers per second, of the charged particles in the solar wind as they blow pass earth. The higher the speed, the greater the pressure is exerted on the ionosphere by the solar wind, and if solar wind pressure is high enough, the ionosphere is "blown away," resulting in fadeouts or blackouts, especially on the higher frequency bands during the day. At night, propagation on the 80 and 60 meter bands may actually be enhanced. This is the same parameter metered in the Solar Wind Dials. See "Solar Wind Dials" below for a more complete discussion.
Band Conditions are self explanatory, except for the bottom of the VHF box; it shows the current Maximum Usable Frequency on VHF due to sporadic E if there are currently sporadic E openings. The bottom bar graph, labeled MS, shows whether meteor scatter activity is present, and if so, when and how strong it will likely be.
Aurora indicates how strong the ionization is in the polar F2 regions is at the moment, and therefore how disturbed HF paths across the polar regions are likely to be. The higher the letter, the more disturbed and actively changing the auroral rings are; the N= number shows how intensively ionized it was at the moment the measurement was taken. When shown in red, the N= number indicates that auroral region absorption is currently taking place because of the intensity of the ionization. If extremely ionized, propagation via E-layer skip, with considerable noise and distortion, is often possible on 6 meters and occasionally even 2 meters by bouncing signals off of the auroral curtains that may be present. This often occurs during the aurora borealis displays at high latitudes a few days after solar flares occur. Otherwise, a high auroral number indicates a "polar cap absorption" event is likely to ocurr, leading to a watery-sounding distortion of SSB signals, a tonal amplitude modulation of AM and CW signals.
Geomagnetic Field describes how quiet the earth's magnetic field is at the moment, and how much a change in it is likely to affect propagation. When it says "active" or "highly active," "Min Storm," or "Maj Storm," QSB can be long and deep, and HF blackouts may occur suddenly and without warning.
Sig Noise Level indicates how much noise (in S-units) is being generated by interaction between the solar wind and the ionosphere. A more active and disturbed solar wind, the greater the noise.
Solar Wind Data
There are three dials on this graphic. The first shows the Magnetic Field Bz Component. This is the polarity and intensity of the solar magnetic field as it interacts with the geomagnetic field here on earth. If the Bz component is positive, the sun's magnetic north pole dominates, and it is the same polarity as the earth's, enhancing the effects on the ionosphere of the earth's magnetic field. The stronger, the better for propagation. If the Bz component is negative, the interplanetary magnetic field is of the opposite polarity of the earth's field, and they tend to cancel each other out, leading to unstable conditions. An intensely negative Bz component can actually cancel out the earth's magnetic field, leading to severe disruptions of radio propagation for extended periods. When the Bz component transits between polarities, as often happens, this is called a "boundary crossing," and is often associated with a brief propagation blackout, lasting from a few seconds to a few minutes. When the bands come back, the pattern of regions to which the bands are then open is often considerably different.
The second dial is the solar wind speed. It is a measure of how fast, in kilometers per second, that the ions in the solar wind are actually moving through space. Along with the proton and electron flux, it makes up the solar wind pressure. The higher the dynamic pressure, the greater the effect the solar wind and the interplanetary magenetic field have on the ionosphere.
Dynamic pressure is the final dial, and it is essentially how hard the ions in the solar wind are pushing against the earth's atmosphere. Wind speed times ion density is how hard the solar wind is pusing against the earth's ionosphere, distorting it and adding ion flux (or neutralizing ions) in the ionosphere. Higher numbers mean more unstable conditions, and the value can rise quite high during the passage of a coronal hole across the earth-effective region of the sun. When this happens, the dynamic pressure can rise dramatically as the "proton storm" bombards the ionosphere.
Auroral Maps
The north auroral map shows the area that is affected by auroral ionization over the arctic at the moment. The more intensely orange the color, the deeper the ionization. Signals that travel through this region are subjected to phase distortion and very rapid selective fading, often giving a single-sideband signal a characteristic "watery" sound. As ionization becomes more intense, particularly after a coronal mass ejection, auroral curtains ("northern lights") can occur and radio signals can be literally bounced off the curtains, though the effects noted above can become extreme, making SSB signals unusable, PSK signals very error-prone, and giving CW signals their own modulation. The same occurs in the southern hemisphere, and the southern map will#show the aurora over the antarctic. When the two maps show auroral rings that are significantly different in shape and intensity, it is usually a signal that a significant geomagnetic storm is in progress, or has just happened, leading to difficult propagation conditions on HF. This is usually the result of a solar flare, which can be confirmed as a sharp spike on the X-ray flux graph.
One needs to understand that these maps do not represent actual measured data. The actual images displayed are one of a library of ten images each, and the one currently displayed is the one most closely representing the observed satellite data during the last satellite pass over the polar region. Often auroral bands and rings can appear in regions which are not represented in these images, so they should be considered only a very rough guide to likely (or possible) locations and intensity for the development or auroral curtains. Measured data show that auroral bands often occur at latitudes considerably lower than those indicated on these maps.
193 Angstrom, Magnetogram and STEREO Behind
The 193 angstrom UV (top of three) shows the earth-facing side of the sun as it appears in light at a wavelength of 193 angstroms in the extreme ultraviolet. Sunspots appear as bright, almost white areas, and the brighter, larger and more numerous they are, the more likely to be radiating brightly in the 304 angstrom wavelength that is of such importance to us, as it is responsible for more than half of the ionization of the F2 layer, improving band conditions. Equally important are the large splotchy dark or black areas. These indicate coronal holes, and when they appear near the center of the image, they allow high-speed protons and electrons from the sun's surface to bombard the earth directly, causing geomagnetic storms. As this happens, either band conditions are enhanced or degraded, but they are always made unstable. The darker and larger the area, the greater the effect.
The Longitudinal Magnetogram image, in the center, courtesy NASA's SOHO satellite, shows the magnetic fields associated with active regions on the sun's surface (this image is taken of the photosphere). What is of interest here is the size and intensity of magnetic fields as well as their direction. White indicates north magnetic poles (where solar plasma, following the field lines, is rising up from the sun's surface), and black is south magnetic poles (where plasma is falling back into the sun). For Cycle 24 sunspots, the north pole is on the left and the south pole is on the right in the northern hemisphere, and the reverse in the southern. The opposite is true for the old Cycle 23 sunspots, and this pattern reverses itself with each 11-year average solar cycle (so the solar magnetic cycle is really a 22-year cycle). The more intense the magnetic fields associated with sunspots are, the greater the potential for sizeable coronal mass ejections, which can cause magnetic storms and disrupt the ionosphere, causing blackouts, when they occur. When the magnetic polar regions within a given active area drift apart, the magnetic field lines are stretched and can even break, flinging any plasma (coronal mass) that is trapped in them, out into space. That is how "coronal mass ejections" occur. In addition, the unconnected magnetic field lines, extending out into space, can sweep across the earth, causing a brief but intense magnetic storm.
The STEREO behind image shows the sunspots that are about to rotate into view. This image, taken from NASA's STEREO spacecraft which is lags roughly 70 degrees behind earth in earth's orbit around the sun, is shot in extreme ultraviolet (195 angstroms) and shows all active regions, including both sunspots and not-yet-erupted-sunspot active regions that are not yet visible from our position on earth. The features along the right-hand edge of this image are visible from earth, and appear just left of center in the two images above, but the left hand portion of this image is the part that has yet to rotate into our view. Watch the left-hand side of this image to learn if there are new sunspots that will soon rotate into view to provide us with improved band conditions in the next week or two, and when they finally appear along the left hand side of the 304 angstrom image at the top, you can ascertain how much effect, if any, they will actually have on radio propagation.
Coronal holes are also visible on this image, in the form of large dark patches. When these rotate into an earth-effective area, the solar wind speed picks up dramatically, causing proton storms that can cause HF radio blackouts for minutes to hours at a time, with signals coming and going. On this view of the sun, a coronal hole in an earth-effective area will appear on the right-hand edge of the image, at about the 3 o'clock position. In the center and to the left, it means a period of HF radio instability will occur when these areas rotate into an earth-effective position in the next few days.
GOES X-ray Flux Data
The two traces in this graph show what the sun's output of X-rays has been over the last three days, in two different wavelength bands, as measured at the two different GOES earth-observation satellites. Numbers on the left-hand side of the graph, chart the power level detected at the satellites, and the letters on the right indicate the order of magnitude as given in the summary. "A" is the lowest at about 1/10th microwatt per square cm, and "X" is the strongest, at 1 milliwatt per square cm. The blue graph is "soft" X-rays that are mostly responsible for fadeouts and D-layer absorption. It is the most volatile, rising further during solar flares. The "hard" X-rays shown on the red graph have an enhancing effect on F2 layer ionization, and can enhance propagation conditions, but too much can cause D-layer blackouts by over-ionizing that layer. A generally rising level of hard X-rays generally mean improving conditions except during flares.
SOHO/celias/SEM Plot
This plot records the last three days of solar radiation in wavelength bands that are of critical importance to hams, as detected by the Celias/SEM sensor on the SOHO spacecraft.
The upper graph, with the ragged red plot, is by far the most important. It shows the whole-disk radiation from the sun of the radiation in the 304 angstrom band. This radiation is emitted by helium atoms in the sun's atmosphere that have been stripped of both of their electrons. This radiation is responsible for about half of all the ionization of the F2 layer of our ionosphere, and that is why it is important
Observations by hams indicate that the trend on the upper chart seem to predict conditions three or four days ahead, so if the trend on this chart is up, it indicates improving band conditions over the next few days, and conversely, a falling trend line indicates band conditions will be deteriorating. The blue line on the lower graph shows the radiation level in the entire band of 1-500 angstroms, and this wavelength band is of some, but lesser, importance. Jagged upward jumps indicate radiation from flares, and an upward jump at the end of the graph means that a flare is in progress, and may lead to a blackout on HF due to D-layer absorption caused by a jump in X-ray radiation.
Calculated Maximum Usable Frequency
This map shows the current maximum usable frequency, as calculated by Solar Terrestrial Dispatch. To use this map, you will need to find the midpoint for any path under 3,000 Km., and for paths greater than 3,000 km (multi-hop), the midpoint for each hop. Look at the nearest MUF curve for each midpoint, and the lowest number will be the maximum usable frequency. Occasionally, hops as much as 4,000 Km. are possible; when this is the case, multiply the values on the map by 1.1 to calculate the MUF for that situation. The green bands in the polar region are the auroral bands, and paths that go through them will be subject to auroral flutter (rapid selective fading, creating a "watery" effect). The optimum frequency to use is normally roughly 1/2 (nightside) to 2/3 (dayside) the maximum usable frequency, depending on current D-region absorption (when X-ray flux is up, the optimum frequency will trend higher). The bands between the grey lines are the "grey line region" where worldwide propagation is often possible on lower frequencies, because of reduced D-layer attenuation. When it is positioned over the midpoint of a given path, propagation may be possible as low as 3 Mhz.
© 2008, Scott Bidstrup, all rights reserved. Todos derechos reservados.