Solar Wind Dials/SIDC Space Weather Forecast - - - North Pole Auroral Status - - - Current D-Layer Absorption Anomaly
	Summary	193 angstrom, HMI Magnetogram, STEREO Behind	304 angstrom, 335 angstrom, Latest Coronagraph	SWPC Analysis, Forecast,, SOHO 304a, Extreme X-ray Trends

What The Data Means

These maps, courtesy Rick Suarez, LU9DA, show current DX cluster results for each band. You can scroll to position the band for the map of your current interest to show real-time spots within the last hour, and the maps will refresh each ten minutes.

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. This parameter is widely watched, mostly for historical reasons - before the launch of satellites that could measure X-ray and extreme UV radiation from the sun directly, this parameter was used as a proxy for those parameters which affect ionization of the F2 layer. It is a good proxy at solar minima, but during periods of intensive solar activity, the correlation breaks down, and at solar maxima, it is more or less useless. A far better gauge is the X-ray flux and 304 angstrom UV flux, which are the direct cause of the ionization. See below.

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. Watching the trend of the K index can be useful. As the K index increases, E-layer ionization often increases, leading to openings in the VHF bands. Conversely, D-layer absorption also increases, leading to weaker signals on the HF bands, particularly the lower ones. Ionization in the F region usually decreases at mid-latitudes, leading to weaker signals at mid and high latitudes, but often increases in the tropical regions at the same time, leading to better signals across the tropics. So as you see the K index rise significantly, aim your VHF antennas towards the polar regions and your HF antennas towards tropical paths.

While the K index is a measure of how much the geomagnetic field has been changing over the last three hours, the current 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.

What to watch for is when the X-ray flux is above the "A" magnitude, the D-layer absorption will increase noticeably, exceeding the usual 10 Mhz. limit, and extending into the 14 Mhz. band or beyond, causing a reduction in signal strength on those bands. If this is made up for in a high 304A number - more than about 130 (see below) - the two will cancel out. But if both are weak together or strong together, band conditions will be poor (though the latter increases the chances of an F2 opening on six meters). If both are exceedingly weak, band conditions on 160m. will be improved at night, but otherwise band conditions will be poor. Band conditions tend to be best when the 304a number is up (above 130), and the X-ray flux is down (in the "A" magnitude).

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. There are two running indexes available for this parameter, one measured by the new Solar Dynamics Observatory, using the EVE instrument, and the other, using data from the older SOHO satellite, using it's SEM instrument. This one is from the SDO's EVE instrument, and the index number here is roughly 1.62 times that of the index on the plot to the right, which comes from SOHO's SEM instrument. I use the EVE index here, rather than the SEM used by the plot to the right, because it is more sensitive to changes and the data is more consistently available, but if you want to watch trends, the chart to the right will serve to show the current trend for the last two days.

This index is of considerable importance to hams, because it is solar 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 together in about equal measure. The solar wind proton and electron inflow is how F2 propagation can remain open at night). Watching this number and observing the trend along with the X-ray flux number in the plot to the right will tell you whether the upper frequency band conditions - mostly 30m through 10m - will be improving or degrading over the next few hours. The minimum for the 304a EVE indext (at solar minimum) is around 150 or so, and the maximum for this index (at solar maximum) will probably end up around 300 (SDO has not yet experienced a solar maximum). If a time is given, it is the time (in GMT) at which the measurement was made - this index is updated frequently because such things as solar flares and coronal mass ejections can affect the number dramatically over short periods. This is a better index to watch, especially at high sunspot numbers, than the older Solar Flux Index everyone has grown accustomed to watching. That is because the old SFI (which measures solar microwave radiation at 2800 Mhz.) was used for many years to serve as a proxy for this parameter, because in the old days before satellites it was not possible to observe this wavelength directly from the surface of the earth. The problem with watching SFI is that the correlation between it and the 304a radiation falls apart at SFI numbers above about 110.

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 (and to a lesser extent, the F2 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., will 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 activity, 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/Forecast

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.

Below these dials is a crawl showing the forecast for the next 24 hours, courtesy the Solar Influences Data Center (SIDC) in Belgium, at http://www.sidc.be/. This crawl forecasts the 10cm. flux, whether solar proton events are expected, the predicted planetary A-index, and whether geomagnetic storms or solar flares are expected during the forecast period. (see summary section for explanation of these data).

Auroral Map

The 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.

One needs to understand that these maps do not represent actual measured data, which is not currently being measured with sufficient resolution to produce a map like this in real time. The actual images displayed are one of a library of ten images, 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.

Current D-Layer Absorption Levels

To view map and read legends, right click on the map and select View Image. It will then be presented on your browser in full size. To return, click your browser's "back" button.

This map, courtesy NOAA's Space Weather Prediction Center, shows the current D-layer absorption anomaly, worldwide. It is important to remember, when using this map, to understand that it is only the current anomaly - how much the current absorption level departs from normal background levels - in other words, how much worse it is than normal. A colored spot in the tropical blue spot indicates that a solar flare is occurring, which may be disrupting communications, and the color indicates the highest frequency affected. The bar chart on the right indicates how much more absorption is present than normal in the affected regions, listed by frequency. When these colors occur in the polar region, it means that the poles are being bombarded by solar protons, which is usually caused by a geomagnetic storm, itself caused by the passage of a coronal hole, which sends high-speed particles earthward. If a disruption is occurring, the blue area at the bottom of the box will indicate when the Space Weather Prediction Center anticipates a return to normal conditions.

Keep in mind that the attenuation anomalies shown on this map are actually for only one trip through the D-layer, and the path taken on that one trip is assumed to be vertical. So actual attenuation will be more than the indicated value; at minimum, twice the indicated value if the path is vertical (straight up and then back down again), and much more than that if the take-off angle is near horizontal (because the signal spends much, much more time getting absorbed while passing through the D-layer to get to the E or F2 layer where it is going to be bent back to earth, and then the same coming back down on the far end). For this reason, the indicated attenuation should be considered only an index, not the true value. If you wish, you can calculate the true path attenuation anomaly from this chart (which can be calculated roughly by dividing the indicated attenuation value by the sine of your takeoff angle, and multiplying the result by two).

193 Angstrom, Magnetogram and STEREO Behind

The 193 angstrom UV courtesy NASA/Solar Dynamics Observatory's Atmospheric Imaging Assemply team (top image 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 HMI Longitudinal Magnetogram image, in the center, courtesy of NASA/SDO and the Helioseismic and Magnetic Imager science team, shows the magnetic fields associated with active regions on the sun's surface. 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 (white and black) 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.

304 Angstrom, 335 Angstrom and Coronagraph Movie

The 304 Angstrom image is the current NASA/Solar Dynamics Observatory image of the sun, taken in the light of doubly-ionized helium by the AIA science team. Since this wavelength of ultraviolet light accounts for about half of all ionization of the F2 layer of the ionosphere, bright features on this image will inform as to what is currently accounting for good conditions when they occur, and lack of bright spots account for correspondingly poor band conditions. If the 304 number in the summary to the left is elevated, but no bright white features are apparent on this image, it means band conditions should be stable and good for several days hence. Conversely, if the 304 number is elevated, but the white bright spots are numerous, band conditions will likely deteriorate when the active regions rotate out of view.

The 335 Angstrom image is the current NASA/SDO-AIA image in ultraviolet light emitted by many-times ionized iron atoms. This image is particularly well suited for seeing active regions in the lower solar corona that are likely to erupt into solar flares. Bright spots in this image can be watched over time to see if they are slowly brightening, and if so, a solar flare can be expected from such a region.

The coronagraph movie used here is produced by a consortium of the Naval Research Laboratory (USA), Max-Planck-Institut fuer Aeronomie (Germany), Laboratoire d'Astronomie (France), and the University of Birmingham (UK). SOHO is a project of international cooperation between ESA and NASA. This coronagraph movie can show you loops of plasma that may be streaming towards the earth, as imaged every few minutes for the last three days from the SOHO satellite. Note that when the ONR is not in communication with the satellite, this movie will not be updated. When you hear about a solar flare or coronal mass ejection, or see evidence of a large one in the X-ray plot to the right, check this image for a brief movie showing the event. Large flashes of light surrounding the solar disk or a large part of it, rapidly expanding in size, indicate a coronal mass ejection, likely headed towards earth, with propagation-disrupting effects expected in a day or two. Note that this coronagraph image is reversed from the other solar images, both left to right and top to bottom. Solar east is on the right side, and the north solar pole is at the bottom. So solar flares that appear on the right side are from areas rotating into view, and on the left, are rotating away from view, opposite of the other solar images on this page. You can see the image in larger size, by right clicking on the image, and then zooming in on the image that results. You can then return to this page by clicking your browser's "back" button.

SWPC Geomagnetic Analysis/Forecast

This analysis and forecast of the geomagnetic field is courtesy the U.S. NOAA's Space Weather Prediction Center. It is more detailed that the SIDC forecast, and is therefore more useful for determining the conditions that are predicted to exist for the three days following the date of issue. The first portion is the analysis of the current state of the geomagnetic field, and the last portion is the forecast; scroll down to section IIB or beyond to get to the forecast.

SOHO/celias/SEM Plot - (304 Angstrom, Short Wavelength Irradiance Trends Plot)

This plot records the last 24 hours of solar radiation in wavelength bands that are of critical importance to hams, as detected by the Celias/SEM sensor on the SOHO spacecraft, and plotted by the University of Maryland. The usefulness of this plot is principally in noting trends - rising or falling.

The upper graph, with the ragged red plot, is the most important. It shows the whole-disk radiation from the sun of the ultraviolet radiation in the 304 angstrom wavelength band. This radiation is emitted by helium atoms in the sun's atmosphere that have been stripped of both of their electrons, and is the radiation is responsible for about half of all the ionization of the F2 layer of our ionosphere - and that is why it is so important.

Anecdotal observations by hams indicate that the trend on the upper chart seems to predict conditions three to four days ahead, so if the general trend on this chart is trending up, it indicates improving band conditions over the next few days, and conversely, a generally falling trend line indicates band conditions will be deteriorating. The blue line on the lower graph shows the aggregate irradiance level in the entire band of 1-500 angstroms (from X-rays through ultraviolet), and this wavelength band is of some, but lesser, importance to hams. If this line is trending down, but the 304a line is trending up, band conditions should be improving, and vice versa. Jagged upward jumps indicate radiation from flares, and an upward jump at the far right 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. That should be evident on the D-layer absorption map, above. High but quiet levels on this chart can mean enhanced band conditions in morning and late afternoon, but with generally poor conditions at high noon on mid-path locations.

© 2011, Scott Bidstrup, all rights reserved. Todos derechos reservados.