Solar activity and HF/VHF propagation page


                                       Information about radio propagation on HF and VHF for Hams and SWL.

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                     Sunspot last 30 days                                         Energetic particles monitor                                  Estimated planetary K-index.
                                                                                                  Data from the last 2 weeks.
          Understanding HF Propagation VE2XIP PDF document.(694 kbyte)
          Understanding solar indices by Ian P., G3YWX PDF document.(538 kbyte)
          Fundamentals of Ionospheric Propagation.  Actual solar-terrestrial indices.  Actual solar-terrestrial indices.

 At 18 minutes past the hour, radio stations WWV and WWVH broadcast the latest solar flux number, the average planetary A-Index
 and the latest mid latitude K-Index. In addition, they broadcast a descriptive account of the condition of the geomagnetic field and a
 forecast for the next three hours. You should keep in mind that the A-Index is a description of what happened yesterday. Strictly
 speaking, the K-Index is valid only for mid latitudes.  Predicted Sunspot Numbers and Radio Flux for next 27 days.  Predicted Sunspot Numbers and Radio Flux for next years.  Recent Solar Indices of Observed Monthly Mean Values.
 VOACAP Online, propagation predictions.

        Pass solar cycles.

Digisonde Station List.
Ionogram from Havana city station..

          An ionogram is a display of the data produced by an ionosonde. It is a graph of the
          virtual height of the ionosphere plotted against frequency. Ionograms are often
          converted into electron density profiles. Data from ionograms may be used to measure
          changes in the Earth's ionosphere due to space weather events.


                                                                                         GOES Solar X-ray Flux.

                                   Click here to see the most recent image of the far side of the sun at

                                   Click here to see Sunspots Last 30 days.





                                                                 Solar X-Rays

                                                          Geomagnetic Field
   VHF Aurora      Status

144 MHz E-Skip  



                                                                                                K index.



                                                                                Current solar images.


                                    Solar Region Summary.



                                                                                Real time solar wind.                         



                                         Solar wind velocity.                                                     Solar wind density.


  Putting it all together

* Higher solar flux levels are generally good for HF
* High K and A indices are generally bad – result in absorption and breakdown of the F region.
* Solar Flux / K index / Solar wind speed and Bz will give you a real-time indication of what bands you should concentrate on.
* Bz going south(-) and an increased solar wind speed (450km/s+) are generally bad news for HF.
* If your signals follow a polar path that cuts through the auroral zone(s) and the K index is high you will have problems.
* Spring/Autumn/Winter are better than Summer as the ionosphere is cooler, denser and MUF is higher during the day. Ionic  composition is different in Winter too. But night time MUFs are higher in summer.
* The opposite is true in the southern hemisphere.
* Spring/Autumn good for trans-equatorial contacts.
* As the sun gets higher D layer absorption grows, but the MUF rises, so follow the MUF up during the day and down at night.
* The center of the visible solar disk is the region that has maximum effect on Earth.
* Check the higher bands for openings for several hours following a solar flare, or a ten-flare event, due to the enhanced E/F layer ionization, possibly temporarily raising the MUF.
* If you’re in a QSO when a major flare causes an HF blackout, it seldom lasts more than an hour. If you’re working a contest, this hint could be useful. Take a break, but don’t QRT!
* X-rays do provide extra ionization to the E/F layers for improved reflectivity and a higher MUF. Exploit the benefits of a solar flare.
* The most damaging effects of a solar flare is actually the arrival of the shockwave 2-3 days later, triggering a geomagnetic storm.
* Often our magnetic field gets very quiet following a strong geomagnetic storm for 12–24 hours. This is an excellent time to work 40–160M due to very low noise levels.
* Use the current K-Index from WWV or the internet to determine the current geomagnetic conditions. The A-Index is actually yesterday’s geomagnetic condition, and does not represent present conditions.
* As soon as the solar storm ceases, HF noise levels become quiet with an elevated MUF, lasting until sundown. Night time conditions on 80-40M can be excellent. The daytime MUF the next day may be elevated as well.
* when the geomagnetic storm subsides. Night time noise levels on 40-80M can be very low.
* The x-rays from flares (class M5.0 or larger) can be intense enough to have a considerable impact on ionospheric radio communications. In some cases, the absorption can be strong enough to completely blackout all radio communications between points more than 3,000 to 4,000 km up to frequencies as high as 10 MHz for a period of between 15 to 30 minutes. Minor absorption can maintain weaker than normal signal strengths for an additional 20 to 30 minutes. These types of major flares are much less frequent than minor M-class flares.




Aurora (also known as "aurora borealis" or "northern lights") is caused by interaction between the Earth's magnetic field and the solar wind (a mix of charged particles blowing away from the sun).  During solar storms, enough of these charged particles make it through to the Earth's upper atmosphere that they interact with the earths natural magnetic field lines.  When enough of these particles collide, energy is released in the form of auroral light.  In addition to creating a pretty light show (mostly in upper latitudes), radio signals scatter off of these particles and can greatly enhance propagation on 6 meters and above. High levels of aurora can also make HF propagation via polar routes difficult.


                                                           Real Time                                                             Real Time
                                               Northern Hemisphere                                      Southern Hemisphere
                                                      Auroral Activity.                                                 Auroral Activity.


                                                                         Northern hemisphere auroral potential.
                                                               Grey line map - One (click here)
                                                               Grey line map - Two (click here)
The grey line is a band around the Earth that separates the daylight from darkness.  Radio propagation along the grey line is very efficient.  One major reason for this is that the D layer, which absorbs HF signals, disappears rapidly on the sunset side of the grey line, and it has not yet built upon the sunrise side.  Ham radio operators and shortwave listeners can optimize long distance communications to various areas of the world by monitoring this area as it moves around the globe.  This map shows the current position of the grey line terminator.

        Click here to see the total Electron Content.       ***    1 TECU = 10E+16 electrons per square meter  _____________________________________________________________________________________________________________

                                                                                Near real time MUF map.

The following map shows Maximum Usable Frequencies (MUFs) for 3000 kilometer radio signal paths.  More importantly, the current sunspot number (SSN) and Planetary A-index are updated every 30 minutes on the bottom of this image.  Additionally, the grey line position, auroral ovals, and sun position are provided.


                                                                                      Near real time MUF map.


                                                               Near-Real-Time F2-Layer Critical Frequency Map.
The following image is a recent high-resolution global map of F2-layer critical frequencies. This corresponds to the maximum radio frequency that can be reflected by the F2-region of the ionosphere at vertical incidence (that is, when the signal is transmitted straight up into the ionosphere). It is also a map showing the current location of the auroral ovals, the sunrise/sunset terminator and the regions of the world where the sun is 12 degrees below the horizon (which estimates the gray-line corridor where HF propagation is usually enhanced).
This map can be used to determine the frequencies that will always be returned to the Earth. Transmitted frequencies higher than the indicated contours (which are given in MHz) may penetrate the ionosphere, resulting in lost power to space. Frequencies lower than the indicated contours will never penetrate the ionosphere. Lower foF2 values indicate a weaker ionosphere and correspond to regions with lower Maximum Usable Frequencies (MUFs). Higher foF2 values indicate a stronger ionosphere and correspond to regions with higher MUFs.
It is important to remember that these contours refer to the transmitted signals that are vertically incident on the ionosphere. All long-distance communications use signals that are obliquely incident on the ionosphere (that is, the radio signals are passing through the ionosphere at an angle instead of head-on).


                                                               Near-Real-Time F2-Layer Critical Frequency Map.

                                                Click here to see the GLOBAL REAL TIME IONOSPHERIC F2 MAP

                                                 Near-Real-Time Map of the F2-Layer Height Maximum.
The following image is a recent global map indicating the altitude above the surface of the Earth where the ionospheric electron density reaches a maximum. It is known as the height maximum of the F2 layer (or hmF2) and is given in kilometers above the surface of the Earth. It is also a map showing the current location of the auroral ovals, the sunrise/sunset terminator and the regions of the world where the sun is 12 degrees below the horizon (which estimates the gray-line corridor where HF propagation is usually enhanced).


                                                      Near-Real-Time Map of the F2-Layer Height Maximum
                                                             Near real time E layer critical frequency map.
The following image is a recent high-resolution global map of E-layer critical frequencies. This corresponds to the maximum radio frequency that can be reflected by E-region of the ionosphere at vertical incidence (that is, when the signal is transmitted straight up into the ionosphere). It is also a map showing the current location of the auroral ovals, the sunrise/sunset terminator and the regions of the world where the sun is 12 degrees below the horizon (which estimates the gray-line corridor where HF propagation is usually enhanced)
Radio communicators most often do not want their signals to spend very much time in this region of the ionosphere. Signals which are reflected within the E-region spend the greatest time in the E-region and are accordingly attenuated the most.
Signals that exceed the E-layer critical frequency (and are vertically incident) will penetrate the E-region and travel toward the F-regions. Signals that are below the critical E-layer frequency will always be reflected back to the Earth.


                                                                 Near real time E layer critical frequency map.
Near-Real-Time Maps of Ionospheric X-Ray Absorption
The following are near-realtime maps of ionospheric absorption produced by solar x-ray activity (solar flares). Enhanced x-ray activity increases absorption on HF radio signal passing through the daylit ionosphere. These maps depict real-time absorption of radio signals (based on current x-rays) on frequencies between 5 MHZ and 30 MHz.

Click on the realtime maps you desire:

5 MHz Absorption Map
10 MHz Absorption Map
15 MHz Absorption Map
20 MHz Absorption Map
25 MHz Absorption Map
30 MHz Absorption Map
        Click here ( ) Professional-grade high-frequency (3-30 MHz) propagation predictions
        Click here ( ) to see  DX Sherlock 2.0 - QSO real time maps
        Click here ( ) to see  D-Region Absorption Prediction



                                                                                         Cycle 21, 22, 23 and 24.



                                                                                                Cycle 24 Prediction.


Sun's 2013 Solar Activity Peak Is Weakest in 100 Years

Though the sun is currently in the peak year of its 11-year solar weather cycle, our closest star has been rather quiet over all, scientists say.

This year's solar maximum is shaping up to be the weakest in 100 years and the next one could be even more quiescent, scientists said Thursday (July 11, 2013).

"It's the smallest maximum we've seen in the Space Age," David Hathaway of NASA's Marshall Space Flight Center in Huntsville, Ala., told reporters in a teleconference. [Solar Max: Amazing Sun Storm Photos of 2013]

During a solar maximum, the number of sunspots increases. These dark temporary regions on the surface of the sun are thought to be caused by interplay between the sun's plasma and its magnetic field. Sunspots are the source of the solar flares and ejections that can send charge particles hurtling toward Earth, which can damage satellites, surge power grids, cause radio blackouts and, more benignly, produce dazzling auroras above the planet. 

About every 11 years, the sun goes through a cycle defined by an increasing and then decreasing number of sunspots. Solar Cycle 24 has been underway since 2011 and its peak was expected in 2013, but there have been fewer sunspots observed this year compared with the maximums of the last several cycles.

Giuliana de Toma, a scientist at the High Altitude Observatory in Colorado, said the sunspots occurring during a calm maximum have the same brightness and area as the ones observed during a more turbulent peak.

"We just have fewer of them and this is normal," de Toma said during Thursday's briefing. "This is why weak cycles are weak."

The quiet maximum is allowing scientists to test their knowledge of how the sun works and hone their predictions of the strength of future solar cycles.

"You might think that having a small cycle is disappointing to us but it's quite the contrary," Hathaway said.

(news from


          Click to see 400 year of sunspot observation.

          Click to get an  Azimutal map.


                                                                             Also you most to see.

HF propagation: The basics by Dennis J., W1LJ/DL  PDF document ( 976 kbyte)
Introduction to HF propagation by IPS Radio and space services  PDF document (1.28 mbyte)
Solar activity and HF propagation  PDF document (987 kbyte)
Transequatorial propagation  PDF document (181 kbyte)  ARRL propagation bulletin.   VHF/UHF qso real time maps.   Make more miles on VHF.   K9LA propagation tutorial.    Worldwide list of HF beacons by G3USF.   Worldwide list of 50 mhz beacons by G3USF.
   NCDXF beacons.   Propagation software, V2.70 (479 kbytes)   Propagation software. (1.0 mbyte)   Propagation software. (two programs 2.7 mbyte)

          e-mail: CO8TW e-mail address

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