HF Radio Propagation Forecast

Practical Approach

The Current Ham Bands' Activity, or

MUF map by KC2G
Forecasting MUF for a 3,000 Km path, i.e.
View HF Bands' Conditions at a glance, or

Real-time MUF and Solar Indices

  How does HF radio wave propagate?

High Frequency (HF) radio waves can propagate in different modes. This website focuses on the propagation of skywaves, via the ionosphere - a region of the Earth's atmosphere that extends from about 48 to 600 Km above the surface. The ionosphere is divided into several layers of plasma created by solar sadiation.

When a HF radio wave is transmitted into the ionosphere, it can be bent by its different layers. The amount of refraction that occurs depends on the frequency of the radio wave and the plasma density. This bending of the radio wave can allow it to travel long distances beyond the horizon, which is why HF radio waves are often used for long-range communication.

In addition to refraction, HF radio waves can also be reflected by the ionosphere. This is particularly true for frequencies below approximately 10 MHz. When a radio wave encounters the ionosphere at a shallow angle, it can be reflected back to Earth, allowing for communication over even longer distances.

Conditions for HF radio wave propagation are affected by the time of day, the season, and the ionospheric condition.

  How Can We Forecast HF Propagation Conditions?

Incredible advances in space technology, SDR (Software Designed Radio), and the internet over the last thirty (30) years have enabled us to study radio wave propagation in ways we never imagined possible.

HF propagation forecasting is the process of predicting how radio waves will travel through the atmosphere. It works by using mathematical models to simulate the behavior of radio waves as they propagate. These models consider signal frequency, the time of day, season, solar cycle, and ionospheric conditions. The predictions are used to determine the best frequencies and times for radio communication. They can also be used to plan antenna systems and optimize radio coverage.

Read below how could HF propagation conditions be estimated?

  How does the sun affect radio communications?
   » This subject is still open to exploration and experimentation

The Sun is "quiet" on average, steadily emitting Electromagnetic Radiation across a broad spectrum that includes Sunlight (infrared, visible, and ultraviolet), radio waves, X-rays, and gamma rays. The Extreme Ultra Violet ionizes the ionosphere. This phenomenon enables long-range skywave communication.

Sunspots show that solar activity is chaotic, i.e. Solar Storms, which are Flare Eruptions and Coronal Mass Ejections (CME). This chaotic Activity alters the Space Weather, which affects the ionosphere and thus selectively influences HF Radio Communication.

The ionosphere becomes more ionized during periods of high solar activity, which improves radio wave propagation. During periods of low solar activity, the ionosphere becomes less ionized, resulting in weaker signal strength.

The ionosphere is affected by a number of factors, including day/night, season, geographical location, sunspot number, polar aurora, and the earth's magnetic field.

    Real-time Band Conditions   Global Conditions  VS   Regional Conditions

DX propagation conditions can be predicted by using at least one of the following options:

(1) Tracking actual band activity with DX clusters and/or
(2) Listening with your own rig, or WebSDR / KiwiSDR or Beacons
(3) Watching MUF map
(4) Simulating the current ionospheric condition and its effect on HF radio waves using applications based on models
      and data collected from recent Solar Activity, Space Weather reports, and remote-sensing of the ionosphere and its layers.

Actual band activity can be provided by DX Clusters, which are computer networks that collect and distribute data on amateur radio DX activities.

The most popular DX Clusters:

1. DXMAPS - shows the most recent QSOs, a view of the propagation conditions in real time
2. DXZone - clusters - captures DX and WWV spots from internet clusters and a local packet.
3. DXWatch - filter - alerts interested hams that there is a DX station on the air.

Reporters of digital modes:

4. PSK Reporter - amateur radio signal reporting and spotting network
5. WSPRnet^map, WSPR Rocks, WSPR Live, etc.

These websites all collect QSO reports, which can show which bands are open and where they are located around the world.

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Alternatively / additionally

(1) Use your own rig to monitor hams' activity:

For instance, I use Malachite DSP with MLA, and report to PSKReporter

(2) Watch the entire LF-MF-HF spectrum at a glance using a Wide-Band WebSDR

(3) or choose KiwiSDR station from the map

You can also follow Beacons and in particular eighteen (18) CW beacons on five designated frequencies: 14.100, 18.110, 21.150, 24.930, 28.200, supported by The International Beacon Project.

  Modes of HF Propagation

1. LOS - Line of Sight propagation: Free Space / Direct Wave and complex reflections, see below)
2. Ground wave propagation: surface wave - vertical polarization only, effective over a conductive ground, below 2 MHz
3. Skywave skip propagation: ״reflection״ by the ionosphere, 3-30 MHz
4. NVIS near vertical propagation: ״reflection״ by the ionosphere, 1.8-10 MHz

Usually, Line of Sight signals would propagate directly between transmitter and receiver, but there could be ״complex reflections״ (by conductive surfaces) ^{ElectronicsNotes, Kogelnik, Wiki}, and various ducting effects that are illustrated later. LOS propagation is uncommon in the HF bands due to its ineffective short range.

Ground wave: Surface propagation occurs when signals follow the contour of the Earth, over hills and beyond the horizon. It is most effective over salty sea water or good conductive ground (vertical polarization only). The effective distance of ground waves drops significantly above 2 Mhz.

Sky wave is the mode of propagation in which the radio signal is reflected by the ionosphere and returns to Earth. It is most effective at frequencies beween 3 and 30 MHz and can be used for long-range communication.

How does Skywave bounced by the ionosphere ?

1. EUV sunlight ionizes the atoms and molecules of the upper atmosphere, releasing free electrons and ions that combine to form plasma.
   The free electrons has an effect on radio waves. The typical densities are, 10⁴-10⁶_{free-electrons/cm³} (or 10¹⁰-10¹² _{free-electrons/m³}).

   The graph below is based on research from U.C.Berkeley Bob Brown, NM7M, Ph.D. The day/night cycle, seasons and solar cycle all have an affect on free electron densities as illustared here and summarized here. Electron densities are higher in the summer than in winter and near the equator than in the poles, because of the more direct solar radiation.

    
2. What differs the various layers of the ionosphere?
   The ionosphere is divided into layers (or regions), D, E, and F from about 48 up to more than 600 Km above the earth`s surface, characterized by different electron densities.
    
   Illustration of Ionospheric layers (regions)
   
   During the day the F layer splits into two layers called F1 and F2, while the D layer vanishes completely at night. These regions do not have sharp boundaries, and the altitudes at which they occur vary during the course of a day and from season to season.

How does the ionosphere affect HF Radio Propagation?

An illustration of Complex Propagation Modes

The shortest Skip zone is the minimal distance that a skywave can be received. The Dead zone is the region where the ground wave signals (at a certain frequency) can no longer be heard up to the point where the skywave first returns to Earth. The angle for a usable skywave can be shallow or steep.

What differs the D, E, F, ionosphere layers?

Sky-Wave reflection from ionospheric layers at different angles

There is a special mode of propagation, NVIS - acronym Near Vertical Incidence Skywave, which is used for communication at short distances (less than 600 km), that are not covered by ground waves, which, as mentioned, are ineffective in HF bands (above 2 MHz). NVIS transmission is made directly upwards and the ionosphere returns the signals back downwards.

NVIS from F or E layers

Long range skywave is commonly used at incident angles greater than zero

For transmissions with an incident angle greater than zero (i.e. not vertical), the maximum frequency that causes a transmission to bend back toward the earth is greater than the critical frequency. This is known as the maximum usable frequency (MUF).

The MUF is proportional to the critical frequency and the incident angle secant (equal to 1/cosine). As a result, the MUF is greater with a higher critical frequency and a larger angle from vertical.

The greatest MUF is associated with the longest range and the smallest transmission angle. Below see illustration of the transmission angle.

Transmission angle

As a result, the maximum MUF occurs at zero transmission angle, i.e. when the transmitted ray is horizontal. This ray will eventually reach the ionosphere and be refracted back due to the curvature of the earth if its frequency is low enough.

Before we define key frequencies for skywave propagation, let's talk about how the ionosphere bounces radio waves.

                  Important frequencies relevant to skywave

f_oF₂ - Critical Frequency: The highest frequency transmitted directly upwards that can be reflected.
MUF - Maximum Usable Frequency: The highest frequency at which radio communications just start to fail.
As a rule of thumb, the MUF is approximately 3 times the critical frequency;
MUF = f_oF₂ / cosθ; MUF factor = 1/cosθ (θ is the incident angle) is a function of the path length if the height layer is known.
 
LUF - Lowest Usable Frequency, below which a gradual decline in signal strength occurs. The LUF is a soft frequency limit, as opposed to the ionospheric skip MUF, which is a sharp hard frequency limit determined by the critical angle.
OWF - Optimum Working Frequency is usually 85% of the MUF.

References: * How is MUF measured? * The Recent MUF measurements

What is Greyline Propagation?

The greyline is a narrow band around the Earth that separates the daylight from darkness. The F layer is illuminated for a longer period of time than the D layer at dawn and dusk.

Greyline illustration

Ham radio operators and shortwave listeners can optimize long-distance communications to various areas of the world by monitoring Grey Line as it moves around the globe. The 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 been built upon the sunrise side.

Global HF & VHF Radio Propagation Conditions

This is a review of the Solar Indices used to forecast Global average propagation
These indices are based on NOAA's published Space Weather data.

The banner to the left, courtesy of N0NBH, Paul L Herrman, is a common sight on many Ham Radio websites.
Every three hours, the Current Solar-Terrestrial Data are updated.
It gives an idea of the Global HF Propagation Conditions, but it cannot show regional variation in HF conditions.

Glossary of "indices" on the left column banner.   SFI - Solar Flux, 2800MHz Radiation (10.7cm) SN - Sunspot Number A - Planetary A Index: Average Geomagnetic Disturbance good conditions A < 10 K - Planetary K Index: Geomagnetic Disturbance for good conditions K < 3 X-Ray in Ionosphere. Scales: A, B, C, M, and  X (from A0.0 to X9.9) affect D-layer 304Å: Total Solar Radiation at 304 Ångstroms (30.4nm) that affects F-layer ionization Pf - Proton Flux: Density of charged protons in the Solar Wind; Impacts E-layer Ef - Electron Flux: Density of charged electrons in the Solar Wind; Impacts E-layer Aurora Indicates how strong the F-layer ionization is in the polar regions Bz - Magnetic Field z perpendicular to Earth's Ecplictic Plane SW - Solar Wind   Aur Lat - Aurora Latitude: Calculation from NOAA - estimate the lowest latitude   EsEU - Sporadic E - Europe. Updated every ½ hour. EsNA - Sporadic E - North America. Updated every ½ hour. EME Deg - Earth-Moon-Earth Degradation/attenuation. Updated every ½ hour.   MUF - Maximum Usable Frequency (MHz), updated every 15 minutes. MS - Meteor Scatter Activity colored bar (updated every 1/4 hour).   GeoMag - Calculated - Earth`s Geomagnetic based on K-Index. Updated every 3 hours. Sig Noise - Calculated every ½ hour: S-units (Solar Wind and Geomagnetic Activity)

Solar indices expansions and clarifications Good Propagation Conditions are when the SFI > 200  and   A < 10  and  K < 3   A & K indices can be used by radio operators to get any sense of how radio signals will propagate globally: K-index quantifies disturbances (in the horizontal component) of the earth's magnetic field in three hourly measurements compared to a “quiet day”; integer values range from 0 - Inactive up to 9 - Extremely severe storm. A-index is a linear measure of the Earth’s field; values range from 0-Very Quiet up to 400-Severe Storm. Predicted sunspot number and Radio Flux at 10.7 cm NOAA / NWS Space Weather Prediction Center: Multi-year forecast of the monthly Sunspot Number and the monthly F10.7   Solar Flux F10.7 cm Radio Emissions Radio waves emitted from the Sun at a frequency of 2800 MHz (10.7 cm) correlate with the Sunspot number as well as several UltraViolet (UV) and visible solar irradiance records.   27-Day Outlook of 10.7 cm Sun Radio Flux and the Earth Geomagnetic Indices Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center.

    The MUF - Maximum Usable Frequency

The MUF is the most important index for specifying regional propagation conditions because it can be used for communication between two points via ionosphere return (sky wave propagation or "hopping") at a specific time. It is measured using an ionosond.

Typical ionodonde modes are vertical and oblique:

An ionosonde transmits HF radio waves vertically or diagonally. The received echoes are analyzed to determine the density of plasma at various heights (48-600 km).

The echo analysis generates an ionogram, which represent plasma density distribution in the ionospheric layers.

A typical ionogram

Ionograms usually contain a dual representation:

1. a series of (more or less) horizontal lines indicating the virtual height
   at which the AM pulse will be echoed as a function of the operating frequency;


2. a curve in vertical direction representing the density of electrons per cubic centimeter
   as a function of height.

 
Typical diurnal changes in frequencies relevant to skywave

MUF - maximum usable frequency FOT - frequency optimum transmission (or OWF) EMUF - E layer maximum usable frequency LUF - lowest usable frequency

References: * MUF, LUF, FOT/OWF explained * Recent MUF measurements

    Regional HF Conditions

See ballow five maps of regional conditions, all based on recent MUF measurements:
1. Grayline map with a few regional MUF & Global indices ^{updated every 3 hours [N0NBH]}
2. MUF 3000 Km map - Information about HF propagation conditions at a glance ^[KC2G]
     The next 3 maps for Critical MUF / NVIS operation are courtesy of Australian Gov SWS, updated every 15 minutes
3. NVIS map Criticall Frequency at a vertical angle f_oF₂
4. T index Map - f_oF₂ compared to the monthly median
5. f_oF₂ Anomaly compared to the monthly median

    Greyline / Grayline map with "selected" places' local MUF and Global Indices

This map courtesy of N0NBH, Paul L Herrman is updated every 3 hours. It shows day/night, local MUF, and the Global Indices: SFI, SN ^{Sunspot Number}, A&K indices, 304Å, Sig Noise, Geomag.

   MUF 3000 HF Propagation Map - A quick look at current and near-future HF propagation conditions:

The map below was created for amateur radio operators by Andrew Rodland, K2CG, and is updated every 15 minutes.
A radio path of 3,000 Km is being considered for unification. It was developed between 2018 and 2021 to assist Radio Amateurs in finding the best times and frequencies for contacts by displaying HF conditions at a glance.

How to use this map?

The colored regions of this map are rebounded by Iso-Frequency contours illustrate the Maximum Usable Frequency that is expected to bounce off of the ionosphere on a 3000 Km path.

The ham bands are designated by iso-frequency contours: 5.3, 7, 10.1, 14, 18, 21, 24.,8, and 28 Mhz.
For example, if a given area on the map is greenish and lies between the contours labeled "10" and "14," the MUF in that location is around 12 MHz.

The raw data that powers the site is MUF collected by ionosondes all over the world, which are denoted by colored discs to show where the information is coming from. A number inside a disc indicates the local Critical ionospheric frequency, f_oF2. The information from the stations is compiled by Real Time Ionosonde Data Mirror ^{Space Weather Service at NOAA} and Giro, and processed by the IRI model (produced by a joint task group of COSPAR and URSI).

The MUF along a path between any two locations shows the possibility of long-hop DX between those points on a given band. For example, if the MUF is 12MHz, then 30 meters band and longer will work, but 20 meters band and shorter won't. For long multi-hop paths, the worst MUF anywhere on the path is what matters. For single-hop paths shorter than 3000 Km, the usable frequency will be less than the indicated MUF. As one gets closer to vertical, i.e. NVIS, the usable frequency drops to the Critical ionospheric frequency, f_oF2 (as shown in the next map).

Additional Notes:

• This map is the result of research and development made by Andrew Rodland - KC2G, based on a former project made by Matt Smith - AF7TI.
   
• prop.kc2g.com is made possible by funding from WWROF and data from ionosonde operators around the world, distributed through GIRO and NOAA. See Acknowledgments.
   
• This simplified model does not take into account geomagnetic storms and Blackouts due to Elevated X-ray Flare and/or Proton Ejections. Therefore, the MUF(3000) estimation accuracy is insufficient for radio service purposes. Geospace dynamic models are being developed at the moment. Other reasons for low ionospheric parameter accuracy include insufficient measurement coverage of the Earth and errors in estimating ionosphere parameters from vertical sounding data.
   
• Read more about this open-source project: how did it start, what were the goals, and what is needed to be done?
  More information can be found in the PDF.
   
• Roland Gafner, HB9VQQ extended this project with an excellent Animated Map viewing the last 24 hours, in 15 minutes steps.

 NVIS Map shows contours of the Critical ionospheric frequency - f_oF₂,
which is the highest usable frequency for NVIS in units of MHz, obtained from ionograms;
updated every 15 minutes, courtesy of Australian Government Space Weather Services.

   T Index Map - f_oF₂ compared to the monthly global average
Courtesy Australian Government Space Wheather Services

The T index is an ״equivalent sunspot number״ matched to the f_oF₂ obtained from ionograms.
Data is based on Space Weather conditions as reported by the Australian Bureau of Meteorology.

  Current Anomaly Map of critical frequency, f_oF₂, compared to the monthly median

The plot above shows a near real-time f_oF₂ anomaly map. The anomalies are calculated by subtracting the median f_oF₂ for the last days from the currently observed f_oF₂. The current f_oF₂ and dataset are used to calculate the median f_oF₂ the identical time of day and geographical attributes. The anomaly differences are in units of MHz. The regions in red indicate significantly lower frequencies compared to the last 30-day medians.

    "Total Electron Content" Estimate (One Hour)

The Total Electron Content (TEC) of the Earth's ionosphere is an important descriptive quantity - number of electrons integrated between two points along a one-meter-squared-cross-section tube. It is calculated from real-time global f_oF2 data measured by Ionosondes.

Ionospheric TEC is significant in determining the scintillation and group and phase delays of a radio wave through a medium. It is characterized by observing carrier phase delays of received radio signals transmitted from satellites located above the ionosphere, often using GPS satellites. TEC is strongly affected by solar activity.

TEC/TECU provides the number of free electrons per square meter (x1016) for a shell height of 400 km. This map is based on measurements collected from ionosonde stations around the world, it provides near real-time information and data service for the current state of the ionosphere, related forecasts, and warnings. Credit: Ionosphere Monitoring and Prediction Center (IMPC) of the European Space Agency`s network of space weather services.   Roland Gafner, HB9VQQ made an excellent Animated Map. See additional references on this topic.

Solar influence

Two types of Solar Phenomena affect HF skywave communication, regular emission, and chaotic activity:

1. Regular Solar Emission: Electromagnetic Radiation of all kinds in a wide spectrum from below HF to gamma rays. Extreme UV radiation - EUV - is the most important for HF radio communication.
   It ionizes Earth's ionosphere.

   see below the measured spectral lines of a "quiet Sun" at Extreme Ultra Violet EUV:

   The EUV spectrum of the Sun, as measured by the SDO instrument flown aboard a rocket in April 2008

   Solar Spectra in the Extreme UV (100-1200 Å) are capable of ionizing molecules by a single-step energy transfer.
   This light is emitted from the upper transition region and the chromosphere ^{NASA, UCAR}.

   Peak (He II) EUV radiation at a wavelength of 304 Ångstroms is the most important solar emission contributing to half of the Ionospheric F Layer ionization.

    

   What makes the ionospheric layers distinct?   See graph of plasma density vs altitude.

   Illustration of Ionospheric layers at noon
   
   1. F-layer ^~10¹² electrons/m³ at 150-600 km, consists H⁺, He⁺ Hydrogen and Helium ionized by 100-1000Å EUV
   2. E-layer ^~10¹¹ electrons/m³ at  90-150 km, consists O₂⁺ Oxygen ionized by 10-100Å EUV
   3. D-layer ^~10¹⁰ electrons/m³ at  48-90 km, consists NO⁺ Nitric Oxide ionized by 1216Å UVC
   Moreover, X-ray Solar Flares, 1-10 Å (hard X-ray), enhance D-layer, causing Blackout events.
    
2. Chaotic Solar Activity can cause geomagnetic storms and interfere with HF radio communication.

   For centuries, people have observed sunspots without understanding what they are.
   Nowadays we know that these are indicators of Solar Storms that may cause geomagnetic storms and disrupt HF radio communication.

   Chaotic activity includes Flares and Coronal Mass Ejections (CME) associated with Solar Wind.

   These elements (radiation and ejected ionized matter) affect the Space Weather, which further modifies the ionosphere that has a significant impact on HF Radio Communication.

   Sunspots VS Flares, SOHO (ESA & NASA):

   Sunspots are small areas of the Sun's surface with particularly strong magnetic forces that appear darker due to their lower temperature.

   The image on the left shows Sunspot dots in visible light. The image on the right shows the Sun at an Extreme Ultraviolet (EUV) wavelength of 304 Ångstroms (30.4 nanometers).

   These two images of the Sun, courtesy of UCAR - Center for Science Education, were taken on February 3, 2002,
   by NASA`s Solar and Heliospheric Observatory (SOHO) satellite.

   ---

   During solar maximum, there are many sunspots, while during solar minimum, there are few.

   Sunspots can take on a variety of shapes and sizes. They can also change size and shape and live for hours, days, or even months. Click here for references about sunspots and their relationship to the solar cycle.

      Live Solar Events and past Solar Activity

• Current Sunspot Regions ^{Space Weather Live Belgium}
• Solar Synoptic Map
  Forecasters at the NOAA Space Weather Prediction Center use synoptic maps to view the various characteristics of the solar surface on a daily basis. They create a snapshot of the features of the Sun each day by drawing the various phenomena they see, including active regions, coronal holes, neutral lines (the boundary between magnetic polarities), plages and filaments, and prominences. This map is a valuable tool for assessing the conditions of the sun and making the appropriate forecast for those conditions.
• Recent Hours Solar Events:
  1. RHESSI NASA
  2. SolarSoft
  3. SolarMonitor
  4. EarthSky
• Recent Hours CME - Corona Mass Ejection, monitored by LASCO
• Recent days:
  1. X-Rays Flares ^Scales
  2. 3 Days X-Ray Flux ^{viewed by GOES}
  3. 3 Days Proton Flux ^{viewed by GOES}
  4. Solar Wind Energy ^{Rice University}
• Recent Month Daily Sunspot Number ^{MET Malaysia}
• Last 30-Day Solar Activity Plot ^AGSWS
• Recent Year Solar Terrestrial Activity ^{Solen-Jan Alvestad}
• Recent Years Unique Blackouts ^NOAA
• Historic Notable Events ^Wikipedia
   
• Solar Cycle Progression - The observed and predicted ​Solar Cycles are depicted in Sunspot Number terms.

  It appears that the new solar cycle 25 is off to a fast start, already surpassing forecasts. Average number of sunspots in January 2023 have reached over 143.6 compared to the predicted 63.4. Solar flux in January 2023 have reached over 182 unites compared to the predicted 100 units.

  ---

  More than 150 years ago extreme events had been observed.

• Carrington Event was the most intense geomagnetic storm, recorded on 1 to 2 September 1859 during solar cycle 10.  
• Comparison of Solar Cycles
  
• Multi-frequency (VHF-SHF) radio bursts superimposed on a persistent background characterize solar flares: Picture Source: Patrick McCauley Mccauley.pi, CC BY-SA 4.0
   
• Different sunspot cycles can have different radio burst distributions at 245 MHz.
  That is to say that the sunspot cycles can vary and that they may not be considered identical.
  
  See an article covering Burst Comparisons, Probabilities, and Extreme Events:
  Solar Radio Burst Statistics in 8 Bands and Implications for Space Weather Effects
  by O. D. Giersch, J. Kennewell, M. Lynch (2017)
   
• Solar radio bursts from the Sun can interfere with communication, radar, and navigation systems (e.g., GPS).
  The forecast of future solar events will be an underestimate of the true burst rate due to the deficiencies in the data archives.
  1 Solar radio emission as a disturbance of radio mobile networks (June 2022).
  3 What a Solar Flare *Sounds* Like When It Reaches Earth (2013)
  2 An analysis of solar noise outbursts and their application to space communication (1971)

    Space Weather

An illustration of the Space Weather environment
 

Credit: European Space Agency/A. Baker, CC BY-SA 3.0 IGO AGU - Advanced Earth and Space Science This is a demonstration of The Lagrange mission that would place a spacecraft at the L1 and L5 Lagrange Points to monitor for hazardous Mass Ejections headed toward Earth. On the right side, you may see around the Globe an illustration of the Magnetosphere, which protects the life on Earth. The magnetosphere is a part of a dynamic, interconnected system that responds to solar, planetary, and interstellar conditions. It is disturbed when solar wind interacts with the space environment surrounding Earth.

        Space Weather Explained

      What is Solar Wind?

The solar wind is a stream of charged particles released from the corona (the upper atmosphere of the Sun). It mostly consists electrons, protons, and alpha particles. i.e plasma.

How long does it take for Solar Wind to reach earth?

The first electrically charged particles (electrons) ejected from a sunspot enter Earth`s atmosphere about 20 to 30 minutes after the storm and the heavier particles would arrive later, from a day (protons) up to four days (alpha particles). The speed of any given jet of solar wind depends on the composition and the interaction of the particles.

Geomagnetic Storms are temporary disturbances of the Earth's Magnetosphere caused by solar wind and/or a cloud of the earth's magnetic field, resulting in ionosphere disturbances.

      Space Weather Reports

Recent Space Weather images courtesy of NOAA SWPC services

Example: Recent 3 days Solar X-ray flux, Proton flux, and Geomagnetic Activity Reference: Index of Space Weather images at NOAA SWPC services

Forecast of Blackouts due to Elevated X-ray Flare and/or Proton Ejections

Explanation: Radio waves are typically reflected near the peak of the F2 layer (~300 km altitude), but along the path to the F2 peak and back the radio wave signal suffers attenuation due to absorption by the lower layers. The D-Region Absorption Prediction model is used as guidance to understand the HF radio degradation and blackouts this can cause.

Observe an animation of the recent eight hours.

Skywave HF Radio Propagation Conclusive Summary

1. Understanding HF radio propagation can help Radio Amateurs to plan their activities.
    
2. Skywaves bounced from the F layer of the the ionosphere are used for global HF communications.
 
3. Solar EUV radiation causes the ionized layers to form.
 
4. Ionospheric Layers summary

5. Signals are refracted or absorbed by the ionosphere layers as a function of frequency, incident angle, and the ionospheric structure determined by the free electron density.
 

Typical Ionospheric electron density profiles Day/Night, and Solar Cycles

 
6. Day/Night cycle: Ionization increases during daylight as illustrated above.
 
7. Seasonal effects: Electron densities are higher in the summer compared to the winter, and nearer the equator compared to the poles, due to more direct solar radiation. HF radio signals are more efficiently reflected in the summer and closer to the equator.
 
8. The seasonal and regional anomalies.
 
9. The graph below illustrates variations in HF radio wave propagation as a function of years and seasons:
   
   
   Sunspot Number and critical frequencies vs Time, courtesy AGSWS.

On the left vertical axis Critical Frequency is shown the highest frequency reflected at noon at near vertical angles from the F2, F1, and E leyers.

The highest F2 layer has greater relative fluctuations in electron density than the lower F1 and E layers, bacuse it is more influenced by the solar activity measured by sunspot sumber, redish line; see units on the right vertical axis.

The information presented above was derived from ionograms collected at noon in Canberra, Australia.

 
10. Communication conditions can be unexpectedly disrupted due to solar storms, which affect the D region. This layer may completely block signals in all the HF bands (3-30 MHz).
     
11. In a typical Solar Flare, X-rays penetrate to the bottom of the ionosphere (to around 80 Km) and enhance the ionization of the D layer that acts both, as a reflector of radio waves at some frequencies and an absorber of lower frequencies. The Radio Blackout associated with Solar Flares occurs in the dayside region of Earth and is most intense when the sun is directly overhead. See Sudden Ionospheric Disturbances (SIDs).
     
12. Solar Protons can also disrupt HF radio communication. These protons are guided by Earth’s magnetic field, such that they collide with the upper atmosphere near the north and south poles. The fast-moving protons have an effect similar to the X-ray flares and create an enhanced D-Layer thus blocking HF radio communication at high latitudes. During auroral displays, the precipitating electrons can enhance other layers of the ionosphere and have similar disrupting and blocking effects on radio communication. This occurs mainly on the night side of the polar regions of Earth where the aurora is most intense and most frequent. See Polar Cap Absorption (PCA) events.
     
13. Solar indices such as SSN, SFI, and A/K are used to quantify the propagation conditions.
14. See The Current Band Conditions at a glance ☺

References

1. Reported Band Activity of Radio Amateurs ^worldwide
    

   DX Clusters

   1. DXMAPS ^website Use DX Maps to understand HF Propagation conditions ^Youtube
   2. DXZone curation of 51 DX clusters nodes
   3. DXWatch ^filter Spot Search and Create Your Filter

   Reporters of digital modes

   4. PSKReporter
   5. HF Signal Propagation Reporter, PSK/JT65/FT-8/CW/JT9 ^{HamRadioConcepts KJ4YZI}
    
   APRS-IS - Automatic Packet Reporting System-Internet Service
    
   6. Find Real-Time Contacts, DX Cluster, Spotter Network, APRS  ^{HamRadioConcepts KJ4YZI}
   7. VHF Propagation Map ^{APRS-IS real-time radio propagation from stations operated near 144 MHz}

   WSPR - Weak Signal Propagation Reporter

   8. WSPRnet ^website
   9. WSPR Rocks
   10. WSPR Live
   11. Weak Signal Propagation Reporter ^Wikipedia
   12. WSPR Explained: How to Get Started With One-Way Ham Radio ^ExtremeTech
   13. Propagation 24 hrs - 60 days ^{WSPR Rocks}

   Beacons

   14. NCDXF Beacon Network ^{see above}
   15. Beacons ^IARU
   16. International Beacon Project (IBP) ^Wikipedia
   17. Amateur Radio Propagation Beacon ^Wikipedia
   18. Ham Radio Beacon List ^Google
   19. Radio propagation beacon ^{HF Underground}
   20. International Beacon Project ^NCDXF
   21. Reverse Beacon Network (RBN) ^About
   22. Beacon monitoring programs ^DXZone
    

---

2. Radio Waves Propagation ^{Basic principles and models}
    
   1. The Rebirth of HF ^{Rohde & Schwarz}
   2. All-In-One Overview: There is nothing magic about propagation ^{José Nunes – CT1BOH (2021)}
   3. Course Overview: Atmospheric Effects on Electromagnetic Systems ^{Naval Postgraduate School}
   4. Overview: Understanding HF / VHF / UHF / SHF Propagation ^{Paul L Herrman N0NBH}
   5. Radio Propagation Tutorial Basics ^{Electronics-Notes}
   6. Electromagnetic Radiation ^Wikipedia
   7. Radio propagation ^Wikipedia
   8. LOS - Line Of Sight propagation ^Wikipedia
   9. Ground wave propagation ^Wikipedia
   10. Ground Wave Propagation Tutorial ^{Electronics-Notes}
   11. Ground wave MF and HF propagation ^AGSWS
   12. Ground Wave Propagation Tutorial ^{Electronics-Notes}
   13. Skywave (skip) propagation ^Wikipedia
   14. Skywaves & Skip Zone ^{Electronics-Notes}
   15. Path length and hop length for HF sky wave VS transmitting angle ^AGSWS
   16. Skip zone ^Wikipedia
   17. Propagation of Radio Waves ^{Basu, VU2NSB}
        

---

3. Ionosphere / Skywave Propagation
           Model > Propagation > Layers / Regions > MUF, LUF, OWF > Seasonal & Anomalies > Probing

   Ionospheric model

   1. Ionization (basics) ^Wikipedia
   2. Plasma (basics) ^Wikipedia
   3. Ionosphere (basics) ^Wikipedia
   4. Introduction to the ionosphere ^{Anita Aikio}
   5. Ionospheric model ^Wikipedia
   6. The Ionosphere ^UCAR
   7. Ten Things to Know About the Ionosphere ^NASA
   8. Ionosphere ^{Electronics-Notes}
   9. The Ionosphere and the Sun ^{Naval Postgraduate School}

   Skywave Propagation

   10. An Introduction to HF propagation and the Ionosphere ^ZL1BPU
   11. Ionospheric propagation Basics ^{Electronics-Notes}
   12. Introduction to Ionospheric HF Radio Propagation ^AGSWS
   13. Understanding HF Propagation ^{Rohde Schwarz}
   14. Understanding HF Propagation ^{Steve Nicols, G0KYA, RSGB}
   15. Radio Propagation 101 ^{Dan Vanevenhoven}

   Layers / Regions

   16. Layers of Ionization ^Wikipedia
   17. Ionospheric D, E, F, F1, F2 Regions ^{Electronics-Notes}
   18. Sporadic E propagation ^Wikipedia
   19. Sporadic E Layer ^{ScienceDirect}
   20. D-Layer ^Wikipedia
   21. Ionospheric D Region ^Britannica
   22. Ionospheric Propagation ^{University of Toronto}
   23. HF Propagation Tutorial - Distribution of ionospheric electrons ^{Bob Brown, NM7M}
   24. Regional and Long Distance Skywave Communications ^{Ken Larson, KJ6RZ}
   25. Transequatorial Radio Propagation ^CO8TW

   MUF, LUF, OWF

   26. MUF Maximum usable frequency ^Wikipedia
   27. Critical frequency ^Wikipedia
   28. Critical frequency, MUF, LUF & OWF ^{Electronics-Notes}
   29. HF Radiation - Choosing the Right Frequency ^{Naval Postgraduate School}
   30. How to use Ionospheric Propagation? ^{Electronics-Notes}

   Ionospheric Variations

   31. Season Rollover – Why do shortwave frequencies have to change? ^{Neale Bateman, BBC}
   32. Persistent anomalies to the idealized ionospheric model ^Wikipedia

   RBN can detect space weather disturbances

   33. Ionospheric Sounding Using Real-Time Amateur Radio Reporting Networks ^AGU

   Ionosphere Probing

   34. Chirping Explained - Passive Ionospheric Sounding and Ranging ^{Peter Martinez, G3PLX}
   35. Chirp reception and interpretation ^{Pieter-Tjerk de Boer, PA3FWM}
   36. Ionosonde ^Wikipedia
   37. Ionogram ^Wikipedia
   38. The DST Group High-Fidelity, Multichannel Oblique Incidence Ionosonde (2018) ^{DOI AGU}
   39. Remote sensing of the ionosphere ^{Google Search}
   40. Ionospheric Characterisation Analysis and Prediction tool (IOCAP) ^SANSA
   41. IOCAP Introduction Video ^SANSA
   42. ICON - Ionospheric Connection Explorer ^Wikipedia
    

---

4. NVIS ^{unique mode of propagation}
    
   1. Analysis of the Ordinary and Extraordinary Ionospheric Modes for NVIS Digital Communications Channels ^{Sensors (Basel)}
   2. NVIS Propagation: Near Vertical Incidence Skywave ^{Electronics-Notes}
   3. NVIS ^Wikipedia
   4. NVIS - Near Vertical Incidence Skywave ^{_{What is it? advantages; antennas; links} Jim Glover KX0U}
   5. Near Vertical Incidence Skywave (NVIS) ^{Ham Radio School}
   6. HF NVIS  ^{Military HF Radio}
   7. NVIS Overview  ^{David Casler KE0OG}
   8. Understanding NVIS  ^{Rohde Schwarz}
   9. Ham Radio NVIS for Regional Communications  ^{Radio Prepper}
   10. NVIS Explained ^AmRRON
   11. NVIS Prediction Map ^WH6FQE
        

---

5. Grey Line Propagation
    
   1. Grey Line HF Radio Propagation ^{Electronic Notes}
   2. Identifying Gray-Line Propagation Openings ^DXLab
   3. Greyline Propagation ^G0KYA
   4. Gray-line Propagation Explained ^{Radio Hobbyist}
   5. Round the world echoes ^G3CWI
   6. An introduction to gray-line DXing ^{Rob Kalmeije}
   7. Greyline Map ^{DX QSL Net}
   8. Greyline Map ^DXFUN
       

---

6. Solar Phenomena affecting Space Weather
    
   1. Solar phenomena ^Wikipedia
   2. Electromagnetic Spectrum ^Wikipedia
   3. Solar Radiation / Sunlight ^Wikipedia
   4. The Active Sun from SDO: 304 Ångstroms ^NASA
   5. Sunspots ^Wikipedia
   6. Sunspot Number ^AGSWS
   7. Sunspot Number and critical frequencies vs Time ^AGSWS
   8. The Lifetime of a Sunspot Group ^AGSWS
   9. Effective sunspot number: A tool for ionospheric mapping and modelling ^{URSI General Assembly 2008}
   10. Solar Cycle ^Wikipedia
   11. Solar Cycle ^NASA
   12. Solar Cycle Progression ^NOAA
   13. Solar Cycle ^AGSWS
   14. Solar Storms ^Wikipedia
   15. Solar Radiation storms ^NOAA
   16. Solar Flares ^Wikipedia
   17. Classification of X-ray Solar Flares ^{https://www.spaceweather.com/}
   18. What is Coronal Mass Ejection ^Wikipedia   Recent-CME
   19. A Media Primer for the Solar Cycle and Space Weather ^NESDIS
   20. Sudden Ionospheric Disturbances (SIDs) ^AGSWS
   21. The Sun and HF radio propagation ^{Electronic Notes}
   22. Presentation: Solar Activity and HF Propagation (2005) ^{Paul Harden, NA5N}

---

7. Solar Indices as a measure of Global HF & VHF Radio Propagation
    
   1. Solar Indices: SFI, SN, A, K, Kp ^{Electronics-Notes}
   2. Solar Indices - Glossary of Terms ^{HamQSL , Paul L Herrman, N0NBH}
   3. What are Solar Flux, Ap, and Kp Indices? ^VK3FS
   4. N2LVI's Quick Guide to HF Propagation Using Solar Indices ^W2VTM
      N2LVI's Quick Guide to HF Propagation Using Solar Indices ^{Kingsport amateur Radio Club 2020}
   5. Solar Index and Propagation Made Easy - HF Ham Radio ^TheSmokinApe
      
   6. Current Ham Radio Propagation Conditions ^{Ham Radio for Non Techies, HR4NT}
    

---

8. Space Weather What impact does it have on HF radio propagation?
    
   1. Space Weather ^Wikipedia
   2. Solar-terrestrial science ^CSA
   3. Solar Wind ^Wikipedia
   4. Space Weather ^{Naval Postgraduate School}
   5. Space Weather Modeling ^NASA
   6. Geomagnetic Storms ^Wikipedia
   7. Geomagnetic Storms ^NOAA
   8. How does Space Weather impact HF radio communication ^NOAA
   9. Space Weather and Radio Communications ^AGSWS
   10. NWS Space Weather Prediction Center ^NOAA
   11. Space weather: What is it and how is it predicted? ^SpaceCom
   12. How to Improve Space Weather Forecasting (2020) ^{Eos, AGU}
   13. How to Assess the Quality of Space Weather Forecasts? (2021) ^{Eos, AGU}
   14. Space Weather Highlights ^AGU
   15. Magnetosphere (MS) ^NASA
   16. Next-Generation Solar Proton Monitors for Space Weather ^Eos
   17. Presentation: Space Weather and Propagation(2019) ^{Martin Buehring, KB4MG}

   Space Weather Agencies & Services

   18. The International Space Environment Service ^ISES
   19. National Oceanic and Atmospheric Administration ^NOAA
   20. International Service Providers ^NOAA
   21. NOAA / NWS Space Weather Prediction Center ^NOAA
   22. Space Weather Prediction Center ^Wikipedia
   23. Canadian Space Agency ^CSA
   24. The Embrace Program ^Brazil
   25. European Space Agency - Space Weather Service ^ESA
   26. Australian Space Weather Forecasting Center - Space Weather Services ^AGSWS
   27. Overview of the Australian Space Weather Alert System 2022 ^AGSWS
   28. Australian Bureau of Meteorology, Space Weather Services ^AGSWS
   29. Space Weather - Met Office ^UK
   30. South African National Space Agency (SANSA) ^SANSA
   31. Mission Space ^LEO
   32. Space Weather Canada
   33. World Meteorological Organiztion ^WMO
   34. American Commercial Space Weather Association ^ACSWA
   35. Space Weather Forecast Japan ^{ISES, RWC}
   36. Korean Space Weather Center ^RRA/KSWC
   37. China-Russia Consortium Global Space Weather Center
    
   

   ---

9. Recent Observations Reports
               Solar > Space > Terrestrial ^{Geomagnetic Indices}, TEC ^{Total Electron Content}, and Propagation
   

   Recent Solar Observations

   1. Recent F10.7 cm Radio Emissions ^NOAA
   2. Recent Blackout Events ^NOAA
   3. Observed CME - Coronal Mass Ejections ^NOAA
   4. ACE Real-Time Solar Wind ^NOAA
   5. Live Solar Events ^{Andy Smith, G7IZU}
   6. Solar Update ^{K7RA ARRL (Google Search)}
   7. Recent 3 days: X-ray, Proton Flux, and Geomagnetic Activity ^NOAA
   8. Space Weather Prediction Center - Index of images ^NOAA
   9. Current Solar Conditions and Ham Radio Propagation ^W5MMW
   10. Today Sun data and HF Propagation ^QRZCQ
       • Effects of Sun Activity (SFI, SN, X-ray, A, Kp) in the last 36 hours
       • Sun Data History in the last 30 days
       • Current Propagation based on WSPRNet
       • Current Propagation based on DXCluster
       • Propagation data in the last 30 days
   11. SolarHam website Latest Imagery of Solar Watch and Alerts of Space Weather
    

   Recent Space Weather Conditions

   12. Space Weather Conditions ^NOAA
   13. Space Weather Conditions ^AGSWS
   14. Live Space Weather ^{Andy Smith, G7IZU}

   Terrestrial

   Recent Geomagnetic Indices

   15. Current Space Weather Parameters ^{Solar Terrestrial Dispatch}
   16. Station K & A Indices for the last 30 days ^NOAA
   17. Magnetospheric MultiScale (MMS) ^Rice
    
   18. Recent TEC - Total Electron Content (calculated)
        
       1. Total Electron Content (TEC) ^Wikipedia
       2. Near-real-time TEC maps ^{ESA - Europen Space Weather Service}
       3. TEC at Ionosphere Monitoring and Prediction Center ^ESA
       4. One-hour Forecast Global TEC Map ^{DLR (ESA)}
       5. Station List ^{DLR (ESA)}
       6. Archive of TEC ^{DLR (ESA)}
       7. North American TEC ^NOAA
       8. Near Real-Time Global TEC Map ^AGSWS

   Recent MUF measurement using ionograms at different locations

   Locations

   19. GIRO - Global Ionospheric Radio Observatory ^{Lowell DIDBase}
   20. Ionosonde Station list ^UML.edu

   Ionograms

   21. Recent Ionograms (Cyprus) ^{University of Twente, Enschede, Netherlands}
   22. Animated Ionograms Latest 24-Hour ^GIRO

   Charts

   23. Current MUF 3000 Km Map updated every 15 minutes ^{Andrew Rodland, K2CG}
   24. Hourly HAP Chart for Stockholm Radio ^AGSWS
   25. Current f_oF2 Plots (World) ^AGSWS
   26. Current f_oF2 Plots (Australasia) ^AGSWS
   27. HF Propagation Charts ^{AGSWS - Hourly Area Predictions (HAP)}
   28. Global HF Propagation ^{Andy Smith, G7IZU}
   29. Usable HF Frequencies for US Amateur Radio ^{Remarkable Technologies, Inc.}
    

---

 
10. Applications and tools for analysing and forecasting HF propagation
     
    1. ^App-Category Band Monitoring - gathering information from DX clusters and/or beacons
       1. Real-time Band Activity of Radio Amateurs
       2. Analyzing Propagation From Active DX Stations ^DXLab
       3. Radio Propagation Maps Based on established contacts ^{Andy Smith, G7IZU}
     
    2. ^App-Category Online Tools
       1. MUF 3000 Km Map ^{Andrew Rodland, K2CG}
          About Developing an Open-Source HF Propagation Prediction Tool ^{Andrew Rodland, KC2G}
       2. What frequency should I use ^{STORADIO, Sweeden}
       3. Radio Propagation Forecasting ^{Basu, VU2NSB}
       4. Proppy Online - HF Propagation Prediction (2022) ^{James Watson, M0DNS}
       5. RadCom online Propagation Prediction Tools ^RSGB
       6. Real-Time HF Propagation Prediction (up-to-date) ^{Hamwaves - Serge Stroobandt, ON4AA}
          Real-time online dashboard of solar activity influencing HF propagation on Earth
        
    3. ^App-Category SFI - Solar Flux and Space Weather Indices
       1. Radio Communications Dashboard Km Map ^{SWPC NOAA}
       2. D Region Absorption Prediction (D-RAP) - Blackout Prediction ^{SWPC NOAA}
       3. 27-Day Outlook of 10.7 cm Sun Radio Flux and the Earth Geomagnetic Indices ^NOAA
       4. Add Solar-Terrestrial Data to your Website ^{HamQSL , Paul L Herrman, N0NBH}
       5. Current Solar Indices - Previous and Forecast Space Weather ^N6RT
       6. Propagation Links ^{eham.net NOAA Alerts, Observations, Scales Activity; DX Cluster WWV announcements, Propagation Links}
       7. SolarHam website Latest Imagery of Solar Watch and Alerts of Space Weather
     
    4. ^App-Category Overviews and Reviews of Forecasting applications
        
       1. What can we expect from a HF propagation model? ^Luxorion Dynamic processes relevant to HF radio propagation are simulated using mathematical models, using numerical procedures. Interactions between the Sun's surface and the Earth's surface are considered using sun, space weather, ionosphere, and atmosphere models, all of which can aid in the prediction of HF radio propagation.
       2. Review of HF Propagation analysis & prediction programs Research Oriented ^Luxorion Some of these propagation programs are only accessible via the Internet via a web interface and provide graphical solutions. Amateurs have also created small applications that simulate various ionospheric effects. Using either near-real-time data or well-known functions, the majority of them achieve extremely high accuracy.
       3. Review of Propagation prediction programs - VOACAP-based ^Luxorion The VOACAP propagation prediction engine is the result of decades of US government-funded HF propagation research stretching back to the dawn of computing. While VOACAP's forecasting capability has been continuously improved as knowledge about HF propagation has increased, its software technology is firmly rooted in the 1980s.
       4. Predicting and Monitoring Propagation ^DXLab
          * Solar terminator display and prediction - shows grey line at any specified date and time
          * Propagation prediction - provides a graphical view of openings by frequency and time using your choice of the included
          VOACAP, ICEPAC, and IONCAP forecasting engines.
        
       5. PropView ^DXLab Rated 8.27 by The DXZone PropView uses the included VOACAP, ICEPAC, and IONCAP propagation prediction engines to forecast the LUF and MUF between two locations over a specified 24 hour period. Results are rendered in an easy-to-understand color-graphic display. You can specify locations via direct latitude/longitude entry. Alternatively, PropView interoperates with DXView to allow location selection via DXCC prefix entry or by clicking on locations on a world map. It can:
          (1) build schedules for the IARU/HF beacon network and automatically QSY your transceiver to monitor each scheduled beacon.
          (2) monitor the NCDXF/IARU International Beacon Network to assess actual propagation and compare it with forecast propagation. Beacon schedules can be assembled by band, by location, or by bearing from your QTH.
          PropView interoperates with Commander and DXView to automatically QSY your transceiver to hear each beacon in your schedule, and to display the location of the current beacon.
       6. Propagation prediction software for ham radio ^DxZone A review
     
    5. ^App-Category Prediction Software using various models
       1. The Advanced Stand Alone Prediction System (ASAPS) ^AGSWS
          Australian Space Weather Forecasting Center offer three software products to predict HF propagation:
          1. GWPS - designed for HF operators working in defence and emergency services
          2. ASAPS Kernel - The Advanced Stand Alone Prediction System designed for government, defence and emergency services
          3. Consultancies - designed for industry, defence and emergency services
          
       2. DX Toolbox - Shortwave / Ham Radio / HF Radio Propagation ^{Black Cat Systems}
          This is a software application that provides a range of tools for HF radio operators, including propagation forecast based on the Solar Terrestrial Dispatch (STL) model. It also includes a real-time solar data display and a grayline map.
       3. HF Propagation (Google Play) ^{Android Package Kit}
       4. HF Propagation (Microsoft Apps) ^{Stefan Heesch, HB9TWS}
       5. DX Propagation (up-to-date) ^DR2W
       6. Proplab-Pro v3: Review ^eHam Manual ^spacew.com
          Proplab-Pro 3.2 (Build 45, March 2023) Three-dimensional ray-tracing ionosphere; can run as standalone; not free.
       7. DXPROP 1.4 (2010) ^{Christian RAMADE (F6GQK)} Rated 6.10 by DxZone
          DXprop freeware (developped for US Navy) is a propagation forecast for radio amateurs that can predict propagation on 12 frequencies.
       8. W6ELProp (2002) ^W6EL Rated: 7.56 by DxZone
          Predicts skywave propagation between any two locations on the earth on frequencies between 3 and 30 MHz
       9. The Propagation Software Pages A collection of links ^AC6V
        
    6. ^App-Category Statistical analysis of past ionospheric characteristics
        
       1. ITU-R-HF-Prop: This is an ITU-R recommendation that provides a method to predict the performance of HF radio systems in a wide range of propagation conditions. The ITUR HF Prop experimental software, was written by G4FKH and HZ1JB, and is based on the ITU-R P.533 method. It uses a probabilistic approach to estimate radio coverage with algorithms that are supposed to be more accurate than other similar programs.
       2. ITURHProp, an improved (2017) point-to-point propagation prediction tool, based on an ITU engine and developed by Gwyn Williams, G4FKH.
       3. HamCAP (VOACAP interface) by Alex Shovkoplyas, VE3NEA. Rated 8.93 by DxZone
     
    7. ^App-Category Mathematical models/Numerical procedures based on solar activity, space wather, geomagnetic fields, ionosphere, ray-tracying taking into account the time of day / earth rotation and orientation:
       1. ITU-R P.533 model
       2. Space Weather Modeling Framework (SWMF)
       3. Global Assimilation of Ionospheric Measurements (GAIM) model
       4. Advanced D-layer Ionosphere Prediction System (ADIPS)
     
    8. ^App-Category Ray-tracing models based on frequency, angle of incidence, and electron density profiles of the ionosphere.
        
       1. IONCAP - Ionospheric Communications Analysis and Prediction HF transmission prediction program for US military and other applications since 1986. It was based Automatic Link Establishment (ALE) Frequency Selection for a Ten-Node Australian High-Frequency Network. This program was clumsy, slow, and complicated, as it only allowed users with a sufficient background in ionospheric physics and computer data entry experience to use it. A new version was developed to fix these flaws while also improving capability to the point where it could be used by a layperson.
       2. ITUR HF PROP: Prediction of HF circuits based on Recommendation ITU-R P.533 model
        
       3. VOACAP (Voice of America Coverage Analysis Program) VOACAP forecats monthly average of the expected reliability with diurnal and seasonal variations, but it does not account for unpredicted ionospheric and magnetic disturbances or anomalies, i.e. what are the expected vsariations of A-index, K-index, and energy densities of solar proton / electron flux, etc.
       4. VOACAP Online Application for Ham Radio ^{Jari Perkiömäki, OH6BG / OG6G}
       5. VOACAP Quick Guide ^{Jari Perkiömäki, OH6BG / OG6G}
       6. How to use VOACAP - Part 1: Overview ^{Jari OH6BG & OH7BG Raisa}
       7. VOACAP Charts for RadCom ^VOACAP
     
    9. ^App-Category Neural network models: These models use machine learning techniques to predict the behavior of radio waves based on input data. They may take into account factors such as solar activity, geomagnetic conditions, and the time of day. The HF Ionospheric Prediction and Solar Terrestrial Data Center uses machine learning algorithms to predict ionospheric conditions.
       1. Neural Network Ionospheric Model (NNIM)
        
    10. ^App-Category Hybrid methods: These methods combine two or more methods to make predictions.

---

 
11. Misc. References
     
    1. Amateur Radio ^Wikipedia
       The name of the hobby "Amateur radio" refers to a non-commercial communication, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communications activity that may use radio transmitters and receivers.
    2. Amateur radio station ^Wikipedia
       Read about different types of stations used by an amateur radio operator.
    3. Radio Amateur ^Wikipedia
       "Radio Amateur" is the person usualy a licensed operator who communicates with other radio amateurs on amateur radio frequencies.
    4. Ionospheric Radio Propagation 1965 (replaced an obsolete pubication of 1948) ^{National Bureau Of Standards}
    5. Basic Radio Propagation Predictions for September 1958, Three Months in Advance ^{National Bureau Of Standards}
    6. SDR - Software Designed Radio ^Wikipedia
    7. Lagrange points (Google Search)
    8. Wave Interaction and Propagation ^ESA
       Space provides a unique perspective from which to investigate the Earth.
       Probing plasma layers in the upper atmosphere is relevant to HF propagation.
        
    9. Solar-Terrestrial Prediction Proceedings | Solar-Terrestrial Prediction Proceedings ^{Richard F. Donnelly, Space Environment Lab, NOAA (1979)}
    10. Recommendation: Propagation Factors Affecting Frequency Sharing In HF Terrestrial Systems ^{ITU 1994}
    11. Recommendation: Ionospheric Characteristics And Methods Of Basic MUF, Operational MUF AND Ray-Path Prediction ^{ITU 1995}
    12. Recommendation: HF propagation prediction method ^{ITU 2001}
    13. Ionospheric Monitoring and Modeling Applicable to Coastal and Marine Environments ^{Ljiljana R. Cander and Bruno Zolesi (2019)}
         
    14. Statistically analyzing the ionospheric irregularity effect on radio occultation ^{M. Li and X. Yue, Atmos. Meas. Tech., 14, 3003–3013, 2021}
    15. Analysis of Ionospheric Disturbance Response to the Heavy Rain Event ^{Jian Kong, Lulu Shan, Xiao Yan, Youkun Wang - Remote Sens. 2022, 14(3), 510}
    16. Analyzing the current ionospheric conditions ^{Google search}
    17. Evaluation of various models for HF propagation prediction ^{SANSA Space Science}
    18. Short and long term prediction of ionospheric HF radio propagation ^{Ann. Geophys., 28, 2227–2236, 2010 by J. Mielich und J. Bremer}
        A modified ionospheric activity index AI has been developed on the basis of ionospheric f_oF₂ observations. Such index can be helpful for an interested user to get information about the current state of the ionosphere. Using ionosonde data.
    19. Comparison of observed and predicted MUF(3000)F2 in the polar cap region ^{Radio Science AGU (2015)}
        Over a four-year period, MUF calculated from ionosonde measurements was compared to values obtained from the Ionospheric Communications Enhanced Profile Analysis and Circuit Prediction Program (ICEPAC), Voice of America Coverage Analysis Program (VOACAP), and International Telecommunication Union Recommendation 533 (REC533) models. Diurnal and seasonal variations are evident in predictions and observations. The VOACAP and ICEPAC models are unable to reproduce the diurnal variation trend observed in summer measurements. These models were statistically analyzed: REC533 performs better in winter and equinox months, while VOACAP performs better in both equinox and summer months. ICEPAC performs poorly during periods of low solar activity.
    20. Investigation of Two Prediction Models of Maximum Usable Frequency for HF Communication Based on Oblique- and Vertical-Incidence Sounding Data (2022) ^{atmosphere MDPI}
        MOFs were compared to predicted MUFs. The INGV model outperformed for MUF prediction over Beijing and its adjacent mid-latitude regions, according to the root-mean-square error comparison.
    21. Radio Propagation Prediction for HF Communications (2018) ^{Dept. of Appl/ Physics & Tel., Midlands State Univ., Gweru, Zimbabwe}
    22. Use of electron density profiles in HF propagation assessment: part 1- Requirements, prediction and forecasting (1991) ^{Advances in Space Research Journal}
    23. A Preliminary Systematic Study of HF Radio Propagation from a Source in the Subarctic Using HAARP and the Ham WSPR Network (2018) ^{Citizen Space Science, Fallen, C. T.}
    24. A simplified HF radio channel forecasting model ^{Advances in Space Research, Volume 69, Issue 6, 15 March 2022, Pages 2477-2488, Moskaleva, Zaalov
        This paper addresses the problem of predicting the maximum electron density in the ionosphere related to the critical frequency (f_oF₂) of the ionospheric F2 layer. The spatial dependence and temporal evolution of f_oF₂ values define the behaviour of an HF propagation channel. This paper proposes the simplified forecasting model to predict electron density profile one day ahead. The prediction method is based on analysis of time series of measured f_oF₂ profile. The data obtained from GIRO network database were used in investigation. Statistics of f_oF₂ daily profile recorded by neighbouring ionosondes during 12 years were built. Comparisons between the observed and predicted vertical ionograms are presented to show the appropriateness of the proposed technique.}
    25. Develop ionosphere computer models to enhance HF radio propagation ^{Military Aerospace 2022}
        Develop new ways to model the ionosphere in real time to help predict the propagation of high-frequency (HF) radio waves for improved communications and sensing.
    26. Ionospheric current ^{Upper Atmospheric Science Division of the British Antarctic Survey}
     

    Last but not least:

The world is changing as the radio amateur spectrum is being sold off to commercial users since few amateurs operate SHF and above.

If you have comments, questions or requests please e-mail.

73 de Doron

חיזוי התפשטות גלים - תנאי תקשורת - ת"ג - חובבי רדיו
التنبؤ بظروف الاتصال لهواة الراديو
预测无线电爱好者的通信条件
아마추어 무선 통신 조건 예측
アマチュア無線家の通信状況を予測する
रेडियो शौकीनों के लिए एचएफ संचार स्थितियों का पूर्वानुमान
Forecasting HF radio conditions for radio amateurs
Прогнозирование условий связи для радиолюбителей
Voorspelling van communicatievoorwaarden voor radioamateurs
Vorhersage der Kommunikationsbedingungen für Funkamateure
Previsão de condições de comunicação para radioamadores
Previsione delle condizioni di comunicazione per radioamatori
Prévision des conditions de communication pour les radioamateurs
Predicción de las condiciones de comunicación para radioaficionados