- The MUF, LUF and ionospheric noise levels may define the HF propagation conditions.
- The SSN and SFI indicate solar activity that affect the MUF. The X-Ray flare may correlate with potential blackouts and fadeouts.
- The K, and A indices quantify geomagnetic activity that may disrupt HF propagation conditions.
- Other Space Weather indices cover a broader range of space-related measurements, including solar and geomagnetic activity.
- HF Propagation Indices are essential for amateur radio operators and other communication services.
Key propagation parameters indices include:
- MUF (maximum usable frequency) is the highest frequency possible for skywave propagation.
- LUF (lowest usable frequency) is the lowest frequency possible for skywave propagation.
- SNR (signal-to-noise ratio) indicates the quality of the received signal compared to background ionospheric noise.
Solar indices (SSN and SFI) vs. geomagnetic indices (K or Kp and A or Ap) are often used as propagation indicators to evaluate prospective HF band propagation conditions. The space weather indices may aid in estimating geomagnetic storms that could completely impair HF radio transmission.
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- Solar Indices are indicators that describe the activity of the sun, particularly in relation to its impact on the Earth's ionosphere and geomagnetic field.
Key solar indices include:
- SSN - Sunspot Number indicates the daily number of sunspots on the sun's surface as viewed over a 24-hour period.
- SFI - Solar Flux Index measures the radio emissions from the sun at a wavelength of 10.7 cm, which correlates with solar activity. It is determined by measuring the strength of a received signal by satellite-borne microwave receivers at 2,800 MHz.
- Solar X-ray flares (1–8 Angstrom) is measured by instruments onboard GOES satellites.
Excessive X-ray flares can cause ionization at the D-layer region, leading to communication difficulties or blackouts.
- Geomagnetic indices
The geomagnetic indices quantify geomagnetic activity, characterized by disturbances in the magnetic field around the Earth.
Geomagnetic indices include:
- The K-index measures geomagnetic activity over a 3-hour period, indicating the level of disturbance in Earth's magnetic field on a logarithmic scale from 0 to 9, with higher values indicating higher disturbances.
- The A-index is a daily average of the K-index values, providing a longer-term view of geomagnetic activity over a 24-hour period.
- The DST-index measures the intensity of the ring current around Earth, which affects geomagnetic activity.
The "planetary indices" are Kp, AP, and Ap:
- The Kp-index is a geomagnetic index estimated over 3 hours with a resolution of 0.33 and a quasi-logarithmic scale. It is derived from measurements from 13 geomagnetic observatories, representing quasi-logarithmic values between 0-9.
- The ap-index is a geomagnetic index estimated over 3 hours, based on K index data from 11 Northern and 2 Southern Hemisphere observatories, with a linear scale of 0-400.
- The Ap-index is a planetary average of the A-Index, a geomagnetic index estimated over 24 hours and presented as a simple moving average of 8 values every 3 hours.
- Space Weather Indices
Space weather indices refer to various measurements that describe the conditions in space, particularly those influenced by solar activity. These indices may help predict and understand the effects of space weather on Earth and its technological systems.
Space weather indices include:
- X-ray flux quantifies the intensity of solar flares that can cause radio blackouts and fadeours
- High solar proton flux hitting Earth's magnetosphere can enhance ionization, leading to increased absorption of HF radio waves, signal degradation, or complete communication blackout. This effect is similar to solar flares, but often more prolonged and affecting larger areas near Earth's poles.
- High solar electron flux can significantly impact HF propagation.
Here are some key effects:
4.3.1 Higher ionization in the D and E regions causes auroral activity that can lead to fading and scattering of the lower HF bands.
4.3.2 Increased noise on the lower bands that makes it harder to receive weak signals.
4.3.3 Enhanced ionization in the F2 region that can improve VHF signal propagation.
Summary:
• Propagation Indices are used to predict radio signal quality based on solar and geomagnetic activity.
• Solar Indices focus on solar activity.
• Geomagnetic Indices measure Earth's magnetic response to solar activity.
• Space-Weather Indices cover a broad range of space conditions affecting Earth.
Understanding these effects can help radio operators adjust their frequencies and strategies to maintain effective communication.
References:
- Circular of Basic Indices for Ionospheric Propagation published by ITU
- Description of propagation indices published by DXMAPS
- HF Radio & Space Weather Dashboard published by EA4FSI
- Geomagnetic Indices in Solar-Terrestrial Physics and Space Weather publication by M. Menvielle & A. Marchaudon
- HF Propagation and Solar-Terrestrial Data by Paul L Herrman, N0NBH
- Propagation related data from NOAA relayed by eHam
- Quick Guide to HF Propagation Using Solar Indices by Doron Tal, 4X4XM
- Real‑Time HF Propagation Space Weather
- Solar activity published by Space Weather Live Belgium
- Current Sunspot Regions published by Space Weather Live Belgium
- Recent Solar X-ray data from the primary GOES satellite published by Space Weather Live Belgium
- The Sun, the Earth, the Ionospher published by ARRL
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