↑ What is the difference between solar indices and propagation indices?

By Doron Tal, 4X4XM
 

Solar indices, geomagnetic indices, and propagation indices are closely related but serve different purposes in understanding and predicting radio wave behavior.

Solar indices are measurements that describe the activity of the sun and its impact on the Earth's ionosphere. The key solar indices are:

  1. Solar Flux Index (SFI): Measures the amount of solar radio noise at a wavelength of 10.7 cm, which correlates with solar activity. Higher values generally indicate better conditions for high-frequency (HF) radio propagation.
  2. Sunspot Number: Indicates the number of sunspots on the sun's surface, which is directly related to solar activity. Higher values generally indicate better HF conditions.
Geomagnetic indices measure the disturbances in the Earth's magnetic field caused by solar activity. The key geomagnetic indices are:
  1. K-index: Measures the magnitude of geomagnetic storms on a scale from 0 to 9, with higher values indicating more severe storms. The lower values indicate quieter geomagnetic conditions.
  2. A-index: Provides a a longer-term (24-hour) view of geomagnetic activity based on the (3-hour) K-index values.
Propagation indices, are derived from solar and geomagnetic indices to predict the quality of radio wave propagation.
They help radio operators understand how well radio signals will travel through the ionosphere. Key propagation indices include:
  1. Maximum Usable Frequency (MUF): The highest frequency at which a radio wave can be transmitted between two points via the ionosphere.
  2. Lowest Usable Frequency (LUF): The lowest frequency at which a radio wave can be transmitted and still be received with acceptable quality.
  3. Signal-to-Noise Ratio (SNR): The ratio of the desired signal to background noise, indicating the clarity of the received signal.

Solar indices measure solar activity, geomagnetic indices measure disturbances in the Earth's magnetic field, while propagation indices use this information to predict radio wave behavior and communication quality. All these indices are essential for understanding and optimizing radio communications.


References:

  1. HF Propagation and Solar-Terrestrial Data Website - Paul L. Herrman, N0NBH
  2. Solar indices - making sence of the numbers for radio propagation - Andrew McColm, VK3FS
  3. The Sun, the Earth, the Ionosphere - Carl Luetzelschwab, K9LA
  4. Understanding Solar Indices - Ian Poole, G3YWX


The project "Understanding HF Propagation" provides a detailed overview and tutorials on HF propagation.

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