↑ What are the Solar Indices?

By Doron Tal, 4X4XM

Solar indices are observations that quantify solar-derived processes which affect skywave propagation. These indices are used to understand and predict the behavior of the ionosphere, in order to optimize terrestrial HF radio communications.

Some of the most commonly used solar indices include:

  1. Sunspot Number: This is a measure of the number of sunspots visible on the Sun's surface, which is an indicator of solar activity. Sunspots are areas of intense magnetic activity that can produce solar flares and coronal mass ejections that can affect the Earth's ionosphere and radio propagation.
  2. Solar Flux Index: This is an indicator of the solar radio energy in the 10.7 cm band, which serves as a gauge of the ionization state of the ionosphere.
  3. K-Index: This is a measure of the level of geomagnetic activity caused by solar storms, which can disrupt radio communications by producing ionospheric disturbances.
  4. A-Index: This is a measure of the level of geomagnetic activity over a 24-hour period, which can affect radio propagation conditions.
Solar indices are typically updated in real-time or near-real-time, and are available online from various sources, including national meteorological and space weather agencies. Radio operators and scientists can use these indices to predict and optimize radio communications, and to study the effects of solar activity on the Earth's ionosphere and atmosphere.

Read an overview about the solar Indices, SSN, and SF. See also an index for HF Radio Propagarion.

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