↑ What are the Solar Indices?

Edited by Doron Tal, 4X4XM

Solar indices are measurements of various properties of the Sun that affect radio propagation, particularly at high frequencies (HF). These indices are used by radio operators and scientists to predict and understand the behavior of the ionosphere and to optimize 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 a measure of the amount of radio energy emitted by the Sun at a frequency of 10.7 cm, which is an indicator of the level of ionization in the Earth's 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.
  5. F-Index: This is a measure of the maximum usable frequency (MUF) for radio communication between two points, based on the critical frequency of the ionosphere at that time and location.
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.

You may find more detailed information in the main webpage, here. See also an index for HF Radio Propagarion.