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As you know, the sun emits into the surrounding space the so-called "solar wind", consisting of plasma. In turn, plasma is a mixture of charged particles. According to the laws of physics, charged particles interact with electromagnetic radiation, causing it to scatter. For this reason, the plasma is not radio transparent, and radio communication in the plasma environment is impossible. The same applies to visible light. However, both radio waves and light propagate quite successfully in space, without visible interference! How do they do it, in the presence of the solar wind? I know that the interaction between plasma and electromagnetic radiation is highly dependent on the physical properties and parameters of the plasma, primarily on the electron temperature and density. I can admit that the cosmic plasma will be radio transparent at distances of 10 - 50 - 100 km. But in space, orders of distance are completely different!

SW energy is enough to cause magnetic storms, northern lights and communication interference on earth, despite the fact that the earth's surface is protected by a magnetic field, and most of the cosmic radiation simply does not fall on it. for this reason, the solar wind certainly cannot be considered weak.

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    $\begingroup$ The density of the solar wind at the Earth orbit is roughly 5 protons per cubic centimeter. At STP on Earth is one mole per 22.4 liters. So the solar wind is about 18 orders of magnitude less dense than air. $\endgroup$
    – Jon Custer
    Commented Jun 10, 2023 at 10:28
  • $\begingroup$ So long as the frequency is above the local plasma frequency, electromagnetic radiation doesn't really care about the plasma (i.e., it doesn't couple to it or show much refraction). $\endgroup$ Commented Jun 11, 2023 at 16:36

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The key parameter here is the plasma frequency. Below the plasma frequency, plasma is opaque to ordinary electromagnetic waves. Above the plasma frequency it's refractive. The refractive index rapidly approaches 1 as frequency increases, so above a few times the plasma frequency the refractive effects are subtle.

The plasma frequency in the solar wind at Earth is usually 10-30 kHz, so above 100 kHz, it has little effect on radio. On the other hand, the Earth's ionosphere has a higher electron density, with plasma frequencies of 2-20 MHz. Radio waves low enough in frequency to be affected by the solar wind plasma can't penetrate the ionosphere.

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