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Why does the lower ionosphere lose much of its plasma after sunset?

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How scientists use lasers to learn about the universe — plasma Learn about the PHELIX (Petawatt High-Energy Laser for Heavy Ion Experiments) laser at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. PHELIX is used for plasma and atomic physics research.

The lower ionosphere (specifically the D, E, and F1 regions) loses much of its plasma after sunset because the primary mechanism for its creation—photoionization—ceases when the Sun is no longer present to provide the necessary solar radiation.2

During the day, photons from the Sun interact with atmospheric gases to produce a steady supply of electrons and positive ions. Once the Sun sets, this production stops. Without the continuous input of energy to maintain the plasma state, the existing electrons and ions undergo dissociative recombination, where they collide and neutralize to form stable gases. Because this recombination process is highly effective at lower altitudes, the plasma density in these regions drops significantly at night. This reduction in plasma is why radio interference, which is often caused by the D region during the day, is minimal at night.1234