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What are the initial phase, main phase, and recovery phase of a geomagnetic storm?

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Diagram of Earth's atmosphere layers-troposphere, stratosphere, mesosphere, and thermosphere-showing how temperature and air pressure change with increasing altitude, with key features like the ozone layer and pressure percentages at various heights. — Ionosphere and magnetosphere The layers of Earth's atmosphere, with a yellow line showing the air temperature at various heights.

A geomagnetic storm is a disturbance of Earth's upper atmosphere caused by solar activity, such as coronal mass ejections. These storms typically progress through three distinct phases:12

Initial Phase: Triggered by the arrival of high-pressure solar wind, this phase begins with a "storm sudden commencement," where the horizontal component of the geomagnetic field increases abruptly across the globe. This elevated field strength persists for two to six hours.12
Main Phase: Lasting 12 to 48 hours, this phase is characterized by a decrease in the horizontal component of the geomagnetic field. This reduction is caused by the inflation of the magnetosphere due to the injection of plasma and the growth of the ring current, which is enhanced by magnetospheric convection and particle energization.12
Recovery Phase: In this final stage, the injected plasma slowly drains into the atmosphere or the interplanetary medium over several days. During this time, the geomagnetic field gradually returns to its pre-storm condition.1