A New Index to Descript the Regional Ionospheric Disturbances During Storm Time

A new index, perturbation index (PI), was introduced to descript the regional ionospheric disturbances during storm time. Taking the statistic relative variations of foF2 for different seasons as normalized basis, we obtained the perturbation magnitude at each station. After an average process for different regional stations in latest several hours, the regional disturbance index was constructed to depict the ionospheric storm magnitude. Taking historical data from 13 stations in China between 2007 and 2017 for example, we checked out its practicability and effect to depict the ionospheric storm characteristics. It is found that the storm time ionospheric disturbance properties are preliminary represented using this index, and the local time, seasonal and some other regular variations caused by solar Extreme Ultraviolet/Ultraviolet (EUV/UV) radiation were removed remarkably. Based on this, we classified the state of ionosphere into seven grades, namely as quiet, minor positive and negative storm, median positive and negative storm, and strong positive and negative storm. It is shown a reasonable distribution of storm events with different grades, and the disturbance variation depicted by PI is well consistent with typical storm morphology. The total storm number is well related with that of geomagnetic storms, both varied versus with the solar cycles with visible lag. We argue that it is convenient to describe the ionospheric disturbances using PI index, and it is helpful for space environment scholars to study the ionospheric storms and for space weather users to monitor and assess potential impacts on their systems.