A statistical study on the characteristics of ionospheric storms in the equatorial ionization anomaly region: GPS‐TEC observed over Taiwan

Abstract

Positive and negative signatures of the ionospheric storms caused by the penetration electric field, disturbance dynamo, neutral wind, neutral composition, etc., have been reported. In this paper, the ionospheric total electron content (TEC) derived from the records of a network of ground‐based GPS receivers in Taiwan is used to statistically study the characteristics such as local time of appearance and duration of the storm signatures of various casuals in the equatorial ionization anomaly (EIA) region during 1994–2003. A bias‐corrected accelerated bootstrap method and a z test are employed for the first time to detect each event, and the overall storm signatures and characteristics, respectively. It is found that the positive signatures that appeared minutes to hours after the geomagnetic storm onset are pronounced on the storm day and the next day, while the negative signatures that started hours after the geomagnetic storm onset can last for as long as the next 4 days. The positive signature is statistically significant and most pronounced, when the intense geomagnetic storm onset occurs during local afternoon, which suggests that the signature may result from a combination of the prompt penetration electric field effect and mechanical effects of equatorward neutral wind. Additionally, the negative signature that is statistically significant and most pronounced in the local afternoon of the storm‐onset day and/or the next day may be produced by the disturbance dynamo or overshielding effects. The long‐lasting negative signature occurred in local midnight‐noon period on days 2–4 after the storm onset may result from the neutral composition disturbances.

Temporal and spatial precursors in ionospheric total electron content of the 16 October 1999 Mw7.1 Hector Mine earthquake

“…Magnetic storm can simultaneously disturb the global ionosphere [cf. Liu et al ., ]. For example, Thomas et al .…”

“…Based on Liu et al . [], many studies detecting SIPs by means of the GPS TEC have been carried out [e.g., Liu et al ., 2004, 2006, 2009, 2010, 2011b; Pulinets et al ., ; Zhao et al ., ; Kakinami et al ., ; Jhuang et al ., ; Le et al ., , ; Thomas et al ., ].…”

Reply to comment by F. Masci and J. N. Thomas on “Temporal and spatial precursors in ionospheric total electron content of the 16 October 1999 Mw7.1 Hector Mine earthquake”

“…Liu et al . [] indicate that positive/negative storm signatures can be induced by various effects of the prompt penetration electric field, disturbance dynamo, neutral wind, neutral composition, overshielding effects, etc., and their associated signatures can last up to 4 days after the storm onset. Figure displays the northward TEC gradient (▽ N TEC) of the GIM in the Hector Mine, Japan, and Europe regions, and the one over Hector Mine yields the great reduction on 10 October 1999.…”

“…[] for the first time introduce and propose a median base to statistically detect ionospheric anomalies regardless knowing casuals. Scientists have been employing the analysis to detect anomalies possibly associated with earthquakes [for example, Liu et al ., , , , , , ] and storms [ Liu et al ., ]. Note that the temporal analysis simply detects possible anomaly, and the spatial analysis is surely required to find whether the detected anomaly specifically appears at a specific location.…”

“…It has been known that the ionosphere can be disturbed by solar flares [ Liu et al ., , ], magnetic storms [ Liu et al ., , , , ; Lee et al ., , ; Lin et al ., , , , , ; Chen and Liu , ; Chuo et al ., ; Li et al ., , ; Huang et al ., ; Balan et al ., , , ; Lekshmi et al ., ; Sun et al ., ], eclipses [ Yeh et al ., ; Huang et al ., ; Liu et al ., , ; Tsai and Liu , ; Lin et al ., ], atmospheric tides [ Lin et al ., ], earthquakes [ Liu et al ., , , , , , , , , , , ], tsunami [ Liu et al ., ; Tsai et al ., ; Kakinami et al ., ], etc. The median base analysis has been employed to detect anomalies possibly related to earthquakes [ Liu et al ., , , ] and disturbances triggered by magnetic storms [ Liu et al ., ] in temporal variations of ionospheric critical frequency f o F 2 and/or GPS TEC (total electron content). Liu et al .…”