Localized Increment and Decrement in the Total Electron Content of the Ionosphere as a Response to the April 20, 2018, Geomagnetic Storm

Carlos Sotomayor-Beltran

doi:10.1155/2018/1986306

Abstract

A moderate geomagnetic storm occurred on April 20, 2018. Using vertical total electron content (VTEC) maps provided by the Center for Orbit Determination in Europe, ionospheric responses to the geomagnetic storm could be identified in generated two-dimensional differential VTEC maps. During the day of the storm the enhancement of the equatorial ionization anomaly (EIA), product of the super-fountain effect was identified. A localized TEC enhancement (LTE) was also observed to the south of the EIA on April 20, 2018. It was also possible to visualize this LTE in a longitudinal section of the EIA as a third crest. The maximum increment of VTEC for the LTE was 204%. This LTE is quite unique because it happened during the expected solar cycle 24 and 25 minimum, and according to a previous study no LTE observation could be done for the last solar two-cycle minimum. The origin of the observed LTE is suggested to be partly product of the super-fountain effect. Finally, a localized TEC decrement (LTD) was observed towards the end of the day, April 20, 2018. Because this LTD consisted in the disappearance of the northern and southern crests of the EIA and this occurred during the recovery phase of the geomagnetic storm, it can be suggested that the LTD origin is due to the westward disturbance electric field. This mechanism was put forward by a past study that also analyzed the responses to a geomagnetic storm (the 2015 St. Patrick’s day storm), being one of the responses the inhibition of both crests of the EIA.

Highlights

It can be observed in the ΔVTEC map that the two enhanced plasma regions that form the equatorial ionization anomaly (EIA) are displaced towards the poles (∼30∘N and ∼25∘S), confirming what it was noticed for other geomagnetic storms in past studies (e.g., [8,9,10,11,12, 28, 29])
The global ionospheric maps (GIMs) is showing this localized total electron density (TEC) enhancement (LTE); there is no doubt when looking at the ΔVTEC map that the LTE is properly displayed showing clearly its complete spatial distribution
Analysis of differential vertical total electron content (VTEC) content maps during the G2 geomagnetic storm that occurred on April 20, 2018, has revealed different ionospheric responses

Summary

Introduction

A noticeable feature in the F layer of the ionosphere is the equatorial ionization anomaly (EIA; [6]) This anomaly consists of two regions of enhanced plasma located at ±15∘ of the magnetic equator. Once high altitudes are reached, the plasma diffuses along the geomagnetic field lines due to pressure gradient forces in conjunction with the action of gravity [7] This whole process is known as the equatorial fountain effect. On the other hand when a geomagnetic storm sets in, it has been previously observed in several studies (e.g., [8,9,10,11,12]) that the EIA is considerably enhanced, which is due to the penetration of the interplanetary electric field from high to low latitudes and which lasts for several hours [13]. Publicly available vertical TEC (VTEC) data from the Center for Orbit Determination in Europe (CODE) were used to investigate the ionospheric responses to the April 20, 2018, geomagnetic storm that happened during the expected time of the solar cycle 24 and 25 minimum [15]

Data and Method

Results and Discussion

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Conclusions