The 2015 St. Patrick's day geomagnetic storm with SYM-H value of -233 nT is an extreme space weather event in the current 24th solar cycle. In this work, we investigated the main mechanisms of the profound ionospheric disturbances over equatorial and low latitudes in the Asian-Australian sector and the American sector during this super storm event. The results reveal that the disturbed electric fields, which comprise penetration electric fields (PEFs) and disturbance dynamo electric fields (DDEFs), play a decisive role in the ionospheric storm effects in low latitude and equatorial regions. PEFs occur on March 17 in both the American sector and the Asian-Australian sector. The effects of DDEFs are also remarkable in the two longitudinal sectors. Both the DDEFs and PEFs show the notable local time dependence, which causes the sector differences in the characteristics of the disturbed electric fields. This differences would further lead to the sector differences in the low-latitude ionospheric response during this storm. The negative storm effects caused by the long-duration DDEFs are intense over the Asian-Australian sector, while the repeated elevations of hmF2 and the EIA intensifications caused by the multiple strong PEFs are more distinctive over the American sector. Especially, the storm time F3-layer features are caught on March 17 in the American equatorial region, proving the effects of the multiple strong eastward PEFs.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016JA022832

Effects of disturbed electric fields in the low‐latitude and equatorial ionosphere during the 2015 St. Patrick's Day storm

The St. Patrick's Day storm of 17th March, 2015 has a long lasting main phase with the Dst reaching a minimum of -223 nT. During the main phase, two strong prompt penetration electric field (PPEF) phases took place; first with the southward turning of IMF Bz around ~1200 UT and the second with the onset of a substorm around ~1725 UT leading to strong equatorial zonal electric field enhancements. The consequent spatio-temporal disturbances in the ionospheric Total Electron Content (TEC) and the resultant modifications in the Equatorial Ionization Anomaly (EIA) over the Brazilian longitudinal sector are investigated in detail. The simultaneous measurements from a large network of GPS receivers, Ionosonde and magnetometers over the Brazilian longitudinal sector are used for this study. In the presence of enhanced zonal electric field, the equatorial F2-layer peak (hmF2) experienced a rapid uplift without any significant change in the base height (h′F); while the F2 layer is redistributed into F2 and F3 layers. The enhanced zonal electric filed due to PPEF led to the strong super fountain effect under which, the anomaly crest departed poleward to ~40o S latitude. In the presence of westward and equatorward wind surge over Brazil with the co-existing disturbance dynamo fields, strong hemispheric asymmetry is seen in the storm time response of EIA during both the PPEF phases.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017JA024009

Electrodynamic disturbances in the Brazilian equatorial and low-latitude ionosphere on St. Patrick's Day storm of 17 March 2015

Geomagnetically induced currents (GICs) represent a significant space weather issue for power grid and pipeline infrastructure, particularly during severe geomagnetic storms. In this study, magnetometer data collected from around the world are analyzed to investigate the GICs caused by the 2015 St. Patricks Day storm. While significant GIC activity in the high-latitude regions due to storm time substorm activity is shown for this event, enhanced GIC activity was also measured at two equatorial stations in the American and Southeast Asian sectors. This equatorial GIC activity is closely examined, and it is shown that it is present both during the arrival of the interplanetary shock at the storm sudden commencement (SSC) in Southeast Asia and during the main phase of the storm approximately 10 h later in South America. The SSC caused magnetic field variations at the equator in Southeast Asia that were twice the magnitude of those observed only a few degrees to the north, strongly indicating that the equatorial electrojet (EEJ) played a significant role. The large equatorial magnetic field variations measured in South America are also examined, and the coincident solar wind data are used to investigate the causes of the sudden changes in the EEJ approximately 10 h into the storm. From this analysis it is concluded that sudden magnetopause current increases due to increases in the solarwind dynamic pressure, and the sudden changes in the resultant magnetospheric and ionospheric current systems, are the primary drivers of equatorial GICs.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016JA023344

Geomagnetically induced currents around the world during the 17 March 2015 storm

The Earth’s upper atmosphere and ionosphere undergoes large and complex perturbations during and after geomagnetic storms. Thermospheric winds driven by enhanced energy and momentum due to geomagnetic activity generate large disturbance electric fields, plasma drifts and currents with a broad range of temporal and spatial scales from high to equatorial latitudes. This disturbance dynamo mechanism plays a fundamental role on the response of the middle and low-latitude ionosphere to geomagnetic activity. In this review, we initially describe the early evidence for the importance of this process and the first simulation study which already was able to explain its main effects on the electrodynamics of the middle and low-latitude ionosphere. We then describe the results of more recent simulations and the extensive experimental work that highlights the importance of this mechanism for ionospheric space weather studies extending to post-storms periods, and present some suggestions for future studies.

Post-Storm Middle and Low-Latitude Ionospheric Electric Fields Effects

Ionospheric response to the 26 August 2018 geomagnetic storm using GPS-TEC observations along 80° E and 120° E longitudes in the Asian sector

We studied the response of the ionosphere (F region) in the Brazilian sector during extreme space weather event of 17 March 2015 using a large network of 102 GPS- total electron content (TEC) stations. It is observed that the vertical total electron content (VTEC) was severely disturbed during the storm main and recovery phases. A wavelike oscillation with three peaks was observed in the TEC diurnal variation from equator to low latitudes during the storm main phase on 17–18 March 2015. The latitudinal extent of the wavelike oscillation peaks decreased from the beginning of the main phase toward the recovery phase. The first peak extended from beyond 0°S to 30°S, the second occurred from 6°S to 25°S, whereas the third diurnal peaks was confined from 13°S to 25°S. In addition, a strong negative phase in VTEC variations was observed during the recovery phase on 18–19 March 2015. This ionospheric negative phase was stronger at low latitudes than in the equatorial region. Also, two latitudinal chains of GPS-TEC stations from equatorial region to low latitudes in the east and west Brazilian sectors are used to investigate the storm time behavior of the equatorial ionization anomaly (EIA) in the east and west Brazilian sectors. We observed an anomalous behavior in EIA caused by the wavelike oscillations during the storm main phase on 17 March, and suppression of the EIA, resulting from the negative phase in VTEC, in the storm recovery phase.

/pdf/positive-and-negative-gps-tec-ionospheric-storm-effects-bfj77wlafz.pdf

Positive and negative GPS‐TEC ionospheric storm effects during the extreme space weather event of March 2015 over the Brazilian Sector

Equatorial and low-latitude positive ionospheric phases due to moderate geomagnetic storm during high solar activity in January 2013

Ionospheric disturbances in a large area of the terrestrial globe by two strong solar flares of September 6, 2017, the strongest space weather events in the last decade

Brunno Augusto Ribeiro

Papers

Positive and negative GPS‐TEC ionospheric storm effects during the extreme space weather event of March 2015 over the Brazilian Sector

Equatorial and low-latitude positive ionospheric phases due to moderate geomagnetic storm during high solar activity in January 2013

Ionospheric disturbances in a large area of the terrestrial globe by two strong solar flares of September 6, 2017, the strongest space weather events in the last decade

Daily and Monthly Variations of the Equatorial Ionization Anomaly (EIA) Over the Brazilian Sector During the Descending Phase of the Solar Cycle 24