Super-fountain Effect Research Articles

Spatio-temporal features of ionospheric disturbances resulting from March 2023 geomagnetic storm: Comparisons with March 2015 St. Patrick’s Day storm

This study explores the ionospheric disturbances induced by the March 2023 geomagnetic storm, offering insights into the complex interplay between space weather events and the Earth’s upper atmosphere. In this regard, data from ionospheric maps (global and regional electron contents) and topside plasma density (provided by the Swarm satellites) have been used. Furthermore, the findings are compared with those of the March 2015 St. Patrick’s Day storm of solar cycle 24, which exhibited notably similar onset conditions. The Global Electron Content (GEC) displays substantial positive surges in the African, Pacific, and American sectors, with a notable enhancement in the American sector on March 24, 2023. During the recovery phase (March-23 storm), negative storm effects are observed across all longitudinal sectors, with greater intensity at low-latitudes compared to mid-latitudes. Moreover, the study highlights discrepancies in positive storm effects when compared to the St. Patrick’s Day storm. During the March-2023, there was no positive storm effect observed in the pacific mid-latitude regions. This longitudinal difference in occurrence of positive storm may be attributed to potential influences from variations in the z-component of the interplanetary magnetic field and energy inputs into the magnetosphere. A super fountain effect is observed exclusively in the American sectors during both storms, exhibiting a noticeable hemispheric asymmetry. The non-uniform planetary distribution of disturbed thermospheric winds likely played a major role in the ionospheric asymmetry in the American region during the 2023 event.

Geomagnetic Storm Variation of Vertical Total Electron Content (VTEC) Over Some Euro-African Stations

Geomagnetic storms are events which have physical effects on some ionospheric parameters that, to some extent,affects the state and dynamics of the ionosphere with important implications on GNSS applications. Here, the total electron content (TEC) of Brussels (50.80oN, 04.37oE), Madrid (40.43oN, 04.25oW) and Irkutsk (52.22oN, 104.32oE), which are all mid-latitude European stations are compared with Libreville (00.35oN, 09.67oE) and Lusaka (15.43oS, 28.32oE) which are equatorial and low-latitude stations respectively. This study is done over two geomagnetic storms that took place in the solstice period of 2004. Deviations of storm time VTEC from solar quiet (Sq) averages are calculated, analysed and presented. Similarities and differences of storm effects are observed in the European stations with enhancements and depressions. Diurnal solar quiet day variations showed high VTEC during the post-noon hours for all the stations. The VTEC deviations during storm time at Libreville lie within, for Lusaka it is. For the mid-latitude European stations, the deviations are lower such that is recorded at Brussels while is recorded for both Irkutsk and Madrid. Enhancement of VTEC during the daytime storm period is attributable to the super-fountain effect caused by the prompt penetration electric fields (PPEFs) into the ionosphere and magnetosphere while low VTEC at night-time is attributed to the process of recombination. Understanding the behaviour of the ionosphere during geomagnetic storms is important and necessary for a better understanding of the applications of GNSS.

Responses of the Indian Equatorial Ionization Anomaly to two CME-induced geomagnetic storms during the peak phase of solar cycle 24

This work analyzes the geo-effectiveness of Coronal Mass Ejection- (CME-) induced storms by investigating the responses of ionospheric Vertical Total Electron Content (VTEC) and the Equatorial Ionization Anomaly (EIA) over the Indian sector to two storms. One of the storms occurred on February 19, 2014 (SYM-H: −120 nT), while the other occurred on June 23, 2015 (SYM-H: −204 nT). Both storms were driven by full halo CMEs. Global TEC maps were used to characterize VTEC variations during the storms. June 23, 2015 storm was characterized with stronger solar progenitors, right from its origin, although the VTEC response to the storm was not influenced by their strong progenitors. The CMEs that caused the selected storms are large (Halo CMEs). We inferred that irrespective of the strength of solar origin of a storm, the response of ionization distribution over equatorial and low-latitude regions to it depends on the season of storm occurrence, local time of the storm onset, and PPEF orientation. From the VTEC variations for the three Indian stations namely, Trivandrum (geographic latitude: 8.52°N, geographic longitude: 76.94°E, magnetic latitude: 0.37°N), Hyderabad (17.39°N, 78.49°E, 10.15°N) and Delhi (28.70°N, 77.10°E, 22.70°N), we observed that EIA disturbances were more prominent over Hyderabad than over Delhi. The February 19, 2014 storm was characterized by a localized EIA crest at latitude a little above Hyderabad, while in June 23, 2015 storm localized EIA crest was observed directly on Hyderabad. IRI-2016 model generally underestimated VTEC at the three Indian equatorial and low-latitude locations. Solar cycle 24 was characterized with low heliospheric pressure due to its weak polar field strength. The lower pressure allowed CMEs to expand greatly as they transit through space. As they expand, the strengths of the magnetic field inside them decrease, and such lower-strength magnetic fields cause geomagnetic storms that are less geoeffective, even when their solar/interplanetary progenitors are strong and healthy. This associated weak polar field strength of solar cycle 24 caused weak fountain effect with the attendant inability to exhibit storm-time super-fountain effect in the dayside of the equatorial/low-latitude regions.

Ionospheric Response along Meridian for the Certain Storm Using TEC and foF2

For a long time, the equivalent ionospheric slab thickness τ has remained in the shadow of ionospheric main parameters: the maximum density, NmF2 (or the critical frequency, foF2), and the total electron content. Empirical global models have been developed for these two parameters. Recently, several global models of τ have appeared concurrently. This paper compares τ of the Neustrelitz equivalent slab thickness model (NSTM), with τ(IRI-Plas) of the IRI-Plas model, and τ(Appr) of the approximation model, constructed along the 30° E meridian using data from several ionosondes. The choice of the model of the best conformity with observational data was made, which was used to study the effects of space weather during several magnetic storms in March 2012. The effects included: (1) a transition from negative disturbances at high latitudes to positive ones at low latitudes, (2) the super-fountain effect, which had been revealed and explained in previous papers, (3) a deepening of the main ionospheric trough. The efficiency of using τ(Appr) and τ(IRI-Plas) models for studying the effects of space weather has been confirmed. The advantage of the τ(Appr) model is its closeness to real data. The advantage of the τ(IRI-Plas) model is the ability to determine foF2 without ionosondes. The efficiency of the NSTM model is insufficient for a role of a global τ model due to the accuracy decreasing with the increasing latitude.

Impact of CME and HSSW driven geomagnetic storms on thermosphere and ionosphere as observed from mid-latitudes

The present paper reports magnetospheric-thermospheric-ionospheric interactions, observed during geomagnetically disturbed periods in 2015–2016 from mid-latitude stations located in the US-Pacific longitudes (~120°W geographic). These interactions have been analyzed for a series of Coronal Mass Ejection (CME) and High Speed Solar Wind (HSSW) driven geomagnetic storms during the moderate solar activity periods. The geomagnetically disturbed periods under consideration in this paper have an interesting feature of the occurrences of one or more HSSW events following an intense CME driven intense geomagnetic storm. Correlations were observed between the solar and geomagnetic parameters, hemispherically integrated Joule heating, changes in O/N2 ratio, corresponding changes in neutral wind velocities and mid-latitude Vertical Total Electron Content (VTEC) in most of the cases. Prolonged effects of neutral wind driven equatorward plasma transport process were noticed during the period of the summer solstice (June 23–26, 2015) which was correlated with the hemispherically integrated Joule heating and ionospheric conductivities. The effects of storm onset were observed during March 17–18, 2015. The influences of the ‘super-fountain effect’ in terms of Prompt Penetration Electric Field (PPEF) were seen during the main phases of the geomagnetic storms from these mid-latitude stations. This is correlated with the strength of Equatorial Electrojet (EEJ).

The effect of space weather on the ionosphere at the 110° meridian during CAWSES-II period

Space weather determines the state of the ionosphere, which is especially important to know during disturbances. To study this state, the period of March 7–17, 2012, which was recommended by SCOSTEP for detailed studies and called CAWSES-II, was selected. In this period, the behavior of parameters of the solar wind (SW) and the interplanetary magnetic field (IMF) show a number of features. In this paper, we study their relationship with the total electron content (TEC) and the critical frequency (foF2) of the ionosphere at the 110° meridian, near which several ionosondes are located, in the range of 20°N-62.5°N. The correlation coefficients of TEC and foF2 with the SW and IMF parameters for the month and the selected period are calculated. The ionosphere showed the considered disturbances in different ways in different latitudinal zones: negative anomalies are observed at high latitudes, and positive ones at low latitudes. A distinctive feature is the presence of signs of a super-fountain effect. Deviations of TEC and foF2 from their medians can be significant. The IRI model reacted in the latitude range 40°N-62.5°N in the form of negative anomalies, although positive anomalies were observed in the TEC. At lower latitudes, no reaction was observed. For all factors (F10.7, Dst, Kp, IMF, Np), three zones (high-latitude, mid-latitude, and low-latitude) are distinguished for different coefficients. The strongest influence of disturbances on the correlation coefficients is observed in the zone of 37.5°N–62.5°N.

Superfountain Effect Linked With 17 March 2015 Geomagnetic Storm Manifesting Distinct F3 Layer

AbstractThe existence of an additional stratification in the daytime equatorial ionospheric F region (the F3 layer) was known since the 1940s. However, its characteristics and the underlying physical mechanism have been uncovered only recently. In this paper, we present and discuss the F3 layer characteristics observed by six ionosondes distributed over equatorial and low latitudes (−20° to +25° dip latitudes) in the Brazilian longitude sector during the strongest geomagnetic storm (DstMin = −223 nT) of solar cycle 24, the St. Patrick's Day storm of 17 March 2015. Two eastward prompt penetration electric field (PPEF) events, as seen in equatorial electrojet, occurred during the main phase of the storm on 17 March 2015, a strong one (~100 nT) at around ~1200 UT and a weak one (~50 nT) at around ~1725 UT. Local time variations in the F3 layer occurrence and ionospheric base height (h′F), peak height (hmF), and peak electron density (Nmax) are investigated. Notably, the F3 layer occurred at all six locations, more distinctly during the stronger PPEF event. The large latitudinal extend in the occurrence of the F3 layer in opposite hemispheres (−20° to +25° dip latitudes) covering the equatorial ionization anomaly crests observed for the first time is interpreted in terms of the combined effect of the super plasma fountain generated by the eastward PPEF and storm time equatorward neutral wind.

Emergence of a localized total electron content enhancement during the severe geomagnetic storm of 8 September 2017

Abstract. In this work, the results of the analysis on total electron content (TEC) data before, during and after the geomagnetic storm of 8 September 2017 are reported. One of the responses to geomagnetic storms due to the southern vertical interplanetary magnetic field (Bz) is the enhancement of the electron density in the ionosphere. Vertical TEC (VTEC) from the Center for Orbit determination in Europe (CODE) along with a statistical method were used to identify positive and/or negative ionospheric storms in response to the geomagnetic storm of 8 September 2017. When analyzing the response to the storm of 8 September 2017 it was indeed possible to observe an enhancement of the equatorial ionization anomaly (EIA); however, what was unexpected was the identification of a local TEC enhancement (LTE) to the south of the EIA (∼40∘ S, right over New Zealand and extending towards the southeastern coast of Australia and also eastward towards the Pacific). This was a very transitory LTE that lasted approximately 4 h, starting at ∼ 02:00 UT on 8 September where its maximum VTEC increase was of 241.2 %. Using the same statistical method, comparable LTEs in a similar category geomagnetic storm, the 2015 St. Patrick's Day storm, were looked for. However, for the aforementioned storm no LTEs were identified. As also indicated in a past recent study for a LTE detected during the 15 August 2015 geomagnetic storm, an association between the LTE and the excursion of Bz seen during the 8 September 2017 storm was observed as well. Furthermore, it is very likely that a direct impact of the super-fountain effect along with traveling ionospheric disturbances may be playing an important role in the production of this LTE. Finally, it is indicated that the 8 September 2017 LTE is the second one to be detected since the year 2016.

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

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.

Satellite drag effects due to uplifted oxygen neutrals during super magnetic storms

Abstract. During intense magnetic storms, prompt penetration electric fields (PPEFs) through E × B forces near the magnetic equator uplift the dayside ionosphere. This effect has been called the dayside super-fountain effect. Ion-neutral drag forces between the upward moving O+ (oxygen ions) and oxygen neutrals will elevate the oxygen atoms to higher altitudes. This paper gives a linear calculation indicating how serious the effect may be during an 1859-type (Carrington) superstorm. It is concluded that the oxygen neutral densities produced at low-Earth-orbiting (LEO) satellite altitudes may be sufficiently high to present severe satellite drag. It is estimated that with a prompt penetrating electric field of ∼ 20 mV m−1 turned on for 20 min, the O atoms and O+ ions are uplifted to 850 km where they produce about 40-times-greater satellite drag per unit mass than normal. Stronger electric fields will presumably lead to greater uplifted mass.

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

AbstractThe St. Patrick's Day storm of 17 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 spatiotemporal disturbances in the ionospheric total electron content 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 ~40°S latitude. In the presence of westward and equatorward wind surge over Brazil with the coexisting disturbance dynamo fields, strong hemispheric asymmetry is seen in the storm time response of EIA during both the PPEF phases.

The magnetic storms of 3–4 August 2010 and 5–6 August 2011: 1. Ground‐ and space‐based observations

AbstractWe have used total electron content (TEC) values from low, middle, and high latitudes recorded over the American continent and density and ion temperature measured in situ by the DMSP‐F15 and F17 satellites during the geomagnetic storms of 3–4 August 2010 and 5–6 August 2011 to study the formation and dynamics of plasma density enhancements that developed during these two storms. Common to both storms are the timing of the main phase that extends between 20 and 24 UT and their seasonality with both storms occurring near the end of the Northern Hemisphere summer solstice. During both storms, TEC data show incipient equatorial anomalies lacking a poleward expansion beyond 20° magnetic latitude. Two large‐scale TEC enhancements were observed at middle latitudes showing a complicated pattern of structuring and merging. The first TEC enhancement corresponds to a storm‐enhanced density (SED) seen between 21 and 01 UT on the following day. The second TEC enhancement was observed over Central America, located equatorward of the SED and apparently moving northward. However, careful analysis of the TEC values indicates that this second TEC enhancement is not transported from lower latitudes through a superfountain effect. Instead, the enhanced plasma has a local origin and is driven by a southward directed meridional wind that moves plasma up the tilted magnetic field lines. DMSP flights passing over the second TEC enhancement show a reduction of the ion temperature, confirming an adiabatic expansion of the plasma as it moves up the field lines. It is concluded that the midlatitude TEC enhancements do not arise from a low‐latitude ionospheric fountain effect.

Midlatitude ionospheric changes to four great geomagnetic storms of solar cycle 23 in Southern and Northern Hemispheres

AbstractThis paper presents an investigation of ionospheric response to great (Dst ≤−350 nT) geomagnetic storms that occurred during solar cycle 23. The storm periods analyzed are 29 March to 2 April 2001, 27–31 October 2003, 18–23 November 2003, and 6–11 November 2004. Global Navigation Satellite System, total electron content (TEC), and ionosonde critical frequency of F2 layer (foF2) data over Southern Hemisphere (African sector) and Northern Hemisphere (European sector) midlatitudes were used to study the ionospheric responses within 15°E–40°E longitude and ±31° to ±46° geomagnetic latitude. Midlatitude regions within the same longitude sector in both hemispheres were selected in order to assess the contribution of the low‐latitude changes especially the expansion of equatorial ionization anomaly (EIA) also called the dayside ionospheric superfountain effect during these storms. In all storm periods, both negative and positive ionospheric responses were observed in both hemispheres. Negative ionospheric responses were mainly due to changes in neutral composition, while the expansion of the EIA led to pronounced positive storm effects at midlatitudes for some storm periods. In other cases (e.g., 29 October 2003), penetration electric fields, EIA expansion, and large‐scale traveling ionospheric disturbances were found to be present during the positive storm effect at midlatitudes in both hemispheres. An increase in TEC on the 28 October 2003 was because of the large solar flare with previously determined intensity of X45 ±5.

Opposite hemispheric asymmetries during the ionospheric storm of 29–31 August 2004

AbstractBy making use of multiple ground‐based and spaceborne instruments, we study ionospheric and thermospheric behavior during the moderately intense geomagnetic storm of 29–31 August 2004 (minimum Dst excursion of −128 nT). Although this storm was far from the strongest in solar cycle 23, it provoked quite interesting effects in the ionosphere, such as opposite hemispheric asymmetries in the ionospheric F layer and in the topside ionosphere and a development of the ionospheric superfountain effect in the postsunset sector. Data from ground‐based GPS receivers and ionosondes revealed large increase in total electron content (TEC) and in NmF2 in the southern hemisphere, whereas in the northern hemisphere, very weak or no effect was observed. On the contrary, the topside measurements indicated the occurrence of a positive storm in the northern hemisphere. Overall, the strongest storm time disturbances were observed in the postsunset sector (~20:30–21:30 LT), where satellite radar altimeters TOPEX and Jason 1, along with the CHAMP satellite showed ~250–400% TEC increase in the middle‐ and low‐latitude regions. The signatures of the ionospheric plasma enhancement were seen up to the height of the Defense Meteorological Satellite Program (DMSP) satellites (~840 km). As for the thermospheric storm, data of the Gravity Recovery and Climate Experiment (GRACE) satellite mission revealed no asymmetry in neutral density data in the evening sector (~17 UT); however, very strong hemispheric asymmetry was observed in the postsunset sector by CHAMP (~21 UT). Overall, neutral density increase in the postsunset sector was found to be much stronger than in the evening sector.

Ionospheric TEC, thermospheric cooling and Σ[O/N2] compositional changes during the 6–17 March 2012 magnetic storm interval (CAWSES II)

A series of four geomagnetic storms (the minimum SYM-H~−148nT) occurred during the March 6–17, 2012 in the ascending phase of the solar cycle 24. This interval was selected by CAWSES II for its campaign. The GPS total electron content (TEC) database and JPL's Global Ionospheric Maps (GIM) were used to study vertical TEC (VTEC) for different local times and latitude ranges. The largest response to geomagnetic activity is shown in increases of the low-latitude dayside VTEC. Several GPS sites feature post-afternoon VTEC “bite-outs”. During Sudden Impulse (SI+) event on March 8th a peak daytime VTEC restores to about quiet-time values. It is shown that the TIMED/SABER zonal flux of nitric oxide (NO) infrared cooling radiation correlates well with auroral heating. A factor of ~5 cooling increase is noted in some storms. The cooling radiation intensifies in the auroral zone and spreads towards the equator. Effects of the storm appear at lower latitudes ~18.6h later. The column density ratio Σ[O/N2] is analyzed based on TIMED/GUVI measurements. Both increases (at low latitudes) and decreases (from auroral to middle latitudes) in the ratio occurs during the geomagnetic storms. We suggest that the column density ratio could be enhanced at low to middle latitudes on the dayside partially due to the superfountain effect (atomic oxygen uplift due to ion-neutral drag). It is suggested that decreases in the Σ[O/N2] ratio at high to middle-latitudes may be caused by high thermospheric temperatures. During SI+s, there is an increase in Σ[O/N2] ratio at auroral latitudes.

Equatorial westward electrojet impacting equatorial ionization anomaly development during the 6 April 2000 superstorm

AbstractWe investigate the forward plasma fountain and the equatorial ionosphere in the topside region during the 6 April 2000 superstorm in the Australian sector at ~0900 LT. Space‐ and ground‐based multi‐instrument measurements, Coupled Thermosphere‐Ionosphere‐Plasmasphere Electrodynamics (CTIPe) simulations, and field‐aligned observations comprise our results. These reveal an unusual storm development during which the eastward prompt penetration electric (E) field (PPEF) developed and operated under the continuous effects of the westward disturbance dynamo E‐field (DDEF) while large‐scale traveling ionospheric disturbances (TIDs) traveled equatorward and generated strong equatorward wind surges. We have identified the eastward PPEF by the superfountain effect causing the equatorial ionization anomaly (EIA)'s development with crests situated at ~±28°N (geomagnetic) in the topside ionosphere at ~840 km altitude. The westward DDEF's occurrence is confirmed by mapping the “anti‐Sq” current system wherein the equatorial westward current created a weak long‐lasting westward electrojet event. Line plots of vertical drift data tracked large‐scale TIDs. Four scenarios, covering ~3.5 h in universal time, demonstrate that the westward DDEF became superimposed on the eastward PPEF. As these E‐fields of different origins became mapped into the F region, they could interact. Consequently, the eastward PPEF‐related equatorial upward E × B drift became locally reduced by up to 75 m/s near the dip equator by the westward DDEF‐related equatorial downward E × B drift. Meanwhile, the EIA displayed a better development as equatorial wind surges, reproduced by CTIPe, increased from 501 to 629 m/s, demonstrating the crucial role of mechanical wind effects keeping plasma density high.

Reply to Tsurutani et al.'s comment on "Storming the Bastille: the effect of electric fields on the ionospheric F-layer" by Rishbeth et al. (2010)

Despite the opening paragraph of the commentary by Tsurutani et al. (2013), it is not clear to which “fundamentally incorrect statements” in Rishbeth et al. (2010) they are referring. The commentary makes three points and we will discuss these in the order in which they appear in Tsurutani et al. (2013). First is a discussion of how total electron content (TEC) enhancements to 200 or more units may appear in the expanded crests of the anomaly, which are located near 25– 30 magnetic latitude. Tsurutani et al. (2013) point out that these enhancements result from the presence of an outward meridional E×B drift originating from a prompt penetration electric field. Rishbeth et al. (2010) agree and cite previous work by Tsurutani et al. (2004), Yin et al. (2004), Basu et al. (2007) and Lin et al. (2005, 2009), all of which show that the appropriate TEC enhancements arise in the presence of enhanced outward meridional E × B drifts. In their comment, Tsurutani et al. (2013) state, “The main point we wish to make from this figure is that the CHAMP data show that the EIAs become displaced from their normal location (∼ ±10) poleward with increasing time.” This point is well recognized and appears in Rishbeth et al. (2010) by citing previous work, such as “. . . Tsurutani et al. (2004) describe a so-called super-fountain effect that creates a poleward displacement of the equatorial anomaly peaks in the presence of enhanced outward meridional E × B drifts. . . ” We conclude that no fundamentally incorrect statements appear in Rishbeth et al. (2010) on this topic. Tsurutani et al. (2013) move forward with their commentary by describing computer simulations of the effects of enhanced meridional E × B drifts. Much of this work is a recapitulation of previously published work, but it appears that the point is to show that TEC peaks appear at 25 to 30 magnetic latitude in such simulations. It may also be appropriate to point out that equatorward meridional winds can also influence the vertical drift motion and associated TEC enhancements at middle latitudes (Lin et al., 2005), and that such winds have been shown to be significant during the particular event simulated by Tsurutani et al. (2013) for their commentary (Basu et al., 2005). Tsurutani et al. (2013) present these simulations to address the question of where the plasma originates and, in this regard, the authors make conclusions that can be easily tested. It is valuable to recall that Rishbeth et al. (2010) state that “. . . TEC enhancements at latitudes beyond 25 degrees cannot generally be attributed to transport from the equator.” The work of Tsurutani et al. (2013) assumes a zonal electric field of 4 mV m−1, which generously translates to a upward drift of 130 m s−1, for a duration of 2 h. If we assume a peak plasma density near 350-km altitude, then a flux tube through this location at 25 magnetic latitude has an apex height above 1800 km. For plasma at the equator, at 350km altitude, moving under the influence of an E ×B drift of 130 m s−1, it will take over 3 h to arrive at 25 magnetic latitude. In their comment Tsurutani et al. (2013) perhaps obfuscate the statement above made by Rishbeth et al. (2010) by later invoking transport from ±20. If 20 is the location that they wish to identify as the plasma source for an enhancem nt at 25, there would be no argument. What is potentially misleading is the statement by Tsurutani et al. (2013) that “Plasma originally from latitudes lower than where the

Effects of strong IMF <I>B<sub>z</sub></I> southward events on the equatorial and mid-latitude ionosphere

Abstract. Dayside ionospheric response to five intense geomagnetic storms (Dst<−120 nT) that occurred in 2001–2005 was investigated by use of simultaneous TEC measurements by the CHAMP, SAC-C, TOPEX/Jason-1 satellites. Since the satellites passed over different longitudinal sectors and measured TEC in different range of altitudes, it was possible to obtain information about altitudinal and longitudinal ionosphere redistribution during these storms. Severe enhancements (up to ~350%) of the equatorial and mid-latitude TEC above ~430 km with concurrent traveling of the equatorial anomaly crests for a distance of 10–15° of latitude were observed during two of the five events analyzed here (6 November 2001 and 8 November 2004). This phenomenon, known as the dayside ionosphere uplift, or the "daytime super-fountain effect", occurred after sudden drop in IMF Bz and consequent penetration of the electric fields to the low-latitude ionosphere. However, the same order Bz negative events caused comparatively weak changes in the dayside TEC (up to ~80 TECU) during the other three events of 18 June 2003, 11 February 2004 and 24 August 2005. At the main phase of these storms there were mostly observed formation of the "typical" dual peak structure of the equatorial anomaly rather than the reinforcement of the fountain effect and the anomaly itself. Possible reasons and factors responsible for the development of the extreme ionosphere effects are discussed in the paper.

Dayside ionospheric uplift during strong geomagnetic storms as detected by the CHAMP, SAC-C, TOPEX and Jason-1 satellites

Ionosphere response to severe geomagnetic storms that occurred in 2001–2003 was analyzed using data of global ionosphere maps (GIM), altimeter data from the Jason-1 and TOPEX satellites, and data of GPS receivers on-board CHAMP and SAC-C satellites. This allowed us to study in detail ionosphere redistribution due to geomagnetic storms, dayside ionospheric uplift and overall dayside TEC increase. It is shown that after the interplanetary magnetic field turns southward and intensifies, the crests of the equatorial ionization anomaly (EIA) travel poleward and the TEC value within the EIA area increases significantly (up to ∼50%). GPS data from the SAC-C satellite show that during the main phase of geomagnetic storms TEC values above the altitude of 715 km are 2–3 times higher than during undisturbed conditions. These effects of dayside ionospheric uplift occur owing to the “super-fountain effect” and last few hours while the enhanced interplanetary electric field impinged on the magnetopause.

Global dayside ionospheric uplift and enhancement associated with interplanetary electric fields

The interplanetary shock/electric field event of 5–6 November 2001 is analyzed using ACE interplanetary data. The consequential ionospheric effects are studied using GPS receiver data from the CHAMP and SAC‐C satellites and altimeter data from the TOPEX/Poseidon satellite. Data from ∼100 ground‐based GPS receivers as well as Brazilian Digisonde and Pacific sector magnetometer data are also used. The dawn‐to‐dusk interplanetary electric field was initially ∼33 mV/m just after the forward shock (IMF BZ = −48 nT) and later reached a peak value of ∼54 mV/m 1 hour and 40 min later (BZ = −78 nT). The electric field was ∼45 mV/m (BZ = −65 nT) 2 hours after the shock. This electric field generated a magnetic storm of intensity DST = −275 nT. The dayside satellite GPS receiver data plus ground‐based GPS data indicate that the entire equatorial and midlatitude (up to ±50° magnetic latitude (MLAT)) dayside ionosphere was uplifted, significantly increasing the electron content (and densities) at altitudes greater than 430 km (CHAMP orbital altitude). This uplift peaked ∼2 1/2 hours after the shock passage. The effect of the uplift on the ionospheric total electron content (TEC) lasted for 4 to 5 hours. Our hypothesis is that the interplanetary electric field “promptly penetrated” to the ionosphere, and the dayside plasma was convected (by E × B) to higher altitudes. Plasma upward transport/convergence led to a ∼55–60% increase in equatorial ionospheric TEC to values above ∼430 km (at 1930 LT). This transport/convergence plus photoionization of atmospheric neutrals at lower altitudes caused a 21% TEC increase in equatorial ionospheric TEC at ∼1400 LT (from ground‐based measurements). During the intense electric field interval, there was a sharp plasma “shoulder” detected at midlatitudes by the GPS receiver and altimeter satellites. This shoulder moves equatorward from −54° to −37° MLAT during the development of the main phase of the magnetic storm. We presume this to be an ionospheric signature of the plasmapause and its motion. The total TEC increase of this shoulder is ∼80%. Part of this increase may be due to a “superfountain effect.” The dayside ionospheric TEC above ∼430 km decreased to values ∼45% lower than quiet day values 7 to 9 hours after the beginning of the electric field event. The total equatorial ionospheric TEC decrease was ∼16%. This decrease occurred both at midlatitudes and at the equator. We presume that thermospheric winds and neutral composition changes produced by the storm‐time Joule heating, disturbance dynamo electric fields, and electric fields at auroral and subauroral latitudes are responsible for these decreases.