scholarly journals Investigation of Unusual Solar Flare Effect on the Global Ionospheric Current System

2018 ◽  
Vol 123 (10) ◽  
pp. 8599-8609 ◽  
Author(s):  
N. M. N. Annadurai ◽  
N. S. A. Hamid ◽  
Y. Yamazaki ◽  
A. Yoshikawa
Keyword(s):  
Solar Flare ◽  
Current System ◽  
Ionospheric Current ◽  
Ionospheric Current System

scholarly journals An intense SFE and SSC event in geomagnetic <i>H</i>, <i>Y</i> and <i>Z</i> fields at the Indian chain of observatories

1997 ◽  
Vol 15 (10) ◽  
pp. 1301-1308 ◽  
Author(s):  
R. G. Rastogi ◽  
D. R. K. Rao ◽  
S. Alex ◽  
B. M. Pathan ◽  
T. S. Sastry
Keyword(s):  
Solar Flare ◽  
Geomagnetic Storm ◽  
Geomagnetic Field ◽  
Current System ◽  
Equatorial Electrojet ◽  
Start Time ◽  
Low Latitude ◽  
Ionospheric Current ◽  
Ionospheric Current System ◽  
Solar Flare Effects

Abstract. Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518 h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in ΔH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. ΔY registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. ΔZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.

scholarly journals High-latitude crochet: solar-flare-induced magnetic disturbance independent from low-latitude crochet

2020 ◽  
Vol 38 (6) ◽  
pp. 1159-1170
Author(s):  
Masatoshi Yamauchi ◽  
Magnar G. Johnsen ◽  
Carl-Fredrik Enell ◽  
Anders Tjulin ◽  
Anna Willer ◽  
...  
Keyword(s):  
Solar Flare ◽  
Electron Density ◽  
High Latitude ◽  
Current System ◽  
Density Ratio ◽  
Auroral Electrojet ◽  
Ionospheric Current ◽  
Latitude Range ◽  
Zonal Current ◽  
Ionospheric Current System

Abstract. A solar-flare-induced, high-latitude (peak at 70–75∘ geographic latitude – GGlat) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77∘ GGlat near local noon detected northward geomagnetic deviations (ΔB) for more than 3 h, with peak amplitudes of >200 nT without any accompanying substorm activities. From its location, this solar flare effect, or crochet, is different from previously studied ones, namely, the subsolar crochet (seen at lower latitudes), auroral crochet (pre-requires auroral electrojet in sunlight), or cusp crochet (seen only in the cusp). The new crochet is much more intense and longer in duration than the subsolar crochet. The long duration matches with the period of high solar X-ray flux (more than M3-class flare level). Unlike the cusp crochet, the interplanetary magnetic field (IMF) BY is not the driver, with the BY values of only 0–1 nT out of a 3 nT total field. The equivalent ionospheric current flows eastward in a limited latitude range but extended at least 8 h in local time (LT), forming a zonal current region equatorward of the polar cap on the geomagnetic closed region. EISCAT radar measurements, which were conducted over the same region as the most intense ΔB, show enhancements of electron density (and hence of ion-neutral density ratio) at these altitudes (∼100 km) at which strong background ion convection (>100 m s−1) pre-existed in the direction of tidal-driven diurnal solar quiet (Sq0) flow. Therefore, this new zonal current can be related to this Sq0-like convection and the electron density enhancement, for example, by descending the E-region height. However, we have not found why the new crochet is found in a limited latitudinal range, and therefore, the mechanism is still unclear compared to the subsolar crochet that is maintained by a transient redistribution of the electron density. The signature is sometimes seen in the auroral electrojet (AE = AU − AL) index. A quick survey for X-class flares during solar cycle 23 and 24 shows clear increases in AU for about half the > X2 flares during non-substorm time, despite the unfavourable latitudinal coverage of the AE stations for detecting this new crochet. Although some of these AU increases could be the auroral crochet signature, the high-latitude crochet can be a rather common feature for X flares. We found a new type of the solar flare effect on the dayside ionospheric current at high latitudes but equatorward of the cusp during quiet periods. The effect is also seen in the AU index for nearly half of the > X2-class solar flares. A case study suggests that the new crochet is related to the Sq0 (tidal-driven part) current.

scholarly journals Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

1999 ◽  
Vol 17 (5) ◽  
pp. 692-706 ◽  
Author(s):  
S. Tsunomura
Keyword(s):  
Magnetic Fields ◽  
Electric Field ◽  
Current System ◽  
Equatorial Region ◽  
Iri Model ◽  
Ionospheric Layer ◽  
Ionospheric Current ◽  
New Model ◽  
Ionospheric Current System ◽  
Field Aligned Current

Abstract. A modeling method is proposed to derive a two-dimensional ionospheric layer conductivity, which is appropriate to obtain a realistic solution of the polar-originating ionospheric current system including equatorial enhancement. The model can be obtained by modifying the conventional, thin shell conductivity model. It is shown that the modification for one of the non-diagonal terms (Σθφ) in the conductivity tensor near the equatorial region is very important; the term influences the profile of the ionospheric electric field around the equator drastically. The proposed model can reproduce well the results representing the observed electric and magnetic field signatures of geomagnetic sudden commencement. The new model is applied to two factors concerning polar-originating ionospheric current systems. First, the latitudinal profile of the DP2 amplitude in the daytime is examined, changing the canceling rate for the dawn-to-dusk electric field by the region 2 field-aligned current. It is shown that the equatorial enhancement would not appear when the ratio of the total amount of the region 2 field-aligned current to that of region 1 exceeds 0.5. Second, the north-south asymmetry of the magnetic fields in the summer solstice condition of the ionospheric conductivity is examined by calculating the global ionospheric current system covering both hemispheres simultaneously. It is shown that the positive relationship between the magnitudes of high latitude magnetic fields and the conductivity is clearly seen if a voltage generator is given as the source, while the relationship is vague or even reversed for a current generator. The new model, based on the International Reference Ionosphere (IRI) model, can be applied to further investigations in the quantitative analysis of the magnetosphere-ionosphere coupling problems.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionosphere-magnetosphere interactions)

Global Pc5 caused by aDP2-type ionospheric current system

2002 ◽  
Vol 107 (A2) ◽  
pp. SMP 8-1-SMP 8-12 ◽  
Author(s):  
T. Motoba ◽  
T. Kikuchi ◽  
H. Lühr ◽  
H. Tachihara ◽  
T.-I. Kitamura ◽  
...  
Keyword(s):  
Current System ◽  
Ionospheric Current ◽  
Ionospheric Current System

Realtime geomagnetic indices for mid-latitudes. MID-R, MID-E, MID-U and MID-L

2020 ◽  
Author(s):  
Antonio Guerrero ◽  
Elena Saiz ◽  
Consuelo Cid
Keyword(s):  
Ring Current ◽  
Current System ◽  
Physical Processes ◽  
Ionospheric Current ◽  
Disturbance Index ◽  
Geomagnetic Indices ◽  
Ionospheric Current System ◽  
Operational Space ◽  
Low Latitudes ◽  
The University

&lt;p&gt;Mid latitudes around 40 degree are influenced by effects typically found at both high and low latitudes. Moreover, the focus of the Solar Quiet ionospheric current system, drifts around these mid-latitudes. Consequently they have been considered as a complicated place to infer the geospace state from the ground and also complicated for practical procedures to generate geomagnetic indices.&amp;#160;&lt;br&gt;The procedure designed at the University of Alcala specially focused on removing solar regular variations at mid-latitudes is delivering a geomagnetic Local Disturbance index (LDi) in realtime. The same procedure can be used to produce global geomagnetic indices when applied to several geomagnetic stations at these latitudes.&amp;#160;&lt;br&gt;We present in this work the high-resolution (one minute) realtime production of ring current and auroral indices (MID-R, MID-E, MID-U and MID-L) similar to the well known Dst and AE indices for mid-latitudes which will help in the understanding of the complex physical processes that emerge at these latitudes. At the same time they fill a gap in the current operational space weather products available for these latitudes.&lt;/p&gt;

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