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  • 1. Falayi, E. O.
    et al.
    Adebesin, B. O.
    Bolaji, O. S.
    The impact of coronal mass ejection on the horizontal geomagnetic fields and the induced geoelectric fields2017In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948Article in journal (Refereed)
    Abstract [en]

    Abstract This work investigates the influence of coronal mass ejection (CME) on the time derivatives of horizontal geomagnetic and geoelectric fields, proxy parameters for identifying GICs. 16 events were identified for the year 2003 from the CORONAS-PHOTON spacecraft. Five of the events (May 29, June 9, October 28, October 29, and November 4) were extensively discussed over four magnetic observatories, were analyzed using the time derivatives of the horizontal geomagnetic (dH/dt) and geoelectric (EH) fields obtained from data of the INTERMAGNET network. It was observed that energy distributions of the wavelet power spectrum of the horizontal geoelectric field are noticed at the nighttime on both 29 May and 9 June 2003 across the stations. Daytime and nighttime intensification of energy distribution of the wavelet power spectrum of the horizontal geoelectric field are observed on both 28 and 29 October 2003 due to strong westward electrojet. The 4 November 2003 event depicts daytime amplification of energy distributions of the wavelet power spectrum across the stations. The highest correlation magnitude is obtained in the event of 4 November 2003 between dH/dt and EH relationships during the intense solar flare of class X 17.4. We observed that the correlation magnitude between dH/dt and EH increases with increase in CME activity. We concluded that the response of the surface impedance model for different stations plays a key role in determining the surface electric field strength, due to large electric field changes at different stations.

  • 2. Falayi, E. O.
    et al.
    Oyebanjo, O. A.
    Omotosho, T. V.
    Okusanya, A. A.
    Storm-time variation of the horizontal and vertical components of the geomagnetic fields and rate of induction at different latitudes2016In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 58, no 7, p. 1208-1218Article in journal (Refereed)
    Abstract [en]

    The paper presents the hourly mean variation of horizontal (H) and vertical (Z) components of the geomagnetic field and the rate of induction ΔH/ΔZ at different latitudes during magnetic storm of 20 March 2001 and 1 October 2001. The results of the analysis revealed that at high latitude stations greater than 60°, the reduction in ΔH component was noticed after the noon time while other stations less than 60° experienced reduction of H in the morning time during the geomagnetic storm. Large amplitude of ΔH and ΔZ were exhibited during the daytime over the equatorial zone, the amplitude decreases from mid latitudes to the dip equator during the nighttime. The daytime enhancement of ΔH at AAE, BAN and MBO suggest the presence of a strong eastward directed current which comes under the influence of electrojet. There were strong positive and negative correlations between ring current (DR) and horizontal component of the magnetic field ΔH. The effect of rate of induction is more significant at high latitudes than lower latitudes, during the geomagnetic storm. More enhancement in rate of induction occurred at nighttime than daytime. This result may be from other sources other than the ionosphere that is magnetospheric process significantly contributes toward the variation of induction.

  • 3. Singh, Anand K.
    et al.
    Sinha, A. K.
    Saini, S.
    Rawat, Rahul
    Auroral electrojets during severely disturbed geomagnetic condition on 24 August 20052015In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 55, no 5, p. 1349-1355Article in journal (Refereed)
    Abstract [en]

    Abstract Very intense and highly dynamic eastward and westward currents flowing in the auroral ionosphere are traditionally monitored by the auroral electrojet indices – AUandAL, respectively. In this study we show that on occasions of intense magnetic activity, entire auroral oval could be dominated by the westward flowing currents, which lead to depression not only in AL index but also in supposedly positive AU index. During negative AU intervals, there could be up to ∼20% underestimation of the total maximum intensity of the auroral electrojet represented by AEindex(defined asAU-AL). A detailed investigation of a well-studied extremely intense event of 24 August 2005 has been carried out. Global prevalence of the westward auroral electrojet was clearly observed at the auroral latitudes during the unusually intense substorm (AL∼-4000nT) on the day. Moreover, along the noon meridian westward electrojet appeared in the auroral region whereas eastward electrojet shifted towards lower latitudes. This paper emphasizes that intense substorms are represented better by AL index than AE index.

  • 4. Zaourar, N.
    et al.
    Amory-Mazaudier, C.
    Fleury, R.
    Hemispheric asymmetries in the ionosphere response observed during the high-speed solar wind streams of the 24-28 August 20102017In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 59, no 9, p. 2229-2247Article in journal (Refereed)
    Abstract [en]

    Abstract This paper presents the geomagnetic and ionospheric responses to a high speed solar wind stream (HSS) impacting the magnetosphere on 24 August 2010. We focus our study on the interhemispheric conjugated behavior. The solar wind speed remained very high during 5days from 24 to 28 August 2010. By using magnetometer and ground-based GPS data from various approximately conjugated magnetic observatories and GPS stations, we studied the hemispheric asymmetries in the magnetic signature, Vertical Total Electron Content (VTEC) and scintillation activity during this HSS event. Geomagnetic activity reveals larger disturbances in amplitude in the Northern Hemisphere (NH) than in the southern Hemisphere (SH), and stronger asymmetries at higher latitudes, than at lower latitudes, between the conjugate observatories. VTEC variations reveal large increases in amplitude in the NH; while these effects are less pronounced in the SH. We investigate also the GPS scintillation activities occurring in the conjugated polar regions under HSSs conditions. At auroral latitudes, our results show a good correlation between the rate of VTEC index (ROTI) and auroral Al index, with more intense phase fluctuations in the NH.

  • 5. Zhu, Jin
    et al.
    Du, Aimin
    Ou, Jiaming
    Xu, Wenyao
    Latitudinal and MLT dependence of the seasonal variation of geomagnetic field around auroral zone2017In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 60, no 3, p. 667-676Article in journal (Refereed)
    Abstract [en]

    Abstract Seasonal variation of geomagnetic field around auroral zone is analyzed in terms of geomagnetic latitude, magnetic local time (MLT) and geomagnetic condition in this study. The study uses horizontal component (H) of geomagnetic field obtained from 6 observatories located in geomagnetic latitude of 57.8°N–73.8°N along 115°E longitudinal line. The results indicate that seasonal variations of geomagnetic field around auroral zone are different combinations of annual and semiannual variations at different latitudinal ranges. Both annual and semiannual variations show distinct MLT dependency: (1) At dayside auroral latitudes (around 72°N geomagnetic latitude), geomagnetic field shows distinct annual variation under both quiet and disturbed conditions. Furthermore, the annual component is mainly contributed by data of dusk sector. (2) At nightside auroral latitudes (around 65°N), geomagnetic field shows semiannual dominated seasonal variation. Under quiet conditions the annual component is comparable to the semiannual component, while under disturbed conditions, the semiannual component is twice as much as the annual component. Under quiet conditions, the semiannual component is mainly contributed by 1300–1400 MLT, while the annual component has two peaks: one is around 1100–1300 MLT and the other is around 2000–2200 MLT. Under disturbed conditions, the semiannual component is mainly contributed by data around midnight, while the annual component is mainly contributed by dusk sector. (3) At subauroral latitudes (around 60°N), annual variation is comparable to semiannual variation under both quiet and disturbed conditions. Both annual and semiannual components show similar MLT dependencies as that of nightside auroral latitudes.

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