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Michael Kosch - One of the best experts on this subject based on the ideXlab platform.

  • The Equatorial Electrojet during geomagnetic storms and substorms
    Journal of Geophysical Research: Space Physics, 2015
    Co-Authors: Y. Yamazaki, Michael Kosch
    Abstract:

    The climatology of the Equatorial Electrojet during periods of enhanced geomagnetic activity is examined using long-term records of ground-based magnetometers in the Indian and Peruvian regions. Equatorial Electrojet perturbations due to geomagnetic storms and substorms are evaluated using the disturbance storm time (Dst) index and auroral Electrojet (AE) index, respectively. The response of the Equatorial Electrojet to rapid changes in the AE index indicates effects of both prompt penetration electric field and disturbance dynamo electric field, consistent with previous studies based on F region Equatorial vertical plasma drift measurements at Jicamarca. The average response of the Equatorial Electrojet to geomagnetic storms (Dst

  • the Equatorial Electrojet during geomagnetic storms and substorms
    Journal of Geophysical Research, 2015
    Co-Authors: Y. Yamazaki, Michael Kosch
    Abstract:

    The climatology of the Equatorial Electrojet during periods of enhanced geomagnetic activity is examined using long-term records of ground-based magnetometers in the Indian and Peruvian regions. Equatorial Electrojet perturbations due to geomagnetic storms and substorms are evaluated using the disturbance storm time (Dst) index and auroral Electrojet (AE) index, respectively. The response of the Equatorial Electrojet to rapid changes in the AE index indicates effects of both prompt penetration electric field and disturbance dynamo electric field, consistent with previous studies based on F region Equatorial vertical plasma drift measurements at Jicamarca. The average response of the Equatorial Electrojet to geomagnetic storms (Dst<−50 nT) reveals persistent disturbances during the recovery phase, which can last for approximately 24 h after the Dst index reaches its minimum value. This “after-storm” effect is found to depend on the magnitude of the storm, solar EUV activity, season, and longitude.

R.g Rastogi - One of the best experts on this subject based on the ideXlab platform.

  • Asymmetries in the Equatorial Electrojet around N-E Brazil sector
    Annales Geophysicae, 2009
    Co-Authors: R.g Rastogi, N. B. Trivedi
    Abstract:

    Abstract. The paper examines the data of geographic northward (X), eastward (Y) and vertical (Z) components of the magnetic field from a dense array of 26 vector magnetometers operated in N-NE Brazil from November 1990 to March 1991. As expected, the daily variation of X showed a minor maximum around 03:00–04:00 LT and a major maximum around 12:00 LT. The daily range of ΔY showed a strong minimum around noon at all stations. The combined ΔY and ΔX indicated the direction of the Equatorial Electrojet currents to be flowing along 25° north of east at the centre and 20° north of east at the edges of the Equatorial Electrojet (EEJ) belt. The centre of the EEJ as defined by the zero intercept of the Z versus latitude was found to be near 1.0° S dip latitude. The Electrojet current was stronger in the northern half than in the southern half of the Electrojet belt. These anomalies are suggested to be due to the abnormal distribution of the mean magnetic field in this region.

  • Some aspects of Equatorial Electrojet in South America
    2007
    Co-Authors: R.g Rastogi
    Abstract:

    The strength of the Equatorial Electrojet is shown to be stronger at 75°W longitudes than at 45°W longitudes inspite of the magnetic field intensity being lower along 45°W than 75°W longitudes. There was significant correspondence in the day-to-day variation of the daily range as well as in the character of daily variation of the horizontal geomagnetic field, H, at two Equatorial Electrojet stations separated by 30° in longitude.

  • Equatorial Electrojet in the East Brazil anomaly region
    Earth Planets and Space, 2007
    Co-Authors: R.g Rastogi, K. Yumoto
    Abstract:

    An examination of the geomagnetic field variations at Equatorial stations in South America has shown that the daily range of the northward field, H, is about 30% larger in Peru than in Brazil. The midday H field vector in Brazil shows a large westward tilt, corresponding to large westward declination at the station. A significant meridional trans-Equatorial current system is suggested for the observed anomaly. The longitudinal variation in the Equatorial Electrojet current strength is suggested to be due to the corresponding variation in the ionospheric electric field rather than to the electrical conductivity.

  • Magnetic storm effects at Equatorial Electrojet stations
    Earth Planets and Space, 2006
    Co-Authors: R.g Rastogi
    Abstract:

    It is shown that there are distinctly two different mechanisms for the interaction of solar wind with the earth’s magnetosphere to produce electric field in the ionospheric heights at low and middle latitudes. A persistent or slowly varying southward Interplanetary magnetic field i.e. negative IMF-Bz generates dawn to dusk electric field at polar latitudes and a westward (dusk to dawn) electric field at dayside Electrojet region which is anti-Sq in direction. A rapid increase of IMF-Bz (northward turning) imposes a westward (dusk to dawn) electric field at all latitudes of the dayside hemisphere. The process involved is the imposition of -V × Bz electric field at the magnetosphere transmitted instantaneously to the magnetic equator through the polar latitudes. The changes in the H field at ground are largest at stations close to the magnetic equator and the midday longitudes. During magnetic storms, associated with the southward IMF-Bz, there are definite enhancements in the decrease of H field at the dayside Equatorial Electrojet stations. These changes may be coincident with the development of auroral or magnetospheric ring currents. These enhancements may be observed during the main phase as well as during the recovery phase of the magnetic storm, but the essential condition is that the IMF-Bz has to be steadily significant southward. Sometimes during the storm period abnormally large changes in H field at day side Equatorial Electrojet regions are observed associated with large sudden changes in IMF-Bz following the second mechanism of solar wind magnetospheric interaction. Thus the Equatorial magnetic storm effects are due to combined effects of disturbance ring current, slow and steady IMF-Bz as well as due to sudden large changes in IMF-Bz.

  • Meridional Equatorial Electrojet current in the American sector
    Annales Geophysicae, 1999
    Co-Authors: R.g Rastogi
    Abstract:

    Huancayo is the only Equatorial Electrojet station where the daytime increase of horizontal geomagnetic field (H) is associated with a simultaneous increase of eastward geomagnetic field (Y). It is shown that during the counter Electrojet period when ?H is negative, ?Y also becomes negative. Thus, the diurnal variation of ?Y at Equatorial latitudes is suggested to be a constituent part of the Equatorial Electrojet current system. Solar flares are known to increase the H field at an Equatorial station during normal Electrojet conditions (nej). At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter Electrojet periods (cej), a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the Equatorial Electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.

Y. Yamazaki - One of the best experts on this subject based on the ideXlab platform.

  • Longitudinal Variation of the Lunar Tide in the Equatorial Electrojet
    Journal of Geophysical Research: Space Physics, 2017
    Co-Authors: Y. Yamazaki, Claudia Stolle, Jürgen Matzka, T. A. Siddiqui, Hermann Lühr, Patrick Alken
    Abstract:

    The atmospheric lunar tide is one known source of ionospheric variability. The subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the Equatorial ionosphere. There is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude. We use magnetic field measurements from the CHAMP satellite during July 2000–September 2010 and from the two Swarm satellites during November 2013–February 2017 to determine, for the first time, the complete seasonal-longitudinal climatology of the semidiurnal lunar tidal variation in the Equatorial Electrojet intensity. Significant longitudinal variability is found in the amplitude of the lunar tidal variation, while the longitudinal variability in the phase is small. The amplitude peaks in the Peruvian sector (∼285∘E) during the Northern-Hemisphere winter and equinoxes, and in the Brazilian sector (∼325∘E) during the Northern-Hemisphere summer. There are also local amplitude maxima at ∼55∘E and ∼120∘E. The longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field. Another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides. A tidal spectrum analysis of the semidiurnal lunar tidal variation in the Equatorial Electrojet reveals the dominance of the westward-propagating mode with zonal wavenumber 2 (SW2), with secondary contributions by westward-propagating modes with zonal wavenumber 3 (SW3) and 4 (SW4). Eastward-propagating waves are largely absent from the tidal spectrum. Further study will be required for the relative importance of ionopsheric conductivities and nonmigrating lunar tides.

  • The Equatorial Electrojet during geomagnetic storms and substorms
    Journal of Geophysical Research: Space Physics, 2015
    Co-Authors: Y. Yamazaki, Michael Kosch
    Abstract:

    The climatology of the Equatorial Electrojet during periods of enhanced geomagnetic activity is examined using long-term records of ground-based magnetometers in the Indian and Peruvian regions. Equatorial Electrojet perturbations due to geomagnetic storms and substorms are evaluated using the disturbance storm time (Dst) index and auroral Electrojet (AE) index, respectively. The response of the Equatorial Electrojet to rapid changes in the AE index indicates effects of both prompt penetration electric field and disturbance dynamo electric field, consistent with previous studies based on F region Equatorial vertical plasma drift measurements at Jicamarca. The average response of the Equatorial Electrojet to geomagnetic storms (Dst

  • the Equatorial Electrojet during geomagnetic storms and substorms
    Journal of Geophysical Research, 2015
    Co-Authors: Y. Yamazaki, Michael Kosch
    Abstract:

    The climatology of the Equatorial Electrojet during periods of enhanced geomagnetic activity is examined using long-term records of ground-based magnetometers in the Indian and Peruvian regions. Equatorial Electrojet perturbations due to geomagnetic storms and substorms are evaluated using the disturbance storm time (Dst) index and auroral Electrojet (AE) index, respectively. The response of the Equatorial Electrojet to rapid changes in the AE index indicates effects of both prompt penetration electric field and disturbance dynamo electric field, consistent with previous studies based on F region Equatorial vertical plasma drift measurements at Jicamarca. The average response of the Equatorial Electrojet to geomagnetic storms (Dst<−50 nT) reveals persistent disturbances during the recovery phase, which can last for approximately 24 h after the Dst index reaches its minimum value. This “after-storm” effect is found to depend on the magnitude of the storm, solar EUV activity, season, and longitude.

  • On the day-to-day variation of the Equatorial Electrojet during quiet periods
    Journal of Geophysical Research: Space Physics, 2014
    Co-Authors: Y. Yamazaki, Arthur D. Richmond, Astrid Maute, Han-li Liu, Nicholas Pedatella, Fabrizio Sassi
    Abstract:

    It has been known for a long time that the Equatorial Electrojet varies from day to day even when solar and geomagnetic activities are very low. The quiet time day-to-day variation is considered to be due to irregular variability of the neutral wind, but little is known about how variable winds drive the Electrojet variability. We employ a numerical model introduced by Liu et al. (2013), which takes into account weather changes in the lower atmosphere and thus can reproduce ionospheric variability due to forcing from below. The simulation is run for May and June 2009. Constant solar and magnetospheric energy inputs are used so that day-to-day changes will arise only from lower atmospheric forcing. The simulated Electrojet current shows day-to-day variability of ±25%, which produces day-to-day variations in ground level geomagnetic perturbations near the magnetic equator. The current system associated with the day-to-day variation of the Equatorial Electrojet is traced based on a covariance analysis. The current pattern reveals return flow at both sides of the Electrojet, in agreement with those inferred from ground-based magnetometer data in previous studies. The day-to-day variation in the Electrojet current is compared with those in the neutral wind at various altitudes, latitudes, and longitudes. It is found that the Electrojet variability is dominated by the zonal wind at 100–120 km altitudes near the magnetic equator. These results suggest that the response of the zonal polarization electric field to variable zonal winds is the main source of the day-to-day variation of the Equatorial Electrojet during quiet periods.

Sudha Ravindran - One of the best experts on this subject based on the ideXlab platform.

B. V. Krishna Murthy - One of the best experts on this subject based on the ideXlab platform.