Browsing by Author "Yamazaki, Yosuke"

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    Simultaneous storm time equatorward and poleward large‐scale TIDs on a global scale
    (American Geophysical Union, 2016-06-19) Habarulema, John Bosco; Katamzi, Zama Thobeka; Yizengaw, Endawoke; Yamazaki, Yosuke; Seemala, Gopi
    We report on the first simultaneous observations of poleward and equatorward traveling ionospheric disturbances (TIDs) during the same geomagnetic storm period on a global scale. While poleward propagating TIDs originate from the geomagnetic equator region, equatorward propagating TIDs are launched from the auroral regions. On a global scale, we use total electron content observations from the Global Navigation Satellite Systems to show that these TIDs existed over South American, African, and Asian sectors. The American and African sectors exhibited predominantly strong poleward TIDs, while the Asian sector recorded mostly equatorward TIDs which crossed the geomagnetic equator to either hemisphere on 9 March 2012. However, both poleward and equatorward TIDs are simultaneously present in all three sectors. Using a combination of ground‐based magnetometer observations and available low‐latitude radar (JULIA) data, we have established and confirmed that poleward TIDs of geomagnetic equator origin are due to ionospheric electrodynamics, specifically changes in E × B vertical drift after the storm onset.
    Palabras clave:Low‐latitude electrodynamicsPoleward and equatorward TIDsRadar
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    The equatorial electrojet during geomagnetic storms and substorms
    (American Geophysical Union, 2015-02-16) Yamazaki, Yosuke; Kosch, Michael J.
    He 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.
    Palabras clave:Equatorial electrojetIonospheric currentsGeomagnetic storms