Browsing by Author "Huang, Chao-Song"
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Item Restricted Long‐duration penetration of the interplanetary electric field to the low‐latitude ionosphere during the main phase of magnetic storms(American Geophysical Union, 2005-11-26) Huang, Chao-Song; Foster, John C.; Kelley, Michael C.It is well known that the interplanetary electric field can penetrate to the low‐latitude ionosphere. It is generally believed that the penetration of electric fields can last only for ∼30 min because of the shielding effect in the ring current. In this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field (IMF). In six cases, the eastward electric field in the dayside equatorial ionosphere, measured by the Jicamarca incoherent scatter radar, was enhanced for 2–3 hours after the IMF turned southward and remained continuously southward. In one case the eastward electric field in the dayside midlatitude ionosphere, measured by the Millstone Hill incoherent scatter radar, was continuously enhanced for ∼10 hours during southward IMF. Since Millstone Hill is close to the equatorward boundary of the auroral zone during magnetic storms, the penetration electric field there may be different from that at the equatorial ionosphere. The most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay. The electric field enhancements in the middle‐ and low‐latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms. The observations show that the interplanetary electric field can continuously penetrate to the low‐latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions.Item Restricted Penetration electric fields: Efficiency and characteristic time scale(Elsevier, 2007-07) Huang, Chao-Song; Sazykin, Stanislav; Chau Chong Shing, Jorge Luis; Maruyama, Naomi; Kelley, Michael C.Penetration of the interplanetary electric field (IEF) to the middle- and low-latitude ionosphere has been investigated for nearly four decades. Most previous studies focused on the correlation between the interplanetary and ionospheric electric field perturbations. Very little attention has been paid to a quantitative relationship except for a recent case analysis by Kelley et al. [2003. Penetration of the solar wind electric field into the magnetosphere/ionosphere system. Geophysical Research Letters 30(4), 1158. doi:10.1029/2002GL016321]. In this paper, we present a statistical result of the efficiency of IEF penetration to the dayside equatorial ionosphere; the efficiency is defined as the ratio of the change of the equatorial ionospheric electric field to the change of the IEF. The Jicamarca incoherent scatter radar has made continuous operation with a coherent scatter mode since 2001, and the radar data of equatorial ionospheric electric fields are used in our statistics. On the basis of data statistics, we derive an empirical value of 9.6% for the efficiency of penetration. We apply this empirical formula to the observations and numerical simulations of storm-time penetration electric fields over a prolonged interval of southward interplanetary magnetic field. The prediction of the formula is in good agreement with case studies and with results from first-principle simulations of the coupled magnetosphere–ionosphere–thermosphere system. We conclude that the IEF can continuously penetrate to the low-latitude ionosphere without significant attenuation for many hours during the main phase of magnetic storms.Item Restricted Plasma drifts and polarization electric fields associated with TID‐like disturbances in the low‐latitude ionosphere: C/NOFS observations(American Geophysical Union, 2016-01-13) Huang, Chao-SongMedium‐scale traveling ionospheric disturbances are often observed at the magnetically conjugate points in the nighttime midlatitude ionosphere. It has been suggested that gravity waves disturb the ionosphere and induce electric fields in one hemisphere and that the electric fields are amplified by the Perkins instability and transmitted along the geomagnetic field lines to the conjugate ionosphere, creating similar disturbances there. However, direct observations of electric fields associated with traveling ionospheric disturbances (TIDs) are very few. In this study, we present low‐latitude TID‐like disturbances observed by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. It is found that ion velocity perturbations are generated in the directions parallel and perpendicular to the geomagnetic field within TIDs. Both the parallel and perpendicular ion velocity perturbations show an in‐phase correlation with the ion density perturbations. For nighttime TIDs, the amplitude of both the parallel and meridional ion velocity perturbations increases almost linearly with the amplitude of the ion density perturbations, and the meridional ion drift is proportional to the parallel ion velocity. For daytime TIDs, the parallel ion velocity perturbation increases with the ion density perturbation, but the meridional ion velocity perturbation does not change much. The observations provide evidence that polarization electric field is generated within TIDs at low latitudes and maps along the geomagnetic field lines over a large distance.Item Open Access Variations of low-latitude geomagnetic fields and Dst index caused by magnetospheric substorms(American Geophysical Union, 2004-05-25) Huang, Chao-Song; Foster, J. C.; Goncharenko, L. P.; Reeves, G. D.; Chau Chong Shing, Jorge Luis; Yumoto, K.; Kitamura, K.We present observations of periodic magnetospheric substorms and corresponding ionospheric disturbances. Since the periodic substorms occur during a stable interplanetary magnetic field, we are able to identify which ionospheric signatures are caused solely by substorms. We find that the low-latitude ionospheric electric field perturbation after substorm onsets is eastward on the dayside and westward on the nightside and that the ground magnetometer northward (H) deviations at middle and low latitudes show an increase (a positive bay) after each substorm onset, no matter whether the magnetometers are located on the dayside or on the nightside. The nightside magnetometer H deviations are closely correlated with the inner magnetospheric magnetic field Bz component during the dipolarization process. The Dst index shows a significant increase of 20–40 nT after each substorm onset. We propose that the increase in the magnetometer H field and Dst index in response to substorm onsets is related to the field dipolarization. In this scenario the nightside magnetosphere earthward of the near-Earth neutral line is highly compressed during the dipolarization, and the magnetic flux density within the inner magnetosphere is greatly enhanced, resulting in an increase in the ground magnetometer H component and in Dst.