Browsing by Author "Ilma, R. R."
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Item Open Access Equatorial ionospheric profiles: a comparative study between IRI model and measurements over Jicamarca(Instituto Geofísico del Perú, 2005-10-22) Ilma, R. R.; Chau Chong Shing, Jorge LuisPresentación oral ofrecida en el XXVlllth URSI General Assembly 2005, New Delhi, 23-29 October 2005. 56.Item Restricted Generation of a severe convective ionospheric storm under stable Rayleigh-Taylor conditions: triggering by meteors?(European Geosciences Union, 2016-02) Kelley, M. C.; Ilma, R. R.Here we report on four events detected using the Jicamarca Radio Observatory (JRO) over an 18-year period, in which huge convective ionospheric storms (CISs) occur in a stable ionosphere. We argue that these rare events could be initiated by meteor-induced electric fields. The meteor-induced electric fields map to the bottomside of the F region, causing radar echoes and a localized CIS. If and when a localized disturbance reaches 500 km, we argue that it becomes two-dimensionally turbulent and cascades structure to both large and small scales. This leads to long-lasting structure and, almost certainly, to scintillations over a huge range of latitudes some ±15° wide and to 3 m irregularities, which backscatter the VHF radar waves. These structures located at high altitudes are supported by vortices shed by the upwelling bubble in a vortex street.Item Open Access On a correlation between the ionospheric electric field and the time derivative of the magnetic field(Hindawi, 2012-02-20) Ilma, R. R.; Kelley, M. C.; Gonzáles, C. A.A correlation of the ionospheric electric field and the time derivative of the magnetic field was noticed over thirty years ago and has yet to be explained. Here we report on another set of examples during the superstorm of November 2004. The electric field in the equatorial ionosphere, measured with the Jicamarca incoherent scatter radar, exhibited a 3 mV/m electric field pulse that was not seen in the interplanetary medium. It was, however, accompanied by a correlation with the time derivative of the magnetic field measured at two points in Peru. Our inclination was to assume that the field was inductive. However, the time scale of the pulse was too short for the magnetic field to penetrate the crust of the Earth. This means that the area threaded by ∂B/∂t was too small to create the observed electric field by induction. We suggest that the effect was caused by a modulation of the ring current location relative to the Earth due to the electric field. This electric field is required, as the magnetic field lines are considered frozen into the plasma in the magnetosphere. The closer location of the ring current to the Earth in turn increased the magnetic field at the surface.Item Restricted On the origin of pre-reversal enhancement of the zonal equatorial electric field(European Geosciences Union, 2009-05-05) Kelley, M. C.; Ilma, R. R.; Crowley, G.In November 2004, a large and variable interplanetary electric field (IEF) was felt in the reference frame of the Earth. This electric field penetrated to the magnetic equator and, when the Jicamarca Radio Observatory (JRO) was in the dusk sector, resulted in a reversal of the normal zonal component of the field. In turn, this caused a counter-electrojet (CEJ), a westward current rather than the usual eastward current. At the time of the normal pre-reversal enhancement (PRE) of the eastward field, the Jicamarca incoherent scatter radar (ISR) observed that the westward component became even more westward. Two of the three current explanations for the PRE depend on the neutral wind patterns. However, this unique event was such that the neutral wind-driven dynamos could not have changed. The implication is that the Haerendel-Eccles mechanism, which involves partial closure of the equatorial electrojet (EEJ) after sunset, must be the dominant mechanism for the PRE.Item Open Access Reconciliation of rocket-based magnetic field measurements in the equatorial electrojet with classical collision theory(American Geophysical Union, 2012-01-14) Kelley, M. C.; Ilma, R. R.; Eccles, V.We provide an explanation for a long-standing (more than 35 years) discrepancy between theory and rocket experiments concerning the peak height of the electrojet current and the magnitude of magnetic field perturbation. The arbitrary correction of the electron-neutral collision frequency by a factor of 4, which has been used to explain these problems, is not necessary if the field line–integrated conductivities are used. Recent research using ground-based magnetometers and CHAMP have also used this constant connection to classical collision theory. These methods arbitrarily change the electron-neutral collision frequency. A field line–integrated theoretical study of the electrojet by G. Haerendel and J. V. Eccles, implemented in this paper, explains the height of the electrojet using classical collision frequency. Furthermore, we argue that since the correction factor is independent of the driving electric field, it is unlikely that anomalous electron collision frequency due to a nonlinear plasma instability (gradient drift) is involved.