Browsing by Author "Ilma, Ronald R."
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Item Open Access Comparison of ionosonde and incoherent scatter drift measurements at the magnetic equator(American Geophysical Union, 2006-01-10) Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge Luis; Ilma, Ronald R.It has been proposed that ionosondes can be used to measure vectorial nighttime ionospheric drifts at F region altitudes. These measurements have been validated at mid and high magnetic latitudes on campaign basis. Here we report concurrent F-region drift measurements made at Jicamarca (11.95°S, 76.87°W), under the magnetic equator, using the main Incoherent scatter radar (ISR) and a digisonde portable ionosonde (DPS). As far as the vertical drift measurements, we show a fair agreement between the two techniques at periods when convection dominates other factors (e.g., around pre-reversal enhancement). At other times, production and recombination dominate, and DPS vertical drifts are not reliable. For the horizontal drift component, we limited our measurements to the zonal component. We find poor agreement, being worse at times when the E region electron density is high (e.g., during the day). The amplitude of DPS zonal velocities are significantly larger than ISR zonal drifts. During the day, we find that the DPS zonal drifts are in better agreement with the drift velocity of the long wavelength equatorial electrojet (EEJ) instabilities. This is to be expected since, the diffraction pattern on the ground - to which any reflection HF drift technique will be sensitive to - is mainly, if not solely, dependent on the electron density structure at EEJ heights, where the electron irregularity density is sufficiently high to diffract the phase front of the F region reflected wave.Item Restricted Evidence for anomalous cowling conductivity in the strongly driven equatorial electrojet and a reconciliation of magnetic field data with theory(Editor no identificado, 2009-08) Kelley, Michael C.; Ilma, Ronald R.; Alken, Patrick; Maus, StefanSeveral days of continuous incoherent scatter radar observations during the November 2004 magnetic superstorm are available, as well as data from the CHAMP [CHAllenging Minisatellite Payload] satellite magnetic fiel d detector. We have found that, for zonal electric fields greater than about 1 mV/m, the linear relationship between CHAMP-deduced electric fields and Jicamarca-measured electric fields breaks down. We find that the observed magnetic field is a factor of two smaller than expected for the largest zonal electric field (3.2 mV/m) observed simultaneously in time and nearby spatially with CHAMP. The fact that similar decreases in the effective conductivity occurred during both normal and counter-electrojet conditions indicates that Farley-Buneman waves must be the source of the physical mechanism for the reduced current. In addition, 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 and the magnetic field perturbation. The correction by a factor of four of the electron-neutral collision frequency thought to explain this problem is not necessary if the field line integrated conductivities are used.Item Restricted On the development of nonlinear waves in the equatorial electrojet(Elsevier, 2013-10) Kelley, Michael C.; Ilma, Ronald R.Theories for the equatorial electrojet (EEJ) have been notoriously difficult to resolve with data. Two of these problems were solved recently and another is discussed in this publication. We initially review solutions to the first two issues: the constant phase velocity of 3 m waves in the EEJ with zenith angle and the disagreement between the observed and calculated altitude of the EEJ current. One remaining problem is the nonlinear nature of large-scale waves in the electrojet that appear as square waves. One possibility is the conversion of free energy into ion acoustic waves, which limits the large-scale wave amplitude to the threshold for producing such waves. Another is the breaking of large-scale waves when the perturbation velocity internal to the wave approaches the wave phase velocity.Item Restricted Spectacular low- and mid-latitude electrical fields and neutral winds during a superstorm(Elsevier, 2010-03) Kelley, Michael C.; Ilma, Ronald R.; Nicolls, Michael; Erickson, Phillip; Goncharenko, Larisa; Chau Chong Shing, Jorge Luis; Aponte, Nestor; Kozyra, Janet U.In November 2004, a major magnetic storm occurred, a lengthy portion of which was recorded by the Upper Atmospheric Radar Chain. On the 9th and 10th, the Jicamarca Radar detected the highest magnitude penetrating electric fields (±3 mV/m) and vertical drifts (±120 m/s) ever seen at this premiere facility. These large and variable drifts were highly correlated with the interplanetary magnetic and electric fields and created a double F layer on the dayside and unusual TEC behavior throughout the low-latitude zone. These solar wind-induced drifts both suppressed and generated irregularities at the magnetic equator at different times. Large-scale thermospheric disturbances were generated by high-latitude heating and tracked through the middle- to low-latitude zones where both parallel and perpendicular plasma drifts created major ionospheric changes. The auroral oval was located at a magnetic L shell of about three for many hours.