Browsing by Author "Kelley, M. C."
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Item Restricted Eddy turbulence parameters inferred from radar observations at Jicamarca(European Geosciences Union (EGU), 2007-03-08) Vlasov, M. N.; Kelley, M. C.; Hysell, D. L.Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007). In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1×103 m2/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007) is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density.Item Restricted Equatorial electric fields during magnetically disturbed conditions 1. The effect of the interplanetary magnetic field(American Geophysical Union, 1979-10-01) Woodman Pollitt, Ronald Francisco; Kelley, M. C.; Farley, D. T.; Fejer, B. G.; Gonzáles, S. A.Radar measurements of E and F region drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF). The east-west component of the IMF appears to be unimportant, but the north-south component has some effect; rapid reversals from south to north are sometimes correlated with reversals of the equatorial east-west electric field during both daytime and nighttime. This is not always true, however, the IMF may reverse without any apparent effect at the equator. Furthermore, large equatorial field perturbations are sometimes observed when the IMF Bz is large and southward but not varying drastically. In this latter case the equatorial perturbations start nearly simultaneously with the onset of auroral substorms, while in the previous case they usually correlate with the onset of the substorm recovery phase. These observations indicate that the IMF does not affect the equatorial electric fields directly. Rather, it is changes in the magnetospheric electric fields and the auroral zone electric field and conductivity distribution (which may or may not be triggered by IMF changes) which alter the worldwide ionospheric current flow and electric field pattern, of which the equatorial observations are an indication.Item Restricted Equatorial electric fields during magnetically disturbed conditions 2. Implications of simultaneous auroral and equatorial measurements(American Geophysical Union, 1979-10-01) Gonzales, C.A.; Kelley, M. C.; Fejer, B. G.; Vickrey, J. F.; Woodman Pollitt, Ronald FranciscoSimultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low latitude ionosphere. These currents flow westward across the dayside. In several cases the zonal equatorial electric field component was nearly identical in form to the zonal auroral component, indicating the close electrical coupling between these regions. Less certain, but equally intriguing, is the evidence presented for a close relationship between the zonal equatorial electric field and the time derivative of the ring current induced magnetic field. Another class of events seems related to rapid changes of magnetospheric convection and a temporary imbalance between the field external to the plasmasphere and the shielding charges in the Alfven layer. Examples of both rapid increases and decreases are presented. The latter seems often to be related to a northward turning of the interplanetary magnetic field.Item Restricted First successful prediction of a convective equatorial ionospheric storm using solar wind parameters(American Geophysical Union, 2008-08-28) Kelley, M. C.; Retterer, J.One of the major challenges of the National Space Weather Program in the United States is to predict the generation of intense turbulence in the equatorial and low‐latitude ionosphere. We term this a convective equatorial ionospheric storm since, much like a thunderstorm, low‐density media erupt upward, releasing stored gravitational energy. This is an important phenomenon since both communication and navigational systems can be severely affected by the associated turbulence. Here, for the first time, we use solar wind data obtained upstream of the Earth and a physics‐based assimilative model to successfully predict such an event during a strong magnetic storm in November 2004.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 Restricted Low‐ and mid‐latitude ionospheric electric fields during the January 1984 GISMOS Campaign(American Geophysical Union, 1990-03) Fejer, B. G.; Kelley, M. C.; Senior, C.; De la Beaujardiere, O.; Holt, J. A.; Tepley, C. A.; Burnside, R.; Abdu, M. A.; Sobral, J. H. A.; Woodman Pollitt, Ronald Francisco; Kamide, Y.; Lepping, R.An alternative approach for estimating E region density profiles using radio occultation total electron content (ROTEC) measurements is presented. In this approach, the F region contribution to the measured ROTEC is removed using the estimated F region from an assimilative model of ionospheric density. E region density profiles are then obtained from a numerical inversion of the residual ROTEC, which is assumed to be the E region contribution to the ROTEC. The proposed technique has been applied to radio occultation measurements made by the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), while the F region specification is obtained from the Ionospheric Data Assimilation Four-Dimensional (IDA4D) algorithm. Examples of E region profiles obtained with this approach are presented and compared with nearby radar measurements at the magnetic equator. The results indicate that accurate estimates of the E region peak height and density can be obtained with this approach. This technique may be applicable to the estimation of E region conductivities with the global coverage provided by the radio occultation measurements.Item Restricted Modeling the low-latitude ionospheric electron density and plasma turbulence in the November 2004 storm period(Elsevier, 2010-03) Retterer, J. M.; Ilma, Ronald; Kelley, M. C.; Chau Chong Shing, Jorge Luis; Valladares, C. E.; Gentile, L. C.; Groves, K.The storm period of 8–12 November 2004 offers an opportunity for insight into the phenomena of low-latitude ionospheric structure during geomagnetically disturbed times because of the strength of the disturbances, the timing of the storms, and the instrumentation that was operating during the interval. We will take advantage of these factors to model the ambient ionosphere and the plasma turbulence responsible for radio scintillation within it, using the AFRL low-latitude ambient/turbulent ionospheric model and the storm-time model features described in the companion paper [Retterer, J.M., Kelley, M.C., 2009. Solar-wind drivers for low-latitude ionospheric models during geomagnetic storms. J. Atmos. Solar-Terr. Phys., this issue]. The model plasma densities show very good agreement with the densities measured by the Jicamarca ISR as well as with the total electron content (TEC) measured by the Boston College South American chain of GPS receivers. The detection by the radar of coherent returns from plasma turbulence match well the times of predicted ionospheric instability. The predicted geographic extent of the occurrence of equatorial plasma bubbles was matched by DMSP satellite observations and our forecasts of scintillation strength were validated with measurements of S4 at Ancon and Antofagasta by stations of the AFRL SCINDA network.Item Restricted Multi-longitude case studies comparing the interplanetary and equatorial ionospheric electric fields using an empirical model(Elsevier, 2007-03) Kelley, M. C.; Nicolls, M. J.; Anderson, D.; Anghel, A.; Chau Chong Shing, Jorge Luis; Sekar, R.; Subbarao, K. S. V.; Bhattacharyya, A.Electric fields have been determined at three longitudes corresponding to Peru, India, and the Philippines. We compare these fields to applying a frequency-dependent linear transfer function (TF) to the dawn-to-dusk component of the interplanetary electric field (IEF). The TF is based on four years of simultaneous observations of the IEF and equatorial data. The model gives good results for the prompt penetrating electric field (PPE) in the case of an oscillatory IEF with a period in the 1–2 h range, when the interplanetary magnetic field remains southward for a long period and, to a lesser extent, when the IEF can be described as a square wave. There is evidence that a disturbance dynamo (DD) effect contributes on the dayside, where it leads to suppression of the normal quiet time pattern. A very strong counter-electrojet was seen at two locations during a time of persistent Bz south and was not predicted by the model or a linear scaling of the IEF. This suggests that suppression (and even reversal) of the E-region dynamo can occur in a large storm. Both the data and the model yielded a long-lived response to a sustained southward interplanetary magnetic field. Previously suggested By effects on equatorial electric fields are confirmed by a sequence of three distinct spikes in the By component of the IMF, one of which had no associated Bz change and yet was reproduced by two independent ground magnetometer-based electric field determinations. The sometimes remarkable agreement of a linear relationship between the equatorial and interplanetary electric fields shown here and elsewhere remains somewhat mysterious for such an apparently complex system.Item Open Access Observations and modeling of post-midnight uplifts near the magnetic equator(European Geosciences Union (EGU), 2006-07-03) Nicolls, M. J.; Kelley, M. C.; Vlasov, M. N.; Sahai, Y.; Chau Chong Shing, Jorge Luis; Hysell, D. L.; Fagundes, P. R.; Becker-Guedes, F.; Lima, W. L. C.We report here on post-midnight uplifts near the magnetic equator. We present observational evidence from digital ionosondes in Brazil, a digisonde in Peru, and other measurements at the Jicamarca Radio Observatory that show that these uplifts occur fairly regularly in the post-midnight period, raising the ionosphere by tens of kilometers in the most mild events and by over a hundred kilometers in the most severe events. We show that in general the uplifts are not the result of a zonal electric field reversal, and demonstrate instead that the uplifts occur as the ionospheric response to a decreasing westward electric field in conjunction with sufficient recombination and plasma flux. The decreasing westward electric field may be caused by a change in the wind system related to the midnight pressure bulge, which is associated with the midnight temperature maximum. In order to agree with observations from Jicamarca and Palmas, Brazil, it is shown that there must exist sufficient horizontal plasma flux associated with the pressure bulge. In addition, we show that the uplifts may be correlated with a secondary maximum in the spread-F occurrence rate in the post-midnight period. The uplifts are strongly seasonally dependent, presumably according to the seasonal dependence of the midnight pressure bulge, which leads to the necessary small westward field in the post-midnight period during certain seasons. We also discuss the enhancement of the uplifts associated with increased geomagnetic activity, which may be related to disturbance dynamo winds. Finally, we show that it is possible using simple numerical techniques to estimate the horizontal plasma flux and the vertical drift velocity from electron density measurements in the post-midnight period.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 local time dependence of the penetration of solar wind-induced electric fields to the magnetic equator(European Geosciences Union, 2009-08-05) Kelley, M. C.; Dao, E.For a period of a few hours, the penetration of electric fields of solar wind origin is at its highest efficiency. In November 2003, five days of continuous vertical drift data were obtained at the Jicamarca Radio Observatory. Here we have isolated a range of frequencies centered at a few-hour period for a five-day period and have explored the local time dependence of the penetration, along with the time delay due to magnetospheric effects. We find that the latter ranges from 15 to 25 min. For the local time dependence, we find that the period of anti-correlation is roughly from 21:00 to 04:00 LT, with positive correlation at other local times.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 Persistence of a Kelvin-Helmholtz instability complex in the upper troposphere(American Geophysical Union, 2005-07-27) Kelley, M. C.; Chen, C. Y.; Beland, R. R.; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge Luis; Werne, J.During the period of 7–14 September 1998 a multiple instrument campaign was conducted at the Jicamarca Radio Observatory (JRO) near Lima, Peru, using a 50-MHz VHF radar and radiosondes. In this paper we discuss the radar and in situ observations and interpret them with insight gained from high-resolution numerical simulations of the Kelvin-Helmholtz instability (KHI). Evidence is presented that a large-scale shear in the upper troposphere on 8 September 1998 becomes locally unstable due to ambient gravity wave activity. Isolated KHI events result and subsequently grow and merge to form a large 3-km mixing layer. A 3-km-deep potential-temperature step is observed at the same altitude at least a full day after the initial observations. Analysis indicates that neither turbulent mixing nor radiative cooling is capable of destroying the fully developed temperature step in the 21 hours available, which lends credence to the hypothesis that the structure persisted for this period of time. Alternately, the structure could be continuously generated by a standing wave associated with mountain wave forcing.Item Restricted Radar scatter from equatorial electrojet waves: An explanation for the constancy of the Type I Doppler shift with zenith angle(American Geophysical Union, 2008-02-26) Kelley, M. C.; Cuevas, R. A.; Hysell, D. L.The first results from the 430 MHz Advanced Modular Incoherent Scatter Radar Prototype (AMISR‐P) at the Jicamarca Radio Observatory were reported by Hysell et al. (2007). We present additional data showing that the phase velocity of Type I echoes is independent of zenith angle, an unexplained property of these waves. We interpret the results using rocket data by predicting the total line‐of‐sight velocity at the four zenith angles used. We find that the radars preferentially detect waves within 10% of Cs in at least four range gates for all beams and up to eight range gates for the 51 JULIA beam. This result is consistent with recent auroral observations that Type I waves are only generated with k vectors near the electron flow velocity, where the latter is the vector sum of the zero‐order drift and the perturbation drift due to large‐scale waves in the equatorial case.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.Item Restricted Seeding and layering of equatorial spread F by gravity waves(American Geophysical Union, 1990-10) Hysel, D. L.; Kelley, M. C.; Swartz, W. E.; Woodman Pollitt, Ronald FranciscoStudies dating back more than 15 years have presented evidence that atmospheric gravity waves play a role in initiating nighttime equatorial F region instabilities. This paper analyzes a spectacular spread F event that for the first time demonstrates a layering which, we argue, is controlled by a gravity wave effect. The 50-km vertical wavelength of a gravity wave which we have found is related theoretically to a plasma layering irregularity that originated at low altitudes and then was convected, intact, to higher altitudes. Gravity waves also seem to have determined bottomside intermediate scale undulations, although this fact is not as clear in the data. The neutral wind dynamo effect yields wave number conditions on the gravity wave's ability to modulate the Rayleigh-Taylor instability process. Finally, after evaluating the gravity wave dispersion relation and spatial resonance conditions, we estimate the properties of the seeding wave.Item Restricted Unexpected rapid decrease in phase velocity of submeter Farley-Buneman waves with altitude(American Geophysical Union, 2008-02-09) Kagan, L. M.; Kissack, R. S.; Kelley, M. C.; Cuevas, R.An unexpected and drastic drop in the phase velocity Vph of Farley‐Buneman (FB) waves with increasing altitude was observed in the equatorial electrojet over Jicamarca. The effect was detected with the newly employed 430‐MHz radar looking vertically. The decrease in Vph was 67 m/s and 36 m/s over 2.4 km for the FB waves moving towards and away from the radar, respectively. By contrast, the 430‐MHz data from 20° west displayed little dependence on altitude. Simultaneous observations with a 50‐MHz radar at 23° and 51° west also displayed little change of Vph with altitude. We show that electron inelastic cooling which defines gradual transition from super‐adiabatic to isothermal processes at 50 MHz (used in majority of observations), becomes unimportant at higher frequencies. The effect is evinced at radar frequencies ≥150 MHz and requires altitude resolution <2 km to be observed. Averaging over >7 km at oblique incidence masks the effect.