William B. Hanson Center for Space Sciences
Permanent URI for this communityhttps://hdl.handle.net/10735.1/3867
The William B. Hanson Center for Space Sciences conducts research in space plasma physics. Its goal is to "advance the understanding of the evolution of Solar system bodies and their interaction with the Sun." Find out more about the Center on its website.
Browse
Browsing William B. Hanson Center for Space Sciences by Subject "Electric fields"
Now showing 1 - 6 of 6
- Results Per Page
- Sort Options
Item An Auroral Boundary-Oriented Model of Subauroral Polarization Streams (SAPS)(Amer Geophysical Union) Landry, Russell G.; Anderson, Phillip C.; 0000-0003-1320-4064 (Landry, RG); Landry, Russell G.; Anderson, Phillip C.An empirical model of subauroral polarization stream (SAPS) electric fields has been developed using measurements of ion drifts and particle precipitation made by the Defense Meteorological Satellite Program from 1987 to 2012 and Dynamics Explorer 2 as functions of magnetic local time (MLT), magnetic latitude, the auroral electrojet index (AE), hemisphere, and day of year. Over 500,000 subauroral passes are used. This model is oriented in degree magnetic latitude equatorward of the aurora and takes median values instead of the mean to avoid the contribution of low occurrence frequency subauroral ion drifts so that the model is representative of the much more common, latitudinally broad, low-amplitude SAPS field. The SAPS model is in broad agreement with previous statistical efforts in the variation of the SAPS field with MLT and magnetic activity level, although the median field is weaker. Furthermore, we find that the median SAPS field is roughly conjugate in both hemispheres for all seasons, with a maximum in SAPS amplitude and width found for 1800-2000 MLT. The SAPS amplitude is found to vary seasonally only from about 1800-2000 MLT, maximizing in both hemispheres during equinox months. Because this feature exists despite controlling for the AE index, it is suggested that this is due to a seasonal variation in the flux tube averaged ionospheric conductance at MLT sectors where it is more likely that one flux tube footprint is in darkness while the other is in daylight.Item Duskside Enhancement of Equatorial Zonal Electric Field Response to Convection Electric Fields During the St. Patrick's Day Storm on 17 March 2015(Blackwell Publishing Ltd, 2016-01-11) Tulasi Ram, S.; Yokoyama, T.; Otsuka, Y.; Shiokawa, K.; Sripathi, S.; Veenadhari, B.; Heelis, Roderick A.; Ajith, K. K.; Gowtam, V. S.; Gurubaran, S.; Supnithi, P.; Le Huy, M.; 0000 0000 3175 0999 (Heelis, RA); Heelis, Roderick A.The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to >550 km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13⁰N and 25.98⁰S magnetic dip latitudes indicating their altitude development to ~1670 km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field B_z.Item Effects of Electric Field and Neutral Wind on the Asymmetry of Equatorial Ionization Anomaly(Blackwell Publishing Ltd) Khadka, S. M.; Valladares, Cesar E.; Sheehan, R.; Gerrard, A. J.; Valladares, Cesar E.The zonal electric field and the meridional neutral wind are the principal drivers that define the geometry and characteristics of the equatorial ionization anomaly (EIA). Here we present the response of the EIA to the variability of the zonal electric field based on measurements of the equatorial electrojet (EEJ) currents and trans-equatorial neutral winds for the generation and control of the asymmetries of the EIA crests of total electron content (TEC) in the western side of the South American continent. The EEJ strengths are determined using a pair of magnetometers. The 24-hr trans-equatorial neutral wind profile is measured using the Second-Generation, Optimized, Fabry-Perot Doppler Imager (SOFDI) located near the geomagnetic equator. The EIA is evaluated using TEC data measured by Global Positioning System (GPS) receivers from the Low-Latitude Ionospheric Sensor Network and several other networks in South America. A physics-based numerical model, Low-Latitude Ionospheric Sector, and SOFDI data are used to study the effects of daytime meridional neutral winds on the consequent evolution of an asymmetry in equatorial TEC anomalies during the afternoon and onward for the first time. We find that the configuration parameters such as strength, shape, amplitude, and latitudinal width of the EIAs are affected by the eastward electric field associated with the EEJ under undisturbed conditions. The asymmetries of EIA crests are observed more frequently during solstices and the September equinox than in the March equinox season. Importantly, this study indicates that the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. This result suggests that a precise observation of the latitudinal TEC profile at low latitudes can be used to derive the meridional wind. ©2018. American Geophysical Union. All Rights Reserved.Item Observations of the Generation of Eastward Equatorial Electric Fields near Dawn(Copernicus Gesellschaft Mbh, 2014-09-19) Kelley, M. C.; Rodrigues, Fabiano S.; Pfaff, R. F.; Klenzing, J.; Kelley, M. C.; Rodrigues, Fabiano S.We report and discuss interesting observations of the variability of electric fields and ionospheric densities near sunrise in the equatorial ionosphere made by instruments onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite over six consecutive orbits. Electric field measurements were made by the Vector Electric Field Instrument (VEFI), and ionospheric plasma densities were measured by Planar Langmuir Probe (PLP). The data were obtained on 17 June 2008, a period of solar minimum conditions. Deep depletions in the equatorial plasma density were observed just before sunrise on three orbits, for which one of these depletions was accompanied by a very large eastward electric field associated with the density depletion, as previously described by de La Beaujardiere et al. (2009), Su et al. (2009) and Burke et al. (2009). The origin of this large eastward field (positive upward/meridional drift), which occurred when that component of the field is usually small and westward, is thought to be due to a large-scale Rayleigh-Taylor process. On three subsequent orbits, however, a distinctly different, second type of relationship between the electric field and plasma density near dawn was observed. Enhancements of the eastward electric field were also detected, one of them peaking around 3 mV m⁻¹, but they were found to the east (later local time) of pre-dawn density perturbations. These observations represent sunrise enhancements of vertical drifts accompanied by eastward drifts such as those observed by the San Marco satellite (Aggson et al., 1995). Like the San Marco measurements, the enhancements occurred during winter solstice and low solar flux conditions in the Pacific longitude sector. While the evening equatorial ionosphere is believed to present the most dramatic examples of variability, our observations exemplify that the dawn sector can be highly variable as well.Item Radar and Satellite Investigations of Equatorial Evening Vertical Drifts and Spread F(Copernicus Gesellschaft Mbh, 2015-11-11) Smith, J. M.; Rodrigues, Fabiano S.; de Paula, E. R.; Smith, J. M.; Rodrigues, Fabiano S.We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of Sao Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) on-board the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18: 00-18: 30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.Item Study of the Equatorial and Low-Latitude Electrodynamic and Ionospheric Disturbances during the 22–23 June 2015 Geomagnetic Storm Using Ground-Based and Spaceborne Techniques(Blackwell Publishing Ltd) Astafyeva, E.; Zakharenkova, I.; Hozumi, K.; Alken, P.; Coïsson, P.; Hairston, Marc R.; Coley, William R.; 0000-0003-4524-4837 (Hairston, MR); Hairston, Marc R.; Coley, William R.We use a set of ground-based instruments (Global Positioning System receivers, ionosondes, magnetometers) along with data of multiple satellite missions (Swarm, C/NOFS, DMSP, GUVI) to analyze the equatorial and low-latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22-23 June 2015, which is the second largest storm in the current solar cycle. Our results show that at the beginning of the storm, the equatorial electrojet (EEJ) and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields (PPEF). The PPEF were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside, and downward drift on the nightside. Furthermore, about 45 min after the storm commencement, the interplanetary magnetic field (IMF) Bz component turned northward, leading to the EEJ changing sign to westward, and to overall decrease of the vertical total electron content (VTEC) and electron density on the dayside. At the end of the main phase of the storm, and with the second long-term IMF Bz southward turn, we observed several oscillations of the EEJ, which led us to conclude that at this stage of the storm, the disturbance dynamo effect was already in effect, competing with the PPEF and reducing it. Our analysis showed no significant upward or downward plasma motion during this period of time; however, the electron density and the VTEC drastically increased on the dayside (over the Asian region). We show that this second positive storm was largely influenced by the disturbed thermospheric conditions. ©2018. The Authors.