Browsing by Author "Varney, Roger H."
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Item Open Access Concurrent observations at the magnetic equator of small-scale irregularities and large-scale depletions associated with equatorial spread F(American Geophysical Union, 2015-11-20) Hickey, Dustin A.; Martinis, Carlos R.; Rodrigues, Fabiano S.; Varney, Roger H.; Milla, Marco; Nicolls, Michael J.; Strømme, Anja; Arratia, Juan F.In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10's-100's km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 10-100 km scales using the all sky-imager, at 3 m scales using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20-21 August, 2014 by locating the radar scattering volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at sub-meter scales by the lower-hybrid-drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.Item Open Access Investigation of the feasibility of meteoric smoke detection with Jicamarca(Instituto Geofísico del Perú, 2009-06) Varney, Roger H.; Kelley, Michael C.; Chau Chong Shing, Jorge LuisDiapositivas presentadas en: CEDAR Workshop 2009 del 28 de junio al 2 de julio de 2009 en Santa Fe, Nuevo México, USA.Item Restricted Observations of electric fields associated with internal gravity waves(American Geophysical Union, 2009-02-07) Varney, Roger H.; Kelley, Michael C.; Kudeki, ErhanAt the Jicamarca Radio Observatory, the vertical drift component yields a very accurate measure of the eastward electric field. Occasionally, this drift component displays a downward phase progression, evidence for a relationship to a gravity wave. We examined the Jicamarca database for events of this type and made an attempt to determine the properties of the associated waves. The only measurables we have are the amplitudes, the frequency in the Earth‐fixed frame, and the vertical wavelength. In order to avoid shorting by the current along magnetic field lines, we argue that the propagation must be close to pure zonal. We then use measurements or models of the zonal plasma drift and argue that the zonal wind should be in the same direction and about 15% higher. Using this estimate, we then determine the frequency in the wind frame by solving the dispersion relation for gravity waves and the Doppler‐shift equation simultaneously. Typical values for the horizontal wavelength, vertical wavelength, and period in the wind frame are 600 km, 350 km, and 25 min, respectively. The typical gravity wave‐induced vertical drift perpendicular to B in these events is a few meters per second. This is marginal at best for seeding the Rayleigh‐Taylor instability. However, larger‐amplitude events may be masked by the development of the plumes themselves. All but two events found thus far occurred at night but the daytime cases are fascinating since the E region is expected to short out such fields.Item Open Access Radars: powerful tools to study the upper atmosphere(Instituto Geofísico del Perú, 2009) Chau Chong Shing, Jorge Luis; Varney, Roger H.Diapositivas presentadas en: CEDAR Workshop 2009 del 28 de junio al 2 de julio de 2009 en Santa Fe, Nuevo México, USA.Item Restricted Sources of variability in equatorial topside ionospheric and plasmaspheric temperatures(Elsevier, 2013-01-17) Varney, Roger H.; Hysell, David L.; Huba, J. D.Jicamarca measurements of electron temperatures at high altitudes (500–1500 km) from the last solar minimum routinely show variations of hundreds of Kelvin from day-to-day. Possible sources of these variations are explored using the SAMI2-PE is another model of the ionosphere including photoelectron transport (SAMI2-PE) model, which includes a multistream photoelectron transport model. Changes to the electric fields, meridional winds, and thermospheric densities can all change the electron densities and temperatures at high altitudes. The high altitude electron temperatures are primarily determined by a balance between heating from photoelectrons which travel up the field lines and thermal diffusion which carries heat back down the field lines. The winds and electric fields will change the altitude and densities of the off-equatorial F-region peaks, especially on the field lines connected to the equatorial arcs. The densities and temperatures in the plasmasphere will self consistently adjust themselves to achieve diffusive equilibrium with the off-equatorial F-regions. Furthermore, decreases in the density and/or altitude of the F-region makes it easier for photoelectrons to escape to high altitudes. These connections between the equatorial plasmasphere, the off-equatorial F-regions, and the neutral thermosphere suggest that high altitude measurements at Jicamarca could be used to study thermospheric variability.