Browsing by Author "Fisher, Daniel J."

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    Comparison of zonal neutral winds with equatorial plasma bubble and plasma drift velocities
    (American Geophysical Union, 2013-03-20) Chapagain, Narayan P.; Fisher, Daniel J.; Meriwether, John W.; Chau Chong Shing, Jorge Luis; Makela, Jonathan J.
    A one-year dataset spanning March 2011-March 2012 of coincident observations of night time thermospheric zonal neutral winds, equatorial plasma bubble (EPB) velocities, and zonal plasma drifts are used to examine the relationship between the thermosphere and ionosphere near the geomagnetic equator over Peru. Thermospheric neutral winds are determined by using a bistatic Fabry–Perot interferometer (FPI) experiment located at Merihill and Nazca in Peru. The ambient plasma drift velocities were obtained using the incoherent scatter radar at the Jicamarca Radio Observatory in Peru. The EPB zonal velocities were estimated utilizing images of the OI 630.0-nm emission recorded by a narrow-field optical imaging system at the Cerro Tololo InterAmerican Observatory in Chile. The joint analysis of these datasets illustrates that the night time and night-to-night variations in the zonal neutral winds, EPB velocities, and plasma drifts are well correlated. This consistent result of the local time variations of the neutral winds with that of EPB and plasma drifts illustrates that the F-region dynamo is, in general, fully activated. However, at times, the magnitude of the EPB velocities and the plasma drifts are different from the neutral winds. It is plausible that such a difference is due either to the effect of polarization electric fields developed inside the EPB or due to the latitudinal gradient of the neutral winds and EPB velocity measurements since the EPB velocities are estimated at a higher latitude, corresponding to an apex altitude of ~400 km, than the wind estimates, which derive from an apex altitude of ~250 km.
    Palabras clave:Equatorial ionosphereIonosphere/atmosphere interactionsIonospheric irregularities
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    Three-Dimensional Wind Measurements and Modeling Using a Bi-Static Fabry-Perot Interferometer System in Brazil
    (University of Illinois at Urbana-Champaign, 2013) Fisher, Daniel J.; Makela, Jonathan.
    The earth’s upper atmosphere has been studied for over a century now, and while a multitude of data has been collected studying the plasma in the ionosphere, there are not equivalent amounts of data on neutrals in the thermosphere to pair with these plasma observations. The Remote Equatorial Nighttime Observatory for Ionospheric Regions (RENOIR) project consists of two observing systems stationed in northeastern Brazil in Cajazeiras (6.87◦S, 38.56◦W) and Cariri (7.38◦S, 36.52◦W) since 2009. They are separated by 232.28 km and each is equipped with a Fabry-Perot interferometer (FPI) to measure neutral wind velocities and neutral temperatures using observations of the 630.0-nm emission caused by the dissociative recombination of O +2. The FPI systems can operate in two different modes: cardinal and common volume (CV). In cardinal mode, each FPI looks at a 45◦ elevation angle towards geographic north, east, south, and west followed by a zenith and laser image. In common volume mode, the two FPIs are synchronized to observe three common locations followed by both a zenith and laser observation. Two common volume points, one to the north and one to the south, are where the two FPIs have the same elevation angle but are looking orthogonal to one another in the horizontal plane. The third point is an inline measurement to the midpoint of the two sites. Vector neutral winds in the horizontal plane can be computed at the two common volume points, and a vertical neutral wind can be found at the inline point. FPIs are phase-based instruments, meaning a zero-reference is needed in order to get an absolute wind measurement. Since there is no practical 630.0-nm lab source, the zero-Doppler source is typically obtained from the zenith airglow measurements because the vertical winds are assumed to be zero across the night. However, the inline zenith measurements give non-zero winds under this assumption, consequently contradicting it. Therefore, the observations of the frequency-stabilized HeNe laser are used as a zero-Doppler reference to improve the derived vertical and horizontal neutral winds. This thesis validates this new technique by both developing an analytical model for the CV winds and by confirming it with results from actual observations made in Brazil.
    Palabras clave:WindInterferometryTemperature