Browsing by Author "Oppenheim, Meers"
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Item Restricted Determining meteoroid properties using head echo observations from the Jicamarca radio observatory(Boston University, 2012) Fucetola, Elizabeth N.; Oppenheim, MeersOver 100 tons of material enters the Earth’s atmosphere every day, mostly in the form of meteoroids less than a millimeter across. As a meteoroid enters the atmosphere, it ablates and forms a plasma. Radars can detect this plasma, which travels at approximately the same speed as the meteoroid, as a head echo. Such observations can determine the speed and trajectory of a meteoroid with high accuracy. A better characterization of these small particles will contribute to our understanding of the Earth’s atmosphere, the solar system, and the local interstellar medium. Meteoroids provide a source of heavy metals at high altitudes that impact atmospheric chemistry and physics. Greater knowledge of the composition and masses of meteoroids will help astronomers understand the material within the solar system and the local interstellar medium. This dissertation focuses on meteoroid head echo observations using the 50 MHz radar at the Jicamarca Radio Observatory. These provide high resolution observations in both range and time. We use this data to evaluate methods of determining meteoroid properties and introduce a technique to determine meteoroid mass which involves fitting range and velocity measurements to an ablation model. This technique is compared with some established mass estimation methods, including scattering mass theory. We find the overall mass distribution for observed meteoroids as well as the spatial distribution of these particles. The peak of our mass distribution, at approximately 10-11 kg, is significantly lower than what is found using specular meteor radars. We illustrate how the spatial distribution varies with meteoroid mass, and how different meteoroid sources appear when different mass ranges are examined. For the smallest meteoroids, only the Apex sources are detected, while all six of the dominant meteor sources are observed with comparable intensity when examining meteors with a mass larger than 10-9 kg. We also directly compare meteor data taken with the 50 MHz radar to observations using a specular meteor radar in a novel experiment using both instruments simultaneously.Item Restricted Improving the accuracy of meteoroid mass estimates from head echo deceleration(Springer, 2007-12) Bass, Elizabeth; Oppenheim, Meers; Chau Chong Shing, Jorge Luis; Olmstead, AliceThis paper examines current techniques used to determine meteoroid mass from high-power, large aperture (HPLA) radar observations. We demonstrate why the standard approach of fitting a polynomial to velocity measurements gives inaccurate results by applying this technique to artificial datasets. We then suggest an alternate approach, fitting velocity data to an ablation model. Using data taken at the Jicamarca Radio Observatory in July 2005, we compare the results of both methods and demonstrate that fitting velocity data to an ablation model yields a reasonable result in some instances where alternate methods produce physically unrealistic mass estimates.Item Open Access Mass distributions found using the Jicamarca Radio Observatory(Instituto Geofísico del Perú, 2010) Bass, Elizabeth; Oppenheim, Meers; Chau Chong Shing, Jorge LuisDiapositivas presentadas en el 2010 CEDAR Workshop, University of Colorado, Boulder, CO, 20-25 June 2010.Item Open Access Measuring MLT winds by tracking meteor trails with incoherent scatter radar: a new method observes rapidly changing winds exceeding 500km/Hr(Instituto Geofísico del Perú, 2009) Oppenheim, Meers; Sugar, Glenn; Slowey, Nick; Bass, Elizabeth; Chau Chong Shing, Jorge Luis; Close, SigridDiapositivas presentadas en: CEDAR Workshop 2009 del 28 de junio al 2 de julio de 2009 en Santa Fe, Nuevo México, USA.Item Open Access Meteor observations as a method of determining atmospheric properties(Instituto Geofísico del Perú, 2008) Bass, Elizabeth; Oppenheim, Meers; Sugar, GlennDiapositivas presentadas en: ISEA 12 - 12th International Symposium on Equatorial Aeronomy, May 18-24, 2008. Crete, Greece.Item Restricted Modeling long duration meteor trails(American Geophysical Union, 2007-12-29) Dyrud, Lars P.; Kudeki, Erhan; Oppenheim, MeersWe constructed a model of the plasma evolution of meteor trails in order to simulate high‐power‐large‐aperture radar observations. This model follows meteor evolution from ablation and ionization to head echo formation and through non‐specular trail reflections. Meteor plasma field aligned irregularities (FAI) result in radar reflections called non‐specular meteor trails. We have updated our model to include the polarizing effects of winds and background electric fields on meteor trail instability. This model incorporates existing meteor physics together with knowledge we gained from the simulations, such as instability physics and anomalous diffusion. Comparing results from this model with large radar observations of head echoes and non‐specular trails shows that we can reproduce many of the observed features, such as the detailed altitude profile and duration of head echoes and non‐specular trails. Specifically when external electric fields are included in our model, the same model predicts both short duration (order of 1 s) and long duration meteor trails (several minutes) depending upon the characteristics of the meteoroid and atmosphere. The addition of a background E‐field or wind also reproduces a commonly observed non‐specular trail feature we call an “extended tail” where the delay time between head echo and non‐specular reflection at the lower altitude portion of the trail increases as the meteor gets lower in the atmosphere. We also demonstrate a dependence on trail duration with the electron density of the background ionosphere.Item Open Access Using non-spectacular radar meteor echoes to monitor lower thermosphere wind profiles(Instituto Geofísico del Perú, 2009) Oppenheim, Meers; Sugar, Glenn; Bass, Elizabeth; Slowey, Nick; Chau Chong Shing, Jorge Luis; Close, SigridWe present a new method of measuring lower thermospheric wind velocity profiles by tracking non‐specular meteor echoes in time. This approach relies on having a radar following plasma irregularities as they are dragged by the neutral wind. This requires a VHF radar with interferometric capability able to point close to perpendicular to the geomagnetic field. Using a small sample of data from the Jicamarca Radio Observatory, we calculated wind speeds and directions between 90 and 110\ km with a range resolution of a few hundred meters. The measurements taken show speeds reaching 150m/s and someAmes changing by as much as 100m/s over a 6km altitude range. With some refinement of the data collection and analysis techniques, we expect that one could obtain high resolution images of lower thermospheric winds as they change in both altitude and time. We will discuss these results, the physics underlying these measurements, and the limitations.