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Browsing Pósters by Subject "Atmosphere"
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Item Open Access Evaluation of topside equatorial spread F spectra estimators using Monte Carlo simulations(Instituto Geofísico del Perú, 2008) Galindo, F. R.; Kuyeng, K. M.; Chau Chong Shing, Jorge Luis; Hysell, D. L.Radar observations typically employ periodic pulses to study any target. This scheme allows a simple processing of the data but the results frequently shows range or frequency aliasing. In order to solve this problem Uppala and Sahr [1] introduced the aperiodic technique (AT) in the radio science community. The AT is based on transmitting pulses at non uniform intervals and allows to study moderately overspread targets. Some equatorial Spread F (ESF) echoes belong to this category, particularly those from the topside. Using this idea Jicamarca Radio Observatory (JRO) has done a couple of experiments to study ESF echoes. Chau et al [2] used the Fast Fourier Transform (FFT) to compute spectra from those experiments and developed some criteria to remove clutter due to the aperiodic sequence. A second scheme of work was introduced by Hysell et al [3] and this scheme uses a Bayesian method to compute the spectra. Continuing this line of research a Monte Carlo simulations of typical echoes from equatorial ionospheric irregularities as well as ground clutter has been done to evaluate different aperiodic pulsing and inversion techniques to estimate the spectra or its corresponding AutoCorrelation Function (ACF). Our main objective is the estimation of the moderately overspread topside equatorial spread F (ESF) spectra. The optimal spectra estimators combined with radar imaging techniques might represent the unique means to estimate the irregularity power and energy spectral density versus wavenumber from the ground.Item Open Access The LISN database: description and initial results(Instituto Geofísico del Perú, 2009) De la Jara, César; Chau Chong Shing, Jorge Luis; Espinoza, J. C.; Veliz, Oscar; Valladares, C.; Bullet, T.The heavy volume of data that GPS, ionosondes and magnetometers are continuously collecting is stored in the LISN server and managed using a set of rules that are intended to provide an efficiently way to manipulate the large data sets and also implement an adequate method to systematically transform all this information into knowledge. LISN integrates multiple data sources and should provide security, integrity and availability in a multi-user environment. Data from the remote stations arrives to the server continuously and is stored, processed and distributed. This data is easily available and in some cases freely accessible to the community promoting research and encouraging collaboration between users.Item Open Access Using JULIA long dataset to find preconditioning evidence of ESF in bottom-type layers(Instituto Geofísico del Perú, 2008) Pinedo, H.; Chau Chong Shing, Jorge Luis; Hysell, D.Recently Hysell et al. [2005] has suggested that the periodic structuring observed in the bottomtype (BT) scattering layers might be used to determine the occurrence or not of full-blown equatorial spread F (ESF) on a given day. The seed or precursor waves may be generated by a collisional shear instability. Preliminary observations at Jicamarca and AL TAIR have shown that such structures present wavelengths of the order of tens or hundreds of kilometers. At Jicamarca periodic structures have been observed using in-beam radar imaging techniques, however such observations are limited to few days in the last five years. On the other hand, routine observations using the JULIA system at Jicamarca have been done since 1996 on approximately 100 days per year on average, using interferometric and dual-beam observations with very narrow beams. Since the bottom-type irregularities drift ata relatively constant speed in the westward direction, using the JULIA narrow beams (～1o), the spatial periodicities might be observed as temporal periodicities in typical range-time intensity maps. In this initial work we present the statistics of the observed bottom-type periodicities and the occurrence of ESF plumes as detected with the JULIA system for years 2006-2008. Besides we presenta time occurrence statistics of a weak bottom-type layer that took place previously to bottom-type layers.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.