Browsing by Author "Sheth, R."
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Item Open Access A high-resolution study of mesospheric fine structure with the Jicamarca MST radar(European Geosciences Union (EGU), 2006-07-03) Sheth, R.; Kudeki, E.; Lehmacher, G.; Sarango, M.; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge Luis; Guo, L.; Reyes, P.Correlation studies performed on data from recent mesospheric experiments conducted with the 50-MHz Jicamarca radar in May 2003 and July 2004 are reported. The study is based on signals detected from a combination of vertical and off-vertical beams. The nominal height resolution was 150 m and spectral estimates were obtained after ~1 min integration. Spectral widths and backscattered power generally show positive correlations at upper mesospheric heights in agreement with earlier findings (e.g., Fukao et al., 1980) that upper mesospheric echoes are dominated by isotropic Bragg scatter. In many instances in the upper mesosphere, a weakening of positive correlation away from layer centers (towards top and bottom boundaries) was observed with the aid of improved height resolution. This finding supports the idea that layer edges are dominated by anisotropic turbulence. The data also suggests that negative correlations observed at lower mesospheric heights are caused by scattering from anisotropic structures rather than reflections from sharp vertical gradients in electron density.Item Restricted Turbulent kinetic energy dissipation rates and eddy diffusivities in the tropical mesosphere using Jicamarca radar data(Elsevier, 2007-06-06) Guo, L.; Lehmacher, G. A.; Kudeki, E.; Akgiray, A.; Sheth, R.; Chau Chong Shing, Jorge LuisThe 50-MHz MST radar at Jicamarca Radar Observatory (JRO) can detect atmospheric turbulence on the Bragg scale of 3 m in the daytime mesosphere (∼60–85 km). Since 2002, the radar was operated for a certain number of days each year collecting 1-min Doppler spectra in four off-vertical (2.5°) beam directions and 150 m resolution. The spectral widths have been used to compute the kinetic energy dissipation rate ε due to atmospheric turbulence. A small beam broadening effect has been removed from the observed spectral widths. The daily median energy dissipation rates ε increase from 5 to 30 mW/kg between 67 and 80 km, and the eddy diffusivities increase from 3 to 20 m2/s, consistent with similar studies conducted by two other large 50-MHz radars in Japan and India. The energy dissipation rates are about the same magnitude as the ε estimates for low-latitudes from a global model and are larger than the averages from rocket observations at high-latitudes, confirming previous comparisons.