Browsing by Author "Feng, Zhaomei"
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Item Restricted Equatorial F-region plasma density estimation with incoherent scatter radar using a transverse-mode differential-phase method(University of Illinois at Urbana-Champaign, 2002) Feng, Zhaomei; Kudeki, ErhanEsta tesis presenta un método de adquisición y análisis de datos novedoso para radar de dispersión incoherente Jicamarca para medir derivas de alta precisión y la densidad ionosférica simultáneamente en las alturas de la región F. Dado que las mediciones de deriva de alta precisión a favor de las señales de retorno de radar con los espectros de frecuencia estrecha posible, Jicamarca derivas observaciones se llevaron a cabo utilizando las ondas de radar transversal polarizadas lineales. la señal vuelve transversal de las vigas se recogen usando un par ortogonal de antenas polarizadas lineales, y la potencia media, así como la diferencia de fase de las salidas de antena están instalados en los modelos de datos adecuados, desarrollados sobre la base de la teoría de dispersión incoherente y la teoría de la magneto-iónico. El modelo de fase diferencial de crudo cuando Bo se caracteriza en términos de campos de las líneas rectas se aplica a los datos de enero de 2000. El modelo de fase diferencial más completa, que tiene en cuenta el ángulo desalineada entre los ejes dipolares de las matrices de Jicamarca ortogonales y noreste geomagnético y direcciones sureste, así como la anchura del haz de radar y la variación de los campos magnéticos, se aplica a la 01 2000 datos de 2002 y junio de datos. Presentamos y comparar los resultados obtenidos con la inversión de diferentes versiones de los modelos de datos y concluir que los detalles geométricos sólo tienen un impacto menor en la inversión. También nos encontramos con que funciona el método de fase diferencial mejor para el 15-min de datos integrada de enero de 2000 al 5-min integrado de junio de 2002, los datos ya que el primero tiene las mayores densidades de electrones, mayor SNR de las señales de retrodispersión, y datos de la fase más usables. Nuestros resultados de la inversión se comparan con los datos ionosonda, y que muestran un acuerdo razonable.Item Restricted F region plasma density estimation at Jicamarca using the complex cross‐correlation of orthogonal polarized backscatter fields(American Geophysical Union, 2004-06-16) Feng, Zhaomei; Kudeki, Erhan; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge Luis; Milla, MarcoThe differential‐phase method for Jicamarca F region density measurements has been modified to fit the real and imaginary components of the cross‐correlation of orthogonally polarized radar returns. The original method [Kudeki et al., 2003; Feng et al., 2003] based on fitting the cross‐correlation phase could only make use of correlation data from lower F region heights since the phase noise in low‐SNR upper F region returns is typically non‐Gaussian. However, upper F region correlation data become useful in the modified method since the fluctuations in real and imaginary parts of cross‐correlation remain Gaussian even under low‐SNR conditions.Item Open Access Incoherent scatter radar plasma density measurements at Jicamarca using a transverse-mode differential-phase method(American Geophysical Union, 2003) Kudeki, Erhan; Woodman Pollitt, Ronald Francisco; Feng, ZhaomeiThe 50 MHz Jicamarca incoherent scatter radar can be used to make very high precision F-region plasma drift measurements with less than a m/s uncertainty and 5 min/ 15 km time/height resolutions. In such measurements the transmitting antenna beam is pointed perpendicular to the geomagnetic field ~ B [e.g., Kudeki et al. , 1999] and backscattered fields consist of magneto-ionic O- and X- components with unequal phase retardations. Detecting the fields with an orthogonal pair of linear-polarized antennas and fitting the average power and differential- phase of the antenna outputs to an appropriate data model we have succeeded in making F-region electron density measurements with data collected during Jicamarca drifts experiments. This procedure provides Jicamarca with a new capability for simultaneous drifts and density measurements at F-region heights.Item Open Access Jicamarca radar observations of the diurnal and semidiurnal tide in the troposphere and lower stratosphere(American Geophysical Union, 2002-04) Riggin, Dennis M; Kudeki, Erhan; Feng, Zhaomei; Sarango, Martin F.; Lieberman, Ruth S.The mesosphere-stratosphere-troposphere (MST) radar at Jicamarca, Peru (12S, 77W), made extended (15 day or longer) observations of the horizontal and vertical winds that were used to infer the diurnal and semidiurnal tides. The measurements were made during several months from mid-1997 through mid-1998 and using a higher-power transmitter and finer range resolution during 10 days of August 1998. The three-component winds are used to estimate amplitudes, phases, and momentum fluxes associated with the tides. Thermal forcing of the diurnal tide is also examined with diurnal water vapor heating rates calculated using data from the NASA Water Vapor Project (NVAP). For the region near Jicamarca the calculations from NVAP showed the temporal variability of the diurnal heating to be dominated by an annual cycle with maximum around the summer solstice. When projected into tidal modes, about 25% of the total water vapor heating rate amplitude near Jicamarca is found to be nonmigrating. The meridional amplitude of the semidiurnal tide was found to be generally greater than the zonal amplitude, although tidal theory predicts that the zonal amplitude should be much greater at the latitude of Jicamarca (assuming the tide was migrating). The phase of the semidiurnal tide lagged (by about 3 hours) the phase expected from surface pressure climatologies. According to tidal theory the migrating semidiurnal tide should transport little meridional momentum flux. However, substantial southward fluxes (vw ∼ −1 × 10−3 m2 s−2) were observed at Jicamarca, and the meridional component of momentum flux was typically larger in magnitude than the zonal component was. The diurnal tide was somewhat weaker, was less coherent, and transported less momentum. The semidiurnal tide had a very long vertical wavelength throughout the troposphere and into the lower stratosphere, while the diurnal tide was only observed to propagate at heights above the tropopause with a much shorter (∼10 km) vertical wavelength. Below the tropopause the dominant diurnal motions were not traveling waves, but rather convective motions that exhibited little phase progression with altitude. These motions were broadly peaked in frequency around 24 hours and were presumably standing oscillations with no horizontal propagation and probably with small horizontal scale. Despite the lack of coherence of these quasi-diurnal motions, the associated vertical wind amplitudes were sizable (∼0.02 m s−1), and thus the fluctuations can presumably transport significant horizontal momentum.Item Restricted Transverse-beam incoherent scatter radar measurements of F region plasma densities at Jicamarca(American Geophysical Union, 2003-08) Feng, Zhaomei; Kudeki, Erhan; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge LuisModels for the self- and cross-correlation of orthogonal polarized quasi-transverse incoherent scatter returns are presented. The models are used to estimate the F region plasma densities with dual-polarization transverse-beam incoherent scatter data collected at the Jicamarca Radio Observatory using a technique introduced by Kudeki et al. [2003]. The cross-correlation model takes into account magneto-ionic propagation effects associated with quasi-transverse O- and X-modes in an inhomogeneous ionosphere. The phase of the cross-correlation provides the information to convert the measured power data into ionospheric density estimates via a least squares fitting procedure.