Browsing by Author "Sato, T."
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Item Restricted Mesospheric winds and waves over Jicamarca on May 23-24,1974(American Geophysical Union, 1979-08-01) Fukao, S.; Sato, T.; Kato, S.; Harper, R.M.; Woodman Pollitt, Ronald Francisco; Gordon, W.E.The VHF radar at Jicamarca (12.0°S, 76.9°W) was used to probe the mesosphere for 24 hours on May 23–24, 1974. The inferred zonal wind shows a strong eastward prevailing component below 75 km for these winter conditions, as would be expected from the annual and semiannual oscillations. The zonal winds are in good agreement in their region of overlap with rocket observations made at Ascension Island (8.0°S, 14.4°W) for the same period. This is the first direct confirmation that Jicamarca VHF observations are measuring mesospheric winds. Substantial wind oscillations are present, but the lack of nighttime echoes precludes a decomposition into tidal components. The dominant periodicity in the short-period oscillations changes with altitude, with the short-period cutoff decreasing from around 10 min at 70 km to 4 min at 80 km. This suggests both a local energy source for the oscillations and the importance of the background temperature structure in determining the wave characteristics. The variation of echo power with height in the two antennas that were used shows that 2–10 times more power was received on the average in the nearly vertical antenna than in the antenna offset from the vertical by 3.45° at heights below 75 km, suggesting the possibility that a ‘partial reflection’ mechanism is important in the 55- to 75-km region at a 50-MHz operating frequency. The powers in the two antennas become nearly equal above 75 km, with the possibility that slightly more power is received in the off-vertical antenna. The continuous scattered power becomes very small above 80 km; however, meteor echoes are frequently observed. Equatorial electrojet echoes dominate the echo returns above 85 km.Item Open Access Power spectra of oblique velocities in the troposphere and lower stratosphere observed at Arecibo, Puerto Rico(American Meteorological Society, 1986-07-26) Larsen, M. F.; Woodman Pollitt, Ronald Francisco; Sato, T.; Davis, M. K.Wind profiles measured with the Arecibo Observatory 430 MHz radar during 1979 and 1980 have been used to calculate frequency and radial wavenumber power spectra. Periods between 2 min and 6 h and vertical wavelengths between 300 m and 13.5 km are covered by the spectra. The data are line-of-sight velocity components obtained with a beam pointing between 5.4° and 15º off-vertical. The presented evidence supports the conclusion that the dominant contribution to the spectra at periods less than 1 h is from the vertical velocity component. The frequency spectra have spectral slopes near -1 for periods of less than 1 h, and the radial wavenumber spectra have slopes between -1 and -3/2. The results are discussed in the context of two-dimensional turbulence and a universal gravity-wave spectrum. We also present the spectra from an event associated with convection in the early evening hours. A strong peak in the spectral energy near the Brunt-Väisälä frequency was present during the convective activity. The energy content at longer periods was found to be enhanced in the ensuing period when the convective energy input at shorter time scales near the Brunt-Väisälä period had diminished.Item Restricted Report from the International Workshop on Remote Sensing in Geophysics Using Doppler Techniques(American Meteorological Society, 1998) Brandolini, A.; Balsley, B. B.; Mabres, A.; Woodman Pollitt, Ronald Francisco; Capsoni, C.; D'Amico, M.; Ecklund, W. L.; Hagfors, T.; Harper, R.; Heron, M. L.; Hocking, W. K.; Lehtinen, M. S.; Rottger, J.; Sarango, M. F.; Sato, T.; Stauch, R. J.; Vaughn, J. M.; Wyatt, L. R.; Zrnic, D. S.Presents a summary of a meeting staged by the International Workshop on Remote Sensing in Geophysics Using Doppler Techniques, which was held on March 5, 1996 in Bellagio, Italy at the Rockefeller Study and Conference Center.Item Restricted Spectral parameter estimation of CAT radar echoes in the presence of fading clutter(American Geophysical Union, 1982-07) Sato, T.; Woodman Pollitt, Ronald FranciscoThe 430 MHz, 2 MW radar at the Arecibo Observatory is currently being used as a stratospheric-troposheric (ST) radar. One of the problems in the automatic analysis of the signals come from the very large amplitude of the ground clutter echoes. The problem is agravated by the fading of these signals, which makes it difficult to discriminate them from the desired stratospheric returns. A parameter estimation technique that parameterizes the first three-spectral moments corresponding to the desired stratospheric signals as well as a few Taylor series coefficients of the auto-correlation function of the clutter is presented. The three first moments can be obtained in this manner even in the presence of clutter 50 dB stronger. The technique automatically takes care of instrumental and processing biases. Spectrum aliasing presents no problem. A sequence of fine altitude and high temporal resolution wind profiles is presented, showing the potential of the instrumental and technique for the study of stratospheric dynamics.