Browsing by Author "Fukao, S."
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Item Open Access An analysis technique for deriving vector winds and in-beam incidence angles from radar interferometer measurements(American Meteorological Society, 1992-02) Larsen, M. F.; Palmer, R. D.; Fukao, S.; Woodman Pollitt, Ronald Francisco; Yamamoto, M; Tsuda, T; Kato, S.We present a method for deriving horizontal velocities, vertical velocities, and in-beam incidence angles from radar interferometer data. All parameters are calculated from the slope and intercept of straight lines fitted in a least-squares sense to the variation of the signal phase as a function of radial velocity for each pair of receiving antennas. Advantages of the method are that the calculations are computationally fast and simple, and the analysis leads to relatively simple expressions for the uncertainty in the velocity measurements.Item Restricted Frequency domain interferometry observations of tropo/stratospheric scattering layers using the MU radar: Description and first results(American Geophysical Union, 1990-11) Palmer, R.D.; Woodman Pollitt, Ronald Francisco; Fukao, S.; Larsen, M.F.; Yamamoto, M.; Tsuda, T.; Kato, S.This paper describes the first results of the implementation of frequency domain interferometry (FDI) using the Middle and Upper (MU) atmosphere radar. A new method of using this FDI data is introduced, which is shown to be useful in studying the dynamics of scattering layers in the troposphere and lower stratosphere. Using this method, the effective altitude resolution of the MU radar has been improved.Item Restricted Gravity wave modulation of gradient drift instabilities in mid-latitude sporadic E irregularities(American Geophysical Union, 1991-07) Woodman Pollitt, Ronald Francisco; Yamamoto, M.; Fukao, S.Recent E region VHF backscatter echoes observed by the MU radar at mid-latitudes show quasiperiodic striations with a fairly constant range vs. time tilt in a RTI display. These features are explained in terms of gravity waves with frequencies close to the Brunt-Väisälä frequency which modulate the shape of sporadic E layers. The conditions of instability, when the magnetic field has a significant dip angle, is revised. Differing from previous work, we argue that conditions of local gradient drift instability are not sufficient and one has to consider the integrated properties of each magnetic filed tube. Stratified sporadic E layers are stable using this new criteria, unless they are distorted to produce unstable integrated gradients. Gravity waves with phase fronts parallel to the magnetic dip angle are capable of producing such distortion, imposing its own temporal and spatial periodicity on the echoes.Item Open Access High-altitude-resolution observation of the upper stratosphere and lower mesosphere using Jicamarca VHF radar(Coleg Prifysgol Cymru Aberystwyth, The University College of Wales, The Departament of Physics, 1991-08) Fukao, S.; Maekawa, Y.; Yamamoto, M.; Tsuda, T.; Yamanaka, M.D.; Nakamura, T.; Kato, S.; Woodman Pollitt, Ronald FranciscoThe high-power VHF radar technique is a powerful tool to lnvestigate winds and turbulence in the middle atmosphere. However, an entire wind or power profile from the upper troposphere to the lower thermosphere. (10-100 km) has not yet been obtained.- Especially, it is very difficult to observe the so-called ''gap region" from 35 to 60 km due to weak echo power. Recently, the Jicamarca VHF radar facility (50 MHz) in Peru has been greatly improved, and a height resolution of 250-500 m is now achieved by pulse compression using 16- or 32-bit complementary codes. This paper presents a preliminary result of Jicamarca radar observations of the upper stratosphere and lower mesosphere, including the "gap region'', conducted on Sept. 24-28, 1990.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.