Browsing by Author "Yamamoto, M."
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Item Restricted Daytime zonal drifts in the ionospheric 150 km and E regions estimated using EAR observations(American Geophysical Union, 2017-08-16) Pavan Chaitanya, P.; Patra, A. K.; Otsuka, Y.; Yokoyama, T.; Yamamoto, M.; Stoneback, R. A.; Heelis, R. A.Multibeam observations of the 150 km echoes made using the Equatorial Atmosphere Radar (EAR), located at Kototabang, Indonesia, provide unique opportunity to study both vertical and zonal E × B plasma drifts in the equatorial ionosphere. In this paper, we focus on estimating daytime zonal drifts at the 150 km (140–160 km) and E (100–110 km) regions using multibeam observations of 150 km and E region echoes made using the EAR and study the daytime zonal drifts covering all seasons not studied before from Kototabang. Zonal drifts in the 150 km and E regions are found to be westward and mostly below −80 m s−1 and −60 m s−1, respectively. While the zonal drifts in the 150 km and E regions do not go hand in hand on a case‐by‐case basis, the seasonal mean drifts in the two height regions are found to be in good agreement with each other. Zonal drifts at the 150 km region show seasonal variations with three maxima peaking around May, September, and January. The zonal drifts at the 150 km region are found to be smaller than the F region drifts obtained from Coupled Ion Neutral Dynamics Investigation (CINDI) onboard Communication and Navigation Outage Forecasting System (C/NOFS) by about 25 m s−1 consistent with the height variations of F region zonal drifts observed by the Jicamarca radar. These results constitute the first comprehensive study of zonal drifts at the 150 km and E regions from Kototabang, Indonesia, and the results are discussed in the light of current understanding on the low‐latitude electrodynamics and coupling.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.