Browsing by Author "Yamanaka, Manabu D."

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    First observation of the upper stratospheric vertical wind velocities using the Jicamarca VHF radar
    (American Geophysical Union, 1993-10) Maekawa, Yasuyuki; Fukao, Shoichiro; Yamamoto, Mamoru; Yamanaka, Manabu D.; Tsuda, Toshitaka; Kato, Susumu; Woodman Pollitt, Ronald Francisco
    The Jicamarca VHF radar (50 MHz) has detected atmospheric echoes in the so-called "gap region" from 30 to 60 km heights. These echoes are, for the first time, discriminated from clutter echoes, using both co-polarized ( co-pol) and cross-polarized (x­pol) arrays to monitor the clutter component which may enter the antenna sidelobes. The atmospheric scatterings in this region are shown to be composed of refractivity layers with thickness as of 1-2 km as in other middle atmospheric height ranges, suggesting that these scatterings are caused by thin turbulent layers. The height profile of infcrred vertical wind velocities indicates a wavy structure. The wave amplitude, as a whole, increases with height, suggesting the activity of upward-propagating gravity waves.
    Palabras clave:Gravity waveMiddle atmosphereUpward propagating wave
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    Gravity waves observed by the Jicamarca VHF radar in the equatorial upper stratosphere
    (ISEA, 1995) Maekawa, Yasuyuki; Soichiro, Fukao; Yamamoto, Mamoru; Yamanaka, Manabu D.; Tsuda, Toshitaka; Kato, Susumu; Woodman Pollitt, Ronald Francisco
    Internal gravity waves are known to play an important role in dynamics of the middle atmosphere. They can transport momentum flux from lower atmosphere to upper atmosphere and sometimes break mean flows or large-scale long-period motions due to dissipation process associatcd with wave flow interaction. However, an entire profile of short period gravity waves has not yet been obtained, since it has been very difficult to detect extremely weak atmospheric echoes from so-called "gap region" of 30-60 km heights. Recently, the Jicamarca VHF radar system in Peru ( Woodman and A.Guillen, 1974), which is one of the largest high-power VHF /UHF radars in the world, has been greatly improved in height resolution, and reliable atmospheric echoes have been, for the first time, detected in the gap regían by the Jicamarca radar with the high-altitude resolution (500 m). This paper presents new observational results on the upper stratospheric short-period vertical wind oscillations, which have never been resolved by the VHF /UHP. radars other than the present revised Jicamarca radar.
    Palabras clave:Gravitational wavesStratosphereRadar