Cooperative wind observation in the upper mesosphere and lower thermosphere with foil chaff technique, the MU radar, and Yamagawa MF radar

An in-situ rocket technique using foil chaff is used to observe wind fields in the mesosphere and lower thermosphere (80-98 km in altitude). We launched two micro-rockets at 1200 and 1315 UT on 14 January 1997 from Uchinoura, Japan (31°N, 131°E). The MU radar (MUR; 35°N, 136°E) and the Yamagawa MF radar (MFR; 31°N, 131°E) simultaneously observed winds at the same heights by means of a meteor scattering and partial reflection echo from the ionosphere received by spaced antennas, respectively. The chaff and MFR winds generally agree well at 80-88 km, while MFR data were missing at the heights >88 km. In the chaff, MFR, and the MUR winds, we have found a coherent structure likely due to a large-scale gravity wave. The chaff results suggest that wind fluctuations with a vertical scale of ~2 km at 82-85 km are quite consistent with gravity wave motions. It is noteworthy that a qualitative agreement is found between the chaff descent speed fluctuations and the wave-induced vertical component, although those vertical velocities are quantitatively inconsistent. On some special occasions chaff velocity might be affected by another process, of which tentative candidates are an apparent motion of the strong echo point in a chaff cloud, and an internal mesospheric 'bore'.