Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsa23a0386o&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SA23A-0386
Physics
2411 Electric Fields (2712), 2435 Ionospheric Disturbances, 2439 Ionospheric Irregularities, 2443 Midlatitude Ionosphere, 2487 Wave Propagation (6934)
Scientific paper
On the night of August 6, 2002, the 46.5-MHz middle and upper atmosphere (MU) radar with 5 beam directions at Shigaraki, Japan, observed typical quasi-periodic (QP) echoes from field-aligned electron density irregularities in the ionospheric E-region. The QP echoes exhibited a wavy structure which had a wavelength of 30 km and propagated southwestward at 100 m/s. During this QP event, an all-sky CCD imager at the MU radar site detected medium-scale traveling ionospheric disturbances (MSTID) in 630 nm airglow images. The MSTID also propagated southwestward at 80 m/s with relative fluctuation amplitudes of 30-50 percent and a wavelength of 300 km. This propagation direction is very similar to the direction of the QP echoes movement. Also, a 630.0 nm Fabry-Perot interferometer at the radar site detected southeastward neutral winds (U) of 106 m/s. U would generate an electric field of 4.5 mV/m through UxB, where B is the geomagnetic field. From these observed values and average F-region electric field of 1.0 mV/m that is derived from previous MU radar observations in summer under high solar activity conditions, we estimate polarization electric fields associated with MSTID are 1.2-2.0 mV/m. When these polarization fields are mapped down along B without attenuation, ExB plasma drift velocities of 28-47 m/s are induced in the E-region. In actual, drift velocities in the QP echoes observed with the MU radar was 42 m/s, which is very consistent with the values (28-47 m/s) estimated above. Moreover, the direction of the ExB drift estimated is almost identical to that of the plasma drift in the QP echoes observed with the MU radar. Thus, the electric fields associated with the F-region MSTID seem to be closely coupled to those that generate QP echoes in the E-region.
Fukao Shoichiro
Ogawa Takuro
Onoma F.
Otsuka Yoichi
Shiokawa Kazuhiko
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