Simultaneous mesosphere/lower thermosphere and thermospheric F region observations during geomagnetic storms

Abstract

Simultaneous mesosphere/lower thermosphere (MLT) and thermospheric F region observations made during geomagnetic storms are presented using the MU radar (35°N, 136°E) in alternate meteor and incoherent scatter (IS) modes, MF radar (45°N, 136°E), optical mesosphere thermosphere imagers (OMTI) (35°N, 136°E) and over 1000 GPS receivers in Japan. The observations were made during one of the MTEC‐S (mesosphere‐thermosphere experiments for coupling studies) campaigns conducted during 23 March to 2 April 2001 when a major storm with Dst reaching −358 nT and a moderate storm with Dst reaching −112 nT occurred and solar activity varied from high to very high (F10.7 = 220 to 270). The campaign has provided zonal and meridional wind velocities at MLT altitudes (80–95 km) over the MU and MF radars; meridional wind velocity in the upper thermosphere (220–450 km) and ionospheric electron density (150–600 km), peak height and plasma drift velocity over the MU radar; all‐sky airglow intensities at 557.7 nm, 630.0 nm, and 777.4 nm wavelengths over the MU radar location; and vertical GPS‐TEC all over Japan. Study of the data indicates that following the major storm, the meridional wind in the upper thermosphere over the MU radar (35°N) becomes weak (less poleward) during daytime and its diurnal amplitude reduces. The winds and tides at MLT altitudes show changes during both nonstorm times and storm times, but this study is not able to confirm any statistically significant changes related to the storms. In the ionosphere, following the onset of the major morning storm, the electron density increases at altitudes near and above the ionospheric peak, which after about 5 hours is followed by large increase in density at all altitudes above about 200 km. On the following night, though the density is generally low, there is a large increase in density in the bottomside for about 3 hours centered at 0230 LT. During this time, a rare intense optical activity has occurred at all wavelengths (557.7 nm, 630 nm, and 777.4 nm) over the low midlatitude location (35°N), and an associated large‐scale traveling ionospheric disturbance (LSTID) has propagated from north to south at F region altitudes.