Here presents selected recent results from my researching activities. Major scientific targets are the upper atmosphere at high latitudes including the ionosphere. I apply optical and radio-wave techniques for remotely measuring there from the ground.
Height-dependent ionospheric responses to the substorm
This paper particularly focused on the height dependencies of the ionosphere. Results show clear evidences of large electric field with corresponding frictional heating and Pedersen currents located just outside the front of the poleward expanding aurora, which typically appeared at the eastside of westward traveling surge. At the beginning of the substorm recovery phase, the ionospheric density had a large peak in the E region and a smaller peak in the F region. This structure was named as C form in this paper based on its shape in the altitude-time plot. The lower altitude density maximum is associated with hard auroral electron precipitation probably during pulsating aurora.
Lower-thermospheric winds and pulsating aurora
This study analyzed the FPI-derived wind (wavelength: 557.7 nm) during DELTA-2 (Dynamics and Energetics of Lower Thermosphere in Aurora-2) campaign in January 2009 in northern Norway. Of particular interest was that wind variation of more than a few tens m/s was found in a darker area that appeared within the pulsating aurora. While we have not yet identified the dominant mechanism of the vertical wind, frictional heating energy dissipated by the electric-field perturbations may be responsible for the increase in ionospheric thermal energy.
Lower-thermospheric winds and auroral patches
This study used three events in November 2010 and January 2012, particularly focusing on the wind signatures associated with the auroral morphology, and found three specific features: (1) wind fluctuations that were isolated at the edge and/or in the darker area of an auroral patch with the largest vertical amplitude up to about 20 m/s and with the longest oscillation period about 10 min, (2) when the convection electric field was smaller than 15 mV/m, and (3) wind fluctuations that were accompanied by pulsating aurora.