Electric field observed during disappearance of nighttime medium-scale traveling ionospheric disturbance at midlatitude

Abstract The S-520-27 sounding rocket was launched from the Uchinoura Space Center in Kagoshima, Japan at 23:57 JST on July 20, 2013. This sounding rocket was launched to verify the hypothesis of the nighttime medium-scale traveling ionospheric disturbance (MSTID) generation mechanism, in which electromagnetic interaction in the ionospheric E and F regions is thought to play an important role. The detrended total electron content (dTEC) map identified the MSTID structure as a northwest – southeast band structure at the time of the rocket launch. This band structure disappeared 30 min after launch, indicating that the rocket was observing the disappearance process of MSTID. The wavefront direction was assumed to be 164.90 ° in azimuth from the dTEC map. The electric field detector on board the rocket observed low-frequency electric fields from DC to 50 Hz in situ. The obtained data were analyzed, and the detrend electric field was derived. The electric field was analyzed by decomposing the MSTID into components perpendicular and parallel to the wavefront. In the low-plasma-density region, the perpendicular and parallel components of the electric field are southwestward and northwestward, respectively. Conversely, in the-high-plasma-density region, the perpendicular and parallel components are the northeastward and southeastward, respectively. These electric fields generated the E × B drift in the equalization direction of the Pedersen conductance gradient of the MSTID. The results show that the electric field played an important role in the disappearance of the MSTID.