Variations of nitric oxide in the mesosphere and lower thermosphere over Antarctica associated with a magnetic storm in April 2012

We report extreme enhancements of the nitric oxide (NO) column density observed with the ground‐based millimeter‐wave spectroscopic radiometer installed at Syowa Station, Antarctica, during a large geomagnetic storm in April 2012. From the NO spectrum line shape and NO column density relationship with solar radiation, we concluded that the NO was emitted in the altitude range between 75 km and 100 km. The column density of NO gradually increased during the recovery phase. In addition to variations on a time frame of several days, we found diurnal variations. The increase of NO was related to precipitated electrons in the energy range of 30–300 keV observed by Polar‐orbiting Operational Environmental Satellite (POES)/The Meteorological Operational (METOP). We found a rapid response (within 1 h) and a one‐to‐one correspondence between them. For the first time, we show that a remarkable increase of the column density of NO is caused by dawn‐dusk asymmetry of the plasma sheet electrons. Key Points Sporadic NO enhancement due to precipitated electrons was clearly detected Correlation between NO intensity and electron flux is analyzed in detail NO increase at UT 0 was caused by dawn‐dusk asymmetry of plasma sheet electrons